稻鸭、稻鱼共作生态系统土壤可溶性有机N的动态和损失

通过田间试验研究了稻鸭、稻鱼共作生态系统土壤可溶性有机N(SON)的动态和损失,及其与土壤微生物量N和水稻吸N量的相关性.结果表明,(1)土壤SON是稻田土壤主要的可溶性N,其中处理CK,RD和RF土壤SON库分别为121.16, 109 30 和113.71 kg/hm2,高于土壤无机N库.(2)土壤SON与土壤可溶性无机N显著正相关(p<0.01);在水稻生育期间,土壤SON含量随水稻的生长而逐渐降低;同时由于鸭和鱼的存在,处理RD和RF土壤SON含量显著低于处理CK;土壤SON与水稻累积吸N量呈显著负相关(p<0.01),表明水稻生长强烈影响着土壤SON.(3)在水稻生长前期,渗漏水各形态N含量最大;溶解性有机N(DON)是稻田渗漏水N素的主要形态;同时,统计分析显示,相对于处理CK,RF土壤SON的下渗淋失量显著降低,RD土壤SON的下渗淋失量则略为降低.(4)水稻生育期间,土壤微生物量N不断地变化着,此外,由于鸭和鱼的存在,相对与处理CK,处理RD和RF土壤显著的提高了土壤MBN.同时,由于水稻吸收和N的淋失,土壤微生物量N与土壤SON不相关.总之,在水稻生长期间,土壤可溶性有机N受水稻吸N、微生物吸N与分解和N淋失的共同作用.

Dynamics of soil soluble organic N in rice-duck and rice-fish ecosystems

Field experiments on dynamics of soil soluble organic N (SON) and correlations with soil microbial biomass N (MBN) and N uptake of rice in rice-duck, rice-fish ecosystems in subtropical region of China were conducted from May to September in 2007. The experimental field was divided into nine plots for three different treatments, and the three experimental treatments were (1) conventional rice field (CK), (2) rice-duck ecosystem (RD) and (3) rice-fish ecosystem (RF). The results showed that soil SON constituted a predominant reservoir of soluble N in paddy fields, and the sizes of soil SON pools in CK, RD and RF were 121.16, 109.30 and 113.71 kg N hm-2,respectively, higher than the sizes of soil soluble inorganic N (SIN) pools in the corresponding treatments. During rice growth, SON was significantly positively related to SIN; moreover, the content of SON decreased gradually along with rice growth. Due to the presence of ducks and fish, the amounts of SON were significantly lower in RD and RF than in CK. The results also indicated SON was significantly negatively related to N uptake of rice, which showed that rice growth strongly affected SON. In the forepart periods of rice growth, contents of different formations of N all were the highest. Dissolved organic N (DON) was the main formation of N in percolation water in paddy fields; moreover, statistical analysis indicated that compared to CK, RD significantly decreased the leakage of SON and RF slightly decreased the leakage of SON. During rice growth, soil MBN changed constantly, and the presence of ducks and fish significantly increased soil MBN; moreover, due to N uptake of rice and N leaching, the soil MBN was not closely related to SON. In conclusion, soil SON was regulated by the interactions of N uptake of rice plants, microbial uptake and decomposition, and leaching in paddy fields during rice growth.