Abstract:

To explore the law of demand for nitrogen at different growth stages of alfalfa, the influences of 3 nitrogen forms (NO₃^--N, NH₄⁺-N and NO₃^--N:NH₄⁺-N was 1:1) and 3 nitrogen levels (0, 105, 210 mg·L^-1) on nitrogen metabolism at different growth stages of ‘Gannong No. 3’ alfalfa was studied with sand culture method. The results showed that the nodule number, nodule weight, nitrogenase activity, nitrate nitrogen content, ammonium nitrogen content, nitrate reductase activity and nitrogen content of ‘Gannong No. 3’ Varity under different treatments of nitrogen forms were significantly higher than those of CK. The mixed nitrogen had the best effect on alfalfa nodule number, nodule weight, nitrogenase activity and nitrogen content, followed by NH₄⁺-N, NO₃^--N was the worst. The 7 tested indexes of 210 mg·L^-1 nitrogen treatments were higher than those of 105 mg·L^-1 nitrogen treatments with all nitrogen forms. The nodule number, nodule weight, nitrogenase activity and nitrogen content of alfalfa were the highest in 210 mg·L^-1 mixed nitrogen treatment; the nitrate nitrogen content and nitrate reductase activity of alfalfa were the highest in 210 mg·L^-1NO₃^--N treatment; the ammonium nitrogen content of alfalfa was the highest in 210 mg·L^-1 NH₄⁺-N treatment. All tested indexes increased first and then decreased with the development of reproductive period except the nitrogen content of alfalfa decreased during reproductive period. There were significant positive correlations between nodule number and nodule weight; and among nodule number, nodule weight and nitrogenase activity.

Key words: ‘Gannong No. 3’, Nitrate nitrogen, Ammonium nitrogen, Nitrogen metabolism

摘要：

为探讨紫花苜蓿(Medicago sativa)不同生育期需氮规律,采用砂培法研究3种氮素形态配比(NO₃^--N, NH₄⁺-N以及NO₃^--N:NH₄⁺-N为 1:1)和3个氮素水平(0, 105, 210 mg·L^-1)对‘甘农3号’ (Medicago sativa ‘Gannong No. 3’)整个生育期氮代谢的影响.结果表明:不同氮素形态处理下,‘甘农3号’的根瘤数、根瘤重、固氮酶活性、NO₃^--N含量、NH₄⁺-N含量、硝酸还原酶活性和全氮含量均显著高于CK,混合态氮对于增加‘甘农3号’根瘤数、根瘤重、固氮酶活性和全氮含量效果最好,NH₄⁺-N次之,NO₃^--N效果最差.氮素浓度为210 mg·L^-1时,各形态配比下7项测定指标均高于105 mg·L^-1,其中根瘤数、根瘤重、固氮酶活性和全氮含量在NO₃^--N+NH₄⁺-N的浓度为210 mg·L^-1最大;NO₃^--N含量和硝酸还原酶活性在NO₃^--N浓度为210 mg·L^-1时最大;NH₄⁺-N含量在NH₄⁺-N浓度为210 mg·L^-1时最大.各项测定指标均随着生育期的推进呈先增大后减小的趋势,全氮含量始终呈减小趋势.整个生育期,根瘤数与根瘤重成极显著正相关关系;根瘤数、根瘤重与固氮酶活性成显著正相关关系.

关键词: &lsquo, 甘农3号&rsquo, NO₃^--N, NH₄⁺-N, 氮代谢