Nutrient Mining, Soil Testing and Plant Nutrient Cycling
Ray WardWard Laboratories, IncKearney, Nebraskawww.wardlab.com
“Guiding Producers Today to Feed the World Tomorrow”
Nutrient Mining, lbs/BuWHEAT
Nutrient lb/bu 60 bu/ANitrogen,N 1.2 72Phosphorus, P2O5 0.52 31Potassium, K2O 0.26 16Sulfur, S 0.12 7Zinc, Zn 0.003 0.18
Nutrient Mining, lbs/BuWHEAT
Nutrient lb/bu 60 bu/AChloride 0.07 4.2Manganese 0.002 0.12Copper 0.0007 0.04Boron 0.001 0.06Molybdenum 0.0004 0.02
Nutrient Content of Wheat Straw
Nutrient lbs per tonNitrogen, N 12Phosphorus, P2O5 2.3Potassium, K2O 29Sulfur, S 4
Nutrient Mining, lbs/BuCORN
Nutrient lb/bu 100 bu/A
Nitrogen, N 0.70 70Phosphorus, P2O5 0.33 33Potassium, K2O 0.23 23Sulfur, S 0.09 9Zinc, Zn 0.001 0.1
Crop Nutrient Mining, lbs/buSOYBEAN
Nutrient lb/bu 45 bu/ANitrogen, N 3.4 153Phosphorus, P2O5 0.77 35Potassium, K2O 1.2 54Sulfur, S 0.18 8Zinc, Zn 0.003 0.09
Soil Nutrients
Mobile NutrientsNutrients that are soluble in the soilNitrate, Sulfate, and Chloride
Immobile NutrientsNutrients that are attached to soil particlesCEC and other surfacesPhosphorus, Potassium, Calcium, Magnesium, Zinc, Iron, Manganese, Copper, Boron, and Molybdenum
Two Approaches for Interpreting Soil Test Values
• Nutrient Sufficiency– Apply just enough to maximize profitability in the year of fertilizer application
• Build – Maintenance– Manage soil tests to desired soil test levels and then apply enough fertilizer to maintain the desired soil values
Which Interpretation is Correct?
• Depends on the Plant Nutrient – Mobile Nutrients like nitrate have to be managed annually
– Immobile nutrients like phosphate and potash can be built up and maintained
• Depends on Land Tenure– Short term land leases dictate using the sufficiency approach
• Limited Resources– Cannot afford to build soil tests or fertilizer prices are high
Where are the Biggest Yields?• Observations over the years I have concluded the best yields come from high‐testing soils.
• Research in Canada with small grains has shown higher yields on high‐testing soils than annual applications of fertilizer on low testing soils.
• Rothamsted Experiment station in England has demonstrated that yields were higher on high testing soils. Crops and Soils, ASA
Importance of PhosphorusTribune (KSU)2004
N, lbs per acre Corn Yield, Bu/A0 6740 9280 118120 103160 136200 162
Importance of PhosphorusTribune (KSU)2004
N+P2O5, lbs/A Corn Yield, Bu/A0+40 9740+40 14880+40 209120+40 228160+40 231200+40 234
Conclusions• Highest crop yield are associated with high soil tests
• Can we continue to reach the higher yield if we use a fertility approach that minimizes fertilizer application, especially phosphorus and potassium?
Mobile Nutrients• Nitrate
– Nitrate is soluble. It moves downward as water moves through the root zone.
– We only want to apply the amount of N that is needed for the current crop.
– Non‐legumes need more N than legumes (soybeans, alfalfa, and peanuts).
– The goal is to have 2 to 5 ppm NO3‐N after harvest.
Nitrogen Requirement
Corn 1.2 lbs N/BuWheat 2.4 lbs N/BuMilo 1.1 lbs N/BuGrass 40 lbs N/TonSunflower 50 lbs N/1000 lbs
Nitrogen Recommendation
N lbs/A = (yield * N req.)lbs of NO3‐N in 24 or 36”
Legume creditManure credit
Irrigation water credit
Nitrogen Recommendation
• An Example• Wheat • 60 bu/A X 2.4 = 144 lbs of N required• Subtract the following• Soil nitrate = 30 lbs of N• Past legume = 20 lbs of N• Amount of N to apply = 94 lbs of N/A
Sulfur• Sulfate is soluble and moves with soil water like nitrate. Do not try to build sulfate. Some soils have sulfate in the subsoil which reduces the need for sulfur.
• Apply sulfur when soil test for sulfate is low.
Sulfur Requirement
Crop Yield Unit LBS of SCorn Bushel 0.18-0.26Soybean Bushel 0.20-0.29Wheat Bushel 0.28-0.35Alfalfa Ton 4.7 – 6.3Grass Ton 2.2 – 3.6
Sulfur Recommendation Example
Wheat 60 bu/A Yield GoalSulfur Requirement is 0.28 to 0.35 lb S/buTotal S Required is 17 to 21 lbs/ASulfate Soil Test is 8 ppm S8 X 2.4 = 19 lbs S/ARecommendation is 0 to 5 lbs S/A
Chloride• Chloride is a soluble ion like nitrate, but does not move as fast as nitrate.
• Many soils are low in chloride where potash fertilizer is not used.
• 0‐0‐60 is potassium chloride, so it is 60 % K2O and 45 % Chloride
• Ammonium Chloride, dry or liquid, is very good chloride fertilizer
Soil test chloride interpretations and fertilizer recommendations for Kansas.
____________________________________________________________Soil Chloride in a 0‐24" sample Cl Recommended*
Category lb/acre ppm lb/acre__________________________________________________________
__Low <30 <4 20Medium 30‐45 4‐6 10 High > 45 >6 0
____________________________________________________________
*Recommendations for corn, sorghum and wheat only.
