Reasons For Differences In Mineral Nutrient Concentrations Of Dryland Wheat Grain Over Different Locations On Loess Plateau

Mineral elements are essential for maintaining the normal growth and metabolism of plants and human.Currently,the global population under malnutrition is over 0.8 billion,of which>66.7%are afflicted by the deficiency of iron?Fe?,zinc?Zn?or other mineral nutrients.Cereal crops,such as wheat,are the main source of human mineral intake.On the Loess Plateau,a typical dryland wheat production region of China,understanding the factors affecting grain nutrient concentrations at different sites,is of great significance to optimize nutrient management and improve grain mineral nutrition quality.The present study investigated 20 cultivars from the major wheat production regions of China in field experiments located at Yongshou and Yangling of Shaanxi province during 2017 to 2019.At each site,the tested wheat cultivars were grown with basal application of 180 kg N/ha,100kg P₂O₅/ha and 75 kg K₂O/ha.At anthesis and maturity,the plant and soil samples were collected to investigate the relationships of soil nutrients,precipitation,grain yield and its components with macro-and micronutrient uptake and translocation,in order to explain the reasons for different grain nutrient concentrations between Yongshou and Yangling.The main results are:1. Significant differences were observed for grain nitrogen?N?,phosphorus?P?and potassium?K?concentrations between Yongshou and Yangling in both years.In 2018,the grain N and K concentrations at Yongshou were 10.6%and 6.7%lower than those at Yangling,while grain P concentration showed no difference between two sites,and the grain yield at Yongshou was 31.7%higher than that at Yangling.In 2019,the grain N and P concentrations at Yongshou were 13.1%and 29.6%higher than those of Yangling,but grain yield and K concentration showed no difference between two sites.Compared to Yangling,soil in Yongshou had higher nitrate N,available sulfur?S?and P which promoted the plant absorption of N and P.In 2018,the increase of grain yield was larger than that of grain N and K uptake and close to that of grain P uptake at Yongshou,resulting in the above differences of grain N,P and K concentrations between two sites.In 2019,the pre-anthesis accumulation,post-anthesis uptake and translocation,and grain accumulation of N and P at Yongshou were higher than those at Yangling.Differently,K uptake and accumulation showed no difference between two sites,but the lower rainfall during the longer filling period at Yongshou was beneficial to the transportation of K to grain,leading to the higher K harvest index.Therefore,the differences of wheat grain N,P,and K concentrations between two sites are the results of the balance between nutrient absorption and grain yield formation,which are affected by soil nutrient supply capacity,climate and phenological factors such as precipitation and the grain filling period.2. Grain calcium?Ca?and magnesium?Mg?concentrations at Yongshou were significantly higher than those at Yangling in both years,but the difference of grain sulfur?S?concentration between two sites varied between two years.In 2018 and 2019,the grain Ca and Mg concentrations at Yongshou were 19.0%and 10.3%and 31.9%and 15.4%higher than those at Yangling.Grain S concentration showed no difference between two sites in2018,while in 2019 the grain S concentration at Yongshou was 10.5%higher than that at Yangling.Soil exchangeable Ca and Mg at both sites were high enough to satisfy the plant requirement,but the lower soil available K at Yongshou promoted the plant absorption of Ca and Mg and the higher soil nitrate N and available S promoted the absorption of S.Grain Ca and Mg accumulation at Yongshou were higher than those at Yangling in both years,and the increase of Ca and Mg accumulation in grain were larger than those of yield,resulting in higher grain Ca and Mg concentrations at Yongshou than those at Yangling.Differently,the aboveground and grain S uptake at Yongshou were higher than those at Yangling in both years,but the increase of S uptake was close to that of yield in 2018 and higher than that of yield in 2019,resulting in the different grain S concentration difference between two sites.Apart from the balance between nutrient absorption and grain yield formation,the differences of grain Ca,Mg and S concentrations between two sites also depend on the interactions of Ca,Mg,and S with other nutrients.3. The concentrations of grain iron?Fe?,manganese?Mn?and copper?Cu?at Yongshou were 9.3%and 29.3%,22.2%and 36.4%,12.7%and 36.8%higher than those at Yangling in2018 and 2019,but the grain zinc?Zn?concentration at Yongshou was 63.1%and 37.3%lower than that at Yangling in two years.Soil available Fe,Zn,and Cu were relatively low for plant growth at both sites.The higher soil available P and less precipitation during the longer grain filling stage at Yongshou benefited the absorption of Fe,Mn and Cu but not Zn,which led to higher aboveground and grain accumulation of Fe,Mn and Cu than those at Yangling,and lower grain Zn accumulation than that at Yangling.Therefore,the variation of grain Fe,Mn,Cu and Zn concentrations is affected by the availability of micronutrients in soil,soil available P,length of grain filling stage,and precipitation.In summary,the soil nutrient supply capacity and the nutrients interactions are the critical factors affecting the variation of wheat grain mineral nutrients concentrations.High soil nitrate N,available P and S promote the plant absorption of N,P,S,Fe,Mn and Cu,high soil available P and low available Zn inhibit Zn absorption,and low soil available K promotes the absorption of Ca and Mg but reduces K absorption.Besides,the length of key growth stages and rainfall also affect the nutrient accumulation in wheat grains.Long periods of pre-anthesis and grain filling and low rainfall during the grain filling promote the absorption of K,Fe,Mn and Cu.In agricultural production,different optimizations of nutrient management should be adopted for different mineral elements,based on the relationships of wheat grain nutrient concentrations with soil nutrient availability,nutrient interactions,and climate and phenological conditions,to improve yield and grain mineral nutrient quality at the same time.