Michigan State University Extension
Soils & Soil Management - Fertilizer - 06029702
07/10/97
Fertilizer Recommendations for Field Crops in Michigan Extension Bulletin E-550A, March 1992
D. R. Christenson, D. D. Warncke, M. L. Vitosh, L. W. Jacobs and J. G. Dahl, Department of Crop and Soil Sciences
Agriculture is coming under closer scrutiny as a contributor to non-point source pollution. When more nutrients are added to the soil-plant system than the crop and soil biology can use, the risk of losing nutrients to groundwater and surface waters increases. Factors such as climate, soil type, slope of the land and soil fertility levels can influence the fate of nutrients applied to the soil.
Adding excess nutrients to soils can cause phosphorus to accumulate in the upper soil profile and increase the risk of contaminating surface waters where runoff and erosion occur.
It can also lead to nitrate being leached down through the soil and into groundwater. Adding extra nutrients can create imbalances in soils which may cause poor plant growth and animal nutrition disorders for livestock eating the crops. Avoid adding surplus nutrients by soil testing at regular intervals, giving nitrogen credits for previous legume crops, giving credit for nutrients from manure and organic material additions, establishing realistic yield goals and following the fertilizer recommendations discussed in this bulletin.
As phosphorus concentrations in soils increase, the risk of losing phosphorus bound to soil particles under erosive conditions also increases. Therefore, practice adequate soil and water conservation practices which control runoff and erosion. For example, conservation tillage can reduce runoff, soil erosion and associated phosphorus loadings to surface waters.
Losses of nitrates to groundwater is a major concern because water with an excess of 10 parts per million nitrate-nitrogen poses a health hazard. Since about half of all Michigan residents obtain drinking water from groundwater, maintaining good quality groundwater is important. Therefore, never exceed the agronomic fertilizer nitrogen recommendation.
Crop producers should adopt nutrient management practices that not only provide the necessary quantities of nutrients to achieve optimum crop yields, but minimize excessive additions of nutrients that may increase the risk of polluting surface and groundwater. Adding quantities of nutrients that supply the needs of crops and avoid excess amounts achieves two desirable goals. First, taking credit for nutrients supplied from all sources used in crop production generates economic benefits to the producer through decreased input costs. Second, protecting surface and groundwater quality from potential non-point source contamination, due to agricultural activities, can best be accomplished when nutrients are applied at recommended agronomic rates. See Extension Bulletin WQ-25 and Research Publication NCR-310 listed in the references section for more information.