北方冬小麦/夏玉米轮作体系土壤氨挥发的原位测定

In Situ Determination of Ammonia Volatilization from Wheat Maize Rotation System Field in North China

采用通气法测定了北方冬小麦 /夏玉米轮作体系田间土壤的原位氨挥发。结果表明 ,与冬小麦施用基肥相比 ,夏玉米追肥后土壤的氨挥发速率很快升高 ,但挥发高峰期持续时间较短 ,最大氨挥发速率亦低于冬小麦。冬小麦拨节期追肥 ,氨挥发速率低且呈波动变化 ,未出现高峰值。从整个生长季节来看 ,冬小麦不施氮和每公顷施氮 1 2 0、2 4 0、36 0 kg时的累计挥发量分别为 4 .4、6 .9、1 3.0、38.4 kg N/hm2 ,夏玉米为 8.4、1 5 .1、2 0 .0、2 6 .1 kg N/hm2。按我国北方冬小麦 /夏玉米播种面积 1 86 4 .4万 hm2 计 ,每年由氨挥发向大气排放的氮素达 2 3.8～ 1 2 0 .2万 t,其中 1 7.2～ 96 .4万 t来自氮肥 ,相当于氮肥投入的 2 .1 %～ 9.5 %。

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