Fertilizers and balanced fertilizer useipni.net/ppiweb/filelib.nsf/0/08A9771E8EB6955D48256DF30012F816... · and plant growth. 8. Balanced fertilizer use ... the concept of BF aims

1. Documentation of research results is an

important precondition of successful

extension.

2. P-fertilizer from national resources.

3. Local “bio-fertilizer” production site. 4. Vietnamese NPK mix based on

standardized imported mineral fertilizers.

5. Comparing balanced fertilizer use (at right) with farmers’ practice (at left).

Fertilizers and balanced fertilizer use...

6. Long -term fertilizer experiments at

representative sites are essential for

regional recommendations.

9. Balanced nutrition of crops (background)

results in optimum productivity.

7. The use of FYM in addition to mineral

fertilizer (left side) improves soil conditions

and plant growth.

8. Balanced fertilizer use (background)

improves crop growth.10. The result of balanced fertilizer use: A

healthy productive crop (left).

...and the results in the field.

33

In spite of Vietnam’s impressive fertilizer

consumption record, fertilizer use

efficiency is estimated to be only at 35–

45% for N fertilizers, and 50–60% for P

and K fertilizers. This is attributed mainly

to farmers’ lack the knowledge in their

proper use.

Balanced fertilization (BF) or balanced

crop nutrition is a relatively new concept

that has been used more widely only since

its introduction through the IFA-sponsored

project Balanced Fertilization for Better

Crops in Vietnam (BALCROP) that was

initiated in 1994 (Box 2-1).

Balanced fertilization

for improved

fertilizer efficiency

Nutrient demand

Crop performance is optimized when all

essential nutrients are provided in

sufficient amounts and held readily

available during crop growth (i.e.

maximum exploitation of yield potential).

Balanced fertilization is the deliberate

application of essential plant nutrients to

soils that are unable to supply these

nutrients in order to meet crop demand at

a specific location. Since agroecosystems

are open and dynamic systems, BF aims

at nutrient supplementation in order to

assist crop performance while minimizing

nutrient losses.

Balanced fertilization (BF) is one of the keys to improving fertilizer use efficiency.

In principle, the concept of BF aims at a dynamic balance between nutrient requirement and

nutrient uptake by crops.

This is achieved by maintaining the equilibrium between nutrients available at different growth

stages; between the supply of nutrients from fertilizers and from natural nutrient pools in

accordance with conditions relevant to the effectiveness of fertilizer nutrient uptake (e.g. soil

properties, water regimes, weather conditions, etc.).

Balanced fertilization also improves nutrient use by crops in crop rotations and farming

systems.

Box 2-1 The concept of balanced fertilization.

34

Sources of nutrients

Nutrients sources can be of mineral or

organic origin. It is desirable (and is one

of the principles of BF) to make full use of

both these sources in an integrated way

that is economically and environmentally

sound. Recently, organic farming has been

promoted as an alternative to common

agriculture in Vietnam. Using organic

fertilizers (obtained from organic wastes)

as sole nutrient sources, organic farmers

claim to provide an optimum nutrient

balance in support of both large

sustainable crop yields and a safe

environment.

Under increasing cropping intensity and

rising food demand in Vietnam, however,

organic fertilizers can only be an additional

source of nutrients as well as a factor for

improving soil physical and chemical

conditions.

In fact, Vietnam’s agriculture depends

increasingly on manufactured (and mostly

imported) fertilizers as major nutrient

sources. Organic fertilizers, especially

farmyard manure (FYM) applied regularly

at rates of 8–10 t crop-1 ha-1, continue to

play an important role beyond the supply

of nutrients by the enhancement of soil

structure, water storage, cation exchange

capacity (CEC) and biological activity.


in relation to soil

nutrient contents

One main characteristic of the majority of

soils in Vietnam is the small amount of

(naturally available) nutrients, which is

insufficient for sustaining high yields. In

addition, many soils are affected by yield-

limiting factors such as severe soil acidity,

aluminum toxicity, saline water intrusion

and a high level of soil alkalinity.

The alluvial soils of the RRD and MRD,

and soils originating from basalt and

limestone, usually have larger contents of

soil N (0.1–0.2%), P (>0.03%) and K (1.5–

2%). Most other soils have small reserves

of total N (< 0.15%), total P (0.03–0.06%)

and total K (0.3–0.5%), and small contents

of plant-available N, P, and K (see Table

2-1).

Crops require N, P, and K nutrients in the

largest quantities, and the availability of

these nutrients in soils is the most

significant factor in fertilizer supply. On

acid soils, Ca and Mg deficiencies are

particularly relevant in the choice of

fertilizer materials used. Where S and Zn

deficiencies occur, fertilizer sources must

provide an adequate supply of these

nutrients. For example, S will not be

supplied where urea, diammonium

phosphate (DAP), and muriate of potash

(MOP) are used as the sole fertilizer

nutrient sources.

Soil fertility status in

Vietnam

The widespread soil fertility decline in

Vietnam is attributed to many factors: soil

erosion, soil nutrient leaching, nutrient

export in crop produce and crop residues

not returned to the soil. In addition, there

has been an increase in crop nutrient

uptake due to cropland intensification as

well as the use of modern high-yielding

35

varieties. The rapid intensification of

agricultural cropland resulted in an

imbalance in fertilizer use, especially

excessive use of fertilizer N in comparison

with other fertilizer nutrients. This

increasing mobilization and uptake of P,

K, and other nutrients from the soil

reserves is termed ‘soil mining’.

In general >50% of cultivated soils in

Vietnam have low nutrient contents.

Results of routine soil testing conducted

recently reveal that 48% of soil samples

are deficient in Mg, 72% in Ca, 80% in K,

and 87% in P.

Nutrient imbalance

At the start of Vietnam’s latest phase of

rapid intensification of croplands (around

1990), it was determined that all soils were

deficient in N. Thus fertilizer N application

caused remarkable yield response. Almost

everywhere in Vietnam, urea as the main

fertilizer N source became an economi-

cally attractive yield enhancer. However,

the rapid increase in fertilizer N use and

the resulting imbalance in fertilizer nutrient

supply have increasingly exploited soil

nutrient reserves of P, K, and other

nutrients, leading to a decline in fertilizer

N response. To reverse this trend, P, K,

and other nutrients must be applied in

fertilizers.

On acid soils, for example, crop uptake of

N increased from 40–50 kg N ha-1 to 120–

130 kg N ha-1 where fertilizer P was

applied. Similarly, application of fertilizer

K substantially enhanced N uptake on the

degraded soils.

Before the 1990s, K fertilizers were hardly

used by farmers in Vietnam, as most

paddy soils had a large content of total K

(1.2–2.1%), and traditional rice varieties

with smaller yield potentials had small

requirements for nutrients. In addition, K

uptake by rice was sufficient due to the

generally lower levels of N application and

application of large amounts of FYM as a

source of K.

Between 1975 and 2000, however, the

area planted annually to rice increased

from 4.9 M ha to 7.8 M ha, i.e. cropping

intensity has increased from 1.2 to 1.9 rice

crops per year over the last 25 years.

Where traditional rice systems were

cropped only once or twice per year, now

three or even four crops per year are

produced on many of Vietnam’s irrigated

lowland soils. During the same period,

traditional local varieties were increasingly

replaced by modern high-yielding

varieties. Average paddy yields in Vietnam

increased from 2.1 to 4.3 t ha-1.

One consequence of this development is

that nutrient requirements for rice per year

and per crop increased substantially.

Where a traditional variety (yielding 2 t

paddy ha-1 yr-1) required annually 30 kg

N, 5 kg P, and 30 kg K ha-1 for grain

production, a 3-crop system (producing 15

t paddy ha-1 yr-1) needs 225 kg N, 38 kg P

(90 kg P2O

5), and 225 kg K (270 kg K

2O)

per ha.

Vietnamese rice farmers learned during

the 1970s and 1980s to meet increasing

N and P demand through judicious

application of fertilizer N and P. With regard

to K, however, it was commonly believed

(and supported by research findings at the

time) that soil K reserves in Vietnam’s

major rice soils – namely those derived

from recent alluvial sediments in river

estuaries – are sufficient to meet even

enlarged requirements, especially where

36

FYM is applied regularly (as in the RRD)

or straw is recycled.

