Optimizing Water Depth, Fertilizer Topdressing, Crab Density and Feed Quantity for Rice-crab Farming

Abstract

【Background】 Rice-fish farming is a common practice in paddy fields to make most of the limited land resources. However, how to balance fertilization and fish density without compromising the environment is an issue that remains largely obscure. The purpose of this paper is to address this based on rice-crab farming in Helan County, Ningxia province. 【Objective】 An experiment consisting of four factors and three levels was conducted in the field. It was designed using the orthogonal test. The four factors with their associated three levels were: Depth of water over the soil surface was 5 cm, 8 cm and 11 cm; fertilizers (urea + biogas residue + biogas slurry) topdressing was (60+1500+3000) kg/hm2, (75+3 000+4 500) kg/hm2, and (90+4 500+6 000) kg/hm2; crab density was 60 kg/hm2, 90 kg/hm2 and 120 kg/hm2; daily feed quantity was 7.2 kg/hm2, 9 kg/hm2 and 10.8 kg/hm2. In each treatment, we measured the growth, yield and quality of the rice and crab. 【Result】 ①Based on their impact on rice yield, the four factors were ranked in the order of fertilizer topdressing >water depth>stock density of crab>daily feed quantity, while for the crab yield their ranking order was stock density >water layer>fertilization>daily feed quantity. The differences between them were at significant level. ②The yields of rice and crab, and the total amino acid content in the crab muscle both increased with the increase in water depth and fertilization. The tasting quality of the rice increased with the water depth first followed by a decline after the water depth exceeded a threshold value. Rice yield and total amino acids of the crab muscle increased first and then decreased as the stock density and daily feed quantity increased. The crab yield and taste of the rice both increased with the increase in stock density, but decreased as daily feed quantity increased. 【Conclusion】 The optimal combination for rice-crab farming was: water depth 11 cm, fertilizer topdressing (90+4 500+6 000) kg/hm2, crab stock density 90 kg/hm2, daily feed quantity 7.2 kg/hm2. Under this combination, the yield of the rice and crab maximized, increasing by 24% and 37.6%, compared with the CK, to 9 799.8 kg/hm2 and 444.6 kg/hm2, respectively. It also improved the taste of the rice and the total amino acid in the crab muscle by 83.71 points and 15.85 g/100g, respectively, an increase of 6.9% and 24.8% compared to those in the CK.

Keywords

• ningxia
• rice-crab farming
• optimal cultivation
• food improvement
• modern ecological irrigation district