Growth, Physiology, Weed Abundance and Yield in Rice (Oryza Sativa L.) Under Three Nutrient Input Systems in the Dry Zone of Sri Lanka

A field experiment was conducted to compare the growth, physiology, weed abundance and yield in rice under three input systems; organic, conventional and integrated, during the 2019 Yala season as the second season of a long-term cropping systems trial. The design used a Randomized Complete Block Design (RCBD), with six (6) replicates for each treatment. The rice variety used in the experiment was Bg 300 and three treatments were based on three input systems such as T1 – Conventional input system (100% Department of Agriculture (DOA) inorganic fertilizer recommendation), T2 – Integrated system (50% of Department of Agriculture (DOA) inorganic fertilizer recommendation +50% of the rate of compost added to organic input system) and T3 – Organic system (No inorganic fertilizers and only compost with the rate of 10000 kg ha^-1). At the panicle initiation and harvesting stages, there was a (p<0.05) significant difference (in rice shoot biomass across the three input systems, with the organic system having the lowest values compared to the other two. At panicle initiation, 50% heading, and harvesting phases, a significant difference (p<0.05) in plant height was noted among the three input systems, with the organic system showing the lowest values at all stages. The organic system had the highest weed count at all three crop stages and no significant difference between integrated and conventional systems. The three input systems had a significant difference in final grain yield at 14 percent moisture. At 14% moisture, there was no difference in final grain yield between conventional and reduced systems (4.85 and 4.67 tonnes/ha) with the organic system having the lowest value (2.74 tonnes/ha). Overall results indicate that reducing inorganic fertilizers by 50% with the combination of organic manure as in the integrated system gives similar final grain yields as the conventional system of new improved varieties like Bg 300 in high potential areas like Anuradhapura. Also, organic systems can show low crop growth and yields due to inadequate nutrient supply through organic materials and high weed density during the first year of transition.