|Douglas Jr, Clyde|
Submitted to: Journal of Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/1998
Publication Date: N/A
Interpretive Summary: Nitrogen movement from soils into surface and ground waters is an important national issue. It is imperative we have precise nitrogen fertilizer recommendations to reduce the contamination of streams and lakes. Under- and over- fertilization represents a significant economic cost for the producer and over fertilization increases the eutrophication potential due to nutrient excess. Soils themselves have compounds that contain nitrogen that can be released through activity of soil microorganisms. We need to know how much nitrogen is being released by soils in order to make more precise fertilizer recommendations. Nitrogen released by soils can be evaluated in the laboratory much quicker than in the field. A series of soils were evaluated for nitrogen release in the laboratory in controlled temperature and moisture conditions. Nitrogen mineralized from the 60 cm soil depth during 49 d laboratory incubation was lineraly related to total soil N. Nitrogen mineralization values from the incubation, corrected for climatic fluctuations in the field, can be used by industry and university personnel to help increase precision of fertilizer recommendations.
Technical Abstract: Nitrogen fertilizer recommendations often do not include the amount of nitrogen mineralized from soil organic matter. Sometime more nitrogen is applied than required by the plant when nitrogen mineralized from soil organic matter is not factored into the fertilizer recommendation. This can result in detrimental effects on plant nutrition, the environment, and producer economics. A range of soils spanning a climosequence (<250 to >700 mm annual precipitation), were sampled, in 20 cm depth increments, to evaluate nitrogen mineralized along an 80 km transect in northeastern Oregon. Soils were incubated at 25C with and without addition of wheat residue, for a maximum of 112 days. The top 20 cm of uncultivated native soils mineralized from 29 to 123 Mg N/ha across the transect while cropped soils mineralized only 28 to 61 Mg N/ha during the extended incubation. Addition of wheat residue immobilized N for 20 to 62 days and decreased the total amount of nitrogen mineralized an average of 33% for both cropped and native soils. In general, native soils mineralized greater amounts of nitrogen with depth than cropped soils.