On-Farm Estimation of Economical and Ecological Optimum Nitrogen Rates for Rice Production: A Field Study of Transplanted Lowland Rice in Central Hills, Nepal

摘要

It is ecologically and economically important to determine the proper amount of nitrogen as required by lowland rice plant since it is a prime limitation to crop yield. The central mid-hills of Nepal is a productive domain of rice, but the sub optimaldose of N by farmers and moreover, the blanket recommendation of N fertilizer by governmental bodies for wider regions without time variation at specific growth stages do less coincide with the dynamic soil property for supply and demand of N in soil-crop system, resulting less synchronized application of N-fertilizer and subsequent loss of applied N with poor recovery efficiency. Thus, the present study was designed to estimate the economically and ecologically safe nitrogen doses for lowland rice bythe principles of site specific nutrient management (SSNM) considering soil spatial variability by evaluating the productivity, profitability and N use efficiency of SSNM based nitrogen rate ( as recommended by Nutrient Expert Rice and Leaf Color Chart)over the farmer’s fertilizer and other government recommended nitrogen management practices for that aera. A field experiment was conducted in 2017 during monsoon in central mid-hills at Bhaktapur, Nepal for field validation of DSS tools like Nutrient Expert~R Rice (NE) and other simple diagnostic kit like Leaf Color Chart (LCC) designed for optimal application of N. Different N levels based on farmers practices, government recommendation, NE based, LCC based and NARC recommended dose were analyzed toevaluate the optimum dose of N for lowland rice in RCBD having 6 replications. The statistical results showed that the productivity of rice could be raised by 14%, profitability up to 21% and N uptake by 29% using N diagnostic tool like LCC. N fertilization remarkably promoted the grain and total biomass yield to the optimum level with LCC- based N dose and started to suppress rice grin yield if N level was increased beyond the LCC recommendation. The rice grain N uptake increased with its application to the level of 114 kg N ha~(-1), but started to decline at 120 kg N ha-1. The higher internal efficiency of N was obtained for the farmers’ fertilizer N practice, receiving comparatively lower dose of N, in which the total uptake of N was lesser than others. The partial factor productivity of N was recorded higher for farmers’ practice and the lowest for NARC recommendation such that PEP-N decreased with increasing rate of N. Therefore, optimum level of N application should be promoted through the useof N friendly DSS tools to maximize yield along with environmental protection and cost effectiveness.