Abstract
Water management and nitrogen application are critical factors in wheat grain yield and protein quality. This study aimed to evaluate the effect of irrigation and nitrogen application on the grain yield, protein content and amino acid composition of winter wheat. Field experiments were conducted in a split-plot design with three replications in high-yielding land on the North China Plain in 2012/2013, 2013/2014 and 2014/2015. Three irrigation treatments were examined in main plots: no irrigation, irrigation at jointing, and irrigation at jointing plus anthesis, while subplots were assigned to nitrogen treatment at four different rates: 0, 180, 240, 300 kg N ha-1, respectively. The results indicated that irrigation at jointing and at jointing plus anthesis improved grain yield by an average of 12.79 and 18.65% across three cropping seasons, respectively, compared with no irrigation. However, different irrigation treatments had no significant effect on grain protein content in any cropping season. Compared with no N treatment, 180, 240, and 300 kg N ha-1 N application significantly increased grain yield, by 58.66, 61.26 and 63.42% respectively, averaged over three cropping seasons. Grain protein and the total, essential and non-essential amino acid content significantly increased with increasing nitrogen application. Irrigation significantly improved the essential amino acid index (EAAI) and protein-digestibility-corrected amino acid score (PDCAAS) compared with no irrigation; however, N application decreased them by an average of 7.68 and 11.18% across three cropping seasons, respectively. EAAI and PDCAAS were positively correlated, however, they were highly negatively correlated with yield and grain protein content.
Highlights
Owing to its ability to adapt to various environmental conditions and its utilization in a wide variety of food products, wheat is the most widely cultivated food crop in the world [1,2]
Evaluation standards of the protein nutritive quality of amino acids have been set using the chemical score (CS) and protein-digestibility-corrected amino acid score (PDCAAS) [14,15], while the biological value is expressed by the essential amino acid index (EAAI)
The results showed that the grain yield of winter wheat was significantly affected by irrigation and nitrogen application (Table 2)
Summary
Owing to its ability to adapt to various environmental conditions and its utilization in a wide variety of food products, wheat is the most widely cultivated food crop in the world [1,2]. Achieving both high yield and grain quality is a major goal in wheat production [3,4]. Protein content and the balance of amino acids largely determine the nutrient quality of wheat grains. To the best of our knowledge, little has been done to determine the effect of crop management practices on EAAI and PDCAAS
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