A soil test for nitrogen availabilty to corn (Zea mays, L) has gained wide acceptance in the northeast region of the United States. The test involves sampling the surface 30 cm of soil during the early part of the growing season. The N0 3 -N present at that time is correlated with the probability of obtaining a yield increase by using sidedress nitrogen fertilizer. The test has been evaluated in 272 yr-site N response experiments in Vermont, Pennsylvania, Connecticut, New York, and New Hampshire. The various states in the region that are now offering a N soil test (Vermont, Pennsylvania, Connecticut, and Maine) have different methods of making recommendations based on soil-test levels. However, 20 to 30 mg NO 3 -N/kg soil is about the critical range above which there is a low 1103

Long‐term aerobic incubations were conducted on soils previously amended with cow and poultry manure, sewage sludge, and mycelium to determine N mineralization potential (No) and N mineralization rate constant (k). Values for No were higher than those reported by other workers. The k values varied among soils sufficiently so that a single value could not be assumed for any one group of soils. Corn (Zea mays L.) was grown on five of the soils used in the incubation study. Soil moisture and soil temperature data from NoN0 and initial mineral N, estimates of N available to the crop. Yield and N uptake correlated well with the parameter No × k, but No alone proved to be a very poor predictor of yield or N uptake. K values, which can be estimated only from lengthy incubations, are required to obtain accurate estimates of N availability.

High rates of N fertilizers and limited crop uptake of N during the growing season can result in excessive accumulation of soil nitrate (NO−3). Soil NO−3 can be decreased with efficient cropping systems. Experiments were conducted in Connecticut from 1987 through 1990 on a Paxton fine sandy loam soil (coarse‐loamy, mixed, mesic Typic Dystrochrept) to determine the effects of N rate and cropping system on soil NO−3. Orchardgrass (Dactylis glomerata L.), red clover (Trifolium pratense L.), a double‐crop system of oat (Avena sativa L.) followed by tyfon [Brassica rapa L. × B. pekinensis (Lour.) Rupr.], maize (Zea mays L.) followed by a cover crop of winter rye (Secale cereale L.), and a fallow system received preplant N at 0, 112, 224, 336, and 448 kg ha−1. Each system was evaluated for two consecutive growing seasons and repeated three times. Nitrogen was applied only in the first growing season. Soil NO−3 at the first autumn sampling generally increased for all systems as N rate increased. Mean spring soil NO−3 levels were only 23% of previous autumn NO−3 levels. By the second autumn sampling, soil NO−3 values were near background levels except in the fertilized fallow system. At the two highest N rates, oat‐tyfon produced the smallest overwinter change in soil NO−3 storage. An oat‐tyfon double crop, orchardgrass, or red clover system should decrease soil NO−3 more effectively than maize or a noncropped fallow when soil NO−3 accumulations are greater than those produced from N inputs equivalent to 224 kg ha−1.

Excessive application of N‐containing fertilizers may result in high concentrations of soil nitrate. Soil nitrate levels can be reduced with cropping systems that best utilize N. Split‐plot design experiments were conducted in Connecticut from 1987 through 1990 on a Paxton fine sandy loam soil (coarse‐loamy, mixed, mesic Typic Dystrochrept) to determine the effectiveness of various cropping systems in utilizing N. Orchardgrass (Dactylis glomerata L.), red clover (Trifolium pratense L.), a doublecrop system of oat (Avena sativa L.) followed by the forage brassica tyfon [Brassica rapa L. × B. pekinensis (Lour.) Rupr.], and maize (Zea mays L.) followed by a cover crop of winter rye (Secale cereale L.) received preplant N at 0, 112, 224, 336, and 448 kg ha−1. Cropping systems were tested three times for two consecutive growing seasons, with N applied only in the first season. Dry matter yield (DMY), N uptake (NUP), apparent N recovery (NREC), and N use efficiency (NUE) were determined. Maize‐rye produced the greatest DMY (18.3 to 22.8 Mg ha−1), followed by oat‐tyfon (9.8 to 16.5 Mg ha−1). Highest NUP (121 to 329 kg N ha−1) and NREC (46.5 to 81.7%) were obtained by oat‐tyfon. The greatest NUE was produced by maize‐rye and oat‐tyfon at 112 kg N ha−1. The oat‐tyfon double crop provides the most effective means for preventing N loss among the systems evaluated for N rates > 112 kg ha−1.

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