Abstract: To explore the law of soil nitrogen transformation and absorption after the application of sheep urine in alfalfa mixed grassland, the greenhouse control experiment was used to study the changes of soil ammonium nitrogen,nitrate nitrogen,soil enzyme activity,aboveground and underground biomass in a mixed grassland of Medicago sativa L.+ Bromus inermis Leyss. and bare field after the applications of four sheep urine as 0 (N1),8.64 (N2),25.92 (N3),43.20 (N4) kg·hm^-2,respectively. The results showed as follows:1) The ammonium nitrogen content in soil after all sheep urine addition reached the peak on the first day;the nitrate nitrogen content in soil reached the peak on the 9th day. 2) On the day of application of sheep urine,the soil urease activity in N1 and N2 treatments were significantly increased,while deceased in N3 treatment;on day the first and 21^st day since the urine adition,the nitrite reductase activities in the soil of the mixed grassland treated with N3 were 283.93 μg·(d·g)^-1and 337.64 μg·(d·g)^-1,which were significantly higher than those treated with N1. 3) The plant height,chlorophyll content,aboveground biomass and protein content of Brmus intermis Leyss. significantly increased after application of the sheep urine in the mixed grassland,but that application had no significant effect on alfalfa. The mixed grassland of alfalfa and smooth brome could regulate the efficiency of nitrogen conversion and absorption of sheep urine,and reduce the risk of environmental release of nitrogen in urine during the production of animal husbandry,which would have a broad application value.

Key words: Mixed grassland, Sheep urine, Nitrate nitrogen, Ammonium nitrogen, Enzyme activity

摘要： 为探究苜蓿(Medicago sativa L.)混播草地施用羊尿后土壤氮素转化和吸收规律。本实验通过温室控制，研究了4个羊尿施用梯度下(0，8.64，25.92，43.20 kg·hm^-2，分别记为N1，N2，N3，N4)，苜蓿+无芒雀麦(Bromus inermis Leyss.)混播草地和裸地的土壤铵态氮和硝态氮含量、土壤酶活性、地上地下生物量等指标的变化规律。结果表明：所有施用羊尿处理的土壤铵态氮含量在第1天达到峰值；硝态氮含量在第9天到达峰值；N1和N2处理下，土壤脲酶活力显著增加，N3处理下脲酶活性降低；羊尿施入提高了亚硝酸还原酶的活性；羊尿施入显著提高了混播草地中无芒雀麦的株高、叶绿素含量、地上生物量、粗蛋白含量，添加羊尿增加无芒雀麦在混播草地中的生物量和竞争力。苜蓿混播可以调控羊尿中氮素转化吸收效率，减少畜牧业生产过程中尿液中氮的环境释放风险，具有广阔的推广应用价值。

关键词: 苜蓿混播草地, 羊尿, 硝态氮, 铵态氮, 酶活力