| Wheat（Triticum aestivum L.）is a stable cereal crop,and approximately 75%of the wheat worldwide is produced in dryland areas.Therefore,improving the grain yield,fertilizer use efficiency,and grain nutritional quality of dryland wheat simultaneously play an important role in alleviating the crisis of global food supply and solving hunger problem.A located research during 2014–2018 was conducted at Wenxi of Shanxi,Yongshou of Shaanxi,and Qingshui of Gansu in the typical dryland wheat areas of Loess Plateau,China.Based on the farm survey and field sample analysis,the field management data including sowing,cultivar,and fertilization,wheat agronomic traits including grain yield,biomass,and yield component,soil physicochemical characteristics,and plant nutrients were collected to evaluate the feasibility of improving grain yield and fertilizer use efficiency,to study the limitations in wheat grain protein concentration and grain zinc concentration,and to explore the regulations for grain yield,production efficiency,and grain nutritional quality improvements under field scales.The main findings were obtained as follows:（1）Sowing early appropriately,using newer cultivars with high biomass and harvest index,and improving the supply ability of soil nitrogen are the key measures to increase wheat grain yield in dryland areas of the Loess Plateau.High-yielding fields had 1936 kg ha–1 higher grain yield than low-yielding fields with an average value of 5773 kg ha–1.Spike number and grains per head were the major reason for the improved grain yield,but grain weight showed no significant effects.Sowing date had the largest effect on grain yield,followed by cultivar,soil total nitrogen,and nitrogen fertilizer rate.The average sowing date of low-yielding fields at the three sites was about three days later than that of high-yielding fields while the sowing rate showed no difference between the two fields.Grain yield had significant positive correlations with nitrogen fertilizer rate and soil total nitrogen concentration.Wheat grain yield,shoot biomass,and harvest index of newer cultivar‘Pubing151’were 50.0%,37.5%,and 12.0%higher than that of older cultivar‘Jinmai47’.With the yield gap between low-and high-yielding fields bridged,soil nitrogen surpluses and greenhouse gas emission intensity decreased by 46.2%and 33.3%,respectively.（2）Decreasing fertilizer rates of nitrogen and phosphorus,and increasing moderate potassium fertilizer are key measures to improve nitrogen,phosphorus,and potassium fertilizer efficiencies,lower greenhouse gas emission rate,and maintain soil nitrogen,phosphorus,and potassium nutrient balances.Among the high-yielding wheat fields,the nitrogen,phosphorus,and potassium fertilizer partial factor productivities ranged from 9.7–64.6 kg kg–1,11.7–147 kg kg–1,and 24.8–309 kg kg–1,respectively.The partial factor productivities of nitrogen,phosphorus,and potassium fertilizers were significantly higher in high-yield&high-efficiency fields than those in high-yield&low-efficiency fields,with44.0%,31.8%,and 20.8%,respectively.Nitrogen,phosphorus,and potassium fertilizer rates,sowing rate,and sowing date had significant negative effects on nitrogen,phosphorus,and potassium fertilizer efficiencies,while the cultivar release date showed a significant positive effect.Compared with high-yield&low-efficiency fields,high-yield&high-efficiency fields had a 22.5%lower nitrogen fertilizer rate,29.2%lower phosphorus fertilizer rate,62.0%lower soil nitrogen surplus,43.0%lower soil phosphorus surplus,and 21.1%lower greenhouse gas emissions.In addition,a suitable amount of potassium fertilizer should be applied by local farmers to alleviate soil potassium depletion,due to high-yield&high-efficiency fields having an average soil potassium surplus of-6.0 kg ha–1.