Effects of improved management and quality of farmyard manure on soil organic carbon contents in small-holder farming systems of the Middle Hills of Nepal

Abstract

Simple and widely adopted sustainable soil management (SSM) practices, especially improvements in the management and quality of farmyard manure (FYM), have enabled many thousands of small-scale farmers in the Middle Hills of Nepal to increase organic matter in their soils. This has been achieved without increases in livestock numbers or in the quantity of manure available. The organic matter contents have increased in all of five time series of on-farm topsoil monitoring over periods of one to three years, at rates varying from 2% to 27%. Overall, the increase from 3.3% organic matter to almost 3.8% was highly significant. Systematic full-profile comparisons of forest soils against arable soils with and without SSM showed that the benefits are not confined to the topsoils, and that there were some lesser increases in the subsoils. Sustainable land management and improved FYM quality significantly improved total nitrogen levels. The effects on available P and K were inconsistent and only occasionally significant, with some indication of K decline in topsoils. The enhanced organic matter status of the soils was also reported to improve structure, workability, and moisture characteristics. The increase in soil organic matter can partially offset some of the substantial losses of carbon storage incurred when the forests were originally cleared, and contributes to the sequestration of atmospheric CO2.