氮肥用量及施用时间对土体中硝态氮移动的影响

NITRATE-N MOVEMENT IN THE SOIL PROFILE AS INFLUENCED BY RATE AND TIMING OF NITROGEN APPLICATION

土连续两年小麦—玉米轮作条件下 ,播前一次施氮量 130～ 5 2 0kghm-2 a-1时 ,氮肥用量对硝态氮在土体中的移动深度没有影响 ,但土壤剖面中残留的硝态氮量随施氮量增加显著增加。播前一次施用氮肥 ,差减法计算的肥料氮表观回收率 (作物携出量和土壤硝态氮的残留量 )为 6 2 %～ 82 7% ;就作物而言小麦的携出率高于玉米 ,在玉米生长季节有更多的硝态氮可能被淋移至土壤剖面的下层。小麦—玉米轮作一年 ,不同的施氮时间对肥料氮的表观回收率以及硝态氮在土壤剖面中的分布、累计没有明显影响。

Nitrogen fertilizer is a potential contaminant of ground water. The purpose of this study was to determine influence of rate and timing of N fertilizer application on N movement in the soil during the crop growing season. Wheat and maize were grown alternately at Yangling, Shaanxi Province from Oct., 1994 to Oct., 1996. An experiment was conducted on effect of N application rate on N movement in cumulic cinnamon soil using urea with four rates that ranged from N 130～520 kg hm -2 a -1 and an experiment on effect of timing of N application on the same soil with three rates and four timings from Oct., 1994 to Oct., 1995. The two experiments were laid out in a randomized complete block with three replications. After each crop harvest, the soil was sampled to a depth of 400 cm and analyzed for nitrate nitrogen. Nitrogen rate had no influence on nitrate N movement in the soil after two years, but NO - 3 N had moved down beyond 200 cm in treatments with N rate higher than 130 kg hm -2 a -1 . N rate increased NO - 3 N accumulation in the soil. The total recovery of N ranged from 62% to 82.7%, higher with wheat than with maize. Timing of application did not influence N fertilizer movement and N recovery, either. It was found that for irrigated wheat-maize rotation system in the region, most of the N recovered came from the top 200 cm of soil, regardless of N fertilizer practices.