Michigan State University recommendations for phosphorus and potassium

Pull out your soil tests and use the following information to assess phosphorus and potassium levels along with your 2009 crop plan to determine where fertilizer will benefit, and where you can save money on nutrients without sacrificing yield. The following charts will help to assess your current soil test levels, showing you where your test values are within the ranges, helping you decide how risky reducing fertilizer will be.

Phosphorus is always most efficient to band 2 X 2 at planting. The price of potash may encourage the use of banding some of it as well. Maximum rates to band at 2 X 2 placement are:


Maximum fertilizer rates to band at 2 X 2 placement  

Lbs. N per acre

Lbs. P2O5 per acre

Lbs. K2O per acre

Max N + K201

Corn

40

100

100

100 (140)

Dry Beans

40

All recommended

60

100

Soybeans

-

100

80

 80

Sugarbeets

40

100

80

 80 (120)

Numbers in ( ) are for clayey soils.

MSU’s recommendations for P2O5 and K2O are based on the Buildup-Maintenance-Draw Down Model, shown below in Figure 1. The lower the level of available nutrients as indicated on a soil test, the greater the probability of a beneficial response to applied fertilizer. The critical level is the soil test level at which 95 percent of maximum yield is expected. This is usually near economic optimum return to fertilizer.

Figure 1.

''

For potassium, both the Cation Exchange Capacity (CEC) and the soil test value are taken into consideration to determine the critical value. Below the critical level, yields will respond to applied nutrients, providing an economic return. Fertilizer recommendations are based on what the crop needs for the coming year and an additional amount of nutrient for building up the soil to the critical level.

Above this critical level is a plateau range called the maintenance range. In this range, fertilizer recommendations are based on crop removal rates that will achieve economic production and maintain the soil test without expecting test levels to rise or fall. Since this is based on crop removal values, the fertilizer recommendation will vary depending on what crop is grown and the yield potential (see Chart 2). 

If soil test values are in the draw down range, no fertilizer will be needed. In this range, it is possible, profitable, and prudent to utilize the nutrients stored in the soil from past fertilizer and or manure applications. Additional resources are available at www.fieldcrop.msu.edu . Follow the link for a complete PDF copy of the Nutrient Recommendations for Field Crops in Michigan, bulletin E2904.

Chart 2


Removal rates of K2O and P2O5 at various yield potentials

Crop

Yield Potential

Estimated P2O5 crop removal

Estimated K2O crop removal

Per acre, per year

Per acre, per yr.

Corn

100

37

27

 per bushel

125

46

34

150

56

41

200

74

54

Alfalfa

3

39

150

 per ton of
 dry  hay
 equiv.

5

65

250

7

91

350

Soybeans

30

24

42

 per bu.

40

32

56

50

40

70

60

48

84

Dry Beans

15

18

24

 per CWT

20

24

32

25

30

40

30

36

48

Sugar Beets

20

26

66

 per ton

25

33

83

30

39

99

35

46

116

Wheat

50

32

19

 per bu.

70

44

26

90

57

33

 
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