Assesmment of precipitation suitable degree from integrated rice-crayfish farming systems in Jianghan Plain of China

Abstract

In recent 10 years, an integrated rice-crayfish farming (IRF) has been developing rapidly in the middle and lower reaches of the Yangtze River in China, and produced significant economic and ecological benefits. However, the IRF mode consumes a large amount of water and brought a great risk of water shortage. In Jianghan Plain, Hubei province, China, there are 4 IRF modes, referring to rotation of rice and crayfish (RRC), rice-crayfish symbiosis (RCS), year-round crayfish farming in paddy fields (YRC), and continuous operation of rice planting and crayfish farming (COR). This study selected the 4 IRF modes to calculate and compare the precipitation suitable degree (PSD) of 17 counties with larger scale of IRF. The results showed that, annual PSD for different IRF modes varied greatly for same county and among different counties, the annually averaged PSD was from 0.52 to 1.06 from the northern to southern Jianghan Plain. Annually averaged PSD from large to small was ranked as RCS>COR>RRC>YRC. The PSD values of IRF was different among different months, and the highly suitable period for PSD was from March to July, and the precipitation of each county (city) fully meet the water demand of rice growth and crayfish farming. In August thorogh November, the spatial distribution of PSD showed largely variation, and the monthly PSD was lower in the northern Plain, and slightly higher in the southern. From December to the next February, the PSD was obviously lower than other stages, even in the south of Jianghan Plain, with high risk of water deficit at the stage. According to the water demand regulation of the 4 IRF modes, the suitable IRF mode was RRC and YRC for the south, and RCS and COR for the north of Jianghan Plain in China. Considering long term negative affects for flooded paddy field, the paddy field used for RCS or COR mode should be changed to other farming system for 1 year or 2 years, such as IRF replaces with rice and wheat (oilseed rape) rotation for 1 year or 2 years after IRF was conducted for 5 years, so as to avoid exacerbating soil gleying.