Agricultural intensification, soil fertility dynamics, and low-cost drip irrigation in the Middle Mountains of Nepal
Creators: name: Von Westarp, Stephanie
Publisher: name: University of British Columbia
Year: 2009

description: The maintenance of soil fertility and access to water are essential to food production. This is of particular relevance to the subsistence-based farming systems of the Middle-Mountains of Nepal, which face tremendous pressure to feed a rapidly growing population. One means in which the demand for increased productivity is being met is through the intensification of agriculture. However, this has caused concerns over the long-term impacts on soil fertility. This study investigated if soil fertility has been compromised through agricultural intensification by comparing the soil status and inputs in intensively managed sites (sampled in 2000) to those of less-intensively managed sites (sampled in 1994). Nutrient budgets for nitrogen (N), phosphorus (P), and potassium (K) were developed to examine if inputs of these nutrients are sufficient to meet crop uptake. Intensive farms utilize significantly more fertilizer and compost than less-intensive sites. The significant rise in fertilizer use has been accompanied by a shift in the use of predominantly urea to diammonium phosphate. This process has been driven by the introduction of potatoes and tomatoes into the cropping rotation and a decline in the use of a pre-monsoon fallow period. Phosphorus inputs to irrigated sites under intensive agriculture are considerably greater than crop uptake requirements, whereas inputs of N and K are insufficient, resulting in negative nutrient budgets. This imbalance has caused a significant increase in the level of available P in the soil and a significant decline in the level of amount of exchangeable K in the soil. In addition, intensification is accompanied by declines in the levels of base cations in the soil, which may indicate soil acidification. Farmers cultivating irrigated land need to address the serious deficits in exchangeable K, while reducing excess P inputs, and taking measures to reduce the potential of soil acidification. In contrast, intensive rainfed sites have large surpluses in N, P, and K budgets. Farmers could therefore reduce their inputs to minimize unnecessary economic expenditures and eutrophication of water sources, without risking a depletion of the soil nutrient pool. Irrigation, as a source of water is the other means of increasing food production. Irrigation is particularly problematic in the rainfed lands of the Middle-Mountains due to topographical factors and water scarcity during the dry winter and pre-monsoon seasons. The performance of low-cost drip irrigation (LCDI), an affordable means of expanding irrigation into rainfed areas, was compared with conventional "Western" drip irrigation and hand watering for the cultivation of cauliflower. Comparisons were made between and among irrigation methods that were deficit irrigated and those that received full irrigation. Deficit irrigation refers to 50% of the estimated daily plant water requirement, whereas full irrigation refers to 100% of the estimated daily plant water requirement. Western drip irrigation produced the lowest cauliflower yields, however differences in cauliflower yield between LCDI and hand-watered irrigation methods were inconclusive. There were no consistent differences in the soil volumetric water content between the three irrigation methods. Deficit irrigation resulted in lower soil volumetric water content and lower cumulative yields; however water-use efficiency was higher for deficit irrigation than for full irrigation. Overall yields were comparable to those observed in California and British Columbia. LCDI appears to be a better long-term strategy as less labour is required and because it results in greater profits once capital costs have been paid. In addition, under deficit irrigation, LCDI produced the greatest cauliflower yields implying that farmers in the water-scarce rainfed areas can viably cultivate an additional crop, increasing their economic and food security.