Effect of Long-Term Integrated Plant Nutrition System (IPNS) in Rice-Wheat Sequence on Soil Biological Health

Rice - wheat is the predominant cropping system especially in the mid hills zone of the state. The system is over-exploitative of the natural resources and consequently leads to degradation in soil health and fertility. Assessment and regular monitoring of soil health is essential for sustainability and minimal environmental degradation. Soil quality consists of physical, chemical and biological components and their interaction with one another. The biological component of soil has been largely ignored so far, though is an important aspect to manage sustainable agriculture, soil health and ecosystem. Numerous studies have been carried out on soil physical and chemical aspects. But in depth analysis of the soil biological health has rarely done. Therefore, the present study was carried out in a long-term experiment on IPNS in rice ? wheat cropping system during 2013-14 at the Bhadiarkhar farm of the university. Twelve treatment combinations viz. T1 - Control (No fertilizer, no manure), T2 - 50% NPK to both rice and wheat, T3 - 50% NPK to rice and 100% NPK to wheat, T4 - 75% NPK to both rice and wheat, T5 - 100% NPK to both rice and wheat, T6 - 50% NPK + 50% N (FYM) to rice and 100% NPK to wheat, T7 - 75% NPK + 25% N (FYM) to rice and 75% NPK to wheat, T8 - 50% NPK + 50% N (wheat cut straw) to rice and 100% NPK to wheat, T9 - 75% NPK + 25% N (wheat cut straw) to rice and 75% NPK to wheat, T10 - 50% NPK + 50% N (green manure) to rice and 100% NPK to wheat, T11 - 75% NPK + 25% N (green manure) to rice and 75% NPK to wheat and T12 -Farmers' Practice (40% NPK and FYM 5 t/ha to both the crops) were evaluated in a randomized block design with four replications. The application of organics viz FYM, wheat straw and green manure and chemical fertilizers increased the number of heterotrophic bacteria, fungi, actinomycetes, and nitrogen fixing bacteria significantly over the control. A definite build up of organic carbon and thereby microbial biomass carbon over its initial value of 0.6% was observed in all the treatments. The highest increase in organic carbon content over control and initial status was observed under T6 where 50% N was substituted through FYM during kharif followed by 100% NPK through fertilizers in rabi. The highest microbial biomass carbon was found under T8 where 50% N was substituted through wheat cut straw during kharif followed by 100% NPK through fertilizers in wheat. Both dehydrogenase and phosphatase activities were stimulated by the application of organic manures and inorganic fertilizers over control. Organic fertilizers were more effective than inorganic fertilizers in increasing the microbial activity. Among the organic sources, FYM and wheat straw were superior to green manure. Microbial index of the soil increased with increase in the level of fertilization. The effect was more pronounced with organics than with inorganics. T6 where 50% NPK through fertilizers and 50% N through FYM to rice and 100% NPK through fertilizers to wheat was applied had highest microbial index of soil. This was followed by T8 (50% NPK through fertilizers and 50% N through wheat straw to rice and 100% NPK through fertilizers to wheat).