More recently there are clear indications

that even on soils with comparatively large

Figure 3-1 Available potassium content (mg K kg-1) in selected topsoils of Northern Vietnam sampled

at the same locations, 1960–63 and 1993. (After Nguyen Vy, 1995)

Ferralitic soil / micashale

Ferralitic soil / basalt

Degraded soil / old alluvium (2)

Degraded soil / old alluvium (1)

Alluvial soil / Thai Binh River

Alluvial soil / Red River

0 20 40 60 80 100 120 140 160 180 200

Available K (mg kg -1

)

1960-63

1993

Table 3-1 Total (HF- HClO4 digest.) and available (1N NH

4O Ac exchangeable) potassium (K) content

in representative rice soils of Vietnam. (After Nguyen Van Chien, 2001; Nguyen My Hoa et al., 1998)

# epytlioS/noitacoL

lairetamtneraP

KlatoT elbaliavA K

% gkgm 1-

1 lioslaivullA stisopedrevirdeR 82.2 9.55 !+

2 lioslaivullA stisopedrevirhniBiahT 86.1 7.25 !+

3 lioslaivullA stisopedreviraM 97.1 0.63 !!+

4 lioslaivullA stisopedrevirmaL 57.1 9.34 !+

5 liosretawpeeD atleDreviRdeR 80.2 2.05 !+

6 liosetaflusdicA atleDreviRdeR 38.1 6.441

7 liosenilaslatsaoC atleDreviRdeR 04.1 9.49 +

8 liosydnaseniraM tsaoctsaehtroN 23.1 1.23 !!+

9 liosdedargedyerG atleDreviRdeR 05.0 3.81 !!+

01 lioslaivullagnuoY stisopedreviroCmaV 07.1 4.651

11 lioslaivullagnuoY stisopedrevirgnokeM 08.1 5.651

21 liosyelG atleDreviRgnokeM 07.1 5.111 +

31 liosenilaS stisopedreviroCmaV 88.1 8.484

41 liosetaflusdicA stisopedreviroCmaV 02.1 8.79 +

51 liosdedargedyerG stisopeddlorevirgnokeM 16.0 8.45 !+

61 liosdedargedyerG etinarG 75.0 7.11 !!+

+ Low (response likely); +! Very low; +!! Deficient

contents of total K (>1.5%), plant-available

K contents were reduced to levels where

response to fertilizer K is commonly

expected (<80 mg K kg-1) due to intensified

cropping (Figure 3-1, Table 3-1).

37

Response to

fertilizer K

A BALCROP fertilizer NPK nutrient

omission trial was carried out in a rice–

rice–maize cropping system on an alluvial

soil of the RRD between 1996 and 2001.

The results indicated an increasing

response to fertilizer K applied at a rate of

210 kg K2O ha-1 annually.

Treatments given the full fertilizer N, P, K,

Ca, Mg, and S nutrient combination([FN)

and farmyard manure at 10 t FYM crop-1

ha-1 (+FYM) were compared to those

where fertilizer K was omitted (-K). Rice

yield response to fertilizer K increased

from 8 to 23.3 kg paddy kg-1 K2O in spring

rice; and from 14.2 to 31 kg paddy kg-1

K2O in summer rice (Figure 3-2).

The response to fertilizer K was generally

larger in summer rice than in spring rice,

Figure 3-2 Yield response to fertilizer N, P and K omitted from a full fertilizer N, P, K, Ca, Mg, and S

nutrient application with and without farm yard manure (FN+FYM, FN) in spring and summer rice grown

on the alluvial soils of the Red River in Ha Tay Province, Northern Vietnam, 1996–2000. (NISF, 2001)

GG

GG

G

G

GG

G

G

G

G

E E

E

E

E

E

E EE

E

E

E

96 97 98 99 '00 '01 96 97 98 99 '00 '01

0

10

20

30

40

G FN-K

E FN+FYM-K

Summer riceSpring rice

-K treatments


G GG

G

GG

GG

G

G

GG

E

E

EE

E E

E

E

E

EE

E

0

10

20

30

40

G FN-P

E FN+FYM-P

-P treatments

GG

G

GG

G

GG

G

G G

G

EE

E

E

E E

EE

E

E

E

E

0

10

20

30

40

Yield response (kg paddy kg-1

fertilizer applied)

G FN-N

E FN+FYM-N


-N treatments

FN: Spring rice = 150 N +120 P2O

5 +60 K

2O +200 CaO +40 MgO +33 S (kg ha

-1);

Summer rice = 120 N +90 P2O

5 +60 K

2O +200 CaO +40 MgO +33 S (kg ha

-1).

FN+FYM: FN + 10 t FYM crop-1 ha

-1

38

indicating that K release from soil K

reserves to the soil solution was

insufficient to meet requirements for a

second rice crop (summer rice) at the

same level as for the first rice crop (spring

rice). The supply of K from FYM (10 t

crop-1 ha-1) was considered to be

inadequate for supporting larger rice

yields. To support summer rice, an

application rate of fertilizer K larger than

the 60 kg K2O ha-1 applied at the time

would be required.

Similarly, in treatments where fertilizer N

and P were omitted (-N, -P) from FN

treatments, response to fertilizer N and P

increased over time and was larger in

summer rice than in spring rice.

Response to fertilizer N in summer rice

was most prominent in 1999–2000 with

~30 kg paddy kg-1 N-1 in FN+FYM

treatments (Figure 3-2).

Compared with N, P, and K, the omission

of Ca, Mg, and S on alluvial soils resulted

in much smaller paddy yield reductions.

Based on cumulative yields of spring and

summer rice, the yield response to these

fertilizers (5-year average) were:

� Ca: ~2 kg paddy kg-1 Ca;

� Mg: 4–5 kg paddy kg-1 Mg; and

� S: ~9 kg paddy kg-1 S.

Response to fertilizer S was distinctively

greater in summer rice (12 kg paddy kg-1

S) compared with spring rice (6 kg paddy

kg-1 S), indicating that limited supply of S

from natural sources and FYM may

increasingly limit the productivity on these

soils.

In 2001, paddy yields for spring rice and

summer rice were 6.8 and 6.6 t ha-1

respectively in FN+FYM treatments,

compared with 5.8 and 4.7 t ha-1 in

treatments that did not receive fertilizer K

(FN+FYM-K). Thus the omission of

fertilizer K on this ‘naturally K-rich’ alluvial

soils of the RRD has reduced the total

paddy yields of two annual rice crops by

2.9 t ha-1 (22%). This yield reduction is

equivalent to a loss of US$ 293 ha-1 gross

income (at current rice prices), while

investment for the required fertilizer K

would have amounted to only US$ 52 ha-1.

This value:cost ratio (VCR) of 5.6 indicates

that the use of fertilizer K in rice-based

systems on the alluvial soils of Vietnam

can improve farmers’ income through

profits of >US$ 200 ha-1 yr-1.

K-supplying power is related to the soils’

weathering stage and the effect of K

supplied in sediments and irrigation water

in the interwoven branches of the Mekong

and Vam Co river systems in the MRD.

The K-supplying power of ten

representative soils of the MRD was

evaluated in a pot experiment (Nguyen My

Hoa, 1997). Results indicate that the

concentration of exchangeable K in the

five alluvial soils representing the major

area cultivated to rice was ‘marginal to

adequate,’ and thus insufficient to support

more than one rice crop without fertilizer

K supply.

Total K contents on these soils are >1.5%.

Despite this, K fertilization is required to

replace the K nutrients removed in crops

and residues in order to avoid a decline in

soil K fertility in the future. Without proper

management, the removal of large

amounts of K with each of the 2–3 crops

per year may cause a reduction in non-

exchangeable K, decomposition of K-

bearing clay minerals and, finally,

K-fixation (which can only be overcome

by very large fertilizer K applications).

39


in relation to organic

fertilizers

With the dramatic increase in the use of

mineral fertilizers in recent years in

Vietnam, the importance of organic

fertilizers as a nutrient source for crops

has declined. The relationship between

mineral and organic fertilizers as nutrient

sources with regard to the nutrient supply

balance, however, is particularly relevant.

In principle it is expected that organic

fertilizers support soil fertility maintenance

by supplying nutrients and enhancing soil

physical conditions, thus creating the basis

for intensive farming by improving mineral

fertilizer effectiveness. Crop yield is thus

generally increased where organic nutrient

sources (e.g. FYM) are applied in addition

to mineral fertilizers (Table 3-2).

