Soil Properties as Influenced by Long Term Herbicide with or without Organic Manure Application in Transplanted Rice-Rice System
Transplanted autumn rice-winter rice is one of the major rice-based cropping systems followed under specific soil type and land situation that faces diverse weed flora and intensity. The soil physical, chemical and biological properties of a long-term trial, being conducted since 2001 at Assam Agricultural University, Jorhat, India were evaluated after completion of tenth crop cycles of rice-rice cropping sequence. Rotational application of pre-emergence, followed by post-emergence herbicide significantly increased grain yield in both the crops. The pH of the soil increased and fractions of soil acidity decreased significantly, while the cation exchange capacity and exchangeable Ca2+, Mg2+ and NH4+ increased significantly by organic manure application for partial N-fertilizer substitution. The application of organic manure significantly increased organic carbon and positively influenced available nitrogen and phosphorous content in soil. The microbial biomass carbon, urease activity were unaffected by herbicide application but were enhanced by organic manure addition. Application of herbicide significantly reduced the acid phosphatase activity in soil, while it had a positive effect on dehydrogenase activity and the effect was pronounced by addition of the organic manure. The effect of rotation of herbicide was not obvious and was limited to a few biological properties.