Effects of water and fertilizer coupling on growth, fruit yield and quality and soil nutrient characteristics of apple saplings

Abstract: 【Objective】In agricultural production, the implementation of water regulation is the key to water-saving irrigation technology. Reasonable water regulation can not only reduce the amount of irrigation, but also improve the quality of fruits and other agricultural products. The application of organic fertilizer combined with reduced chemical fertilizer can increase fruit yield, reduce acidity, improve quality indexes such as soluble solids, and promote soil nutrient release and soil fertility. In this experiment, the coupling test of water regulation and organic fertilizer was carried out on 3-year-old apple saplings to explore an orchard irrigation and fertilization model that promotes the growth of apple fruittrees, improves fruit yield and quality, and improves soil fertility in the Loess Plateau.【Methods】This experiment was conducted at the apple experimental station in Baishui County, Weinan City, Shaanxi Province from 2020 to 2022. The test materials were 3-year-old Ruixue apple saplings. The test set two factors of irrigation and fertilization. Irrigation was set at three levels, 80% (W1), 60% (W2), and 40% (W3) of field capacity; three levels of fertilization were conventional chemical fertilizer (F1), organic fertilizer replacing 20% nitrogen fertilizer (F2), and 40% nitrogen fertilizer (F3), and the control (CK, 80% of field capacity, no fertilization). The growth of fruit trees, fruit yield and quality, and the content of soil nutrients were measured for two seasons.【Results】(1) Reasonable organic fertilizer substitution (F3, F2) and irrigation (W1, W2) promoted the growth of plant height and stem diameter of apple saplings in two years. (2) The highest fruit yield in 2021 and 2022 was in F3W1 treatment and 0.74 kg and 4.84 kg, respectively, which was 10.45% and 51.52% higher than that of conventional fertilization, and 12.12% and 49.85% higher than that of the control group in 2021 and 2022, respectively. (3) Reasonable organic fertilizer substitution amount (F3, F2) and irrigation amount (W1, W2) increased fruit transverse and longitudinal diameters, and the coupling of water and fertilizer had no significant effect on fruit shape index in the two seasons. F3 treatment promoted the decrease of titratable acid content of fruit in two years. The lowest values in 2021 and 2022 were 0.473% and 0.265%, respectively, which were 5.34% and 27.74% lower than the lowest values of conventional fertilization in the same year, and 14.56% and 24.57% lower than the control group, respectively. F3 increased fruit soluble solids in the two years; the maximum values of the two years were 19.26% and 22.20%, respectively, which were 2.85% and 19% higher than in conventional fertilization in the same year, and 23.24% and 37.04% higher than in the control group, respectively. Low irrigation (W3) also increased soluble solids; F3 and high irrigation (W1) treatments increased solid to acid ratio in the two years. The highest values in the two years were 41.33 and 62.82, respectively, which were 31.64% and 24.3% higher than the highest values in conventional fertilization treatment in the same year, and 42.80% and 30.33% higher than in the control group, respectively. (4) The reasonable coupling of water and fertilizer improved soil nutrient indexes in two years. (5) According to the correlation analysis, in 2021, fruit yield was significantly negatively correlated with soil available phosphorus content and available potassium content (p＜0.05); fruit diameters were significantly negatively correlated with soil available phosphorus content (p＜ 0.05); fruit titratable acid content was significantly positively correlated with soil organic matter content and soil pH; and solid to acid ratio was significantly negatively correlated with soil pH (p＜0.01). In 2022, fruit yield, fruit diameters and solid to acid ratio were significantly positively correlated with soil organic matter content (p＜0.05); soluble solids content and titratable acid content were significantly negatively correlated with soil organic matter content (p＜0.05); and solid to acid ratio was significantly positively correlated with soil total nitrogen content (p＜0.05).【Conclusion】Organic fertilizer replacing chemical fertilizer and reasonable water regulation can promote the growth of fruit trees and improve fruit yield and quality and soil fertility. Combined with the growth of fruit trees, fruit yield, fruit quality, soil fertility improvement effect, organic fertilizer replacing 40% nitrogen fertilizer (F3) combined with 80% soil field water holding capacity (W1) is a optimal irrigation and fertilization mode for local orchards.