Sorghum

1. Sorghum Fertility
Brian Arnall
Oklahoma State University
Dept Plant and Soil Sciences

2. Outline
• Nitrogen
• Phosphorous
• Potassium
• pH
• Micro’s

3. 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!!!!!!

4. Nitrogen
• Determined by Yield Level
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
Grain Yield

6. Strips and Sensors

7. • Independent of Yield
Phosphorous
Enter Values
5.25
0.36
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
Yield Potential, bu/ac
Price of sorghum, $/bu
Cost of P2O5, $/lb

8. 0
50
100
150
200
250
300
350
0 10 20 40 65
Soil Test P
$/acre
Yield Loss Cost
Cost of P Fertilizer
0
20
40
60
80
100
120
140
160
180
200
0 10 20 40 65
Soil Test P
$/acre
Yield Loss Cost
Cost of P Fertilizer
Cost of P Fertilizer Med
Cost of P Fertilizer High
0
50
100
150
200
250
300
350
400
0 10 20 40 65
Soil Test P
$/acre
Yield Loss Cost Low
Yield Loss Cost Med
Yield Loss Cost High
Cost of P Fertilizer
Enter Values
5.25
0.36
60
Yield Potential, bu/ac
Price of sorghum, $/bu
Cost of P2O5, $/lb
Enter Values
5.25
0.60
80
Price of sorghum, $/bu
Cost of P2O5, $/lb
Yield Potential, bu/ac
Enter Values
5.25
0.90
120
Price of sorghum, $/bu
Cost of P2O5, $/lb
Yield Potential, bu/ac

10. • Independent of Yield
Potassium
Enter Values
5.25
1.10
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
Yield Potential, bu/ac
Price of Sorghum, $/bu
Cost of K2O, $/lb

12. Variability
Soil Test K variability among 24 1-acre cells in a field, 2001
0
50
100
150
200
250
300
350
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
K
Area STK Point STK
Soil test P variability among 24 1-acre cells in a field, 2001
0
65
130
195
260
325
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
Area STP Point STP

13. pH Issues
Wheat
pH Rel Yld Yield Econ $
3.8 0 0 214.00
4.1 0.3 12 149.80
4.5 0.6 24 85.60
5 0.85 34 32.10
5.5 0.95 38 10.70
6 1 40 0.00
Average Yld 40 Grain $ 5.35
Sorghum
pH Rel Yld Yield Econ $
4.5
5
5.3 0.82 66 74.44
5.7 0.88 71 48.17
5.9 0.95 76 21.89
6.2 1 80 0.00
6.9 1 80 0.00
Average Yld 80 Grain $ 5.2
Mixed Reports, some state more Al tolerant and others show less.

14. Nutrient
Iron
Manganese
Copper
Zinc
Boron
Chlorine
Molybdenum
Soil (lb/a)*
14,000 – 1,100,000
40 – 6,000
4 - 200
20 - 600
4 - 200
40 – 1,800
0.4 - 10
*Range of total in soils. From Chemical Equilibria in Soils.
W.L.Lindsay, 1979. Wiley & Sons.
Crop (lb/a)**
1
0.8
0.08
0.6
0.08
4
0.0008
**Calculated for 2 ton crop yield (67 bushel wheat).
Micronutrients Needed by all Crops

15. Nutrients not found deficient in
Oklahoma crops.
• Calcium.
–Liming prevents Ca
deficiency.
• Manganese.
• Copper.
• Molybdenum.

16. Nutrients seldom found deficient
in Oklahoma crops.
• Magnesium.
• Sulfur.
• Iron.
• Zinc.
• Boron.
• Chlorine.

17. Mg
Yellowing between veins, old leaves
Dolomitic Lime Sul-po-Mag, K-Mag

18. Sulfur
Can look like N, Yellowing between veins
Gyp, S, Ammon Sulfate

19. Iron
Yellowing between veins, new leaves
Ferrous Sulfate, ect

20. 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

21. Soil Testing
Just Do It!

22. Thank You!
• Corn and Sorghum Nutrient Need Pete’s
Sheets coming soon