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

Abstract

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.

Bacterial communities in paddy soil and ditch sediment under rice-crab co-culture system

“…Fertilizer improves soil fertility significantly, and the continuous input of feed also increases nutrient elements in the sediment (Liang et al 2013 ; Liu et al 2019a ). Our study found that TN, TP, AP and AN in paddy soil and ditch sediment increased compared with the initial stage under the rice-crab co-culture system.…”

Influence of nitrogen substitution at an equivalent total nitrogen level on bacterial and fungal communities, as well as enzyme activities of the ditch bottom soil in a rice–fish coculture system

“…48 The implementation of feeding practices can enhance fish production without negatively impacting rice yield, and the consistent provision of fish feed also results in the accumulation of nutrients in the ditch bottom soil. 4,49 In the present study, we found that S75 treatment significantly increased rice yield and reduced fish yield compared with S0, S25 and S50 treatments, whereas S0 and S25 treatments significantly reduced rice yield and increased fish yield compared with S50 and S75 treatments, respectively (Table 1), suggesting that inadequate basal fertilizer tends to affect rice yield, whereas overuse of the fish feed and basal organic fertilizer also causes the accumulation of nutrients in the ditch bottom (Figs 1 and 2). Ayub et al 50 also reported that chicken manure can increase the organic matter content of the pond bottom soil.…”

A Multi-Medium Analysis of Human Health Risk of Toxic Elements in Rice-Crayfish System: A Case Study from Middle Reach of Yangtze River, China

“…Briefly, freshwater crayfish (Procambarus clarkii) and rice (Oryza sativa) were selected for co-culture in this study. The experiment plot was divided into a small area, with 20 m (L) × 12 m (W), and rice cultivation occupied about 60% of the total area of the plot; the depth of the ditch was 1.0 m. Rice was transplanted in May and harvested in October [16].…”