Macronutrients

Tim Shaver & Richard FergusonUniversity of Nebraska-Lincoln

C, H, O = 95% of plant weight

N, P, K = Primary (macro) nutrients

Ca, Mg, S = Secondary nutrients

Micro-nutrients = B, Cu, Fe, Mn, Mo, Zn, Cl

Essential Plant Nutrients (16):

Mass Flow◦ Dissolved nutrients in water flowing toward

the root.◦ Soluble and abundant elements (N, Ca, Mg,

S) Diffusion

◦ Movement of nutrients from an area of high concentration to an area of low concentration

◦ Low concentration area created by active uptake of nutrients at the root (K and P)

Interception ◦ Root growth explores new soil regions

How Do Nutrients Reach the Roots?

N is the most frequently deficient nutrient in crop production.

The ultimate source of N is N2 gas, which is 78% of the earth’s atmosphere.

Higher plants cannot metabolize N2, therefore, N2 must be converted to plant available N.

Nitrogen:

N2 can be converted to plant available forms through several processes:

◦ Symbiotic microorganisms (legumes)◦ Non-symbiotic microorganisms◦ Lightning (electrical discharges) forming N oxides◦ Synthetic manufacture (N fertilizers)

Plant available forms:Nitrate (NO3

-)

Ammonium (NH4+)

Nitrogen:

1) Atmospheric, plant, & animal residue N is added to the soil.

2) Organic N in residue is mineralized to NH4+ by soil

organisms (mineralization).

3) Most NH4+ is converted to NO3- by nitrifying bacteria

(nitrification).

4) NH4+ and NO3- are taken up by plants.

5) Various loss mechanisms

Plant Available N Formation:

Used in the formation of proteins which provide the framework for plant structures in which biochemical reactions occur.

N is an integral part of chlorophyll (photosynthesis).

N is associated with high photosynthetic activity, vigorous growth, and dark green color.

Nitrogen Functions:

Generally stunted, and yellow in appearance.

N Deficiency:

Anhydrous Ammonia:◦ NH3 + 2O2 H+ + NO3

- + H2O

Urea:◦ (NH2)2CO + 4O2 2H+ + 2NO3

- + CO2 +H2O

Ammonium Nitrate:◦ NH4NO3 + 2O2 2H+ + 2NO3

- + H2O

N Fertilizers:

Monoammonium Phosphate:

◦ NH4H2PO4 + O2 2H+ + NO3- + H2PO4

- +H2O

Diammonium Phosphate:

◦ (NH4)2HPO4 + O2 3H+ + 2NO3- + H2PO4

- + H2O

N Fertilizers:

Phosphorus is an essential plant nutrient

◦ Energy Transfer (ATP)◦ Good Supply of P

Increased root growth Early maturity Greater straw strength in

cereals

Phosphorus:

Importance Second most important nutrient for crop growth◦ Lower need than N

P is a relatively immobile nutrient

Fewer loss mechanisms in the environment than N

Can become unavailable in the soil.

Band application on winter wheat

Monoammonium Phosphate:

◦ NH4H2PO4 + O2 2H+ + NO3- + H2PO4

- +H2O

Diammonium Phosphate:

◦ (NH4)2HPO4 + O2 3H+ + 2NO3- + H2PO4

- + H2O

Phosphorus Fertilizers:

Phosphorus Deficiency Symptoms in Plants

Stunted in Growth Abnormal dark-green color Reddish -purple color (Severe deficiency symptom)

◦ Often seen in early spring on low phosphorus sites.

◦ Often as soils warm, phosphorus deficiency symptoms disappear.

Essential plant nutrient

Next to nitrogen, crops absorb more K than any other nutrient

Soil K is related to soil minerals (feldspar, mica) and not organic matter like N and P

Western Nebraska has high quantities of K due to the mineral makeup of the soil and climate (low weathering).

Potassium (K):

Depending on soil type, 90 to 98% of K is in relatively unavailable forms.

Over time, soil minerals weather, slowly releasing K to more plant available forms.

Absorbed by roots as K+ ion.

Responsible for enzyme activation and water uptake (osmotic “pull”).

Potassium (K):

Potassium chloride (KCL)

Potassium sulfate (K2SO4)

Potassium magnesium sulfate (K2SO4•MgSO4)

Potassium nitrate (KNO3)

Nebraska soils with 125ppm or greater considered sufficient.

Potassium (K) Fertilizer:

Potassium Deficiency:

Urea Example:

◦ (NH2)2CO

◦ Molecular Weight (from periodic table): N = 14(2)=28 H = 1(4)=4 C = 12(1)=12 O = 16(1)=16

60N = 28/60 = 46%

N Content Determination:

Efficient N fertilizer use requires that credit is given for sources of N already available in the soil.

◦ Residual Nitrate (NO3)◦ Organic Matter Mineralization◦ Organic Materials (Manure)◦ Previous Crop (Legumes)◦ Irrigation (NO3 Content)

Nitrogen Rates:

Nitrogen cycle (source: http://www.epa.gov)

Nitrogen fertilizer rates can be substantially reduced by accounting for N Credits.

N credits can vary widely.

◦ Deep soil sampling◦ Material analysis◦ Previous crop credit◦ Irrigation water sampling

Nitrogen Rates:

Soil scientist uses hydraulic probe to extract soil samples (Photo courtesy of USDA NRCS).

Nitrogen rates can be determined using UNL Extension publications specifically written for individual crops.

