Determining organic-inorganic fertilizer application threshold to maximize the yield and quality of drip-irrigated grapes in an extremely arid area of Xinjiang, China

Abstract

Imbalanced water and fertilizer systems have limited the yield and quality of grapes in extremely arid areas. The combined application of organic (OF) and inorganic fertilizers (CF) has been proven to be one of the practical approaches to improving yield and quality. Nevertheless, very few studies have focused on the irrigation amount in organically fertilized and drip-irrigated grapes. Hence, in this study, four combined application ratios of organic and inorganic fertilizers (70%OF + 30%CF, 50%OF + 50%CF, 30%OF + 70%CF, and 0%OF + 100%CF), and four irrigation amounts (630, 675, 720, and 765 mm) were set coupling in a two-year field experiment. Generally, under four irrigation levels, combined organic-inorganic fertilizers increased soil nutrients and improved seedless white grape growth, yield, and quality. The results of the combined fertilizer application treatments showed that the content of available nitrogen (55.97–102.60%), available phosphorus (49.41–124.74%), and available potassium (60.70–124.33%) in soil increased significantly compared with those values under a single application of inorganic fertilizer. In addition, the combined application increased the length of new shoots and leaf midribs (grapes) by 3.16–11.88% and 7.35–15.15%, respectively; this application mode also significantly enhanced transpiration rate (Tr), stomatal conductance (Gs), and net photosynthetic rate (Pn). Furthermore, the grape yield increased by 6.68–19.12%, and the fruit quality notably improved (except for the index of fruit shape). Under the four irrigation amounts, two-year average yields were reported as 17.53, 20.60, 23.31, and 22.71 kg/ha, respectively. Additionally, we used four evaluation methods to assess the fruit quality and compared their correlations with the comprehensive evaluation model. And we concluded that the principal component analysis method (PCA) is best suited for evaluating drip-irrigated grapes’ quality. Then, we applied the PCA to seek proper irrigation management; the results displayed that a suitable irrigation amount of 720 mm and the ratio of organic-inorganic application of 50% organic fertilizer + 50% inorganic fertilizer is recommended. However, further research is required to investigate the effects of soluble and complete organic fertilizers application on drip-irrigated grapes.