From 1996 to 2001, there was a consistent

increase in the yields of spring rice and

summer rice on alluvial and degraded soils

of the RRD when 10 t FYM crop-1 ha-1 were

added to the FN treatment (fertilizer N, P,

K, Ca, Mg, and S nutrient combination)

(Figure 3-3). On average, yield increases

due to FYM was ~13% in spring rice and

Table 3-2 Response to fertilizer

plus farmyard manure (FYM) as

compared to fertilizer NPK nutrient

application in selected cropping

systems of Vietnam. (Data

collected from on farm trials

conducted between 1991 and

2000)

# porC lioS tnemtaerTdleiY

%∆aht 1-

10 eciR lioslaivullAKPN

MYF+KPN

57.4

13.521

20 eziaM lioslaivullAKPN

MYF+KPN

54.3

33.462

30 enacraguS lioslaivullAKPN

MYF+KPN

06.76

06.963

40 eciRliosdedargeD

muivulladlO

KPN

MYF+KPN

23.3

20.412

50 stundnuorGliosdedargeD

muivulladlO

KPN

MYF+KPN

86.1

19.141

60gnirpS

naebyos

liosdedargeD

muivulladlO

KPN

MYF+KPN

42.2

23.24

70 eziaMliosdedargeD

muivulladlO

KPN

MYF+KPN

27.6

82.78

80 eziamretniWliosdedargeD

muivulladlO

KPN

MYF+KPN

12.4

97.441

90 eziamretniWliosdedargeD

muivulladlO

KPN

MYF+KPN

54.6

04.6)1(

01 occaboTliosdedargeD

muivulladlO

KPN

MYF+KPN

14.1

85.121

11 egnarOloslarreF

elahsyalC

KPN

MYF+KPN

84.9

60.016

21 aeTloslarreF

muivulladlO

KPN

MYF+KPN

86.0

38.022

40

Figure 3-3 Effect of fertilizer N, P, K, Ca, Mg, and S nutrient application with and without farmyard

manure (FYM) on paddy yield of spring and summer rice of alluvial and degraded soils of the Red

River Delta in Vietnam, 1996–2000.


BB

B B BB

B B

B

BB

B

J

J J JJ J

J J

J

JJ

J

0

2

4

6

8

10

Yield (t paddy ha-1

)

B FN

J FN+FYM


B B B B

B

B

B B

BB

B

BJ

J J J

J

J

JJ

JJ

J J

96 97 98 99 '00 '01 96 97 98 99 '00 '01

0

2

4

6

8

10

B FN

J FN+FYM

Degraded soils

Alluvial soils


5 +60 K

2O +200 CaO +40 MgO +33 S (kg ha

-1);


5 +60 K

2O +200 CaO +40 MgO +33 S (kg ha

-1).


-1

Figure 3-4 Effect of fertilizer N, P, K, Ca, Mg, and S nutrient application with and without farmyard

manure (FYM) and after omission of fertilizers N (-N treatments), P (-P treatments) and K (-K

treatments) on green bean yield of coffea robusta on lateritic soils derived from basalt in Dak Lak

Province,1996–2001.

B

BB B B

B

EE E E

EE

0

1

2

3

4

5

6

Yield (t green bean ha-1

)

B FN

E FN+FYM

FN treatments

BB

B BB

B7 7

7

77

7

-N treatments

BB

B BB

B7 7

7

77

7

96 97 98 99 '00 '01

-K treatments

BB

B BB

B7 7

7

77

7

96 97 98 99 '00 '01

0

1

2

3

4

5

6 -P treatments

41

~18% in summer rice on alluvial soils; on

degraded soils, yield increases of ~16%

in spring rice and ~9% in summer rice

were observed. The application of 10 t

FYM crop-1 ha-1 increased grain yield of

winter maize grown after spring and

summer rice on alluvial and degraded soils

by ~14% and ~12% respectively.

Comparatively, the effect of FYM on yield

of coffea robusta on a ferralitic soil in Dak

Lak Province, Southern Vietnam was not

as significant (Figure 3-4). The average

green bean yield increased by only ~6.5%

in the same period (1996–2001). In

treatments where fertilizer N, P or K was

omitted from the FN applications, green

bean yields were reduced to 1.6, 2.7 and

1.7 t ha-1 respectively (compared with 4.5t

ha-1 on average). The application of 10 t

FYM crop-1 ha-1 in these treatments

increased yields to 2.2, 3.1 and 3.3 t ha-1

respectively. The supply of N, P, and K in

FYM, however, was obviously insufficient

to raise coffee yields beyond these levels

(Figure 3-4).

The comparison above underlines the

general finding that FYM sources in the

uplands of Vietnam contain less plant-

available nutrients than FYM from the

nutrient-richer lowland environments.

Over time, Vietnamese farmers have

collected organic matter from the upland

areas for fuel, animal feed, and other

purposes, transferring the resulting

organic wastes (e.g. ashes, FYM) to their

lowland rice fields. The considerable

amount of nutrients contained in these

materials was thus accumulated in the

arable lowlands while their transfer

contributed to the exploitation of soil

nutrient resources and decline of soil

fertility in the surrounding uplands.

A combination of fertilizers N, P, K, Ca,

Mg, and S with 25 t FYM ha-1 was applied

to coffea arabica on a ferralitic soil derived

from gneiss in Phu Tho Province, Northern

Vietnam. These FN+FYM treatments

resulted in green bean yields of 1.7 and

2.1 t ha-1 in the 2nd and 3rd years after

planting. Comparatively, the yields in FYM

only treatments were 0.7 and 1.1 t ha-1

respectively.

The same treatments applied to coffea

arabica on a similar soil in Son La Province

in 1999 resulted in yields of 2.0 and 1.4

ha-1 respectively. These results indicate

that even large application rates of FYM

may not provide nutrients in the quantities

required to exploit the yield potential of a

crop, and that a good balance between

organic and inorganic nutrient sources will

enhance the effectiveness of mineral

fertilizers. In most of the soil types where

experiments were carried out, FYM

applications increased fertilizer N

effectiveness significantly. Rice yields for

example, are largest when the N rate

supplied in manure is ~30% of total N

application.

Organic fertilizers also have a large effect

on the efficiency of K fertilizers. On soils

where total K content is 1.5–2.0%, an

application of 10 t FYM crop-1 ha-1 (1 ton

of FYM provides 2.5–3.0 kg K2O) can

support paddy yields of 5–5.5 t ha-1 without

additional K fertilizer applications. Thus on

many soils derived from alluvial

sediments, only a small quantity of

additional fertilizer K is required to sustain

larger rice yields.

On the alluvial soils of the RRD (total K

content 1.5–2.0%), spring and summer

rice yields of ~6.0 and ~5.7 t ha-1

42

respectively were maintained over five

years in FN treatments that received 10 t

FYM crop-1 ha-1 but no fertilizer K nutrients

(FN+FYM-K). When 60 kg K2O ha-1

fertilizer K was included, average yields

increased to ~6.8 and ~6.7 t ha-1

respectively. This indicates a response of

13–16 kg paddy per kg K2O applied in

fertilizer. In the FN+FYM-K treatments, the

succeeding 3rd season crop (winter maize)

in the rice-rice-maize system failed to

produce grain yield during the 2000/2001

season. These results clearly show that

in spite of the large soil K reserve in these

alluvial soils, the amount of K supplied in

10 t FYM crop-1 ha-1 and K released from

the soil is insufficient for supporting three

cereal crops per year. When fertilizer K

was included (FN+FYM), the maize crop

grain yields averaged ~3.8 t ha-1 (Figure

3-5).

The role that organic fertilizers have in the

rain-fed upland cropping systems is quite

different from its role in the irrigated

lowland rice-based systems. Most upland

soils are deficient in organic carbon, thus

the effects of organic inputs go beyond the

nutritional aspects. As a source of organic

matter, their contribution to the improve-

ment of soil physical characteristics is very

significant. Without the application of

mineral fertilizers (especially fertilizer N),

however, the effectiveness of FYM is quite

low.

In the case of sole FYM application, for

example, the response is only 30 kg of

maize grain t-1 FYM. When the FYM

application is combined with fertilizer N,

this response is increased to 126 kg of

grain t-1 FYM.

Organic fertilizers can be used to reduce

P-fixation on soils with a large P-sorption

capacity (which are common in Vietnam).

The use of FYM, crop residues, or green

manure improves the effectiveness of both

organic and mineral fertilizers significantly

in this respect.

