Friday, 14 July 2006

Assessing Biological Soil Quality for a Few Long-term Experiments in Sub-tropical India.

Biswapati Mandal1, S.K. Ghoshal1, G.C. Hazra1, Debashis Majumdar1, J. Chowdhury2, H. Ghosh2, R.N. Samantaray3, and A.K. Mishra3. (1) Bidhan Chandra Krishi Viswavidyalaya, Kalyani, 741235, India, (2) Central Research Institute for Jute and Allied Fibres, Barrackpore, India, (3) Central Rice Research Institute, Cuttack, India

Biological attributes of soil are sensitive to its management practices. Conjointly they represent biological soil quality that is useful for comparing the performance of different soil management practices in aggrading and/or degrading soil quality. In a collaborative study involving three institutions, we tried to identify important indicators for assessing biological soil quality and evaluate the impact of different management practices on its aggradation/degradation using 4 long-term fertility experiments with organic and inorganic sources of nutrients and different cropping systems in sub-tropical region of India. The relative impact of five treatments viz., control, only N, only NP, NPK and NPK + organics vis-ец-vis a fallow on biological soil quality was assessed. Altogether 24 biological attributes were analysed. Yield, sustainable yield index and crop quality were chosen as the goal variables. Minimum data-set were formulated screening through a number of statistical tools viz., randomised block design, Kruskal-Wallis до2 test, principal component analysis etc. and the results were subsequently validated using hierarchical cluster analysis and multiple regression analysis. Biological soil quality index was then computed using standard techniques. Results showed that application of nitrogen alone caused a net deterioration even more than the control treatment, while balanced application of NPK caused a slight aggradation but inclusion of organics with NPK caused a significant aggradation (as % over fallow) in biological soil quality. However, the indicators identified for assessing such quality and their relative contributions to such quality index varied under different cropping systems and with soil types. Inclusion of organics with NPK always showed a high value of quality index for all the cropping systems and soil types. Results provided a comprehensive tool for delineating healthy vis-ец-vis unhealthy soils and also helped to assess the relative efficacy of different management practices in aggrading/degrading biological soil quality.

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