P contamination from agricultural land is often blamed for much of the P addition to these lakes. Because of the concerns about additional P contamination of Michigan lakes and the lack of good response data on higher testing soils, MSU does not recommend P fertilizer on soils testing above 600 lb P per acre. MSU P fertilizer recommendations based on P soil test level and yield goal are given in Table 3. MSU recommends more P than is removed at low soil test levels, maintenance amounts at medium soil test levels, and less than is removed at high soil test levels. Recommendations vary, depending on the yield goal.
Higher yields require higher rates of P fertilizer than lower yields because of greater removal.
Studies conducted by MSU show that P fertilizer has no significant effect on tuber solids. Phosphorus Fertilizer Placement Most of the P fertilizer added to soil is precipitated out in an unavailable form-only small amounts remain in soil solution. For this reason, band applications alongside the seed pieces are more efficient than broadcast applications. Any P fertilizer that is applied to potatoes should be applied in bands 2 inches to the side and 2 inches below the seed pieces at planting time. Soil pH and texture greatly affect phosphorus availability.