Effect of Shrimp-Based Cropping Systems on Salinity and Soil Fertility in a Coastal Area of Bangladesh: A Village-Level Study

The present study analysed soil salinity and some essential soil nutrients for rice plant as affected by a shrimp-based cropping system in a coastal area of Bangladesh. The study was conducted in a village located in Satkhira district. Two main cropping systems, the shrimp-boro rice cropping system and the aman rice-boro rice cropping system, are mainly practised by local farmers in the study village. Soil and water samples were collected from the plots of these cropping systems and chemical analysis was done to measure the salinity level of the soil and water as well as to find out the nutrient status of the soil. The data was also collected for economic analysis and estimated rice and shrimp yield from the local farmers. The results revealed that the soil salinity level of the shrimp-boro rice cropping system was higher than that of aman rice-boro over the consecutive years of 2010, 2011 and 2012. The soil was found to be moderately saline. The organic matter content, potassium, calcium, magnesium and sulphur levels of the soil in the shrimp-boro rice system were increased, while the total nitrogen, phosphorus, boron and zinc availability decreased. It was also found that the yield of boro rice was 4,950 kg/ha whereas the aman rice yield was 3,020 kg/ha and that for shrimp the yield was calculated as 268 kg/ha for one growing season (six months). The total income from boro rice, aman rice and shrimp was calculated as 127,760 Tk, 87,118 Tk and 149,476 Tk, respectively. The paper concludes that although some nutrient elements were available in adequate amounts, salinity kept these nutrients from being taken up by the rice plants since salinity changes the osmotic pressure of the soil solution system. This may ultimately lead to a reduction in rice yield and threaten the sustainability of the local shrimp-boro rice cropping system.