In Situ Determination of Ammonia Volatilization from Wheat Maize Rotation System Field in North China
In Situ Determination of Ammonia Volatilization from Wheat Maize Rotation System Field in North China
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作者：
Wang Zhao
土壤氨挥发是农田氮素流失的重要途径，也是大气和环境污染的主要来源。我国北方土壤以石灰性土壤为主，pH值偏高，为土壤养分流失创造了有利条件，而我国北方地区的集约化种植、过量施氮和不合理施肥又使土壤养分流失加剧。冬小麦（Triticusp aestvum L.）和夏玉米（Zea Mays L.）是这一地区的主要作物，小麦和玉米轮作是共同的种植制度。为了了解该地区氨挥发的严重性，于1998年10月至1999年10月在北京中国农业大学进行了轮作系统的田间试验。试验以不施氮肥为对照，施氮量分别为120、240和360 kg/hm 2，施磷量为26 kg/hm 2，以尿素为氮肥，过磷酸钙（含磷5.2%）为磷肥。磷肥在小麦播种前与表土混匀作底肥，氮肥分两次施入，一半与磷肥一起施入，另一半于1999年4月9日小麦拔节期追施。1998年10月8日播种冬小麦。小麦收获后，1999年6月21日立即播种夏玉米，施氮量与冬小麦相同。夏玉米不施磷肥，于7月5日玉米3叶期施一半氮肥，8月5日玉米10叶期施另一半氮肥。采用通气法测定了该轮作体系不同时期施氮后土壤氨挥发损失。结果表明，在不同的生长季节和施氮水平下，氨挥发速率和氨挥发量不同。对于冬小麦而言，施氮后土壤氨挥发立即发生。0、60、120、180 kgN/hm 2处理的挥发速率分别为0.27、0.57、1.96、5.53kgN/（hm 2·d）。施肥后第17天，各小区氨挥发速率差异不显著。1998年10月8日至11月18日测定期间，各小区氨挥发累积量分别为2.9、4.8、10.5和35.7kgN/hm 2。而小麦拔节期追施氮肥后，土壤氨挥发速率较低，稳定在0 0 1 ~ 0 17 kgN/（hm 2·d）之间。在1999年4月10日至5月15日的测定期内，不同样地的氨累积排放量分别为1.5、2.1、2.4和2.7kgN/hm 2。在小麦全生育期，施氮量分别为0、120、240和360 kg/hm 2时，氨的释放总量分别为44、69、130和384 kg/hm 2。夏玉米生长期氨挥发速率较高，追施氮肥后氨挥发速率增加较快。在3叶期，施肥后第1天达到最高值，分别为0、60、120和180 kgN/hm 2，分别为0 33、1 82、3 33和5 41 kgN/（hm 2·d）;在10叶期，施肥后第2天达到最高值，分别为0 70、1 82、3 33和5 41 kgN/（hm 2·d）。2 5 0、3 11和3 2 5 kg N/（hm 2·d）。然而，高速挥发只持续了较短的时间。施肥后7 d，施氮小区挥发速率降至最低，施氮小区与不施氮小区挥发速率差异不显著。不同处理的氨挥发累积量
Ammonia volatilization from soil is an important pathway for fertilizer N loss from field, and also a major source for air and environment pollution. Majority of soils in north China are calcareous ones with higher pH that has created a condition favorable for such loss, and intensive cropping with over application of N fertilizer and unreasonable fertilization practices has made the situation more serious. Winter wheat ( Triticusp aestvum L.) and summer maize ( Zea Mays L.) are major crops in this area and a rotation of wheat followed by maize constitutes the common cropping system. For understanding the seriousness of ammonia volatilization in this area, experiments were carried out on a field with the rotation system at China Agriculture University in Beijing from October 1998 to October 1999. N fertilizer was applied at the rates of 120, 240 and 360 kg N/hm 2 respectively with no N fertilizer as control, and 26 kg P/hm 2 was applied for all the N levels, using urea as N fertilizer and calcium superphosphate (containing 5.2% of P) as P fertilizer. The P fertilizer was uniformly mixed with topsoil as base just before wheat being sown, and the N fertilizer was applied twice: one half being supplied with P fertilizer together, and the other half being dressed on April 9, 1999 at wheat elongation stage. Winter wheat was sown on October 8, 1998. After wheat being harvested, summer maize was sown immediately at June 21, 1999 with the same N rates as winter wheat. However, for summer maize, the phosphate fertilizer was not applied and one half of the N fertilizer was dressed on July 5 at 3 leaf stage of maize, and the other half on August 5 at 10 leaf stage. Ammonia volatilization from soil of this rotation system was determined by venting method immediately after N fertilizer was applied at different stage. The obtained results showed that the rates and the amounts of volatilized ammonia differed in different growing seasons and with different N rates. For winter wheat, ammonia volatilization occurred immediately after N fertilizer was added to soil followed by wheat sowing. It was gradually increased to the maximum value at the 3rd to 5th day with the corresponding volatilized rates of 0 27, 0 57, 1 96 and 5 53 kg N/(hm 2·d) respectively for the plots received 0, 60, 120, 180kg N/hm 2. Since then it was decreased slowly and no significant difference could be observed among the volatilization rates of different plots at the 17th day after fertilization The cumulative amounts of the volatilized ammonia from each plot were 2.9, 4 8, 10 5 and 35 7 kg N/hm 2 during the determined period from October 8 to November 18, 1998. However, after dressing of N fertilizer at the elongation stage of wheat, the ammonia volatilization from the soil kept low, stable rates, which fluctuated from 0 01 to 0 17 kg N/(hm 2·d). The cumulative amounts of ammonia emitted from different plots were 1 5, 2 1, 2 4 and 2 7 kg N/hm 2 during the determining period from April 10 to May 15, 1999. For the entire growing stages of wheat, the total amounts of ammonia released from the field were 4 4, 6 9, 13 0 and 38 4 kg N/hm 2, correspondingly to the N rates of 0, 120, 240 and 360 kg/hm 2. During the growing season of summer maize, the ammonia volatilization rate was high and increased more quickly after dressing of N fertilizer. At 3 leaf stage, it reached the highest rates at the 1st day after fertilization, which were 0 33, 1 82, 3 33 and 5 41 kg N/(hm 2·d) for the plots added 0, 60, 120 and 180 kg N/hm 2 respectively, and at 10 leaf stage, the highest rates were found at the 2nd day with the corresponding values of 0 70, 2 50, 3 11 and 3 25 kg N/(hm 2·d). However, the high speed of volatilization continued only for a shorter period. Seven days after fertilization, the volatilization rates for the plots received fertilizer had decreased to the lowest values, being of no significant difference among plots with and without N fertilization. The cumulative amounts of ammonia volatilized from different p