关键词: 碱性肥料, 镉污染, 水稻, 稻米镉含量

Abstract: We examined the effects of six different cropping patterns on the content, composition and migration of soluble nitrogen in cropland soils in Guizhou karst region. The results showed that the contents of soil soluble inorganic nitrogen (SIN),  soluble organic nitrogen (SON) and  soluble total nitrogen (TSN) ranged from 3.75 to 95.15 mg·kg^-1, 21.17 to 155.91 mg·kg^-1 and 28.76 to 188.95 mg·kg^-1, with a mean value of 26.49, 59.76 and 86.25 mg·kg^-1, respectively. The contents of SIN under different cropping patterns were as the following order: chive-ginger rotation land> chive-maize rotation land> chive-waterlogged and fallowed land> chive-chive continuous cultivation land> chivefallowed land> chive-rice rotation land. For SON, the order was: chive-chive continuous cultivation land> chive-ginger rotation land> chive-maize rotation land> chivewaterlogged and fallowed land> chive-fallowed land> chive-rice rotation land. For TSN, the order was: chive-ginger rotation land> chive-chive continuous cultivation land> chive-maize rotation land> chive-waterlogged and fallowed land> chive-fallowed land> chive-rice rotation land. SON and NH₄⁺-N were the main components of soil soluble nitrogen. The SON/TSN ratios were more than 60%, with the highest of 82.4%. The contents of SIN and SON decreased with soil depth at 0-60 cm layers. Our results indicate that cropping patterns have significant impacts on the content and composition of soluble nitrogen in cropland soil. SON is the major form of nitrogen loss from cropland soil, which should be paid attention to.

Key words: alkaline fertilizer, Cd pollution, rice, Cd concentration of rice.