By Robert Lucas and Darryl Warncke Dept. of Crop and Soil Sciences Michigan State University Michigan has about 4.5 million acres of land classified as organic soils. These soils in their natural state are commonly associated with wetlands, but their ecosystem can be quite diverse. They were formed by the accumulation of plant residues under water or in poorly drained areas with low oxygen content. The goal of this bulletin is to emphasize how organic soils relate to nonpoint pollution both in the natural and managed state, and to bring out ways to manage these soils for maintaining water quality. Organic Soil Defined Soil scientists describe organic soils as "histosols." These soils are commonly referred to as peat when undeveloped and fibrous in texture. When peat soils are drained and developed for crop production, the fibrous plant residues decompose into finely divided organic particles. These soils are then referred to as muck soils. To be classified as organic, a soil must exceed 20% organic matter. Many tilled organic soils exceed 50%, and undeveloped sites exceed 70%. Organic soils were formed in former pot holes, lakes and glacial river valleys: examples of "eutrophication" under natural environments. Only 125,000 acres of Michigan's extensive organic soils are used in agriculture. Of this acreage, about 35,000 acres are intensely farmed with such crops as sod, potatoes, onions, carrots, mint, celery and radishes. The gross agricultural value in recent years of the intensely farmed crops is about $90 million. Organic soils in their natural state are very low in mineral elements essential for plant growth. Deficiencies are particularly high in acid peats, which depend upon fallout from airborne sediments and rainwater for minerals. With the above information, we can better understand what management practices are needed to reduce nonpoint sources of chemical contamination in our waters.

Nitrogen (N) Nitrogen, a constituent of soil organic matter, usually ranges from 1.0 to 1.7% for acid peats and 1.8 to 2.5% for nonacid organic soils. When organic matter decays, nitrogen is mineralized and eventually forms nitrate nitrogen (NO3-N). Studies on cultivated vegetable mucklands in New York showed the annual mineralized rate varied from 320 to 530 lb of N per acre. Of this amount, only about 10%' of the mineralized form wasfound in drainage water. The remainder was found to be denitrified to form gaseous nitrous oxide (N2O). Investigations on the mucklands of Florida, likewise, showed high levels of denitrification. In the New York study the maximum observed concentration of NO3-N in the drainage water was 35 ppm (mg/liter) and the average was 15 ppm. At the Michigan Muck Experimental Farm in 1969, it was found that 17 lb of NO3-N per acre per year were transported in the drainage water. The content in the water was always less than 7 ppm. Both the New York and Michigan studies showed high NO3-N in the March-April drainage water when the ischarge rate was highest. Both wind and water erosion can also be major contributors to organic nitrogen added to lakes. (This source is discussed later.) Suggestions for reducing NO3-N in the leachable and drainage water: Do not apply nitrogen fertilizer in the fall or winter season. Reduce nitrogen rates in preplant fertilizer, and apply the balance when plants are actively growing. Because of a high organic matter decomposition rate when the soil temperature is high, nitrogen fertilization for muckland crops is seldom needed during July and early August. Grow cover crops to utilize available nitrogen remaining after harvest rather than leave the field without plants.