Macronutrients

1. Macronutrients Tim Shaver & Richard Ferguson University of Nebraska-Lincoln

3. Essential Plant Nutrients (16): • 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

4. How Do Nutrients Reach the Roots? • 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

5. Nitrogen: • 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.

6. 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+)

7. Plant Available N Formation: • 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

8. Nitrogen Functions: • 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.

9. N Deficiency: • Generally stunted, and yellow in appearance.

10. N Fertilizers: • Anhydrous Ammonia: • NH3 + 2O2 H+ + NO3- + H2O • Urea: • (NH2)2CO + 4O2 2H+ + 2NO3- + CO2 +H2O • Ammonium Nitrate: • NH4NO3 + 2O2 2H+ + 2NO3- + H2O

11. N Fertilizers: • Monoammonium Phosphate: • NH4H2PO4 + O2 2H+ + NO3- + H2PO4- +H2O • Diammonium Phosphate: • (NH4)2HPO4 + O2 3H+ + 2NO3- + H2PO4- + H2O

12. Phosphorus: • Phosphorus is an essential plant nutrient • Energy Transfer (ATP) • Good Supply of P • Increased root growth • Early maturity • Greater straw strength in cereals

13. 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. Importance Band application on winter wheat

14. Phosphorus Fertilizers: • Monoammonium Phosphate: • NH4H2PO4 + O2 2H+ + NO3- + H2PO4- +H2O • Diammonium Phosphate: • (NH4)2HPO4 + O2 3H+ + 2NO3- + H2PO4- + H2O

15. 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.

17. Potassium (K): • 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).

18. 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”).

19. Potassium (K) Fertilizer: • Potassium chloride (KCL) • Potassium sulfate (K2SO4) • Potassium magnesium sulfate (K2SO4•MgSO4) • Potassium nitrate (KNO3) • Nebraska soils with 125ppm or greater considered sufficient.

20. Potassium Deficiency:

22. N Content Determination: • 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 60 N = 28/60 = 46%

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

24. Nitrogen Rates: • 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 Soil scientist uses hydraulic probe to extract soil samples (Photo courtesy of USDA NRCS).

25. Nitrogen Rates: • Nitrogen rates can be determined using UNL Extension publications specifically written for individual crops. • These publications are located at: http://www.ianrpubs.unl.edu

26. Nitrogen Rates: • UNL recommendations can be determined from tables or from equations (corn example, In: EC117):

27. Nitrogen Rates: • 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] Photo courtesy of USDA NRCS

28. Nitrogen Rates: • 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 Photo courtesy of USDA NRCS

29. Nitrogen Rates: • 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 *Photos courtesy of USDA NRCS

30. Nitrogen Rates: • 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 Photo courtesy of USDA NRCS

31. Secondary and Micronutrients Tim Shaver Nutrient Management Specialist UNL WCREC

32. Secondary and Micronutrients: • 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.

33. Micronutrient Sources: • Soil minerals • Soil organic matter • Crop residue • Manures/organic amendments • Fertilizers, Pesticides • Irrigation water • The atmosphere

34. Zinc (Zn): • 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

35. Zinc Deficiency:

36. Zinc Fertilizer: • 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.

37. Iron (Fe) Chlorosis: • 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

38. Fe Deficient Corn

40. Iron Fertilizers: • 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

41. Sulfur (S): • 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)

42. Sulfur Deficiency:

43. Sulfur Fertilizers: • 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

44. Application Methods: • 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 Using Global Position System equipment for precision application of fertilizer. (Photo courtesy of USDA NRCS).

45. Application Methods: Pre-plant: • Band: • Surface (Dribble) • Subsurface (Knife) • Broadcast: • Surface • Incorporated Nutrient Applicator (Source: http://www.deere.com)

46. Application Methods: • At Planting: • Band • Surface • Subsurface • Below and to side of seed • Starter (pop up) Application of anhydrous ammonia fertilizer at planting time (Photo courtesy of USDA NRCS).

47. Application Methods: After Planting • Sidedressing • Anhydrous • Fluid Sources (UAN) • Surface and Subsurface • Topdress • Solid and Liquid Sources Nitrogen being applied to growing corn (Photo courtesy of USDA NRCS).