Phosphorus Recommendations
Soil test ppm P Rating lbs P2O5/A0‐5 Very Low 60‐1406‐12 Low 35‐7513‐25 Medium 20‐4526‐50 High 0‐3051+ Very High None
Phosphorus (My Goals)• Ideal Phosphorus Soil Test:
– Dryland areas = 22‐28 ppm P– Irrigated/high rainfall areas = 30‐40 ppm P
• How to Get There – Soil texture: loam or heavier
• 18 lbs of P2O5 to raise soil P test 1 ppm P
– Soil texture: sand to sandy loam • 12 lbs of P2O5 to raise soil P test 1 ppm P
Phosphorus
• How to Get There Example for a silt loam– Soil test is 15 ppm P and I want to get to 25 ppm P
• 25 – 15 = 20 ppm increase• 10 X 18 = 180 lbs of P2O5• 180 / .52 = 346 lbs of 11‐52‐0• How many years do you want to take to get there? Divide by the number of years . This application is in addition to amount you normally apply.
Potassium Recommendations
Soil Test ppm K Rating lbs K2O0-40 Very Low 90-20041-80 Low 50-12081-120 Medium 25-60121-200 High 0-35201+ Very High None
Potassium (My Goals)• How to Get There Example for a silt loam
– Soil test is 120 ppm K and I want to get to 160 ppm K
• 160‐120 = 40 ppm increase• 40 X 9 = 360 lbs of K2O• 360 / 0.60 = 600 lbs of 0‐0‐60• How many years do you want to take to get there? Divide by the number of years . This application is in addition to amount you normally apply.
Zinc
• I have found that the best way to correct a low zinc soil test is to broadcast enough zinc sulfate (33 to 36 % Zn) to raise the zinc soil test above 1 ppm.
• One pound of actual zinc will raise the zinc soil test 0.1 ppm Zn.– Zn recommendation = (1.0 – Zn soil test) times 10– Zn soil test = 0.60: (1.00 – 0.60) X 10 = 4 lbs of Zn/A
Copper• Copper soil tests are low in a few area of the Plains.
• For most crops I like to see a copper (Cu) value of 0.20 ppm P. For a few crops like potatoes I try to raise the Cu soil test to 0.60 ppm Cu.
• Three pounds of Cu will raise the soil test 0.10 ppm Cu
• Cu rec. = (0.20 ‐ .12) X 3 = 2.4 lbs of Cu
Boron• Boron is less soluble than some of the anions.• But boron has a narrow safe range. Do not try to build B soil test. Boron should be applied when the B soil test is less than 0.25 ppm, except for cotton, peanuts and sugar beets that need 0.50 ppm B.
• B recommendation = One pound of B will raise the soil test 0.10 ppm B. Example: for wheat, corn, milo, etc.
• 1.5 – (5 x 0.20) = (1.5 – 1.0) = 0.5 lbs B
No Till Fertilizer Program
• It is best to “knife in” nitrogen• Do not do a weed and feed program for N• Phosphorus and other nutrients can be broadcast or placed in a band
• Second alternative for N is stream on UAN or broadcast urea
• Split application is necessary for sandy soils.
Nutrient Cycle?
1. Nutrients are removed from the land any time grain or forage is transported from the area.
2. How are the nutrients replaced? Higher yields ‐the more nutrients that have to be replaced.
3. Carbon and some nitrogen comes from the air.4. Other nutrients have to come from soil minerals,
decomposition of organic matter, manures and fertilizer.
Calcium and Magnesium• Lime
– 480 lbs of Ca per ton of 60 % ECC • Wheat
– 9 lbs of Ca per ton of dry forage– 2.8 lbs of Mg per ton of dry forage
• Turnips– 66 lbs of Ca per ton of dry forage– 7 lbs of Mg per ton of dry forage
Carbon/Organic Matter
• Soil Organic Matter – Carbon and all plant nutrients
• 1 % OM in 8 inches of Soil is 24,000 lbs/A• This Quantity of OM Holds About 1400 lbs of
N and 200 lbs of S per Acre.
No‐Till Sulfur Deficiency
• Most of the Sulfur in the soil is held in the organic matter portion of the soil
• The idea is the build soil organic matter to improve soil quality and health and increase soil productivity.
• 100C : 10N : 1.4S
A/C Greenfix BlendAbove Ground Biomass Test Results
10/11/2010 (4 reps)High Low Avg.
Yld. T/A 2.95 2.05 2.39
Nutrients in #/A
C 2373 1743 1958
N 125 105 118
P205 18 10 14
K20 232 134 187
Ca 99 46 67
Mg 14 9 11
S 18 9 15
Zn 0.72 0.41 0.63
Fe 2.94 1.87 2.20
Mn 0.35 0.24 0.28
C:N =16.6
Grass % Brassica % Legume %
0 41 59
Soil Organic Matter
• Enhance crop productivity• Build soil fertility• Improve structure• Build aggregate stability• Increase nutrient retention• Increase water holding capacity
Nutrient Balance and Carbon Sequestration.
Net carbon sequestration requires other nutrients.
7 – 10 units of C per unit of N
50 –60 units of C per unit of P
70 – 80 units of C per unit of S
Balanced fertilization is needed for both crop uptake and carbon sequestration!
Rattan Lal, 27 Jan., 2000
C
N P
KS
ZnCa
Mg
Mn
Bo
Cletc.
C
Soil carbon is the “Keystone” for all soil physical, chemical and biological processes and properties.
N PK Ca
Mg S
Zn Mn
Cl Bo
Management platformfertility, variety, irrigation, species, cover crop, manure, rotations, tillage, soil type, erosion, timing,
Carbon is a “keystone” in nutrient cycling!