Sorghum Fertility
Brian Arnall
Oklahoma State University
Dept Plant and Soil Sciences
Outline
• Nitrogen
• Phosphorous
• Potassium
• pH
• Micro’s
Soil Testing
• OSU, Ward, ect. $10 - $15
– 20 lb N $9
– 20 lb P $7.2
– ¼ Ton Lime $5-10
» Per Acre!!!!!
• Some Co-Ops and Fertilizer Dealers,
– Take and Process samples for FREE!!!!!!
Nitrogen
• Determined by Yield Level
Grain Yield N
lbs / ac bu / ac lb / ac
2000 36 30
2500 45 40
3000 54 50
4000 71 70
4500 80 85
5000 89 100
7000 125 160
8000 143 195
9000 161 230
Strips and Sensors
Phosphorous
• Independent of Yield
Enter Values
Price of sorghum, $/bu 5.25
Cost of P2O5, $/lb 0.36
Yield Potential, bu/ac 100
STP Index Sufficiency P2O5 Needs Yield Loss w/o P
lb /ac % lbs/ac bu/ac
0 40 60 60
10 60 50 40
20 80 40 20
40 95 20 5
65 100 0 0
Enter Values Enter Values Enter Values
Price of sorghum, $/bu 5.25 Price of sorghum, $/bu 5.25 Price of sorghum, $/bu 5.25
Cost of P2O5, $/lb 0.36 Cost of P2O5, $/lb 0.60 Cost of P2O5, $/lb 0.90
Yield Potential, bu/ac 60 Yield Potential, bu/ac 80 Yield Potential, bu/ac 120
350
300 200
180
250 400 Yield Loss Cost
160
350 Cost of P Yield Loss Cost
Fertilizer
$/acre
200 140
Cost of P Fertilizer Loss Cost Low
Yield
120 300
$/acre
150 Yield Loss
Cost of P Fertilizer Med Cost Med
100 Yield Loss
Cost of P Fertilizer High Cost High
250
$/acre
100 80 Cost of P Fertilizer
200
60
50
40 150
0 20 100
0 0 10 20 40 65
50
0 10
Soil Test P 20 40 65
0
0 Test
Soil10 P 20 40 65
Soil Test P
Potassium
• Independent of Yield
Enter Values
Price of Sorghum, $/bu 5.25
Cost of K2O, $/lb 1.10
Yield Potential, bu/ac 100
STK Index Sufficiency K2O needs Yield Loss w/o K
lb /ac % lbs/ac bu/ac
0 40 100 60
75 65 75 35
125 80 50 20
200 95 30 5
250 100 0 0
Variability
Soil Test K variability among 24 1-acre cells in a field, 2001
350
Area STK Point STK
300
250
Soil Test K
200
150
100
50
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Cell Soil test P variability among 24 1-acre cells in a field, 2001
325
Area STP Point STP
260
Soil Test-P
195
130
65
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Cell
pH Issues
Sorghum Wheat
pH Rel Yld Yield Econ $
pH Rel Yld Yield Econ $
4.5
3.8 0 0 214.00
5
5.3 0.82 66 74.44 4.1 0.3 12 149.80
5.7 0.88 71 48.17 4.5 0.6 24 85.60
5.9 0.95 76 21.89 5 0.85 34 32.10
6.2 1 80 0.00 5.5 0.95 38 10.70
6.9 1 80 0.00 6 1 40 0.00
Average Yld 80 Grain $ 5.2 Average Yld 40 Grain $ 5.35
Mixed Reports, some state more Al tolerant and others show less.
Micronutrients Needed by all Crops
Nutrient Soil (lb/a)* Crop (lb/a)**
Iron 14,000 – 1,100,000 1
Manganese 40 – 6,000 0.8
Copper 4 - 200 0.08
Zinc 20 - 600 0.6
Boron 4 - 200 0.08
Chlorine 40 – 1,800 4
Molybdenum 0.4 - 10 0.0008
*Range of total in soils. From Chemical Equilibria in Soils.
W.L.Lindsay, 1979. Wiley & Sons.
**Calculated for 2 ton crop yield (67 bushel wheat).
Nutrients not found deficient in
Oklahoma crops.
• Calcium.
–Liming prevents Ca
deficiency.
• Manganese.
• Copper.
• Molybdenum.
Nutrients seldom found deficient
in Oklahoma crops.
• Magnesium.
• Sulfur.
• Iron.
• Zinc.
• Boron.
• Chlorine.
Mg
Yellowing between veins, old leaves
Dolomitic Lime Sul-po-Mag, K-Mag
Sulfur
Can look like N, Yellowing between veins
Gyp, S, Ammon Sulfate
Iron
Yellowing between veins, new leaves
Ferrous Sulfate, ect
Micro Nutrients
• Zinc, Bronze between Margin and Midrib.
Bleaching on either side of Midrib
Zinc Sulfate, Zinc Chloride, Zinc Chelate
• Boron, Borax
• Chloride, Upper Leave Wilt,
Muriate of Potash
which K is usually also deficient
Soil Testing
Just Do It!
Thank You!
• Corn and Sorghum Nutrient Need Pete’s
Sheets coming soon