| Wheat is the main food crop in Northwest China’s dry lands.Micronutrients and health are often neglected in the pursuit of high yields.At present,about 2 billion people in the world suffer from "hidden hunger",especially the deficiency of zinc and selenium.Therefore,increasing the content of zinc and selenium in wheat grain is one of the important ways to improve human health.Soil application and foliar spraying had good zinc and selenium strengthening effect on grain,but soil application had low utilization rate,foliar spraying had many influencing factors and the effect was unstable.In addition,high soil available P also restricted the absorption of zinc and selenium in wheat.Therefore,this study took dryland winter wheat as the research object.Field experiments were conducted in Hongdong,Shanxi,Yongshou,Shaanxi and Qingshui,and five treatments were set for farmers,including fertilization,optimized phosphorus application,optimized phosphorus application + soil application,optimized phosphorus application + foliar spraying,and optimized phosphorus application + soil application + foliar spraying,to study the optimization measures for improving the zinc and selenium nutrition of dryland winter wheat grains on the basis of high yield.To explore the key soil factors limiting the increase of zinc selenium content in wheat grain.The main research results are as follows:(1)The average wheat grain yield in Hongdong,Shanxi,Yongshou and Qingshui was 6.1 t/ha under optimal phosphorus application.Compared with farmer fertilization,optimal phosphorus application had no significant effects on grain yield,phosphorus content and phosphorus uptake,but increased phosphorus fertilizer utilization efficiency by 27%,zinc and selenium content by 3.3 mg/kg and 0.019mg/kg,respectively.The results showed that the optimal phosphorus application rate could improve the utilization of phosphorus fertilizer and the content of zinc and selenium in wheat grains on the basis of ensuring wheat yield.(2)The average zinc content and selenium content were 34.1 mg/kg and 40.0mg/kg in Hongdong,Shanxi Province,Yongshou,Shaanxi Province and Qingshui,Gansu Province,respectively,under optimal phosphorus + soil application and optimal phosphorus + foliar spraying,respectively.Compared with the control,zinc content in grains increased by 5.87 mg/kg and 11.3 mg/kg and selenium content in grains increased by 0.257 mg/kg and 0.254 mg/kg under optimal phosphorus + soil application and optimal phosphorus + foliar spray treatment,respectively.However,the optimal phosphorus application and soil application did not achieve the target enrichment value(40～60 mg/kg)of zinc content in wheat grains,while the effect of foliar spraying was not stable due to the influence of environmental factors,and did not reach the standard of selenium enrichment in wheat grains(0.100～0.300 mg/kg).In the bran,compared with the control,the average zinc content in the three test sites increased by 15.1 mg/kg and 27.5 mg/kg under optimal phosphorus + soil application and optimal phosphorus + foliar spraying,respectively,to 81.1 mg/kg and 93.5 mg/kg.The average bran selenium content was increased by 0.303 mg/kg and 0.313 mg/kg to0.361 mg/kg and 0.371 mg/kg,respectively.In the flour parts,compared with the control,the average zinc content of flour under optimal phosphorus application + soil application and optimal phosphorus application + foliar spray increased by 0.82mg/kg and 2.53 mg/kg to 10.4 mg/kg and 12.1 mg/kg,respectively.The average selenium content in flour increased by 0.230 mg/kg and 0.221 mg/kg to 0.261 mg/kg and 0.252 mg/kg,respectively.In conclusion,the effect of optimal phosphorus + soil application and optimal phosphorus + foliar spraying on zinc nutrition in bran was higher than that in flour,and the effect of selenium nutrition in bran and flour was basically the same.(3)The average Zn and Se contents in the grains of Hongdong,Yongshou and Qingshui were 44.9 mg/kg and 0.579 mg/kg,respectively,under chemical phosphorus application,soil application and foliar spraying.Compared with the control,the zinc and selenium contents in grains increased by 16.6 mg/kg and 0.541 mg/kg,respectively,under the optimal phosphorus application,soil application and foliar spraying treatment,and the target zinc and selenium enrichment values were reached at all test sites.In the bran,compared with the control group,the zinc and selenium contents in the bran under the optimal control measures of phosphorus application,soil application and foliar spraying increased by 40.3 mg/kg and 0.594 mg/kg to 106mg/kg and 0.647 mg/kg,respectively.Compared with the control group,Zn and Se contents in flour under the optimal control measures of phosphorus application,soil application and foliar spraying increased by 3.31 mg/kg and 0.501 mg/kg to 12.9mg/kg and 0.545 mg/kg,respectively.Considering the zinc and selenium content of each part,the optimization of phosphorus application,soil application and foliar spraying had the best strengthening effect.(4)Excessive P application limited the absorption of zinc and selenium in wheat,mainly because excessive P in soil inhibited the colonization of AM fungi in roots.The optimal phosphorus application increased the AM colonization by 19% and decreased the soil available P by 6.7 mg/kg.The optimal phosphorus application and soil application treatment increased the content of available zinc and selenium in soil by 0.05 mg/kg and 0.003 mg/kg,respectively,which was beneficial to improve the zinc and selenium absorption of winter wheat grains in dry land.Based on optimal phosphorus application,soil application of zinc and selenium fertilizer can significantly increase the content of soil available zinc and selenium by 3.8 times and4.2 times.The soil nitrate nitrogen content decreased by 3.3 mg/kg,the soil available potassium decreased by 1.5 mg/kg,the soil available iron,manganese and copper increased by 0.01 mg/kg,0.08 mg/kg and 0.01 mg/kg respectively,and the soil p H increased by 0.01,but no significant difference was reached.In conclusion,the optimization of phosphorus application combined with soil application and foliar spraying of zinc and selenium fertilizer can maximize the enrichment of zinc and selenium nutrients in grain and flour on the basis of ensuring wheat yield.Optimal phosphorus application could increase the utilization rate of phosphorus fertilizer and AM colonization,and improve the ability of wheat root to absorb zinc and selenium.Soil application of zinc and selenium fertilizer can increase the available zinc and selenium content of soil.Foliar application of zinc and selenium fertilizer can rapidly increase the absorption of zinc and selenium of grain and improve the utilization efficiency of zinc and selenium fertilizer.The best technical measures were to optimize phosphorus application,soil application and foliar spraying by comprehensively evaluating wheat yield,grain zinc and selenium nutrition enhancement effect and fertilizer utilization efficiency. |
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