Variations in soil nutrient dynamics and their composition in rice under integrated rice-crab co-culture system

Rice-crab co-culture (RC) is an environmentally friendly, agri-aquaculture technique, however, its knowledge about soil nutrients status and their composition in rice grain has remained unexplored. The aim of current study is to explore this deficiency. Thus, a field survey and a field experiment were combinedly carried out at Panjin City, China. The field survey with 16 fields each for rice-monoculture (RM) and RC was conducted without influencing conventional cultural practices. The field experiment was conducted with four treatments: rice-monoculture (RM), 3000 crabs ha−1 without feed (RC3000), 6000 crabs ha−1 with feed (RC6000), and 12,000 crabs ha−1 with 2 × feed (RC12000). Results showed an increase in soil nutrients and improved nutrient accumulation in rice with the RC system. Soil organic carbon, macronutrients (nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg)), microbial biomass carbon, and nitrogen, micronutrients (copper, zinc (Zn), and manganese) were improved. From the field survey, results indicated significant improvement in grain TN (9.4%), calcium (Ca, 22.1%), Mg (7.1%), and Zn (26.1%) in RC system compared to RM system. In field experiment, the concentrations of Ca, Mg, and Zn were increased as follows: i) Grain Ca in RC3000 (23.9%) and RC6000 (17.1%), ii) Mg in RC3000 (12.6%), RC6000 (16.3%), and RC12000 (11.8%), iii) Zn in RC3000 (10.8%), RC6000 (5.7%), and in RC12000 (14.8%). The RC system has also improved nutrients translocation from soil to plant biomass that was the key reason to increase nutrient composition in rice. The results implied that the improvement of rice yield was by the increased nutrient in soil and the higher nutrient translocation capacity from soil to rice under the proper culturing crab density.