S. Kar and Samarendra Sahoo. Indian Institute of Technology, Dept of Agricultural and Food Engineering, Kharagpur, 721302, India
The production of rice is kept at a low level in the Red and laterite agro-climatic zone of West Bengal, India, by soil acidity, low recovery of water and Nitrogen (N) and poor management of soil and input resources. Alleviation of the soil constraints and maximization of water and N use efficiencies of rice in this zone essentially require an in-depth knowledge about the dynamics of water and N in relation to agro-management practices. To maximize water and N use efficiencies of rice crop by selecting the most suitable combination of agro-management practices, a comprehensive investigation field experiments as well as modelling study was conducted in a acid lateritic sandy loam soil. The main goal of the investigation is to evaluate the effects of tillage depth, liming, soil moisture regime, application of polymer coated urea and split application of N on water and N dynamics under rice crop, and quantify the effects of agro-management practices on yield, water and N use efficiencies of rice. The fluxes of water and NO3-N below root zone of rice was also simulated with the help of Root Zone Water Quality Model (RZWQM). The agro-management practices studied in the field experiments included puddling of soil to 10 cm (P1) and 20 cm (P2) depths with power tiller, application of lime @ 0.0 t ha-1 (L0) and 1.5 t ha-1 (L1), 10 ±2 cm continuous flooding (W1) and rainfed soil moisture regime (W2), application of polymer coated urea (CU) and uncoated urea (U) @ 100 Kg N ha-1, as well as two (2S) and four split (4S) applications of urea. The commercial powdered lime (CaCO3) was applied one month before the puddling operation. The full dose phosphatic (SSP) and potassic (MOP) fertilizers were broadcasted at the time of puddling and nitrogenous fertilizer, urea, was applied @ 100 kg per hectare in two and four equal splits. Rice (variety IR-36) was grown under flooded conditions. The flow pattern of water in rice field was estimated from the data of water pressure measured with the help of piezometers installed at 15, 45, and 75 cm soil depths. Soil solution extract was collected from rice fields with the help of soil water samplers and its content of NO3-N and NH4 -N was measured with the help of Ion meter. The results of the investigation indicate that the deep percolation loss can be effectively reduced by shallow puddling and liming of soil under rice crop. The leaching losses of water soluble N can be significantly reduced by four split application of polymer coated urea and by adopting deep puddling and rainfed soil moisture regime for rice crop. The maximum recovery of N by rice can be attained by applying lime @ 1.5 t ha-1 in combination with deep puddling, continuous flooding and four split application of polymer coated urea. The combination of liming, deep puddling, continuous flooding for rice and four split application of polymer coated urea is the best combination of agro-management practices for maximum grain yield. The water flux below root zone of rice crop, and NO3-N flux below root zone are reasonably predicted by the RZWQM model. The matching between simulated and measured fluxes of NO3-N was closest with four split application of urea under relatively dry soil moisture regime. Low values of Standard Error, Relative Error and Root Mean Square Error and high value of Nash-Sutcliffe Simulation Efficiency reflect to high predictability of RZWQM.
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