Soil characteristics also determine the

time of fertilizer application. On light-

textured soils with a low CEC, it is

necessary to split fertilizer applications, in

particular fertilizer N and K as these are

easily leached on such soils. Phosphorus

fertilizers are commonly applied in one

basal rate, but on acid soils (especially

acid sulfate soils) this rate should be split

into two.

Figure 3-5 Effect of fertilizer N, P, K, Ca, Mg, and S application with and without K and farmyard

manure (FYM) on paddy yield of spring and summer rice and grain yield of winter maize grown in a

rice–rice–maize system on the alluvial soils of the Red River, 1996–2001.

BB

B B B

B B

B

BB

BB

B

B

GG

G GG

GG

G G

G

G

G

G

G

J

J J JJ

J J

J

JJ

J JJ

J

E

EE E E

E E

E

E

E

E

E

E E

96 97 98 99 '00 96 97 98 99 '00 98 99 '00 '01

0

2

4

6

8

10

Crop yield (t kg-1

)

B FN

G FN-K

J FN+FYM

E FN+FYM-K

Spring rice Summer rice Winter maize


5 +60 K

2O +200 CaO +40 MgO +33 S (kg ha

-1);


5 +60 K

2O +200 CaO +40 MgO +33 S (kg ha

-1);

Winter maize = 180 N +120 P2O

5 +90 K

2O +200 CaO +40 MgO +33 S (kg ha

-1);


-1

43


in relation to crops

and varieties

Crops differ substantially with regard to

their nutrient requirements. Groundnut, a

calcophil crop, for example, requires Ca

in relatively larger amounts than many

other crops. In degraded soils with low

contents of Ca and Mg, the application of

lime and/or fertilizer Ca can increase

groundnut yields by 9–10% and 11%

respectively. Besides supplying Ca as a

nutrient, lime also reduces soil acidity and

improves the soil environment for legumes

with regard to biological N2-fixation. The

excessive use of lime, however, decreases

groundnut yield due to an over-represen-

tation (imbalance) of Ca2+ as compared to

Mg2+ and K+ on the surface of cation

exchangers in the soil.

Modern high-yielding varieties require

more nutrients from soils and fertilizers

than traditional low-yielding varieties.

Research results indicate that traditional

rice varieties in Vietnam such as Chiem

chanh, Chiem bau, and Ba trang take up

only 18–20 kg N ha-1 and 3–4 kg P2O

5 ha-1;

this is only 10–15% of the amounts of N

and P taken up by improved varieties.

Similarly, hybrid rice takes up much larger

quantities of K per crop compared with

improved varieties of rice (Table 3-3). As

a consequence of the countrywide

introduction of modern crop varieties in

Vietnam, the total uptake of nutrients per

hectare of cultivated area has increased

rapidly over the last 20 years.

Nutrient uptake ability by crops is also

affected by soils and fertilizer materials.

Thus when applying the principles of

balanced fertilization to different cropping

patterns, it is important to balance nutrient

requirements and supply for the whole

cropping system, and as well to take into

account residual effects of previous crops

in this respect.

Table 3-3 Rice varieties and their

nutrient uptake. (Project 02A-06-01.

1990)

yteiraV aht(dleiY 1- )ahgk(ekatpU 1- )

N P2O

5K

2O

hnahcmeihC 04.1 2.52 2.4 -

uabmeihC 31.1 3.91 0.3 -

gnartaB 68.0 6.41 5.2 -

èM 70.1 8.61 3.3 -

ecirdevorpmI 5.5-0.5 021-001 05-04 021-001

ecirdirbyH 0.7-5.6 081-051 08-07 002-081

44


in relation to other

nutrients

Before the 1960s, the use of manufactured

fertilizers was not common in Vietnam:

most farmers planted only one crop per

year, using traditional varieties with low

productivity that required relatively small

amounts of nutrients (Table 3-3). Since

then, however, farmers have started using

manufactured fertilizers, especially

imported N fertilizers in (at the time) the

form of sulfate of ammonia (SA). During

this period when fertilizer was introduced

to Vietnam, fertilizer N was the over-riding

yield-limiting factor in all crops. Although

only small amounts of fertilizers were

applied, their use induced a rapid

agricultural production increase in

Vietnam, particularly in the case of rice.

Phosphorus fertilizers were seldom used

for yield improvement. However, research

studies during the 1970s indicated that,

due to increasing land intensification,

fertilizer P had by then become the most

prominent yield-limiting nutrient factor in

Vietnam, after fertilizer N.

Fertilizer K became an important yield-

limiting nutrient factor only after modern

rice varieties were introduced widely in the

1980s. Response to fertilizer K was

particularly prominent on light-textured

soils with small K reserves. In the 1990s,

the increasing use of hybrid varieties by

rice growers in Northern Vietnam and

maize farmers throughout the country,

together with the introduction of improved

planting materials to crop sectors other

than rice, also had a significant role in

making K the limiting factor.

When taking a balanced fertilization (BF)

approach, it is important to take nutrient

interactions into consideration. The

significant impact that BF has on yield

response and profitability is discussed

below.

N-P balance

As mentioned previously, N was the most

limiting nutrient factor in crop yield in the

1960s, but during 1970–80 P replaced N

in this respect. Increased P fertilizer use

efficiency is attributed to the use of modern

varieties, increased number of crops per

year, and excessive use of N.

The studies on alluvial soils, slightly acidic

soils, and acid sulfate soils have shown

that fertilizer N efficiency increases when

applied in balance with fertilizer P. When

fertilizer N is used alone, a much larger

application of fertilizer N is required per

kg paddy yield, compared to the amount

required when fertilizers N and P are

applied together (Tables 3-4 and 3-5).

Soil P availability may decline rapidly with

increasing cropping intensity, thus causing

a decrease in the uptake efficiency of N

and other nutrients. When fertilizer P was

omitted from FN treatments (fertilizer N,

P, K, Ca, Mg, and S nutrient combination)

in a rice-rice-maize crop rotation grown on

the alluvial soils of the RRD, yields

declined increasingly over the five years

of experimentation.

Table 3-4 Balanced fertilization and rice yield on

acid sulfate soils. (Project 02A-06-01. 1990)

tnemtaerT dleiY

aht 1-

deriuqerNrezilitreF

tgk 1- yddap

srezilitreftuohtiW 83.0 -

N06 58.1 8.04

P06+N062O

573.3 02

45

The omission of P in treatments that also

did not receive FYM (FN-P) resulted in

repeated crop failure in the 3rd season

crop (winter maize). By the winter season

of 2000/2001 (after five years of

experimentation), even the addition of 10

t FYM crop-1 ha-1 (FN+FYM) could not

provide sufficient P for grain production

in maize (Figure 3-6).

Paddy yields of spring and summer rice

were reduced by 1.8–2.2 t paddy ha-1 in

treatments that did not receive fertilizer P

during the 5th year of experimentation, in

spite of a judicious supply of other

nutrients in fertilizer and FYM. Results

from the full crop cycle in 2000/2001

indicate that fertilizer N use efficiency was

reduced to ~30% due to omission of

fertilizer P (FN-P), compared with ~60%

in FN treatments.

For spring rice, treatments that did not

receive fertilizer P (FN-P), the average

fertilizer N requirement was 28 kg t-1

paddy. This was reduced to 22 kg t-1 paddy

in treatments that received the FN+FYM

treatments. For summer rice, the average

fertilizer N requirement was reduced from

27 to 18 kg t-1 paddy in summer rice. We

can thus conclude that fertilizer P is

essential for efficient rice production in

Vietnam’s most fertile lowland soils.

Similarly, results for winter maize also

indicated a smaller efficiency when only

N was applied. In this case, fertilizer

profitability, at a value:cost ratio (VCR) of

1.98, was also small. When fertilizer N

was applied together with fertilizer P,

however, the VCR increased to 2.47.

When fertilizer N was applied in addition

to P and K, the VCR was further increased

Table 3-5 Relationship between

fertilizers P and N. (Project 02A-06-

01. 1990)

sliosfoepyT

deriuqerNrezilitreF

tgk 1- yddap

PtuohtiW

noitacilppa

PhtiW

noitacilppa

slioslaivullareviRdeR 72-32 32-91

slioslaivullareviRgnokeM 02-81 81-61

htroNehtfosliosetaflusdicA 63-43 82-62

htuoSehtfosliosetaflusdicA 43-03 02-71

Figure 3-6 Effect of fertilizer N, P, K, Ca, Mg, and S nutrient application with and without P and

farmyard manure (FYM) on paddy yields of spring and summer rice, and grain yield of winter maize

grown in a rice-rice-maize system on the alluvial soils of the Red River, 1996–2001.


