Optimal water and nitrogen strategy for watermelon under CO2 enrichment by considering multiple indicators
Description
The accurate and efficient management of water and nitrogen is essential for the effective intensive agricultural production. To investigate the coupling effect of water and nitrogen under the enriched CO2 concentration, and realize a precise water and fertilizer management mode, we conducted an experiment over two study years in 2020 and 2021, including two CO2 concentrations, C1 (400 ppm) and C2 (800 ppm), two nitrogen levels, N1 (644.0 kg/ha) and N2 (1288.1 kg/ha), and three irrigation levels, I1 (80% evaporation (Ep)), I2 (100% Ep), and I3 (120% Ep). The results showed that CO2 enrichment had a significant effect on nitrogen and potassium content in fruits, while increasing nitrogen fertilizer inhibited the absorption of fruit potassium. Elevated CO2 alleviated the negative effect of low water on element contents, especially improving fruit phosphorus content by 10.0% and 26.0% in the two study years, respectively. Elevated CO2 increased total soluble sugar content in fruits, while increased irrigation promoted yield. The interaction of CO2 × I significantly increased free amino acids by 6.2% and 9.4% in the two study years, and the interaction of CO2 × N × I had a significant effect on quality indexes except for free amino acids of 2020. Based on correlation and path analysis, fruit potassium content had a significant positive contribution to lycopene, and fruit nitrogen content had an important contribution to yield, with direct path coefficients of 0.755 and 0.904 for the two study years, respectively. Considering yield, quality, and efficiency using TOPSIS model, the optimal combination was determined as nitrogen of 644.0 kg/ha and irrigation of 957.3-1159.6 m3/ha under CO2 800 ppm. The results could provide a theoretical and practical basis for water and nitrogen management in watermelon production under the increasing CO2 concentration in the future.