Studies on relationship of soil carbon fractions with crop productivity and soil health under long term fertilizer experiments in rice-wheat cropping system on a mollisols
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Date
2016-01
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Study was conducted during 2012-13 to assess the relationship between soil carbon fractions with crop productivity and soil health in an ongoing long term fertilizer experiment at N. E. Borlaug Crop Research Centre, G. B. Pant University of Agriculture and Technology, Pantnagar during 41 years of continuous fertilizer use. For study, surface and sub-surface soil samples were collected from individual plots and were analyzed for soil physico-chemical properties and organic carbon fractions. Observed results showed that application of 100% NPK+FYM@ 15 t ha-1 gave highest grain yield of rice (51.87 q ha-1) and wheat (46.17 q ha-1) which was significantly higher than all other fertilizer treatments. Due to continuous cropping no perceptible change in pH was observed. The status of organic carbon showed a declining trend over the years. In control, it reduced to one third of original level of organic carbon (1.48%), whereas combined use of NPK fertilizers and FYM restored its initial status. Availability of nutrients was found lower in deeper soil layers (15-60 cm) than in surface layer (0-15 cm). In absence of P, K and Zn addition, continuous cropping drastically reduced their availability in soil over the years. The bulk density exhibited an increasing trend with increase in soil depth (0–60 cm) in respective treatments. Physical properties of soil were improved with integrated nutrient management system. The greatest accumulation of different carbon fractions were observed with 100% NPK + FYM treatment while control plot showed the lowest value. Irrespective of depths, the balanced application of NPK (100% NPK) showed higher accumulation of soil organic carbon fractions over imbalanced use of fertilizers (100% N or 100% NP). All the treatments showed higher accumulation of soil organic carbon fractions in surface soil as compared to sub-surface soil. Cultivation without fertilization decreased the organic carbon fractions. Active and passive fractions of soil organic carbon were maximum with combined application of NPK and FYM at all the soil depths. The data with respect to rice and wheat yields with different organic carbon fractions viz., TOC, POC, Aggt C, MBC, MBN, KMnO4-C, WSC, HWEC, Humic C, Fulvic C and Humin C, revealed positive and significant correlations while bulk density showed negative correlation. The results indicated that integrated use of fertilizer and FYM enhanced the soil organic carbon fractions whereas continuous rice-wheat cropping without fertilizer use decreased the soil properties and soil organic carbon fraction