5 +60 K

2O +200 CaO +40 MgO +33 S (kg ha

-1);


5 +60 K

2O +200 CaO +40 MgO +33 S (kg ha

-1);


5 +90 K

2O +200 CaO +40 MgO +33 S (kg ha

-1);


-1

BB

B B B

B B

B

BB

BB

B

B

GG

G G

G G GG

G G

G G G G

J

J J JJ

J J

J

JJ

J JJ

J

EE

E EE E

E E

E

E

E EE

E

96 97 98 99 '00 96 97 98 99 '00 98 99 '00 '01

0

2

4

6

8

10

Crop yield (t ha-1

)

B FN

G FN-P

J FN+FYM

E FN+FYM-P

Spring rice Summer rice Winter maize

46

to 2.8. Table 3-6 provides data to verify

BF’s impact on yield response and

profitability.

On the alluvial soils of the Thai Binh River

and acid sulfate soils of Northern Vietnam,

similar results were obtained for white

potato in the 2000/2001 winter season.

With a balanced fertilizer NPK and FYM

application, uptake of all three nutrients

was enhanced by up to 50%, with tuber

yields increasing by up to 40% (Table 3-

7). This response was induced mainly by

the substantial increase in fertilizer K rates

in the BF treatments. In contrast,

insufficient K release from soil reserves

and FYM in the standard farmers’ practice

(FP) limited uptake of N and P.

Much of Vietnam’s upland soils are derived

from Fe/Al-rich parent materials and have

undergone extreme weathering. On the

majority of these soils, the small contents

of plant-available P (often due to

P-fixation) limit modern agricultural

production to the extent of crop failure.

In hybrid maize grown on a ferralitic soil

in Binh Phuoc Province, Southern

Vietnam, a combination of fertilizer N, P,

K, B, Cu, and Zn nutrients with FYM and

dolomitic limestone provided yields of >5

t grain ha-1 in 1998. No grain yield was

received in treatments without fertilizer P.

In 1999 a large initial rate of 300 kg P2O

5

ha-1, together with fertilizer N (120 kg N

ha-1), K (120 kg K2O ha-1), and dolomitic

limestone (2 t ha-1) was applied to maize

grown in four farms on the lateritic upland

soils of Binh Phuoc Province, Southern

Vietnam. Grain yields of nearly 2.9 t ha-1

on average were obtained, compared with

0.45 t ha-1 achieved under common FP

using fertilizer N only.

tnemtaerT

dleiY *esaercnidleiY ycneiciffE

RCVaht 1-

eziamgk

gk 1- tneirtun

rezilitrefoN 54.0 - - -

N 84.1 30.1 6.8 89.1

PN 08.2 53.2 2.11 74.2

K 54.0 0 0 0

KN 31.2 86.1 0.8 52.2

KPN 57.3 03.3 0.11 08.2

Table 3-6 Balanced fertilization for

maize on the alluvial soils of the

Red River. (* Yield increase

compared with treatments with no

fertilizer applied).

Table 3-7 Effect of balanced fertilization (BF) compared with farmers’ practice (FP) on N, P and K

nutrient uptake of winter potato grown on the alluvial and acid sulfate soils of Northern Vietnam.

epytlioS

tnemtaerT ekatputneirtuN rebuT

dleiyP:N2O

5K:

2O MYF N P K

ahgk 1- aht 1- ahgk 1- aht 1-

,slioslaivullA

reviRhniBiahT

66:64:721)PF( 0.41 2.27 2.21 2.711 52.71

021:09:051)FB( 0.41 1.49 5.51 0.541 83.12

sliosetaflusdicA51:54:041)PF( 5.7 7.96 2.6 5.99 95.41

021:09:051)FB( 5.21 0.301 0.9 7.631 32.02

47

These examples show clearly that soil

fertility recapitalization in the highly

weathered acid upland soils of Vietnam

has to begin with an ameliorative fertilizer

P and dolomite applications. The larger P,

Ca and Mg availability will require an

adequate supply of fertilizer N, K, S, and

micronutrients, in order to increase crop

yield and biomass production (which help

to reduce soil erosion and, if residues are

properly recycled, will assist in building soil

fertility).

N-K balance

The relation between N and K in crops is

known to be of special importance and

their interaction in crop productivity can be

either antagonistic or synergistic. Because

of this relationship, scientists view K as a

major factor in adjusting N supply for

crops.

As discussed earlier, fertilizer K use

among Vietnamese rice farmers has been

minimal (or not at all) for many decades.

Therefore the role of K in rice productivity

has not been proven except on light-

textured soils with small contents of soil K

(e.g. degraded and sandy soils). As

intensification and the use of modern

varieties are becoming more commonly

practiced, K requirements in lowland

cropping systems have started to rise and

response to fertilizer K have increased

significantly.

Soil type factor

Recent studies have revealed an

increasing number of cases in which the

application of fertilizer N and P to rice on

some soil types results in similar yields to

zero fertilization. For example, N and P

fertilization increased paddy yields by 1.17

t ha-1 on the alluvial soils of the RRD. On

the degraded soils of the RRD, however,

yields increased by only 0.12 t ha-1. Similar

results were obtained on alluvial soils in

comparison with the grey soils of the

Southern MRD (Tables 3-8 and 3-9).

Yield responses after fertilizer K was

added to the fertilizer N and P combination

indicate that fertilizer K use efficiency is

Table 3-8 Effect of fertilizer N/K

balance on rice yield (t ha-1) on soils

rich in potassium. (* Yield increase

compared with treatments with the

least fertilizer applied). (# Source:

Do Trung Binh, 1995)

tnemtaerT

slioslaivullaDRR slioslaivullaDRM #

dleiY *esaercnidleiY dleiY *esaercnidleiY

aht 1- aht 1-


PN 25.4 71.1 90.4 -

KPN 57.4 32.0 45.4 54.0

Table 3-9 Effect of fertilizer N/K

balance on rice yield (t ha-1) on soils

poor in potassium. (* Yield increase

compared with treatments with the

least fertilizer applied). (# Source:

Do Trung Binh. 1995)

tnemtaerT

sliosdedargedDRR sliosdedargedDRM #

dleiY *esaercnidleiY dleiY *esaercnidleiY

aht 1- aht 1-


PN 72.2 21.0 98.2 -

KPN 23.3 50.1 90.4 02.1

48

strongly related to the indigenous K-

supplying capacity (soil K content). On

soils that are rich in K (e.g. alluvial soils),

fertilizer K use efficiency is only 2–4 kg of

paddy kg-1 K2O; however, it can reach 8–

13 kg or more paddy kg-1 K2O on degraded

and sandy soils.

Response to fertilizer K was observed in

a rice-rice-maize cropping system on

degraded soil (derived from old alluvial

sediments of the Red River, Northern

Vietnam). In K omission treatments

(fertilizer N, P, Ca, Mg, and S nutrient

combination), spring rice yields increased

from 5 to >22 kg paddy kg-1 K2O applied

between 1996 and 2000. Summer rice

yields increased from 8 to >32 kg paddy

kg-1 K2O applied in the same period. Yield

response to fertilizer K was only slightly

smaller in treatments that also received

additional FYM of 10t FYM crop-1 ha-1

(Figure 3-7).

Response to fertilizer K in the 2nd crop

(summer rice) was generally larger than

in the 1st crop (spring rice). When a 3rd crop

(winter maize) was grown in 1999 and

2000, fertilizer K response amounted to

24–27 kg maize grain per kg K2O.

These results indicate that an application

of fertilizer K is an absolute necessity on

these soils in order to grow more than one

crop successfully. Since soil K reserves

on these light-textured soils are likely

exhausted by a single rice crop, K supply

from 10t FYM crop-1 ha-1 would be

insufficient to meet nutrient demands from

subsequent crops.

Quantity factor

The role of N-K balance becomes more

important where larger rates of fertilizer N

are applied. Studies on alluvial soils

indicate that fertilizer K use efficiency is

small if N supply is <120 kg fertilizer N ha-1

with FYM (10 t FYM crop-1 ha-1). Efficiency

is enhanced where N supply is increased

>150 kg N ha-1. The effect is even more

pronounced on degraded soils.

