Aquaculture Feeds Can Be Outlaws for Eutrophication When Hidden in Rice Fields? A Case Study in Qianjiang, China.

Water eutrophication caused by agricultural production has become one of the most important factors that impede sustainable rural environmental governance in China. As a result, the Chinese central and local governments want to reduce the use of nitrogen and phosphorus fertilizer and gain socioeconomical profit simultaneously by promoting crayfish and rice integrated system (CRIS) in the rural areas with abundant water resources. In this article, we investigated whether CRIS in Qianjiang, Hubei, the origin place of the system in China, contributes to fulfilling the governments' expectations. We found that CRIS efficaciously cuts the fertilizer rate in rice production and boosts farmers' incomes because crayfish has a demand for water quality and holds a large internal market requirement. However, higher profit encourages farmers to expand crayfish production and thus discourages the initiatives in rice production. The area of the ditch for crayfish production expands ceaselessly and exceeds the limit of regulation of CRIS. As a result, the CRIS in the areas has emerged as a practice of aquaculture but in farmland. This is a regulatory gap. The input-output analysis of CRIS by material balance method can also reveal that excessive feed for crayfish has become a new source of agricultural pollution. Beyond that, due to the changed irrigation system and increased water exchange frequency of CRIS, the pollution has transformed from passive distribution to active, which will increase the risk of water eutrophication on a large area.

Effects of different tillage and straw return on soil organic carbon in a rice-wheat rotation system.

Soil management practices, such as tillage method or straw return, could alter soil organic carbon (C) contents. However, the effects of tillage method or straw return on soil organic C (SOC) have showed inconsistent results in different soil/climate/cropping systems. The Yangtze River Delta of China is the main production region of rice and wheat, and rice-wheat rotation is the most important cropping system in this region. However, few studies in this region have been conducted to assess the effects of different tillage methods combined with straw return on soil labile C fractions in the rice-wheat rotation system. In this study, a field experiment was used to evaluate the effects of different tillage methods, straw return and their interaction on soil total organic C (TOC) and labile organic C fractions at three soil depths (0-7, 7-14 and 14-21 cm) for a rice-wheat rotation in Yangzhong of the Yangtze River Delta of China. Soil TOC, easily oxidizable C (EOC), dissolved organic C (DOC) and microbial biomass C (MBC) contents were measured in this study. Soil TOC and labile organic C fractions contents were significantly affected by straw returns, and were higher under straw return treatments than non-straw return at three depths. At 0-7 cm depth, soil MBC was significantly higher under plowing tillage than rotary tillage, but EOC was just opposite. Rotary tillage had significantly higher soil TOC than plowing tillage at 7-14 cm depth. However, at 14-21 cm depth, TOC, DOC and MBC were significantly higher under plowing tillage than rotary tillage except for EOC. Consequently, under short-term condition, rice and wheat straw both return in rice-wheat rotation system could increase SOC content and improve soil quality in the Yangtze River Delta.

[Short-term effects of different tillage modes combined with straw-returning on the soil labile organic carbon components in a farmland with rice-wheat double cropping].

A two-year (2009-2011) field experiment was conducted to study the effects of different tillage modes, straw-returning, and their interactions on the soil total organic carbon (TOC) and labile organic carbon (LOC) components (easily oxidizable organic carbon (EOC), water-soluble organic carbon (WSOC), and microbial biomass carbon (MBC)) at the soil depths of 0-7, 7-14, and 14-21 cm in a farmland with rice-wheat double cropping. In all treatments of straw-returning, the TOC and LOC contents in each soil layer were significantly higher than those without straw-returning. Under plowing tillage, the MBC content in 0-7 cm soil layer was significantly higher than that under rotary tillage, but the EOC content was in adverse. Rotary tillage made the TOC content in 7 - 14 cm soil layer being significantly higher, as compared with plowing tillage. The TOC, WSOC, and MBC contents in 14-21 cm soil layer under plowing tillage were significantly higher than those under rotary tillage. Plowing tillage combined with rice and wheat straws-returning made the soil TOC content being higher than the other treatments.