[Response of water coupling with N supply on maize nitrogen uptake, water and N use effi- ciency, and yield in drip...

Water and nitrogen are two major limiting factors for upland crop growth and development in arid region. Optimizing regulation irrigation schedule, rates and coupling with N fertigation is an effective way for realizing crop production improvement as well as water and nutrient use efficiency enhancement. In the present study, a field trial was carried out to study the influence of water (4500, 6750, 9000 m³ · hm⁻²) coupling with N (0, 225, 330, 435, 540 kg · hm⁻²) supply on maize dry matter accumulation, N uptake, yield and nitrogen fertilizer use efficiency in drip irrigated high cultivated density (≥ 105000 plant · hm⁻²) condition. There was an obvious tendency that the amounts of corn dry matter accumulated and plant N absorbed increased with levels of water and N supply, however, those decreased gradually when the N applied rate beyond 435 kg · hm⁻² and irrigation level above 9000 m³ · hm⁻². For instance, the effect of irrigation level on corn dry matter accumulation order exhibited W₆₇₅₀ (36359 kg · hm⁻²) > W₉₀₀₀ (35077 kg · hm⁻²) > W⁴⁵⁰⁰ (33451 kg · hm⁻²), the sequence of amount of N absorbed showed N₄₃₅ (462.0 kg · hm⁻²)> N₅₄₀ (459.4 kg · hm⁻²) > N₃₃₀ (423.4 kg · hm⁻²) > N₂₂₅ (348.1 kg · hm⁻²), the amount of N absorbed in N₄₃₅ treatment increased by 9.1% and 32.7%, respectively, in contrast with treatments of N₃₃₀ and N₂₂₀, whereas, the amount of N absorbed in N₅₄₀ decreased by 0.6% than that in N₄₃₅ treatment. The highest N absorption rate increased with N application rate increasing within N supply range of 0-435 kg · hm⁻², it reached peak value of 6.57 kg · hm⁻² · d⁻¹ at N application rate of 435 kg · hm⁻²,then had decline trend with increasing N rate. Both irrigation and N supply exerted a significant role on maize yield as well as yield component of kernel number per spike and kernel mass per spike. An obvious positive interaction was obtained between water and nitrogen, moreover, the effect of N on yield was substantially higher than that of irrigation. N fertilizer use efficiency increased with increasing N level within N supply range of 0-435 kg · hm⁻² and then dropped markedly when N rate above 435 kg · hm⁻² It was found that the water productivity of irrigation (WP i increased with increasing N level, while, that decreased with increasing irrigation rate. At the suitable irrigation range of 4500-6750 m³ · m⁻² the WP of 2.57-3.80 kg · m⁻³could be achieved. The maximum corn yield of 18072 kg · hm⁻² as reached at N rate of 567.0 kg · hm⁻² The best N rate of 427.9-467.7 kg N · hm⁻² btained the optimum yield of 17109-17138 kg · hm⁻² with the nitrogen partial factor productivity of 122 kg N · hm²and nitrogen use efficiency of 45.0% reached. In sum, optimizing water coupling with N supply was the effective strategy for realizing corn yield improvement as well as resources of water and N use efficiency in drip irrigation condition in arid region.