Evaluation And Regulation Of Wheat Grain Yield And Critical Nutrient Concentrations In Major Wheat Production Areas In China

Wheat plays a critically important role in food production in the world and our country. Increasing yield per unit area is the key of wheat production in the limited and decreasing cropland. Protein is an important quality indicator of wheat, and in less developed countries like China, dietary protein intake is largely dependent on grain protein. Amino acids supplied by the dietary protein play an important role in regulating the body’s growth as well as in organization repair, maintenance and renewal. Iron, zinc, and selenium are essential trace elements for human body, and approximately one half of the world population suffer from trace element deficiency. Wheat is the major source of dietary protein and trace elements intake for residents in China, especially for those in the northern China, and understanding and increasing protein content and trace element concentration especially the typically limited elements such as iron, zinc and selenium is of great significance for improving human health and nutrition. Therefore in the present study, we collected 655 post-harvest wheat grain samples growing in field conditions from 22 provinces(municipalities), and determined the content of protein, amino acid, iron, zinc and selenium of wheat grain. And regression relation was established between nitrogen application rate and yield and between nitrogen application rate and protein content, using 1212 and 1110 set of nitrogen application rate-yield data and nitrogen application rate-protein content data, and then determined proper nitrogen rate to achieve both high yield and protein content. And also, a field experiment of foliar-selenium application with wheat as test crop was conducted in 30 comprehensive experimental stations of China Agricultural Research System on Wheat in 14 provinces(municipalities), in order to investigate factors that influence wheat grain selenium concentration and to develop agronomic measures that could increase selenium concentration. Main results obtained are as follows:1. Multi-year and multi-site samplings and measurements showed that protein contents of wheat grain were low in major wheat production areas in China, and lysine was the first restrictive amino acid, and the low lysine content and low proportion of essential amino acids to total amino acids both influenced nutritive value of wheat protein. The average grain protein contents of spring and winter wheat were 13.7% and 12.7%, respectively. In spring wheat, 45%, 22%, and 33% of samples met the protein standard for strong, medium, and weak gluten wheat, while the portion was 18%, 24% and 58% in winter wheat, respectively. The ratios of essential to total amino acids in spring and winter were both 28.8%. Protein content decreased in the trend of from the north to the south, and from the east to the west. In addition, the single and the total essential amino acid content decreased from the east to the west. Lysine was the limiting amino acids, and amino acid score averaged 53 in spring wheat and 56 in winter wheat. Except histidine and tryptophan, significant and positive correlations between different amino acids were observed for both spring and winter wheat, with correlation coefficient greater than 0.3. Each amino acid showed significant and positive correlation with protein content, with correlation coefficient greater than 0.2 to 0.4, but proportion of essential amino acids to total amino acids significantly and negatively correlated with protein contents for both spring and winter wheat, with correlation coefficient both being-0.31.2. Through multi-year and multi-site samplings and measurements and field experiments, we raised a nitrogen recommendation method to balance the grain yield and protein content, and evaluated nitrogen use efficiency, economic benefit and environmental impact of this method. The recommended nitrogen application rate during wheat season for the winter wheat-summer maize rotation region, winter wheat-rice rotation region, and rainfed winter wheat regions in China was 208 to 230, 150 to 195, and 117 to 134 kg ha-1, respectively. Although the recommended nitrogen rate was comparable to or lower than the investigated farm average in each region, wheat yield and protein content at the recommended nitrogen rate was 1% to 19% and 2% to 9% higher than the farm average yield and protein content. Compared with the excessive nitrogen rates used by farmer, the recommended nitrogen rates reduced nitrogen input by an average of 39 to 84 kg ha-1, however, the recommended nitrogen rates increased wheat yield, grain protein content, nitrogen partial factor productivity, and economic benefit by 4% to 28%, 2% to 8%, 7 to 24 kg kg-1, and 564 to 2951 Yuan ha-1, respectively; in addition, the recommended nitrogen rates reduced the soil residual inorganic N after wheat harvest, nitrate leaching and direct nitrous oxide emissions in a whole wheat season by 8% to 27%, 29% to 52%, and 19% to 36% in the three regions, respectively.3. Multi-year and multi-site samplings and measurements showed that iron and zinc concentrations of wheat grain were low in major wheat production areas in China, and grain iron and zinc concentrations were significantly and negatively correlated with grain yields. Grain yields were found as high as 5423 and 6565 kg ha-1 for spring and winter wheat, respectively, with a corresponding grain iron concentration of 48.2 and 45.1 mg kg-1, and Zn concentration of 30.4 and 30.3 mg kg-1. 63% and 72% of the spring and winter wheat samples had iron concentration lower than the recommended level of 50 mg kg-1, and 88% and 87% had zinc concentration lower than the recommended level of 40 mg kg-1. Regionally, grain Fe and Zn concentration was found to be lower in high-yielding regions. Grain Fe concentration was significantly and positively correlated with Zn concentration for both spring and winter wheat. For each 1 mg kg-1 increase in grain Zn, the Fe concentration increased by 0.6 and 0.3 mg kg-1 for spring and winter wheat, respectively. However, the Fe and Zn concentration was significantly and negatively correlated with grain yield: for every 1000 kg ha-1 increase in grain yield, the Fe concentration decreased by 2.1 and 1.3 mg kg-1 for spring and winter wheat, respectively, and the Zn concentration decreased by 0.9 and 1.3 mg kg-1, respectively. In spring and winter wheat, there existed wheat grain samples with both high iron and zinc concentrations and high grain yield, which indicated that through variety breeding, fertilization or other measures, wheat grain iron and zinc concentrations could be increased to above the recommended standard, and at the same time maintain high yield.4. Multi-year and multi-site samplings and measurements and a multi-site field experiment of foliar-selenium application on wheat showed that selenium concentration of wheat grain was low in major wheat production areas in China, and grain selenium concentration was positively correlated with the available soil selenium concentration and selenium concentration of plant before jointing, and foliar-selenium application was an effective measure to increase grain selenium concentration. The average wheat grain selenium concentration was 64.6 μg kg-1, which was too low to meet the selenium requirement for people who rely primarily on wheat-derived foods, and no sample was found to have selenium concentration reach the toxic level. Selenium in different regions exhibited higher concentration in northern regions than that in southern regions, while it was higher in western regions than in eastern regions. Results from the multipoint field experiments showed that foliar application of sodium selenite did not significantly affect wheat grain yield, but significantly increased grain selenium concentration. For 1 g Se ha-1 applied, grain selenium concentration was increased by an average of 5.3 μg kg-1, and applying 51 g Se ha-1 could increase the selenium concentration from the average of 31 μg kg-1 to above 300 μg kg-1. Grain selenium concentration was not influenced by yield, but under no selenium applied it was significantly and positively correlated with the available soil selenium content in 0-20 cm soil layer and with selenium content of plant before jointing. For each 1.0 μg kg-1 increment of available soil selenium content from 6.3 to 30.7 μg kg-1, the grain selenium content without selenium applied increased by an average of 2.1 μg kg-1, and for each 1.0 μg kg-1 increment of selenium content of plant before jointing from 0 to 147.2 μg kg-1, the grain selenium content without selenium applied increased by an average of 0.7 μg kg-1. Grain selenium content with selenium applied as well as selenium biofortification index were both significantly and positively correlated with selenium content of plant before jointing. For each 1.0 μg kg-1 increment of selenium content of plant before jointing, the grain selenium content with selenium applied increased by an average of 5.7 μg kg-1, and selenium biofortification index increased by an average of 0.043 μg kg-1(g ha-1)-1.