冬小麦/夏玉米轮作中NO_3^-N在土壤剖面的累积及移动

ACCUMULATION AND MOVEMENT OF NO_3^-N IN SOIL PROFILE IN WINTER WHEAT-SUMM ER MAIZE ROTATION SYSTEM

通过田间试验研究了冬小麦 /夏玉米轮作中NO- 3 N在土壤剖面的累积及移动 ,结果表明 ,尿素施入旱地土壤后 ,硝化作用一般在 7d之内完成 ,NH+ 4 N只在施肥后的短期内保持较高浓度 ,其它时期NH+ 4 N含量基本在 1～ 3mgkg- 1 范围内 ,土壤剖面不同层次NH+ 4 N一般也低于 4mgkg- 1 ,NH+ 4 N的含量不能反映土壤有效氮的水平。土壤剖面中的NO- 3 N随施氮量的增加而显著升高。在低施氮量条件下 (N <12 0kghm- 2 ) ,NO- 3 N主要在 0～ 40cm土层内移动 ,但当施氮量高于N 2 40kghm- 2 时 ,冬小麦季即有相当数量的氮移出 0～ 10 0cm土体。NO- 3 N在土体中的移动存在着很大的年际变化 ,在干旱年份 ,即使夏玉米季 ,NO- 3 N向深层移动的可能性也很小。试验年份中 ,除 1999年夏玉米季发生了较严重的气体损失以外 (该季节特别干旱 ) ,其余季节损失的肥料氮主要以NO- 3 N的形式在深层土壤剖面中累积 ,这在两个试验点的结果相当一致。

Accumulation and movement of NO - 3-N in soil profile in winter wheat/summer m aize rotation system was studied in field experiments. The results showed that n itrification completed in 7d after urea was applied into soil. High concentr ati on of NH + 4-N only appeared in short period after fertilization and NH + 4 -N concentration in other times was 1～3 mg kg -1 . NH + 4-N concentration in different soil layers was lower than 4 mg kg -1 generally. So the content o f NH + 4-N could not reflect soil available nitrogen level. NO - 3-N in s oi l profile was significantly increased with nitrogen fertilizer rate increasing. NO - 3-N movement mainly occurred in 0～40 cm with low nitrogen rate(N<120 kg hm -2 ), but large amount of NO - 3-N moved below 100 cm even in win ter wheat growth season with high nitrogen rate. The movement of NO - 3-N had a gre at different between years. In drought year, the possibility of NO - 3-N movi n g to deeper layer was low even in summer maize growth season. Except large amoun t of gas loss occurred in 1999 summer maize season (extremely drought in this se ason), the loss nitrogen fertilizer mainly accumulated in deeper layer in other season, which was consistent in two sites.