These publications are located at:

http://www.ianrpubs.unl.edu

Nitrogen Rates:

UNL recommendations can be determined from tables or from equations (corn example, In: EC117):

Nitrogen Rates:

Soil Nitrate Yield Goal (bu/ac)ppm 60 90 120 150 180 210 240 270

Organic Matter 1%Recommended N rate based on soil N, yield goal and soil organic matter (lb N/acre)

1 90 120 155 185 220 250 280 3153 75 105 140 170 200 235 265 2956 50 80 115 145 180 210 240 2759 25 60 90 120 155 185 215 25012 5 35 65 100 130 160 195 22518 0 0 20 50 80 115 145 17524 0 0 0 0 35 65 95 130

UNL Corn N Recommendation Algorithm:

◦ N need (lb/ac):

35+(1.2 x EY)-(8 x N ppm)-(0.14 x EY x OM)-credits

[35+(1.2xEY)-(8xNO3-Nppm)-(0.14xEYxOM)-credits]

Nitrogen Rates:

Photo courtesy of USDA NRCS

Algorithm Example:◦ Expected Yield (EY) = 200 bu/ac; OM = 2%◦ Soil Nitrate (Surface 8 inches) = 5 ppm

[35+(1.2xEY)-(8xNO3-Nppm)-(0.14xEYxOM)-credits]

35+(1.2 x EY(200)) = 240-(8 x N ppm(5))= 40-(0.14 x EY(200) x OM%(2)) = 56

35 + 240 – 40 – 56 = 179 lbs N/ac

Nitrogen Rates:

Photo courtesy of USDA NRCS

N Credits:◦ Previous Soybean: 45 lbs/ac

◦ Previous Alfalfa: 150 lbs/ac (70-100% stand) 120 lbs/ac (30-69% stand) 90 lbs/ac (0-29% stand)

◦ Water: 1 ppm N = 2.7 lbs/ac

Nitrogen Rates:

*Photos courtesy of USDA NRCS

N Credit Example:◦ Previous Crop: Soybean (45 lbs/ac)◦ Water: 3 ppm (3 x 2.7 = 8 lbs/ac)

◦ N recommendation: 179 lbs/ac

◦ N Credits: 45 + 8 = 53 lbs/ac

◦ N recommendation (credits): 126 lbs/ac◦ Table recommendation: 155 – 180 lbs/ac

Nitrogen Rates:

Photo courtesy of USDA NRCS

Secondary and Micronutrients

Tim ShaverNutrient Management Specialist

UNL WCREC

N, P, K = Primary (macro) nutrients

Ca, Mg, S = Secondary nutrients

Micro-nutrients = B, Cu, Fe, Mn, Mo, Zn, Cl

Zn, Fe, and Sulfur most common deficiencies in NE.

Secondary and Micronutrients:

Soil minerals Soil organic matter Crop residue Manures/organic amendments Fertilizers, Pesticides Irrigation water The atmosphere

Micronutrient Sources:

Corn and dry beans sensitive

Other crops more tolerant

Deficiency expression◦ Stunted crop, short internodes◦ Reduced chlorophyll production◦ Striping on corn leaves◦ Often seen early in season then visual symptoms

may disappear

Zinc (Zn):

Zinc Deficiency:

Water solubility controls fertilizer Zn availability (40 to 50% required)◦ ZnSO4, Lignosulfonate, ZnEDTA are best

ZnEDTA is 2 to 5 X more effective than other high water soluble sources.

Zinc Fertilizer:

Wide spread problem from western US to Iowa

Lack of chlorophyll caused by plant’s inability to take up Fe from soil

Severity depends on crop & soil

Major problem of lawns and gardens

Iron (Fe) Chlorosis:

Fe Deficient Corn

◦ FeSO4·7H2O

◦ Foliar – 1% FeSO4·7H2O solution◦ FeEDDHA◦ Oxysulfates, FeGels, FeSO4·H2O

Look for cheaper sources of by-product ferrous sulfate

Foliar a last resort

Iron Fertilizers:

S is a secondary nutrient

Required for protein formation

Deficiencies primarily on sandy soils

Early season deficiency more common with cool, wet soils (no or reduced till, high water table, river valleys)

Sulfur (S):

Sulfur Deficiency:

Sulfates◦ 21-0-0 (24% S)◦ K or K-Mg sulfates (18% S)◦ CaSO4 (16-18% S)

◦ ZnSO4 (14% S)◦ Phosphates (16-20-0{15%}: newer have low S)

Thiosulfates◦ 12-0-0-26S (ATS)◦ 0-0-25-17S (KTS)

Elemental S◦ 90% - 99% S depending on granulation

Sulfur Fertilizers:

Fertilizer placement options generally involve surface or subsurface applications.

This depends on:◦ Crop and crop rotation◦ Soil test level◦ Mobility in the soil◦ Equipment availability

Application Methods:

Using Global Position System equipment for precision application of fertilizer. (Photo courtesy of USDA NRCS).

Pre-plant:

Band:◦ Surface (Dribble)◦ Subsurface (Knife)

Broadcast:◦ Surface◦ Incorporated

Application Methods:

Nutrient Applicator (Source: http://www.deere.com)

At Planting:

Band◦ Surface

◦ Subsurface Below and to side of seed

◦ Starter (pop up)

Application Methods:

Application of anhydrous ammonia fertilizer at planting time(Photo courtesy of USDA NRCS).

After Planting

Sidedressing◦ Anhydrous◦ Fluid Sources (UAN)

Surface and Subsurface

Topdress◦ Solid and Liquid Sources

Application Methods:

Nitrogen being applied to growing corn (Photo courtesy of USDA NRCS).