Effect of fallow and fertilization on soil mineral nitrogen in summer maize

The relation between fallow, fertilization and soil inorganic nitrogen dynamics in the growth phase of summer maize was studied by field experimentation. The results indicate that the amount of nitrate nitrogen residue in the 0 ～ 200 cm soil layer, especially the 0 ～ 100 cm soil layer, is decreases significantly by planting summer maize. However, there is no observed significant effect of planting summer maize on residue amount of ammonia nitrogen and its distribution along profile. The amount of nitrate nitrogen residue in 0～200 cm soil under maize at silking is 198.1 kg·hm^-2, that under fallow is 562.2 kg·hm^-2, which is 364.1 kg·hm^-2higher than the former. Application of nitrogen fertilizer markedly increases soil nitrate nitrogen residue, also affecting its distribution in the soil profile. However, nitrogen fertilizer application has no obvious effect on residue amount and profile distribution of ammonia nitrogen. The amount of nitrate nitrogen residue under fertilization at the emergence period of summer maize is 857.3 kg·hm^-2; that of non-fertilization is 165.7 kg·hm^-2, 4.2 times less than the former. Compared with non-fertilization, nitrogen fertilization can increase nitrate nitrogen content, not only in the surface soil, but also in the 200 cm soil layer at seedling stage. At harvest, nitrate nitrogen content of fertilization treatment in soils deeper than 60 cm significantly increases, and is highest at 180 ～ 200 cm soil depth.