Temporal Variations in Soil Nutrient Dynamics of Rice-Prawn Integration in Acid Saline Pokkali Soils of Kerala, India

Abstract

The acid saline Pokkali soil represent to a fragile ecosystem often below sea level, where the traditional Pokkali rice cultivation and shrimp farming are practiced. Because of the unique and specific ecological conditions, a single crop of rice is taken in the low saline phase of production cycle (June to mid-October), followed by prawn farming during the high saline phase (November to April). These lands are frequently subjected to high tidal inundation and subsequent building up of salinity in soil. The soil physical and chemical properties are thereby influenced by these factors and hence needs to be thoroughly studied. Therefore, the present investigation was conducted to evaluate the soil properties before and after rice- prawn cultivation in Pokkali soils and to relate he temporal variations in soil nutrient dynamics. The experiment was conducted for five consecutive years viz., 2015-16, 2016-17, 2017-18, 2018-19 and 2019-20 in the Pokkali fields of Kumbalangi, Ernakulam district, Kerala where rotational rice-prawn cultivation has been carried out for the past few decades. The change in pH, EC, organic carbon and available nutrient levels were studied by chemical analysis during the period of both rice and prawn cultivation. The tidal and fluvial effects varied with the climate in each year and this resulted in variations in nutrient dynamics.  Effects were more pronounced after the harvest of prawn than the harvest of rice in the case of soil pH, EC, available K, Ca, Mg, Fe, and exchangeable Na. The seasonal variation of temperature as a result of rainfall and water intrusion brings about changes in acidity, salinity and availability of soil nutrients. Hence proper management of the crops is essential to maximize the yields and prevent crop loss due to improper natural resource management.