Experimental Study On Coupling Utilization Effect Of Water And Nitrogen In Maize In Semi-Arid Region Of Western Heilongjiang Province

Hei long jiang province is an important grain production base in China,and corn is the most planted crop in the region.Ensuring the grain production and stable yield in heilongjiang province is of great significance not only to the food security of the province,but also to the food security of the country.The annual and seasonal distribution of rainfall in heilongjiang province is uneven and the spatial difference is obvious.In the upland planting mode,although the irrigation area continues to expand,rain-fed agriculture is still the main mode.Due to the lack of accurate and effective irrigation mode,drought and water shortage often occur during the growing period.At the same time,the unreasonable application of fertilizer,especially nitrogen fertilizer,has become an important factor restricting the sustainable development of agriculture.It will play an important role in ensuring food security to adopt efficient irrigation method and seek reasonable proportion of water and fertilizer.Water and nitrogen,as two important factors affecting crop growth,affect the improvement of crop yield and quality,and improve crop water and nitrogen utilization efficiency,which is crucial to improve crop yield and relieve the pressure of local agricultural water.This experiment was conducted in Zhao Zhou county water conservancy science experimental station in the western region of heilongjiang province.The irrigation quota is set at three levels:1)W1:40mm,2)W2:60mm,and 3)W3:80mm.Nitrogen application dosage was set at four levels:1)N0:0 kg/hm²,2)N1:180 kg/hm²,3)N2:240 kg/hm²,4)N3:300 kg/hm².From April to October in2018.On the basis of the water-nitrogen coupling experiment,micro-zones were added in the experimental plot,and the ¹⁵N stable isotope tracer technology was used to explore the whereabouts of fertilizer nitrogen labeled by ¹⁵N under the condition of water-nitrogen coupling.This experiment focused on exploring the effect of water-nitrogen coupling on maize yield,water consumption and water use efficiency.Cumulative distribution and transport of dry matter;Cumulative distributio n and transport of fertilizer nitrogen,cumulative distribution and transport of soil nitrogen,and residues of fertilizer nitrogen and inorganic nitrogen in soil after harvest.The main findings are as follows:（1）L_AI at different growth periods shows a trend of increasing first and then decreasing with the increase of irrigation water and nitrogen application.Increasing nitrogen application and irrigation water can promote the improvement of L_AI;meanwhile,the combination of medium and high nitrogen application and medium irrigation water can ensure the maintenance of L_AI at a relatively high level during the grouting stage and the maturity stage.The plant height in the jointing stage,tassel stage and grouting stage showed an increasing trend,and the period from jointing stage to tassel stage was the rapid growth stage of plant height,and the increase rate of each treatment was 17.80%～36.22%.The plant height treated with N3W2 was the highest in the jointing stage,tasseling stage and maturity stage.（2）With the growth period,P_nincreased first and then decreased,and increased first and then decreased with the increase of nitrogen application and irrigation water.Stomatal conductance and transpiration rate showed similar trends,and stomatal conductance and transpiration rate showed a trend of increasing first and then decreasing with the growth stage,and most of the treatments were shown as>in tasting stage and>in grouting stage.The stomatal conductance and transpiration rate were increased by increasing the amount of nitrogen and irrigation.（3）The yield of N2W2 treatment is the maximum in these treatments which is 14170.99 kg/hm²,and the yield of nitrogen treatment were increased by 9.45%～68.24%compared with N0W1treatment.Maize yield increased first and then decreased with the increase of nitrogen and irrigation application.With the increase of nitrogen application and irrigation,the water consumption of maize during the whole growth period was increasing.The highest water consumption was in jointing stage,which was slightly higher than that in tasseling stage.The WUE of N2W2 treatment was the largest,and increased first and then decreased with the increase of nitrogen application and irrigation amount.（4）The dry matter accumulation of maize under different treatments during the growth period was basically the same,and the dry matter accumulation was increased with the advance of the growth stage.The fastest growth rate of dry matter was from the spinneret to the filling stage,and the growth pattern of slow-fast-slow was observed in the whole growth period.The dry matter transshipment volume and the contribution rate of grains were shown as bracts of stem>leaf>spike leaf,and the N2W2 treatment were the largrest in the accumulation and contribution rate of dry matter.（5）If making a comparison of nitrogen accumulation in each organ at maturity stage,the best was grain,then was leaf,stem,the last was ear leaf.The proportion of nitrogen in fertilizer was the highest in the spinneret stage,followed by the stem.In the mature stage,the proportion of nitrogen in grain fertilizer was the highest（71.63%～77.10%）,followed by the proportion of leaves,and the proportion of stem and spike leaves was close.With moderate nitrogen application regime,the nitrogen accumulation in plants was the highest.The nitrogen transference amounts of each organ was shown as leaf>stem>ear leaf,nitrogen transference amounts of the whole plant of maize was increased in nitrogen applied treatment compared with no nitrogen applied treatment,and nitrogen transference amounts of N2W2 treatment was the highest,which was significantly different from other treatments（P<0.05）.The order of contribution rate of nitrogen grain in different organs were expressed as leaf>stem>ear leaf.Nitrogen transformation in various organ accounted for18.29%～44.29%of the nitrogen accumulation in the grain,and the N2W2 plot had the best value.（6）The nitrogen in maize plants,66.70%～75.05%came from the accumulation of soil nitrogen.The accumulation of soil nitrogen in maize plants was increased first and then decreased with the increase of nitrogen application.The amount of soil nitrogen involved in transformation was greater than the amount of fertilizer nitrogen.The ¹⁵N transformation and soil nitrogen transformation of various organs of maize were expressed as leaf>stem>stem leaves.22.43%～39.45%of nitrogen transformation in plant came from fertilizers,the moderate water and nitrogen treatment could keep higher oil nitrogen transformation.（7）The nitrogen fertilizer recovery rate ranged from 21.27%to 44.64%,and N2W2 treatment had the highest nitrogen utilization rate.At the level of 240 kg/hm² nitrogen application,the plant fertilizer nitrogen accumulation was the highest,accounting for the largest proportion of nitrogen application.When the nitrogen application increased to 300 kg/hm²,the fertilizer nitrogen accumulation only accounted for 21.67%～31.23%.The results showed that the yield and water use efficiency reached the optimal level when the irrigation was 60 mm and the nitrogen application was 240 kg/hm²,which was in line with the goal s of water saving and high yield.Nitrogen is most efficient at this time,reducing the risk of environmental pollution.The leaf area index and net photosynthetic rate had obvious advantages under this ratio of water and nitrogen.The accumulations of fertilizer nitrogen and soil nitrogen were the highest in all treatments,and the accumulations of dry matter and nitrogen before flower s were sufficient,which provided a guarantee for the formation of yield and the accumulation of nitrogen in grains.