Kuo S, Huang B, Bembenek R
Washington State University, Puyallup, WA 98371, USA.
ScientificWorldJournal. 2001 Oct 25;1 Suppl 2:22-9. doi: 10.1100/tsw.2001.267.
Biculture of nonlegumes and legumes could serve as cover crops for increasing main crop yield, while reducing NO3 leaching. This study, conducted from 1994 to 1999, determined the effect of monocultured cereal rye (Secale cereale L.), annual ryegrass (Lolium multiflorum), and hairy vetch (Vicia villosa), and bicultured rye/vetch and ryegrass/vetch on N availability in soil, corn (Zea mays L.) yield, and NO3-N leaching in a silt loam soil. The field had been in corn and cover crop rotation since 1987. In addition to the cover crop treatments, there were four N fertilizer rates (0, 67, 134, and 201 kg N ha(-1), referred to as N0, N1, N2, and N3, respectively) applied to corn. The experiment was a randomized split-block design with three replications for each treatment. Lysimeters were installed in 1987 at 0.75 m below the soil surface for leachate collection for the N 0, N 2, and N 3 treatments. The result showed that vetch monoculture had the most influence on soil N availability and corn yield, followed by the bicultures. Rye or ryegrass monoculture had either no effect or an adverse effect on corn yield and soil N availability. Leachate NO3-N concentration was highest where vetch cover crop was planted regardless of N rates, which suggests that N mineralization of vetch N continued well into the fall and winter. Leachate NO3-N concentration increased with increasing N fertilizer rates and exceeded the U.S. Environmental Protection Agency's drinking water standard of 10 mg N l(-1) even at recommended N rate for corn in this region (coastal Pacific Northwest). In comparisons of the average NO3-N concentration during the period of high N leaching, monocultured rye and ryegrass or bicultured rye/vetch and ryegrass/vetch very effectively decreased N leaching in 1998 with dry fall weather. The amount of N available for leaching (determined based on the presidedress nitrate test, the amount of N fertilizer applied, and N uptake) correlated well with average NO3-N during the high N leaching period for vetch cover crop treatment and for the control without the cover crops. The correlation, however, failed for other cover crops largely because of variable effectiveness of the cover crops in reducing NO3 leaching during the 5 years of this study. Further research is needed to determine if relay cover crops planted into standing summer crops is a more appropriate approach than fall seeding in this region to gain sufficient growth of the cover crop by fall. Testing with other main crops that have earlier harvest dates than corn is also needed to further validate the effectiveness of the bicultures to increase soil N availability while protecting the water quality.
非豆科植物与豆科植物的间作可以作为覆盖作物，提高主作物产量，同时减少硝酸盐淋失。本研究于1994年至1999年进行，测定了单作的谷物黑麦（黑麦草）、一年生黑麦草和毛苕子，以及黑麦/苕子和黑麦草/苕子间作对粉质壤土中氮有效性、玉米产量和硝态氮淋失的影响。该田地自1987年以来一直实行玉米和覆盖作物轮作。除了覆盖作物处理外，还对玉米施用了四种氮肥施用量（0、67、134和201千克氮/公顷，分别称为N0、N1、N2和N3）。试验采用随机区组设计，每个处理重复三次。1987年在土壤表面以下0.75米处安装了渗滤计，用于收集N0、N2和N3处理的渗滤液。结果表明，苕子单作对土壤氮有效性和玉米产量影响最大，其次是间作。黑麦或黑麦草单作对玉米产量和土壤氮有效性要么没有影响，要么有不利影响。无论氮肥施用量如何，种植苕子覆盖作物的地方渗滤液中硝态氮浓度最高，这表明苕子氮的矿化在秋冬季节仍持续良好。渗滤液中硝态氮浓度随氮肥施用量增加而增加，即使在该地区（太平洋西北部沿海）玉米推荐施氮量下，也超过了美国环境保护局10毫克氮/升的饮用水标准。在高氮淋失期平均硝态氮浓度的比较中，单作的黑麦和黑麦草或间作的黑麦/苕子和黑麦草/苕子在1998年秋季干燥天气下非常有效地减少了氮淋失。可淋失氮量（根据追肥前硝酸盐测试、施用氮肥量和氮吸收量确定）与苕子覆盖作物处理和无覆盖作物对照在高氮淋失期的平均硝态氮相关性良好。然而，对于其他覆盖作物，这种相关性不成立，主要是因为在本研究的5年中，覆盖作物在减少硝态氮淋失方面的效果参差不齐。需要进一步研究确定在该地区，将接力覆盖作物种植到夏季生长的作物中是否比秋季播种更合适，以便覆盖作物在秋季获得足够的生长。还需要对收获日期比玉米早的其他主作物进行测试，以进一步验证间作对提高土壤氮有效性同时保护水质的有效性。
