Effects of humic acid on japonica rice production under different irrigation practices and a TOPSIS-based assessment on the Songnen Plain, China

The responses of rice production to irrigation and fertilization under varying field conditions have been determined in previous studies. Obtaining a better understanding of the intrinsic mechanisms by which irrigation and fertilization regulate rice production can support field operations and recommendations. This study investigated the potential role of humic acid as opposed to traditional nitrogen fertilizer (urea) for regulating rice production under different irrigation conditions by identifying dry matter, radiation use efficiency (RUE) and grain yield indicators. Fifteen treatments were designed in combination with a field test; three irrigation practices (control irrigation (C), flood irrigation (F) and wet irrigation (W)) and five fertilization levels (100% urea (T1), 30% humic acid and 70% urea (T2), 50% humic acid and 50% urea (T3), 70% humic acid and 30% urea (T4), and 100% humic acid (T5)) were tested. The results demonstrated that the humic acid applications and irrigation practices affected rice production, and the lowest leaf area index (LAI) value was obtained under the WT2 treatment. Under the T4 and T5 treatments, the dry matter contents were significantly higher than those measured under the T2 treatment under the same irrigation practices. When comparing the average RUE variation within each experiment during the whole study period, the highest RUE values obtained in 2018 and 2019 were 2.21 and 2.09 g∙MJ⁻¹, respectively, both of which were obtained under the CT5 treatment. The grain yield and irrigation water use efficiency (WUEᵢ) obtained under the CT5 treatment were better than those obtained under other treatments. Multi-objective decision-making and evaluations based on the improved Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) method showed that the T5 treatment performed best under the control irrigation conditions. Planting rice under control irrigation practices combined with humic acid applications can effectively reduce the amount of irrigation water required and increase rice production. Control irrigation not only meets the current grain yield requirements but also plays a role in conserving water, while the application of humic acid reduces the required amount of urea.