Tim Shaver & Richard Ferguson University 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 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 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. 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+) 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 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. Generally stunted, and yellow in appearance. Anhydrous Ammonia: ◦ NH3 + 2O2 H+ + NO3- + H2O Urea: ◦ (NH2)2CO + 4O2 2H+ + 2NO3- + CO2 +H2O Ammonium Nitrate: ◦ NH4NO3 + 2O2 2H+ + 2NO3- + H2O Monoammonium Phosphate: ◦ NH4H2PO4 + O2 2H+ + NO3- + H2PO4- +H2O Diammonium Phosphate: ◦ (NH4)2HPO4 + O2 3H+ + 2NO3- + H2PO4- + H2O Phosphorus: Phosphorus is an essential plant nutrient ◦ Energy Transfer (ATP) ◦ Good Supply of P Increased root growth Early maturity Greater straw strength in cereals Band application on winter wheat 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. Monoammonium Phosphate: ◦ NH4H2PO4 + O2 2H+ + NO3- + H2PO4- +H2O Diammonium Phosphate: ◦ (NH4)2HPO4 + O2 3H+ + 2NO3- + H2PO4- + H2O 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). 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 chloride (KCL) Potassium sulfate (K2SO4) Potassium magnesium sulfate (K2SO4•MgSO4) Potassium nitrate (KNO3) Nebraska soils with 125ppm or greater considered sufficient. 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% Efficient N fertilizer use requires that credit is given for sources of N already available in the soil. Nitrogen cycle (source: http://www.epa.gov) ◦ ◦ ◦ ◦ ◦ Residual Nitrate (NO3) Organic Matter Mineralization Organic Materials (Manure) Previous Crop (Legumes) Irrigation (NO3 Content) 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). Nitrogen rates can be determined using UNL Extension publications specifically written for individual crops. These publications are located at: http://www.ianrpubs.unl.edu UNL recommendations can be determined from tables or from equations (corn example, In: EC117): Soil Nitrate ppm 1 3 6 9 12 18 24 Yield Goal (bu/ac) 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) 90 120 155 185 220 250 280 315 75 105 140 170 200 235 265 295 50 80 115 145 180 210 240 275 25 60 90 120 155 185 215 250 5 35 65 100 130 160 195 225 0 0 20 50 80 115 145 175 0 0 0 0 35 65 95 130 UNL Corn N Recommendation Algorithm: ◦ N need (lb/ac): Photo courtesy of USDA NRCS 35 +(1.2 x EY) -(8 x N ppm) -(0.14 x EY x OM) -credits [35+(1.2xEY)-(8xNO3-Nppm)-(0.14xEYxOM)-credits] 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 Photo courtesy of USDA NRCS 35 + 240 – 40 – 56 = 179 lbs N/ac 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 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 Photo courtesy of USDA NRCS ◦ N recommendation (credits): 126 lbs/ac ◦ Table recommendation: 155 – 180 lbs/ac Tim Shaver Nutrient 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. Soil minerals Soil organic matter Crop residue Manures/organic amendments Fertilizers, Pesticides Irrigation water The atmosphere 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 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. 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 ◦ ◦ ◦ ◦ 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 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) 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 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). Pre-plant: Band: ◦ Surface (Dribble) ◦ Subsurface (Knife) Broadcast: ◦ Surface ◦ Incorporated Nutrient Applicator (Source: http://www.deere.com) 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). 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).