Water and nitrogen management scheme of melon based on yield−quality−efficiency matching perspective under CO2 enrichment

Abstract

Rising CO2 concentration in the atmosphere may modulate the response of plants to water and nitrogen, and the existing research is not sufficient to support the fine management of water and nitrogen under CO2 rise. To determine the optimal water and nitrogen strategy for melon production under CO2 enrichment in the future, we conducted an experiment with 12 treatments over three growing seasons. The effects of water nitrogen coupling on the yield, quality, and water−nitrogen use efficiency of oriental melon (Cucumis melo L. Qianyu No. 6) under CO2 enrichment were investigated and evaluated comprehensively. The treatments included two CO2 concentrations, C1 (400 ppm) and C2 (800 ppm), three irrigation levels, I1 (80% evaporation (Ep)), I2 (100% Ep), and I3 (120% Ep); two nitrogen levels, N1 (S: 184.77 kg ha–1, F: 147.21 kg ha–1) and N2 (S: 369.54 kg ha–1, F: 294.42 kg ha–1). The result showed that the yield increased with increasing levels of irrigation and nitrogen, and enriched CO2 significantly increased the yield by 10.3 − 22.9%. N2 showed a significant promoting effect on the ratio of marketable fruit in the two spring seasons. Enriched CO2 significantly increased free amino acid of I1. C2 coupled with I1 significantly reduced nitrate content by 30.9%, 14.9% in 2020 F and 2021 S, respectively. The interaction of C*I was significant in irrigation water−use efficiency (IWUE) and nitrogen−use efficiency (NUE). In particular, C2 coupled with I2 increased IWUE by 40.5%, 18.7% and NUE by 43.9%, 13.9% in the two spring seasons, respectively. Ten indicators from three categories of yield, quality, and efficiency were used to establish the evaluation system of melon and were comprehensively evaluated based on Fuzzy−Borda model combined three single models. Based on the combined evaluation model, intermediate irrigation combined with higher nitrogen input was best for melon production under CO2 enrichment. This finding suggested that melon sustainable production should control irrigation and adequately increase nitrogen fertilizer to trade−off fruit, quality, and efficiency for the expected future higher CO2 concentrations.