Root-zone mineral nitrogen changes as affected by crop sequence and tillage.
1994
Meek B.D. | Carter D.L. | Westermann D.T. | Peckenpaugh R.E.
Crop sequence and tillage affect soil mineral N (NH4 plus NO3) and NO3 leaching below the root zone following alfalfa (Medicago sativa L.). A 2-yr field experiment was conducted in south-central Idaho to determine the effect on soil NO3 levels of a corn (Zea mays L.)-wheat (Triticum aestivum L.) rotation compared with a bean (Phaseolus vulgaris L.)-bean rotation and to demonstrate improved N utilization with a corn-wheat rotation. Alfalfa, growing on an irrigated Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid), was killed in October 1989 with herbicide. Treatments were: (i) BT-BT: conventional tilled bean grown in 1990 and 1991; (ii) CNT-WNT: no-till silage corn grown in 1990, and no-till winter wheat grown in 1990-1991; and (iii) CT-WT: same as CNT-WNT but under conventional tillage. Similar amounts-of soil N were mineralized the first (275 kg N ha-1) and second (213 kg N ha-1) year after killing the alfalfa in all treatments. The BT-BT treatment had the highest growing-season soil mineral N (up to 251 kg ha-1, 0-0.45-m depth) because the N uptake by bean was lower (187 kg N ha-1) than corn (252 kg N ha-1, average of CT-WT and CNT-WNT treatments) in 1990 and later than winter wheat uptake in 1991. Most wheat N uptake had occurred by late June when bean uptake was just starting. A rotation that follows alfalfa with corn or a crop with a similar N uptake pattern, instead of bean, will save N fertilizer, lower soil NO3 levels, and reduce NO3 leaching potential.
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