applications have also caused large losses up to 86% of the nitrogen and 94% of the phosphorus can
be lost in a single runoff event.
The method of fertilizer and manure application greatly affects the potential for losses in runoff.
Broadcast fertilizer should be incorporated wherever possible. Timmons et al. (1973) found disk
incorporation of fertilizer decreased dissolved nutrient losses 25-50% compared to surface application
and plow-down incorporation decreased losses by about one half.
If manure is broadcast it should be incorporated immediately. Point injection of liquid fertilizer
at 5 cm depth did not decrease nutrient losses compared to unfertilized plots (Baker and Laflen, 1982).
However research shows that the incorporation or injection of animal wastes can eliminate losses of
nitrogen through erosion and volatilization while increasing crop yields (NWQEP 1982a) .
Watershed demonstrations show that application rates can be reduced in a voluntary program.
Farmers in the Delaware RCWP have used soil and manure testing to determine manure and fertilizer
application rates. Split application of nitrogen with side banding has minimized losses by matching
fertilizer placement and timing to crop needs. Phosphorus applications have been reduced by 50%.
After a seven year period BMPs have not decreased total nitrogen to the watershed outlet. Total
phosphorus has decreased by 71% (Ritter et al. 1989) but the changes in total phosphorus may be
attributable practices associated with the reduction of suspended sediments, but also a reduction in
fertilizer application (WRANCC 1986).
In the Minnesota RCWP, the development of nitrogen budgets for farmer's fields includes
accounting for manure and legumes. Early spring application of nitrogen dropped by 50% and total
nitrogen applied decreased by 20% (NWQEP 1989). Other major practices in the watershed include
conservation tillage, contour strips, permanent vegetative cover, and animal waste management
systems. Thus far, only annual median daily loadings of suspended solids and nitrite have shown a
significant decreasing trend. AGNPS modeling comparing pre and post-implementation conditions for a
2-year, 24 hour storm estimate an 8% improvement in dissolved nitrogen concentration and a 13%
improvement in total nitrogen in sediment loading. Soluble phosphorus concentrations improved 22%
and the total phosphorus in sediment improved 15% (Wall et al. 1989).
The soil acts as a buffer or a large nutrient reservoir, releasing nitrate-nitrogen to the ground
water on a continual basis and where phosphorus has been over-applied, immediate loading reductions
due to nutrient management cannot be expected (NWQEP 1989).
To develop a strong nutrient management program, utilize the most advanced technology
accessible and provide a framework for reporting progress. Changes in management practices can
conflict with traditional farming methods. Sufficient time is required to educate farmers about efficient
methods to manage farm costs and protect water resources .
4.2-16
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