Under these conditions, it is clear that

fertilizer K increases N use efficiency in

rice. Nitrogen use efficiency is usually 15–

G G

G G

G

G

G

G

G

G

G

G

E E

EE

E

E

E

EE

E

E

E

96 97 98 99 '00 '01 96 97 98 99 '00 '01

0

10

20

30

40

Yield response (kg paddy kg-1

K2O)

G FN-K

E FN+FYM-K

Spring rice Summer rice

FN: Spring rice: 120 N + 90 P2O

5 + 120 K

2O + 200 CaO + 40 MgO + 33 S (kg ha

-1);

Summer rice: 90 N + 60 P2O

5 + 90 K

2O + 200 CaO + 40 MgO + 33 S (kg ha

-1);


-1

Figure 3-7 Yield response to fertilizer K (omitted from a fertilizer N,P, K, Ca, Mg, and S nutrient

combination) with and without farmyard manure (FYM) in spring and summer rice grown on degraded

soils derived from old alluvial sediments of the Red River in Bac Giang Province, 1996–2001. (NISF,

BALCROP Annual Reports 1997–2002)

49

30% without K application, but it can be

as high as 39–49% when applied together

with fertilizer K.

Potassium also plays an important role in

regulating N supply, and can assist in

improving uptake of N and other nutrients

in rice as well as other crops (Table 3-10).

In 1996 a fertilizer nutrient omission trial

was initiated on degraded soils in Bac

Giang Province to monitor average

fertilizer N requirement. In treatments that

received the full fertilizer nutrient

combination inclusive of fertilizer K and

FYM, fertilizer N requirement was 24 kg

N t-1 paddy for spring rice, and 20 kg t-1

paddy for summer rice. By comparison, in

treatments that did not receive fertilizer K,

fertilizer N requirements for spring rice

were 39 kg N t-1 paddy and 35 kg N t-1 and

summer rice.

Seasonal factor

Recent studies have shown that the N/K

balance is also affected by seasonal

factors. The comparatively higher

temperatures during the summer season

in Northern Vietnam are likely to cause an

increase in soil K diffusion. Hence crops

will take up more K from the soils

compared with other seasons. Lower

temperatures and lack of sunlight, on the

other hand, were found to decrease

fertilizer K-use efficiency. Hence, during

the winter season fertilizer K-use efficiency

is smaller. In general, therefore, winter

crops in Northern Vietnam would require

larger applications of fertilizer K.

Crop factor

Studies on maize indicate that balanced

N-K fertilization is comparatively more

efficient in maize than in rice. Yield

increase in terms of maize grain due to

BF amounted to 3.3 t ha-1 on alluvial soils;

3.77 t ha-1 on degraded soils; 1.17 t ha-1

on grey soils; and 0.39 t ha-1 on ferralitic

soils. It is concluded that BF practices for

maize crops are more profitable on

degraded and grey soils compared to

alluvial and ferralitic soils (Tables 3-11 and

3-12).

NfoetaR

lioslaivullA sliosdedargeD

dleiY dleiY

*esaercni

dleiY dleiY

*esaercniKtuohtiW KhtiW KtuohtiW KhtiW

ahgk 1- aht 1-

0 27.4 36.4 90.0- 41.3 14.3 72.0

06 01.5 50.5 50.0- 56.3 06.4 59.0

09 14.5 55.5 41.0 88.3 42.5 63.1

021 78.5 90.6 22.0 12.4 30.6 28.1

051 34.6 28.6 93.0 29.3 51.6 32.2

081 73.6 78.6 05.0 15.3 95.5 80.2

012 24.5 73.6 59.0 10.3 36.4 26.1

Table 3-10 N/K balance for rice (hybrid rice). (* Yield increase due to K application)

50

Nutrient balance

between macro- and

secondary nutrients

The rapidly increasing use of fertilizer N,

P, and K nutrients in cultivated areas of

Vietnam has also increased the

requirement for other nutrients (secondary

and micronutrients). One major reason for

this development is the predominant use

of single fertilizer nutrient sources in

Vietnam.

For example, continuous addition of

fertilizers with large NPK contents (e.g.

urea, DAP, and MOP) induces S

deficiency. In other cases, the preferred

use of DAP and single superphosphate

(SSP) over fused magnesium phosphate

(FMP) has induced Mg deficiency. Thus

NPK nutrient supply from the addition of

fertilizers with large contents of these

nutrients has not always increased N, P,

and/or K efficiency to the extent that is

expected, as it may cause detrimental

conditions for the supply and uptake of

other nutrients.

Studies comparing the efficiencies of urea

with SA or DAP, SSP, and FMP have

shown that the use of fertilizers containing

secondary nutrient elements (Ca, Mg, and

S) and micronutrients is more beneficial

to crop performance compared with single

nutrient fertilizers.

For example, fertilizer N applied at a rate

of 30% as SA and 70% as urea increased

coffee yield by 8–16%. Similar results were

obtained for maize and groundnut. The

yield increase in these cases is explained

by the response to fertilizer S supplied

together with N in SA (Table 3-13).

A comparison of DAP, FMP and SSP as P

sources for coffea robusta was conducted

on a ferralitic soil in Dak Lak Province, and

soil samples were collected before the

Table 3-11 Maize yield in

relationship of N/K balance. (Cong

Thi Yen, 1995; Do Trung Binh.

1995)

tnemtaerT

laivullA

slios

dedargeD

slios

yerG

slios

citilarreF

slios

aht 1-

rezilitrefoN 54.0 44.0

PN 08.2 54.0 74.2 31.5

KPN 57.3 12.4 46.3 25.5

Table 3-12 Effectiveness of

balanced fertilization for maize.

(* value:cost ratio)

tnemtaerT

decudorpeziamgk

tneirtungkrep*RCV

laivullA

lios

dedargeD

lios

laivullA

lios

dedargeD

lios

aht 1-

PN 2.11 50.0 74.2 0

KPN 0.11 6.21 08.2 02.3

Table 3-13 Effectiveness of balanced fertilization

for maize. (Nguyen Thi Hien, 1995)

stnemtaerT aht(dleiY 1- ) %

PN 43.1 001

aCPN 64.1 901

KPN 05.1 211

aCKPN 56.1 321

51

experiment and again five years later. The

largest green bean yield was consistently

attributed to FMP application (Figure 3-8).

Soil sample analyses also revealed that

while all three fertilizer P sources had

caused a similar increase in soil contents

of available P during the course of

experimentation, only the use of FMP

resulted in the maintenance of

exchangeable Ca and Mg and pH in the

treated topsoil (Figure 3-9). It is concluded

that the supply of Ca and Mg (contained

in FMP) in addition to P, improved nutrient

supply and was beneficial to the root

environment of coffea robusta on this acid

soil, to the extent that yields in FMP

treatments were larger than those in DAP

and SSP treatments.

Figure 3-8 Effect of fertilizer P

nutrient sources on green bean

yield of coffea robusta on a ferralitic

soil derived from basalt in Dak Lak

Province, 1997–2001. (NISF,

BALCROP Annual Report 2002)

97 98 99 '00 '01

0

1

2

3

4

5


)

No P

DAP

FMP

SSP

Fertilizer nutrient application: 300 N + 300 K2O + 100 P

2O

5 (50% in May

+ 50% in July) as DAP (diammonium phosphate), FMP (fused

magnesium phosphate), and SSP (single superphosphate) (kg ha-1

yr-1).

Figure 3-9 Effect of fertilizer P nutrient sources applied to coffea robusta on a ferralitic soil derived

from basalt in Dak Lak Province before (1997) and after five years of experimentation (2001). (NISF,

BALCROP Annual Report 2002)

Fertilizer nutrient application: 300 N + 300 K2O + 100 P

2O

5 (50% in May + 50% in July) as DAP (diammonium phosphate),

FMP (fused magnesium phosphate), and SSP (single superphosphate) (kg ha-1

yr-1).

SSP

FMP

DAP

No P

0 1 2 3 4 5 6 7

P sources

pHKCl

After 5 yearsBefore experiment

0 10 20 30 40 50

Available P (mg kg-1

)

SSP

FMP

DAP

No P

0 1 2 3

Exchangeable Ca (cmol kg-1

)

0 1 2 3

Exchangeable Mg (cmol kg-1

)

.

52

Combined SSP and FMP fertilization

usually benefits crop performance on the

upland soils in Vietnam; this is attributed

to a more gradual release of P from these

sources and the beneficial effect of other

nutrients such as S, Ca, and Mg. On acidic

upland soils, the alkaline character of FMP

not only balances the acidic character of

SSP, but may also cause a liming effect,

thus reducing the P-fixation potential of

these soils. On alkaline soils, combined

FMP and SSP fertilization increases the

solubility of phosphorus in FMP, while the

high Si content of FMP supports the

formation of Al3+ compounds, which can

reduce alkaline toxicity.

