Dean Jill E, Weil Ray R
1109 HJ Patterson Hall, Dep. of Environmental Science and Technology, Univ. of Maryland, College Park, MD 20742, USA.
J Environ Qual. 2009 Feb 6;38(2):520-8. doi: 10.2134/jeq2008.0066. Print 2009 Mar-Apr.
Brassica cover crops are new to the mid-Atlantic region, and limited information is available on their N uptake capabilities for effective N conservation. Forage radish (Raphanus sativus L. cv. Daikon), oilseed radish (Raphanus sativus L. cv. Adagio), and rape (Brassica napus L. cv. Dwarf Essex) were compared with rye (Secale cereale L. cv. Wheeler), a popular cover crop in the region, with regard to N uptake ability and potential to decrease N leaching at two sites in Maryland. Plants were harvested in fall and spring for dry matter and N analysis. Soil samples from 0 cm to 105 to 180 cm depth were obtained in fall and spring for NH(4)-N and NO(3)-N analyses. Ceramic cup tension lysimeters were installed at depths of 75 to 120 cm to monitor NO(3)-N in soil pore water. Averaged across 3 site-years, forage radish and rape shoots had greater dry matter production and captured more N in fall than rye shoots. Compared with a weedy fallow control, rape and rye caused similar decreases in soil NO(3)-N in fall and spring throughout the sampled profile. Cover crops had no effect on soil NH(4)-N. During the spring on coarse textured soil, pore water NO(3)-N concentrations in freeze-killed Brassica (radish) plots were greater than in control and overwintering Brassica (rape) and rye plots. On fine textured soil, all cover crops provided a similar decrease in pore water NO(3)-N concentration compared with control. On coarse textured soils, freeze-killed Brassica cover crops should be followed by an early-planted spring main crop.
芸苔属覆盖作物对大西洋中部地区来说是新事物，关于它们有效固氮的氮吸收能力的信息有限。在马里兰州的两个地点，将饲用萝卜（Raphanus sativus L. cv. Daikon）、油菜萝卜（Raphanus sativus L. cv. Adagio）和油菜（Brassica napus L. cv. Dwarf Essex）与该地区一种常见的覆盖作物黑麦（Secale cereale L. cv. Wheeler）在氮吸收能力和减少氮淋失潜力方面进行了比较。在秋季和春季收获植物以进行干物质和氮分析。在秋季和春季采集0厘米至105至180厘米深度的土壤样本进行铵态氮和硝态氮分析。在75至120厘米深度安装陶瓷杯张力渗压计以监测土壤孔隙水中的硝态氮。在3个地点年份的平均值中，饲用萝卜和油菜的地上部分在秋季比黑麦地上部分有更高的干物质产量且吸收了更多的氮。与杂草休耕对照相比，油菜和黑麦在秋季和春季使整个采样剖面的土壤硝态氮有相似程度的减少。覆盖作物对土壤铵态氮没有影响。在春季质地较粗的土壤上，冻死的芸苔属（萝卜）地块的孔隙水硝态氮浓度高于对照地块以及越冬的芸苔属（油菜）和黑麦地块。在质地较细的土壤上，与对照相比，所有覆盖作物都使孔隙水硝态氮浓度有相似程度的降低。在质地较粗的土壤上，冻死的芸苔属覆盖作物之后应种植早播的春季主要作物。