（3）Enhancing the plant uptake abilities of nitrogen,phosphorus,and potassium nutrients,other than the nitrogen,phosphorus,and potassium transfer abilities was the key to increasing wheat grain protein concentrations in the drylands of the Loess Plateau.The grain protein concentration of high-yield&high-protein fields was 27.6%higher than that of high-yield&low-protein fields with an average value of 14.9%,while grain yield,shoot biomass,harvest index,and yield component showed no significant differences between the two fields.Compared with high-yield&low-protein fields,high-yield&high-protein fields had 25.1%,16.3%,and 16.4%higher nitrogen,phosphorus,and potassium requirements per megagram grain,and no differences in the harvest indexes of nitrogen,phosphorus,and potassium.Nitrogen,phosphorus,and potassium fertilizer rates,soil mineral nitrogen,and available potassium concentration were significantly higher in high-yield&high-protein fields than those in high-yield&low-protein fields,with 16.0%,30.3%,41.1%,27.9%,and 25.1%,respectively,soil p H showed no difference,while soil organic matter,total nitrogen,and Olsen-phosphorus concentrations maintained at higher levels.With the grain protein concentration increased,grain phosphorus,magnesium,sulfur,iron,and zinc concentrations were improved by 16.3%,6.3%,16.3%,8.2%,and 13.4%,respectively,while grain potassium and calcium concentrations showed no significant change.（4）Zinc fertilizer application is the basis of grain zinc biofortification in zinc-deficient fields,while lowering phosphorus fertilizer rate and soil phosphorus concentration,increasing soil mineral nitrogen concentration,and using newer cultivars with high grain zinc uptake potential could further improve the grain zinc concentration under zinc adequate fields.At Qingshui of Gansu,no fields achieved the target grain Zn concentration≥40 mg kg–1,with a mean value of 22.8 mg kg–1.Overuse of phosphorus fertilizer and low soil available zinc concentration were the major limitations for increasing grain zinc concentration.At Yongshou of Shaanxi,two fields reached≥40 mg kg–1 grain Zn concentration with a significant‘yield dilution effect.The two fields had a 16.0%lower P fertilizer rate,51.4%lower soil Olsen-P,and 31.5%higher grain Zn uptake than the other fields.The fields at Wenxi of Shanxi had an average grain Zn concentration of 34.8 mg kg–1,with 18.3%of sampled fields reaching≥40mg kg–1.Compared with the fields of grain Zn concentration＜40 mg kg–1,the fields of grain Zn concentration≥40 mg kg–1 had no difference in grain yield,24.2%and 12.2%lower phosphorus fertilizer rate and soil Olsen-phosphorus,and 47.2%,37.5%,and 36.3%higher soil available Zn,grain Zn concentration,and grain Zn uptake,respectively.The cultivar was also a key factor for the grain Zn concentration.In this research,a 48.9%of yield increase was observed in the newer cultivar‘Yun20410’,with 16.4%higher grain Zn concentration and73.7%higher grain Zn uptake.In short,the yield variation of dryland wheat was mainly attributed to the spike number and grains per spike on the Loess Plateau.With early sowing,using newer cultivars with high biomass and harvest index,and improving soil nitrogen supply ability,about 34%of grain yield could be increased in low-yielding fields.Decreasing nitrogen and phosphorus rates and increasing suitable potassium fertilizer rates could improve nitrogen,phosphorus,and potassium fertilizer efficiencies,lower soil nitrogen,phosphorus surpluses,and greenhouse gas emissions,and maintain soil potassium balance meanwhile in high-yielding fields.Grain protein concentration was mainly affected by the uptake abilities of nitrogen,phosphorus,and potassium.Optimizing nitrogen,phosphorus,and potassium fertilizer rates and enhancing the nutrient supply abilities of nitrogen,phosphorus,and potassium were the key measures for improving grain protein concentration.The integrated measures,e.g.,applying Zn fertilizer,lowering phosphorus fertilizer rate,maintaining soil phosphorus at a suitable level,enhancing soil nitrogen supply capacity,and using newer cultivars with high yield and high Zn uptake abilities could improve wheat grain Zn concentration with with the yield increase in drylands of Loess Plateau. |
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