05 Jan 2017

Study on N and P runoff losses from cotton field in Jianghan Plain of Hubei

N and P are not only the main plant nutrition but also the main non-point pollution substances of farmland. As the great demand of agricultural production in China, more and more N and P fertilizers were used in farmland in last four decades. At the same time, more and more N and P from applied fertilizers were lost through ground runoff with rainfall, irrigation and drainage, and further resulted in non-point pollution. It was reported that there were 63.6% of the lakes in the country have problem of eutrophication and half of them mainly caused by fertilizer N and P. Jianghan Plain area of Hubei province is located in the middle stream of Yangtze River and is one of the most important grain, oilseed and cotton crops production bases in Hubei with large rate of N and P fertilization. Therefore, under the support of IPNI China program, the Soil and Fertilizer Institute of Hubei Academy of Agricultural Science carried out some field experiments to investigate the N and P runoff losses from cotton fields in the plain in recent years. The field experiments mainly focused on two treatments—no fertilization treatment and farmer’s conventional fertilization practice. The runoff water in each plot was collected and analyzed.

The results showed that the runoff events usually occurred in raining season (March to August) with rainfall rates 212.4-325.9 mm, and the runoff volume increased with the rise of rainfall in the runoff formation period. The coefficient of the cotton field runoff averaged at 25.96%. In the farmer’s conventional fertilization practice plot, the annual N loss from cotton field were 36.14 kg/ha to 89.52 kg/ha, the P loss at the same period were 0.42 kg/ha to 10.07 kg/ha respectively. These loss rates were considerable different between different years. Nitrate N was the main way of nitrogen loss, which accounted for 64.2%-92.8% of the nitrogen loss in our research period (2 years). The next N loss form was particle nitrogen, and the loss rate of ammonium N was very little.

Particle P was main form of P loss in the cotton field, next was the dissolved phosphorus. The amount of particle phosphorus loss was increased significantly in the year with larger rainfall during the runoff formation period, which accounted for more than 90% of total P loss. During these periods in the different years, the coefficients of N and P losses were 5.4% and 3.1% respectively. The rates of nitrogen and phosphorus losses were promoted by increase fertilization rates, and also increased with the rainfall rates increase during the runoff formation period, while reduced with the increase of crop coverage. Therefore, to reduce the fertilizer N and P loss, we should take the key factors such as right fertilization rate, right fertilization time, right N and P fertilizer products and right plant densities into consideration in future.

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