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  FO-00792     Revised 1993 To Order   

Understanding Phosphorus In Minnesota Soils


Table 1. The effect of banded and
broadcast phosphate on corn yield
when soil test levels for P are low.
Phosphate Applied
lb P2O5/acre		 Placement Yield
bu./acre
0 - 122
40 starter 146
100 broadcast 148
Soil test P (Bray and Kurtz #1) = 6 ppm; study conducted
at the Southwest Experiment Station, Lamberton

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Table 2. Soybean yields as affected by the rate
of phosphate applied (1986-1988 ave.)
Location
Phosphate Applied Waseca Lamberton
lb./acre - - - - - bu./acre - - - - -
0 31 27
23 33 29
46 35 30
69 36 30
92 37 32
Soil Test P (ppm): 5 3.5
(Bray and Kurtz #1)

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Table 3. Interpretation of plant analysis values for phosphorus.
Crop Plant part and sampling stage deficient low sufficient high
- - - - - - - - - % P- - - - - - - - -
corn whole plant; 12 in. height - - .40 > .80
ear leaf at tasseling < .16 .16 .25 > .50
small grain Top leaves, boot stage < .16 .16 .21 > .50
alfalfa upper 1/3 of plant, early bloom < .16 .16 .25 > .70
sunflowers 5th leaf at flowering < .15 .15 .30 > .50
Adapted from Soil Testing and Plant Analysis, Soil Science Society of America (1973). Values subject to modification as research develops.

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