施氮对西藏农田土壤有机碳及酶活性的影响

探明不同施氮量对拉萨农田土壤有机碳和酶活性的影响,设计5个试验处理(T1~T5):0、75、150、225 kg N/hm~2以及当地适宜施肥量:150 kg N/hm~2,135 kg P_2O_5/hm~2,分别于播种前和青稞收获后采集各处理0~20 cm土壤样品测定其总有机碳、活性有机碳、腐殖质碳、胡敏酸和富里酸含量、蔗糖酶活性、多酚氧化酶活性和脲酶活性。研究结果表明:拉萨农田土壤有机碳总量偏低,活性有机碳比例较大,土壤腐殖化率较低。短期内施用氮肥能通过增加土壤活性有机碳而使土壤总有机碳含量增加,但降低土壤腐殖质碳含量,提高土壤HA/FA。施用氮肥短期内可以使当地农田土壤有机碳含量增加,T4施氮量可以优化土壤微环境,利于土壤酶活性升高和土壤有机碳的积累。

N Application Affects Soil Organic Carbon and Enzyme Activities in Tibet Farmland Soil

To explore the effects of different nitrogen application rates on soil organic carbon and enzyme activities in Lhasa farmland, a field experiment was conducted with five treatments (T1-T5): 0, 75, 150, 225 kg N /hm2, and 135 kg P2O5/hm2, respectively. The application rates of 225 kg N/hm2 and 135 kg P2O5/hm2 were considered as the suitable fertilization amounts. 0-20 cm soil samples were collected before and after harvest of highland barley, to determine the biochemical properties including total organic carbon, labile organic carbon, humus carbon and humic acid content, and sucrase, polyphenol oxidase and urease activities, respectively. The results showed that the total amount of soil organic carbon and the humification rate were low in Lhasa farmland, however, the proportion of active organic carbon was large. Short- term application of nitrogen fertilizer increased soil total organic carbon by raising soil active organic carbon and improved soil HA/FA, however, reduced soil humus carbon content. In the short term, the application of nitrogen fertilizer might increase the soil organic carbon content in local farmland, T4 can optimize the soil microenvironment, and improve soil enzyme activities and soil organic carbon accumulation.