Effects of the irrigation strategies of accumulated solar radiation on cucumber yield and quality under different soil textures in the greenhouse

Water resource is very deficient in the world. Agricultural water consumption is accounted for a large proportion of the total. Especially, high consumption can be found in the protected cultivation of vegetables, due to the great scale and multiple cropping index. Hence, it is urgent to develop water-saving irrigation for protected cultivation. However, simple and practical technology is still lacking in practical production. In this study, three typical soil textures (loam, clay loam, and sandy loam) were adopted for vegetable cultivation. Cucumber was selected as the experimental material, because of its wide cultivation areas. A field experiment was carried out from 2021-08-02 to 2021-12-24 in the Chinese solar greenhouse in Beijing, China. Cultivation density was set as 2.57 plants per square meter. Three irrigation treatments for each soil texture were performed from the fruiting period in the form of drip irrigation. The accumulated solar radiation reached up to the setting value (15, 20, 25 MJ/m²), corresponding to the onset of the irrigation system. The data logger was reset and recounted in the control system. There was consistency in the total irrigation amount under the same accumulation of solar radiation for each soil texture. A systematic investigation was made to explore the effects of different irrigation strategies on the growth and quality of autumn-winter cucumber under the above soil textures. The average air temperature varied from 11.5 to 25.6 ℃ during this experiment. There were 35 days below 12 ℃ during nighttime. The daily solar radiation on the plant canopy varied from 0.18 to 11.87 MJ/(m²·d). Meanwhile, the average water vapor deficit during the daytime varied from 0.11 to 3.75 kPa. Results showed that the irrigation strategies with different accumulated solar radiations caused the ‘high frequency and low irrigation amount’ and ‘low frequency and high irrigation amount’. However, there was no influence of different irrigation strategies on the fruit yield and irrigation water use efficiency using the same total irrigation amount under the same soil texture. Greater photosynthetic rate, leaf area, plant height, and number of internodes were obtained, when the accumulated solar radiation of 25 MJ/m² was set as the irrigation starting point, together with each irrigation amount of 3.22, 3.56, and 2.77 mm for the loam, clay loam, sandy loam, respectively. The highest contents of soluble sugar and vitamin C and the lowest nitrate content were all achieved, when the accumulated solar radiation of 20 MJ/m² was set as the irrigation starting point, together with the irrigation amount of 2.59, 2.85, and 2.22 mm for the loam, clay loam, sandy loam, respectively. Meanwhile, there was no significant difference in soil textures on the contents of soluble sugar, soluble protein, and vitamin C. Therefore, controlling accumulated solar radiation can be expected to serve as the irrigation starting point for the feasible irrigation strategy in protected cultivation. Meanwhile, the discrepant parameters of accumulated solar radiation as an irrigation starting point should be considered for the different cultivation goals under various soil textures.