JWSS - Journal of Water and Soil Science

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To determine the proper nitrogen fertilizer rates and its application times for achieving high grain and oil yields of rapeseed cultivar, Hyola 401, a research was carried out in paddy fields of Rice Research Institute of Iran in Rasht during two cropping seasons. A factorial experiment was conducted in a completely randomized block design with three replications. The experimental factors were pure nitrogen fertilizer rate at five levels of 0, 60, 120, 180 and 240 Kg ha-1 and fertilizer application times at five levels of all fertilizer at planting 1/3 at planting + 2/3 in stem elongation 1/3 at planting + 1/3 in stem elongation + 1/3 before flowering 1/3 in 3-4 leaf stages + 1/3 in stem elongation +1/3 before flowering 1/4 at planting + 1/4 in 3-4 leaf stages + 1/4 in stem elongation + 1/4 before flowering. The results of statistical analyses showed that from amony nitrogen rates, application of 240 Kg N ha-1 and 180 Kg N ha-1 with average production of 2505 Kg ha-1 and 2596 Kg ha-1 respectively showed the highest grain yield and were in the same group. of Nitrogen application times, application of 1/3 at planting + 1/3 in stem elongation + 1/3 before flowering had the highest grain and oil yields with average of 2155.3 Kg ha-1 and 9865 Kg ha-1, respectively. Maximum oil percentage was observed in control treatment (without N-fertilizer application) and the highest oil yield was obtained for nitrogen rates of 180 and 240 Kg ha-1. Also, the highest growth period was observed for the treatment of 240 Kg nitrogen with 206.3 days. The results showed that nonsignificant difference exists between the nitrogen rates of 180 and 240 Kg ha-1 in grain and oil yields. Therefore, the rate of 180 Kg ha-1 is recomended due to less fertilizer consumption and prevention of destructive effect on the environment

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Nitrate leaching from agricultural lands can pollute groundwater, and the degree of pollution caused significantly depends on agricultural practices implemented on farms. Field studies required to evaluate the effects of various agricultural management strategies on nitrate leaching are expensive and time consuming. As a result, it is suggested to use crop models to simulate the effects of management practices on nitrate leaching. Plant growth models such as DSSAT software package can simulate daily plant growth and development, and also are capable of simulating daily nitrate leaching and nitrogen uptake by plants. However, it is required to evaluate the performance of any model before using it for any specific region. In this study, the performance of nitrogen balance model of DSSAT software package was evaluated to simulate nitrate leaching from the root zone of silage maize at different levels of applied water and nitrogen fertilizer. The experiment consisted of three levels of nitrogen fertilizers, including zero, 150 and 200 kg N ha-1 and four levels of applied water 0.7SMD (soil moisture depletion), 0.85SMD, 1.0SMD and 1.13SMD. Nitrate-nitrogen leaching from 36 plots at the 60 cm depth during the growing period was measured by soil moisture suction equipment (ceramic suction cups, CSC). After calibrating the model by using field data, its performance was evaluated to simulate nitrate leaching. Maximum amount of N leaching 8.4 kg N ha-1 was obtained from over irrigation treatment with the application of 150 kg nitrogen per hectare. The model simulated nitrate leaching for this treatment as 7.8 kg N ha-1. The model consistently underestimated the nitrate leaching however, it followed the behavior of nitrate leaching during the growing season. In deficit irrigation treatments, the nitrate leaching was very low and close to zero and the model simulated the same result accordingly. The results showed that the model, in addition to phenological stages and performance indicators, can simulate nitrate leaching from the root zone and could be used to evaluate the effects of various irrigation and fertilizer management strategies on nitrate leaching.