Consequently the combined application of

SSP and FMP can bring about yield

increases on acid as well as alkaline soils.

Combined SSP and FMP fertilization

resulted in paddy yields increase of 9.2%

(0.37 t paddy ha-1) compared with FMP

alone, and 5.8% (0.24 t paddy ha-1) when

compared with SSP alone. Combined SSP

and FMP fertilization also gave similar

results in groundnut, increasing yield by

10.3% (0.19 t ha-1) compared with

separate applications of FMP and SSP.

The effects of fertilizer omission on coffea

arabica on ferralitic soils in Phu Tho

Province were observed over three years

(Figure 3-10). The omission of Ca, Mg, and

S from a FN+FYM application (=100)

resulted in substantial reductions in yields

that averaged about 25%, 33% and 36%

respectively when calculated over the

observation period. When micronutrients

Zn, B, and Cu were omitted from the FN

treatment, reduction rates of 21%, 36%

and 24% were recorded. The average

green bean yield of coffea arabica was

reduced by ~54% in treatments that

received only FYM (no fertilizer nutrients).

This example underlines the importance

of fertilizer nutrients – macro-, secondary,

and micronutrients – in maintaining crop

production on the highly-weathered

upland soils of Vietnam.

Figure 3-10 Three-year average reduction (%) of green bean yield of coffea arabica due to the

omission of fertilizer N, P, K, Ca, Mg, S, Zn, B, and Cu nutrients from a full fertilizer with farmyard

manure application (FN+FYM=100) on ferralitic soils in Phu Tho Province, 1998–2000. (NISF,

BALCROP Annual Reports 1999, 2000 and 2001)

FYM only

FN+FYM-Cu

FN+FYM-B

FN+FYM-Zn

FN+FYM-S

FN+FYM-Mg

FN+FYM-Ca

FN+FYM-K

FN+FYM-P

FN+FYM-N

-60 -50 -40 -30 -20 -10 0

Yield reduction in green bean yield (%)

53

In a similar fertilizer omission experiment

on a rice–rice–maize system on the

alluvial and degraded soils of the RRD

over six years, it was observed that paddy

yields were reduced progressively over

time (Figure 3-11).

On alluvial soils, yield reduction due to the

omission of fertilizers Ca, Mg, and S was

generally larger in the 2nd rice crop

(summer rice, 18–20% reduction) than in

the 1st rice crop (spring rice, ~15%

reduction). This indicates that the nutrient

supplied in the 10 t FYM crop-1 ha-1 is not

sufficient to compensate for the omission

of fertilizer Ca, Mg, and S on these soils.

On degraded soils, the omission of

fertilizer Mg caused the largest yield

reduction (24–26%) in spring rice. The

omission of fertilizer S caused a yield

reduction in summer rice in Year 6 (24%)

that was substantially greater compared

to Year 1 (9.5%). Similarly, the omission

of fertilizers Ca and Mg caused yield

reductions in summer rice that were larger

in Year 6 than in Year 1 (Figure 3-11).

Although yield reductions caused by the

omission of fertilizers N, P, and K in these

experiments were comparatively greater,

it is clear from these results that the

omission of ‘secondary’ nutrients in

fertilizers can cause yield reductions of

>1 t paddy ha-1 in the intensified rice

systems of Vietnam, regardless of soil

fertility conditions and soil reserves of Ca,

Mg, and S.

Figure 3-11 Paddy yield reduction (%) of spring and summer rice due to the omission of fertilizer N, P,

K, Ca, Mg, and S nutrients from a full fertilizer with farmyard manure application (FN+FYM=100) on

alluvial and degraded soils of the RRD, 1996 and 2001. (NISF, BALCROP Annual Reports 1997–2002)

54

In the same nutrient omission trial on

degraded soils, dry matter (DM)

accumulation, measured at three growth

stages of spring and summer rice and

winter maize during the 2001/2002 crop

rotation, reveals the impact of Mg and S

on biomass production and crop

development. Differences between full

nutrient supply (FN+FYM) and omission

plots were largest at harvest. Clearly, the

omission of fertilizer K has a spectacular

effect on DM production, increasingly

noticeable throughout the cropping

sequence (Figure 3-12). The omission of

K reduced DM of spring rice, summer rice

and winter maize at harvest by ~5, 7.3 and

12.2 t ha-1 respectively, compared with

treatments that received the FN+FYM

application. In contrast, DM reductions due

to fertilizer Mg and S omission were

smaller, but were still significant enough

to cause grain yield reductions of >1 t ha-1.

The omission of fertilizer Mg reduced DM

of the three crops (at harvest) by 2.9, 2.7

and 3.3 t ha-1, while the omission of S

reduced DM by 2.4, 3.1 and 3.7 t ha-1

respectively (Figure 3-12).

In a fertilizer N, P, K, Ca, Mg, S, Zn, B,

and Cu nutrient omission trial on coffea

robusta grown on ferralitic soils of Dak Lak

Province from 1996 to 2001, the omission

of fertilizers Mg, S, and Zn each caused

yield reductions averaging 0.7–0.8 t green

bean ha-1 yr-1 compared with the FN+FYM

treatment (Figure 3-13). Although the

reductions are much smaller than those

arising from the omission of fertilizer N, P,

and K, these results reinforce the point that

the application of secondary nutrients and

micronutrients in fertilizers does have an

impact on crop productivity.

In all the above cases, the supply of

nutrients from fertilizers and FYM was

combined. In general (and this is to be

expected), the efficiency of fertilizer

nutrient use decreased due to the addition

of FYM. This effect was found to be largest

in the case of fertilizer micronutrient use

when compared with macronutrient during

an experiment conducted with coffea

robusta on ferralitic soils derived from

basalt in Dak Lak Province between 1996

and 2000 (Figure 3-14).

B

B

B

B

B

B

B

B

B

J

J

J

J

J

J

J

J

J

G

G

G

G

G

G

GG

GG

G

G

G

G

G

G

G

G

Ñ

Ñ

Ñ

Ñ

Ñ

Ñ

Ñ

Ñ

Ñ

Til. PI Har. Til. PI Har. 7—9L Tas. Har.

0

2

4

6

8

10

12

14

16

t ha-1

B FN

J FN+FYM

G FN-K

G FN-Mg

Ñ FN-S

Spring rice Summer rice Winter rice

Figure 3-12 Effect of fertilizer N, P, K, Ca, Mg, and S nutrient applications with and without K, Mg, S,

and farmyard manure (FYM) on dry matter accumulation at three growth stages of spring and summer

rice (tillering [Til.], panicle initiation [PI], harvest [Har.]) and winter maize (7–9 leaves [7–9L], tasseling

[Tas.], harvest [Har.]) grown in a rice–rice–maize system on degraded soils of the Red River in

Northern Vietnam, 1996–2001/2002. (NISF, BALCROP Annual Report 2002)


5 +120 K

2O + 200 CaO + 40 MgO + 33 S (kg ha

-1);


5 + 90 K

2O + 200 CaO + 40 MgO + 33 S (kg ha

-1);


5 +150 K

2O +200 CaO +40 MgO + 33 S (kg ha

-1);


-1

55

Figure 3-13 Effect of fertilizer nutrient with and without N, P, K, Ca, Mg, S, Zn, K, Mg, S and FYM

application on green bean yield of coffea robusta on a ferralitic soil derived from basalt in Dak Lak

Province, 1996–2001. (NISF, BALCROP Annual Reports, 1997–2002)

FN: 300 N + 100 P2O

5 + 300 K

2O + 300 CaO + 50 MgO + 60 S + 12 Zn + 12 Cu + 5 B (kg ha

-1 yr

-1).

