Study On The Utilization Of Water And Nitrogen And The N-Fertilizer Balance Under Water Saving Irrigation

Basing on the research achievements of water saving irrigation for rice both inland and abroad, the experiment was carried out in the lysimeter with middle rice (hybrid) in Zhanghe irrigation experimental station, Hubei from May to September in 2003. And it was designed two water irrigation treatments: continuous flooding (WO) and water saving irrigation (W1) with three nitrogen levels: OkgN/hm² (N0), 120 kgN/hm² (N1-¹⁵N fertilizer) and 180 kgN/hm² (N2), which were applied in three fertilizer methods: F1 (basal 30%+tillering 30%+panicle initiation 30%+ flowering 10%), F2 (basal 50%+panicle initiation 50%) and F3 (basal 50%+tillering 30%+panicle initiation 20%). The objective of the study was to quantify N-fertilizer application on rice growing season, nitrogen loss, N-fertilizer balance and water productivity. The main results were as follows:1. Water saving irrigation could improve the absorbability and utilization of nitrogen by rice, and it was demonstrated by that the nitrogen content of roots, stems and leafs of rice in the vegetative growth stage was higher under the water saving irrigation than under the flooding irrigation, and there were few differences between two irrigation methods in the reproductive growth stage. According to the accumulation of nitrogen, the accumulation in the roots and grains was higher under the water saving irrigation than under the flooding irrigation, but that in stems and leafs was lower under the water saving irrigation than under the flooding irrigation. The above indicated that water saving irrigation benefits the absorption and utilization of nitrogen by rice in the vegetative growth stage and the transfer of nutrient to the productive organs in the reproductive growth stage.2. The relationship between the nitrogen content in the percolation water and the fertilizer quantity was positive, so the nitrogen loss of treatments with high N-fertilizer was higher than the others. The total nitrogen loss under flooding irrigation was significantly higher than that under water saving irrigation. Among the fertilizer application methods in the whole growing season, the nitrogen loss of Fl was least and that of F3 was second lest and the F2 was most.3. The N-fertilizer use efficiency measured by direct method showed that of Fl and F2 was higher under the water-saving irrigation than under the flooding irrigation, but that of Fl was contrary. N-fertilizer use efficiency measured by isotope method was higher under the water-saving irrigation than under the flooding irrigation, furthermore, it had a trend that NUE went down with increasing the rate of N-fertilizer application.4. The different water and nutrient conditions changed the biological characters of rice and affected the plant configuration and grain yield. Water saving irrigation partly restrained invalid tillers and kept the leaf area index (LAI) of rice appropriate level in the whole growing season. And the growth of individuals under water saving irrigation was better than that under flooding irrigation. So the rice had a good basic for high yield under water saving irrigation.5. On the same fertilizer level, the yield of Fl and F2 was higher under the water-savingirrigation than under the flooding irrigation but that of F3 was contrary.6. Water saving irrigation can improve water productivity significantly. The water layer in the field with water saving irrigation was very shallow and sometimes there was no water layer in the field. So the percolation and evapotranspiration of water was decreased and water productivity was improved.7. The experiment researched nitrogen in the percolation water and residual N-fertilizer in the soil, and established the balance equation of N-fertilizer in the rice field. It was primarily clear that the scale of nitrogen absorbed by plants, residual in the soil, loss from percolation water, and the loss of gas nitrogen under different water treatments. And the proportion absorbed by rice of N-fertilizer was less than 2/5; the percentage left in the soil was about 1/4; the scale of N-fertilizer loss from percolation water was less than 0.5%; the loss of gas-N was largest: 2/5-1/2.