Assessment of soil properties and yield under diverse input systems in Alfisols for rice (Oryza sativa L.) crop

Today's agricultural system relies heavily on synthetic inputs for higher yields. Prolonged use of chemical inputs pollutes and degrades the farming lands and it should go through a transition period to achieve soil fertility. Sri Lanka needs research to identify the potential and challenges of organic or integrated plant nutrient management strategies, particularly during the transition phase. More information is lacking on the soil fertility dynamics and yield performance among these diverse input systems for rice (Oryza sativa L.) hybrids as they were bred under conventional management. Main objective of this study was to compare the final grain yield between conventional (100% Department of Agriculture, DOA recommendation) reduced (50% DOA + 50% organic manure) and organic systems with great attention to soil fertility dynamics within its first transition year. The experiment was carried out in Puliyankulama, Anuradhapura during Yala season 2019. Soil samples were analysed for different fertility parameters. The final grain yield and yield parameters were also determined. Data were subjected to analysis of varience (ANOVA) using SAS software to distinguish treatment effects. With time stages, ammonium nitrogen (N), nitrate N, available phosphorous (P), and microbial biomass carbon (MBC) fluctuation among different input systems were significant (P<0.05). Nitrate N and available P revealed a significant increment within the organic system from the first transition year. Initial 77.27 mg kg^-1 nitrate N of organic system reached up to 144.16 mg kg^-1 at the end of the first transition year while available P surged from 2.25 to 15.1 mg kg^-1. Conventional and reduced systems produced similar final yields for rice as 4.9 and 4.7 t ha^-1, correspondingly while 2.7 t ha^-1 final yield produced by organic input system. The results suggest a potential to replace inorganic chemical fertilizers by 50% with organic manure without much impact on the yield while reducing the cost of production applied for commercial fertilizers. Overall, long-term investigations are needed to confirm soil fertility dynamics and final grain yield of rice within its transition period.