NITROGEN-UTILIZATION OF SELECTED CROPPING SYSTEMS IN THE US-NORTHEAST.1. DRY-MATTER YIELD, N-UPTAKE, APPARENT N-RECOVERY, AND N-USE EFFICIENCY

Excessive application of N-containing fertilizers may result in high c oncentrations of soil nitrate. Soil nitrate levels can be reduced with cropping systems that best utilize N. Split-plot design experiments w ere conducted in Connecticut from 1987 through 1990 on a Paxton fine s andy loam soil (coarse-loamy, mixed, mesic Typic Dystrochrept) to dete rmine the effectiveness of various cropping systems in utilizing N. Or chardgrass (Dactylis glomerata L.), red clover (Trifolium pratense L.) , a double-crop system of oat (Avena sativa L.) followed by the forage brassica tyfon [Brassica rapa L. x B. pekinensis (Lour.) Rupr.], and maize (Zea mays L.) followed by a cover crop of winter rye (Secale cer eale L.) received preplant N at 0, 112, 224, 336, and 448 kg ha(-1). C ropping systems were tested three times for two consecutive growing se asons, with N applied only in the first season. Dry matter yield (DMY) , N uptake (NUP), apparent N recovery (NREC), and N use efficiency (NU E) 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 oa t-tyfon. The greatest NUE was produced by maize-rye and oat-tyfon at 1 12 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).