Minimization of Soil and Nutrient Losses in Maize-based Cropping Systems in the Mid-hills of Central Nepal

Soil nutrient depletion is a major concern in terms of resource utilization and optimization of production in the middle hills of Nepal. Soil and nutrient losses from agricultural land is responsible for pollution of surface waters and this reduces the productive capacity of land. A field experiment was initiated in May 2001 on acidic sandy loam soil in Kavre district; Nepal to investigate the efficiency of widely recommended researchable options for soil conservation. The experimental plots were set up as a two factorial design with three main factors (mulching, reduced tillage and conventional farmers' practice as control) and were divided on the basis of cropping patterns (maize sole and maize inter-cropped with soybean). Soil N, P, K, and OM losses were determined from soil eroded in runoff. Nutrient loss in premonsoon period (in the month of May) was highly significant among the management practices. Much of nutrient (60 to 90 percent of annual) losses occurred during this period. As compared to conventional farmers' practice, mulching reduced annual soil organic matter loss by 52 percent, annual total nitrogen by 46 percent, annual available P2O5 by 32 percent and annual exchangeable K2O by 53 percent in maize – mustard cropping system. Similarly, in maize + soybean mustard cropping system, the annual loss of these nutrients were reduced by 58, 49, 26 and 60 percent, respectively. Reduced tillage, on the other hand, produced higher soil loss and hence more nutrient and organic matter loss as compared to mulching practice because of freshly prepared plots and hence less vegetation and more compaction. INTRODUCTION Soil erosion by water may have both positive and negative effects depending on the type, magnitude, and extent of erosion. Geologic erosion is responsible for the formation of the most fertile alluvial soils (Indus valley, Indo-Gangetic plains, Nile delta) that have supported intensive agriculture for millennia for many ancient civilizations (Lal, 1998). However, sheet erosion is a serious problem because of its adverse impacts on agronomic productivity, the environment and ecosystem balances. Sheet erosion, in fact, usually occurs at such a slow rate that its cumulative effects may take decades to become apparent. Miller (1992) has illustrated the nature of this form of soil erosion: ‘removal of one millimeter of soil, an amount easily lost during a rain, is so small that it goes undetected; but the accumulated soil loss at this rate over a 25 years period would amount to 25 mm an amount that would take about 500 years to replace by natural processes’. As a result of soil loss, plant nutrients are removed; texture is changed; structure deteriorates; production capacity is reduced; fields are dissected and the sediments produced pollute streams and lakes and pile up on bottomlands, in stream channels and in reservoirs (Troeh et al. 1980). Transport and deposition of eroded material as well as substances dissolved in runoff and attached to soil particles lead to negative impacts on agricultural land and adjacent water bodies (Klik, 2000), water quality decline (Wood, et al. 2000; Richards, 2002), eutrophication (Gruhn et al. 2000; Zemenchik,