FN+FYM: FN + 10 t FYM ha-1 yr

-1

B

BB B B

B

JJ J J

JJ

GG

G GG

GE E

E

EE

E

0

1

2

3

4

5

6


)

B

BB B B

B

JJ J J

JJ

GG G G G

G

EE

E E E E

B

BB B B

B

JJ J J

JJ

G

G G G GG

EE E E E

EB

BB B B

B

JJ J J

JJ

G G

G GG

G

E

E

E E

EE

0

1

2

3

4

5

6

B

BB B B

B

JJ J J

JJ

G

G G G G GE E

E E E EB

BB B B

B

JJ J J

JJ

G

GG G G

GE

E E E EE

0

1

2

3

4

5

6

B

BB B B

B

JJ J J

JJ

GG

G G GG

E EE E

EE

96 97 98 99 '00 '01

B

BB B B

B

JJ J J

JJ

G

G

G GG GE

E E E

E E

0

1

2

3

4

5

6

B

BB B B

B

JJ J J

JJ

GG

G G GG

E EE E

EE

96 97 98 99 '00 '01

0

1

2

3

4

5

6

-B treatments

-S treatments

-Ca treatments

-P treatments

-Zn treatments

-Mg treatments

-K treatments

-N treatments

-Cu treatments

B FN

J FN+FYM

G FN-[fert]

E FN+FYM-[fert]

56

Conclusions

As a result of the insights gained

throughout the course of the Balanced

Fertilization for Better Crops in Vietnam

(BALCROP) project, the principles of BF

are today more widely practiced in

Vietnam’s agriculture than in the past.

Improvements have been observed not

only with regard to the rates and ratio of

fertilizer NPK consumption, but also in

terms of fertilizer use in relation to soil

characteristics (Table 3-14).

Throughout Vietnam, the benefits of

BF have been demonstrated on farms

in numerous locations involving

representative soils and typical cropping

systems (Figure 3-15).

Figure 3-14 Efficiency of fertilizer N, P, K, Ca, Mg, S, Zn, B, and Cu nutrient use (kg green bean kg-1

fertilizer nutrient applied) with and without farmyard manure (FYM) based on average annual green

bean yield of coffea robusta grown on ferralitic soils derived from basalt in Dak Lak Province, 1996–

2000. (NISF, BALCROP, Annual Reports 1997–2001)

Table 3-14 Rates and ratios of fertilizers used for rice in North Vietnam.

epytlioSrednuraeY

yevrus

N P2O

5K

2O

P:N2O

5K:

2O

ahgk 1-

,slioslaivullA reviRdeR2991 2.67 4.62 0.2 3:53:001

8991 5.901 8.45 5.74 34:05:001

reviRhniBiahT,slioslaivullA2991 1.78 0.04 0.2 2:64:001

8991 6.49 9.26 5.93 24:66:001

sliosdedarged-yerG2991 5.96 6.63 0.31 91:35:001

8991 7.59 6.63 0.96 27:83:001

saeralatsaocnisliosydnaS2991 7.97 3.93 0.41 81:94:001

8991 6.38 3.73 6.44 35:54:001

N P2O

5K

2O CaO MgO S Zn B Cu

0

10

20

30

40

50

60

Fertilizer efficiency (kg green bean kg-1

fertilizer nutrient)

9.9 9.2

18.717.5

9.88.5

1.2 0.9

96.4

9.57.7

34.2

28.3

50

32

10.89.2

FN

FN+FYM

57

Spring rice

Summer rice

Early rainy season rice

Early rainy season rice

Maize

Winter maize

Winter maize

Groundnut

Groundnut

Spring soybean

Summer soybean

Crop

3.38

1.89

4.78

2.98

3.48

2.79

5.01

3.39

3.81

3.28

3.45

2.8

4.21

0.45

1.68

1.19

3.04

1.51

2.24

1.83

1.75

0.83

NPKNP

Winter maize

Sweet potato

Groundnut

Soybean

Tea

Tobacco

Coffee

Pepper

0 1 2 3 4 5 6 7

6.720

6.933.73

2.21

1.84

1.48

0.7

2.81

2.51

1.521.07

3.64

1.81

4.42

2.52

Orange

Cassava

Sugarcane

0 10 20 30 40 50 60 70 80 90

Yield (t ha-1

)

9.48

6.48

24

16.489.3

77.4

Figure 3-15 Effect of balanced NPK application as compared to farmers’ practice (NP) on yield of 22

selected crops grown on major soil types in Vietnam, 1991–2001.

58

When BF was compared with FP in on-

farm demonstrations in Northern Vietnam

during the years 2000 and 2001, crop

Figure 3-16 Effect of balanced fertilization (BF) as compared to farmers’ practice (FP) on yield of

typical crops and cropping sequences in Northern Vietnam, 2000. (NISF, BALCROP Annual Report

2001)

tneirtuN

ahgk(etarnoitacilppA 1- )

gnirpS

tundnuorg

remmuS

ecir

retniW

otatop

PF FB PF FB PF FB

MYF k0 k8 k8 k8 k71 k81

N 83 46 901 77 721 051

P2O

539 39 64 39 38 09

K2O 52 28 79 95 131 001

OaC 0 872 - - - -

tneirtuN


gnirpS

tundnuorg

remmuS

ecir

retniW

otatop

PF FB PF FB PF FB

MYF k8 k8 k8 k8 k41 k41

N 721 721 201 201 721 051

P2O

544 78 63 76 64 09

K2O 05 38 05 38 66 021

tneirtuN


gnirpS

tundnuorg

remmuS

ecir

retniW

otatop

PF FB PF FB PF FB

MYF k5 k8 k1 k5 k8 k31

N 511 021 011 09 041 051

P2O

583 09 51 06 0 09

K2O 0 06 0 09 51 021

Winter potato

Summer rice

Spring rice

0 5 10 15 20 25

Yield (t ha-1

)

20.23

14.59

5.86

4.44

5.54

4.14 Acid sulfate soils

Hai Phong Province

Winter potato

Summer rice

Spring rice

0 5 10 15 20 25

Yield (t ha-1

)

21.38

17.25

5.64

5.03

6.05

5.37 Alluvial soils

Hai Dzuong Province

Winter potato

Summer rice

Spring rice

0 5 10 15 20 25

Crop

Yield (t ha-1

)

15.49

11.19

4.35

3.58

6.05

5.37

BFFP

Alluvial soils

Nam Dinh Province

yields increased by up to 222% while net

profit gains of > US$600 ha-1 were

achieved (Figures 3-16 and 17).

59

Figure 3-17 Effect of balanced fertilization (BF) as compared to farmers’ practice (FP) on yield of


2002)

Coffee arabica

0 0.5 1 1.5

Yield (t ha-1

)

1.13

0.35 Ferralitic soils

Phu To Province

Tea (fresh)

0 5 10 15 20 25

9.56

7.97 Ferralitic soils

Phu To Province

Degraded soils

Bac Giang Province

Winter potato

Late summer rice

Summer soybean

Spring rice

13.9

11.6

4.12

3.8

1.7

1.54

5.18

4.8

Winter soybean

Summer rice

Spring rice

1.6

1.2

5.63

5.27

5.98

5.36 Alluvial soils

Ha Tay Province

Winter potato

Summer rice

Spring rice

20.23

14.59

5.86

4.44

5.54

4.14 Acid sulfate soils

Hai Phong Province

Winter potato

Summer rice

Spring rice

Crop

21.38

17.25

5.64

5.03

6.05

5.37

BFFP

Alluvial soils

Hai Dzuong Province

60

Here within the framework of the

BALCROP project, plant nutrition based

on applied sciences has been introduced

to a wide variety of crops and crop systems

on representative soils located on farmers’

fields in Vietnam. Details of major

experiments conducted during Phase I

and II of BALCOP are presented in the

following sections. The recorded fertilizer

nutrient omission experiments in rice-

based systems and coffee may be viewed

as the first long-term fertilizer trial involving

six nutrients and FYM in Vietnam and the

whole of SE Asia.

The results achieved provide the

foundation for implementing Phase III of

the project which anticipates to establish

balanced fertilization as a common

practice throughout Vietnam in a network

involving farmers, extension workers,

scientists, and decision-makers during

2003–2005.

OFD1 OFD2 OFD3 OFD4 Coffee Tea

-1000

0

1000

2000

3000

4000

5000

US$

FP BF

Figure 3-18 Effect of balanced fertilization (BF) as compared to farmers' practice (FP) on net income of


2002)

OFD1 = Spring rice - summer rice - winter soybean on alluvial soil of the RRD in Ha Tay province

OFD2 = Spring rice - summer soybean - late summer rice - winterpotato on degraded soil in Bac Giang province

OFD3 = Spring rice - summer rice - winterpotato on alluvial soil of the Thai Binh river in Hai Dzuong province

OFD4 = Spring rice - summer rice - winterpotato on acid sulphate soils in Hai Phong province

Coffee = Coffea arabica on ferralitic soil in Phu Tho province

Tea = Tea on ferralitic soil derived from clay scale in Phu Tho province

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