Effects of variability in fertiliser application on hill

country production economics

Allan Gillingham (Research Consultant)Alister Metherell

Hill pastures Hill pastures

All hill country is All hill country is variablevariable

This means This means differences in differences in pasture growth pasture growth potentialpotential

Often in complex Often in complex patternspatterns

““Lost” pasture production can Lost” pasture production can occur in two ways:-occur in two ways:-

The same rate of fertiliser being The same rate of fertiliser being applied to different production applied to different production zoneszones

Variation in fertiliser application Variation in fertiliser application rate within a zonerate within a zone

Factors affecting “lost” Factors affecting “lost” productionproduction

Fertiliser application rate factors Fertiliser application rate factors Land productivity, and initial nutrient Land productivity, and initial nutrient

statusstatus Fertiliser residual propertiesFertiliser residual properties

What causes variability in What causes variability in application rateapplication rate

Swath shapeSwath shape Discharge rateDischarge rate Track spacingTrack spacing Cross wind / altitudeCross wind / altitude Aircraft speed Aircraft speed

Estimation of CV%Estimation of CV%

Usually use a single swath shape Usually use a single swath shape and overlap this at a range of track and overlap this at a range of track spacingsspacings

To date the accuracy of track spacing To date the accuracy of track spacing has depended on pilot skill and has depended on pilot skill and experienceexperience

Now GPS increasingly being used for Now GPS increasingly being used for guidance and job recordguidance and job record

Results show that even with GPS Results show that even with GPS track spacing CV% may be up to track spacing CV% may be up to 33%.eg 15m 33%.eg 15m ±± 5m 5m

Difficult to estimate without GPSDifficult to estimate without GPS

Assume CV = 66% ?Assume CV = 66% ?

Variability in discharge along the Variability in discharge along the flight path also varies flight path also varies

For superphosphateFor superphosphate

– – Helicopter CV % = 12-27Helicopter CV % = 12-27

- Fixed wing CV % = 37-67- Fixed wing CV % = 37-67 What effect does this have on spread What effect does this have on spread

CV% estimates?CV% estimates?

Effects of variations in aircraft Effects of variations in aircraft altitude and speed, and in cross wind altitude and speed, and in cross wind not included in this evaluationnot included in this evaluation

What are the effects of land What are the effects of land productivity and initial nutrient (P) productivity and initial nutrient (P) status?status?

eg “High” (stocking rate =20/ha; eg “High” (stocking rate =20/ha; Olsen P =30)Olsen P =30)

“ “Medium” (SR = 19; P =15)Medium” (SR = 19; P =15)

“ “Low” (SR = 4; P =8)Low” (SR = 4; P =8)

Probability of fertiliser application Probability of fertiliser application rate occurring on any one site rate occurring on any one site estimated by @Risk analysis.estimated by @Risk analysis.

Effects of variability in fertiliser Effects of variability in fertiliser application rate on soil P and application rate on soil P and productivity assessed by OVERSEER productivity assessed by OVERSEER analysisanalysis

Selected swath shapeSelected swath shape Cresco with superphosphate Cresco with superphosphate

R&R Distribution Pattern

0

50

100

150

200

250

10.5

8.0

6.0

4.0

2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

22.0

24.0

26.0

28.0

at Bout Width of 12m

% o

f M

ean

Rat

e

Random variationRandom variation

Added random variation in track Added random variation in track spacing of up to 33 or 66% and spacing of up to 33 or 66% and variation in flow rate of 50%variation in flow rate of 50%

R&R Distribution Pattern

0

50

100

150

200

250

10.5

8.0

6.0

4.0

2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

22.0

24.0

26.0

28.0

at Bout Width of 12m

% o

f M

ean

Rat

e

Results:Results:

Fertiliser application rate Fertiliser application rate and and

Soil PhosphateSoil Phosphate

Variation in fertiliser application rate with Variation in fertiliser application rate with 66% variation in 12m track spacing66% variation in 12m track spacing

Distribution for Fertiliser P

Mean = 26.4

X <=4995%

X <=75%

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0 5 10 15 20 25 30 35 40 45 50 55 60 65

kg P / ha

Variability of overall spreadVariability of overall spread(CV%)(CV%)

33% track error = 3033% track error = 30

33% track plus 50% flow error= 4233% track plus 50% flow error= 42

66% track error = 4866% track error = 48

66%track plus 50% flow error = 5866%track plus 50% flow error = 58

Soil P test distribution with 66% Soil P test distribution with 66% variation from 12m track spacingvariation from 12m track spacing

Distribution for Olsen P Year 10

Mean = 30.12

X <=36.6495%

X <=24.065%

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

20 25 30 35 40 45

Olsen P

ResultsResults

Pasture dry matter productionPasture dry matter production

Dry Matter

13300

13400

13500

13600

13700

1 2 3 4 5 6 7 8 9 10

Year

kg

DM

/ h

aEffect of variability in fertiliser Effect of variability in fertiliser

application rate on pasture DM application rate on pasture DM productionproduction

Even SpreadMean

±1 S.D.

95%5%

ResultsResults

All scenarios showed less than 1% All scenarios showed less than 1% depression in long term (10 yr) mean depression in long term (10 yr) mean pasture DM production due to pasture DM production due to variability in P fertiliser application variability in P fertiliser application raterate

ConclusionsConclusions

Variability in fertiliser application rate Variability in fertiliser application rate has little effect on average pasture has little effect on average pasture production because of-production because of-

Compensating random rate effectsCompensating random rate effects High residual properties of P High residual properties of P

fertiliserfertiliser

ConclusionsConclusions

These results differ from situations These results differ from situations where exactly the same where exactly the same patternpattern of P of P application occurs at every application occurs at every applicationapplication

This is unlikely to occur in hill countryThis is unlikely to occur in hill country

NitrogenNitrogen

Straight line Straight line responseresponse

Little effect of Little effect of variabilityvariability

in fertiliser rate in fertiliser rate

on pasture on pasture

responseresponse

Nitrogen response

0

2000

4000

6000

8000

0 30 60 90

Rate of N fertiliser

Past

ure

prod

uctio

n

Thank Thank

youyou