| A controlled study of irrigation and nitrogen (N) was conducted in Shiyang River basin to investigate the effects of different irrigation and N supply levels on growth characteristics, hay yield, water use efficiency (WUE), soil water content, accumulation and distribution of nitrate N (NO3--N) concentration and plant N uptake of alfalfa (Medicago sativa L). A complete randomized block split-plot design was employed, with irrigation regimes (conventional irrigation (330 mm), 20 % water-saving irrigation (264 mm) and 40 % water-saving irrigation(198 mm)) and N fertilizer application rates (0, 40, 80, 120 kg N·hm-2) as the main-plot and split-plot, respectively. Our results were showed in following:1. Effects of different irrigation and nitrogen N supply levels on plant height and ration of stem to leafN supply level has a relative low effect on plant height. The plant height was increased with the amount of irrigation and the increases of plant height in conventional irrigation and in 20 % water-saving irrigation were 3.14 and 7.55%, respectively compared with 40% water-saving irrigation. When the N rate was 40 kg N·hm-2, the ration of stem to leaf was reached the highest (the mean was 1.12 across the first and the second mowing), while the ration of stem to leaf was decreased significantly with the amount of irrigation.2. Effects of different irrigation and nitrogen N supply levels on hey yieldThe hay yield of M. sativa was increased with the amount of irrigation. The increases of the total hay yield of 3 times mowing (7796 kg·hm-2) in conventional irrigation were 7.8 and 2.5%, respectively compared with that (7232 kg·hm-2) in 40% water-saving irrigation and that (7603 kg·hm-2) in 20% water-saving irrigation. When the N rate was 40 kg N·hm-2, hey yield was reached the maximum (the total hay yield of 3 times mowing was 8223 kg·hm-2), and the increases of the total hay yield at the rate of 40 kg N·hm-2 application were 15, 16 and 7%, respectively compared with 0, 80 and 120 kg N·hm-2 application.3. Effects of different irrigation and nitrogen N supply levels on water use efficiencyThe water use efficiency (WUE) of M. sativa was decreased significantly with amount of irrigation, and the increases of WUE in 40 % water-saving irrigation (15.56 kg·hm-2·mm-1)were 12.3 and 23.5%, respectively compared with 20 % water-saving irrigation (13.86 kg·hm-2) and conventional irrigation (12.60 kg·hm-2·mm-1). When the N rate was 40 kg N·hm-2, the WUE was reached the highest (15.18 kg·mm-1·hm-2).4. Effects of different irrigation and nitrogen N supply levels on soil water content and water consumptionThe soil water content in 0 - 120 cm depth was increased with the amount of irrigation. When the N rate was 80 kg N·hm-2, soil water content in 0 - 40 cm depth was reached the highest among other N application levels. The water consumption of M. sativa was increased significantly with amount of irrigation; also the higher of N application enhances the water consumption in late growth stage of M. sativa. The water consumption rate was the lowest from seeding to branching stage, while was the highest from budding to flowering stage among growth stages.5. Effects of different irrigation and nitrogen N supply levels on NO3--N concentrationThe NO3--N concentration in soil layers was increased with nitrogen application, particular in the surface layer (0 - 40cm), and the soil NO3--N concentration was decreased significantly with amount of irrigation.6. Effects of different irrigation and nitrogen N supply levels on Optimum N applicationIn Hexi oasis of Shiyang River basin, N fertilizer applied at rates higher than the optimum requirement for M. sativa uptake may lead to more NO3--N accumulation in soil profile and the potential risk of N leaching. Optimum requirement for M. sativa uptake was less than 40, 80 and 120 kg N hm-2, respectively under 40 % water-saving irrigation condition, 20% of irrigation water and conventional irrigation conditions.7. Effects of different irrigation and nitrogen N supply levels on nitrogen contentNitrogen content of leaf and stem was increased significantly with N application. When the N rate was 80 kg N·hm-2, the nitrogen content of leaf (37.57) and stem (21.76 g kg-1) was reached the highest. Nitrogen content of leaf and stem was decreased with amount of irrigation, and the increases of nitrogen content of leaf in 40 % water-saving irrigation were 6.56 and 7%, while the increases of nitrogen content of stem were 14.83 and 17.43%, respectively compared with 20 % water-saving irrigation.8. Effects of different irrigation and nitrogen N supply levels on nitrogen uptakeNitrogen uptake in leaf and stem was increased significantly with N application. When the rate of N application was 80 kg N·hm-2, the N uptake of leaf and stem was reached the highest. The increases of nitrogen uptake of leaf in 80 kg N·hm-2 were 17.31,14.39 and 28.20 %, while the increases of stem were 15.23,14.86 and 47.68% , respectively compared by 120, 40 and 0 kg N·hm-2 application. N uptake in leaf and stem was increased with amount of irrigation, and increases of nitrogen uptake of leaf in conventional irrigation was 7.29 and 11.45%, while the increases of stem were 17.24 and 27.76%, respectively compared by 20 % water-saving irrigation and 40 % water-saving irrigation.9. Effects of different N supply levels on nutrition qualityCrude protein content of leaf and stem was increased significantly with N application. When the rate of N application was 80 kg N·hm-2, the crude protein content of leaf (23.48%) and stem (13.60%) was reached the highest. Crude fibers content of leaf and stem was decreased significantly with N application, but crude fat content of leaf and stem was increased significantly with N application.10. Effects of different irrigation levels on nutrition qualityThe content of crude protein and crude fibers of leaf and stem was decreased significantly with the amount of irrigation, and the increases of crude protein content of leaf in 40 % water-saving irrigation were 6.56 and 7%, while the increases of stem was 14.83 and 17.43 %; and the increases of crude fibers content of leaf were 0.2 and 11.61 %, while the increases of stem were 0.76 and 10.51%, respectively compared by 20 % water-saving irrigation and conventional irrigation. Irrigation has no significant effect on crude fat content of leaf and stem. |
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