Michigan State University Extension
Soils & Soil Management - Fertilizer - 06109719
07/10/97
Nutrient Management to Protect Water Quality Extension Bulletin WQ-25, January 1996
Maurice L. Vitosh and Lee W. Jacobs Extension Soil Specialists Department of Crop and Soil Sciences Michigan State University
Crop rotations can be very beneficial in a successful crop production system. For example, a corn-soybean rotation is preferable to a continuous corn rotation because continuous corn requires more N fertilizer to obtain the optimum yield. Some of the noted yield improvement may be due to the rotational effect better disease, insect and weed control, and improved soil filth and some to N fixation by soybeans. Other non-legume rotations also have been shown to produce better yields of corn with less N fertilizer.
Forage crops such as Sudangrass and alfalfa are well suited to recovering nitrate N from soils and thereby preventing excessive nitrate leaching. Although alfalfa fixes its own N. it does so only when all of the nitrate N in the soil is gone. Alfalfa's deep rooting system makes it ideal for taking up N that has moved deep in the soil profile. The disadvantage of alfalfa is that it is slow to establish, so a longer growing period is needed before it can prevent nitrate leaching.
Cover crops such as rye can be very beneficial in preventing wind and water erosion. They protect the soil surface from erosion and thereby reduce the risk of nutrient losses by runoff as soluble nutrients or erosion as sediment. Cover crops may also be used as green manure crops to take up nitrate and prevent it from being leached to ground water. This practice is well suited to many soils in Michigan and could be used more effectively than it is now. One of the keys to utilizing cover crops successfully is to get them established in early fall so that they have a chance to take up excess nitrate N before winter dormancy and excessive precipitation occur.