橡胶林氮肥穴施下的氨挥发和氮淋洗损失

氨挥发和氮淋洗是氮肥损失的重要途径,导致严重的环境污染。有关橡胶林氮肥穴施后的氨挥发和氮淋洗损失问题的研究鲜见报道。本研究设置0 kg/hm²（对照）、100 kg/hm²（低氮）、230 kg/hm²（中氮）、400 kg/hm²（高氮）的施氮水平,分别采用通气法和渗漏盘法研究橡胶林尿素穴施后的氨挥发和氮淋洗损失特征。结果表明,旱季氨挥发损失过程大致在14~20 d内完成,雨季基本在7~10 d完成;氨挥发峰值在旱季较雨季延迟,旱季大概施肥后6~13 d达到峰值,而雨季1~3 d即达到峰值;与对照相比,低氮、中氮和高氮处理的氨挥发损失大致为9.32~21.54 kg/hm²。氮淋洗损失主要发生在雨季（5—11月）,且以硝态氮淋洗为主;橡胶林氮肥穴施条件下的氮淋洗损失约为2.36~9.00 kg/hm²;随着施氮量的增加,氨挥发和氮淋洗损失均呈增加趋势。综上,橡胶林氮肥穴施后的氨挥发和氮淋洗损失并不高,其施氮量不宜超过230 kg/hm²。

Ammonia Volatilization and Nitrogen Leaching under Specific Cave-applied Nitrogen Fertilization of Rubber Plantation

Both ammonia (NH₃) volatilization and nitrogen (N) leaching are important pathways for N loss and a lot of relevant studies have been carried out in agro-ecosystems. At the other hand, the application of N fertilizer has gradually become an important measure to improve the productivity of plantations. It is helpful to understand the process of N cycling in ecosystem by defining the direction and flux of N loss in different plantations under specific climate-soil conditions, which is also an important basis for optimal management of N fertilizer and formulation of emission reduction measures for plantation. Rubber tree (Hevea brasiliensis) is a typical tropical tree cash crop. In order to prevent the runoff loss of nutrients in rubber plantation, management measures of fertilizer cave application were gradually formed in production. However, this locally concentrated fertilization may also cause serious NH₃ volatilization and N leaching losses. Due to the high spatial variability of nutrients caused by cave-applied fertilization and lack of quantitative studies on these loss processes, little is known about NH₃ volatilization and N leaching loss after N fertilizer application in cave-applied method in rubber plantation. We used vented chamber method and pan lysimeter to study NH₃ volatilization and N leaching loss after urea cave application in rubber plantation at levels of 0 kg/hm² (CK), 100 kg/hm² (LN), 230 kg/hm² (MN) and 400 kg/hm² (HN). The results showed that the loss of NH₃ volatilization was completed within 14?20 days in dry season and 7?10 days in rainy season. NH₃ fluxes peaked later in dry season, 6-13 days after fertilization, as compared to 1?3 days in rainy season. Compared with the CK, the NH₃ volatilization losses were increased to 9.32?21.54 kg/hm² in the N treatments (LN, MN and HN). N leaching concentrated in the rainy season (May to November), and nitrate leaching was the main process of nitrogen leaching loss. Under specific cave-applied nitrogen fertilization in rubber plantation, N leaching losses was 2.36?9.00 kg/hm². N fertilization rate increased the NH₃ volatilization and N leaching losses. In conclusion, NH₃ volatilization potential was low in rainy season due to frequent occurrence of rainfall events. In the dry season, the arid soil conditions prolonged the hydrolysis process of urea and aggravate the loss of NH₃ volatilization. The NH₃ volatilization has the characteristic of high loss in dry season and low loss in rainy season. The loss of N leaching in rubber plantation varied greatly from year to year, and concentrated in rainy season. The main loss of N leaching was nitrate leaching, and nitrate leaching accounted for 77%?90% of the total N leaching amount. The loss of NH₃ volatilization and N leaching in rubber plantation was not high under the unique ecological conditions and special fertilization methods.