# Optimization of Water and N Regulation for Mung Bean (Vigna radiata L.) Cultivation Under Drip Irrigation Using TOPSIS Method in Mollisols Region of Northeast China

## TL;DR

This study finds the best water and nitrogen levels for growing mung beans in Northeast China using a decision-making method called TOPSIS.

## Contribution

The study introduces a TOPSIS-based optimization model for water and nitrogen regulation in mung bean cultivation under drip irrigation.

## Key findings

- The W3N1 treatment (60-80% soil water and 40 kg/ha N) achieved the highest yield and efficiency in the first year.
- Increasing nitrogen levels at W1 irrigation improved plant height, stem diameter, and yield in the second year.
- TOPSIS analysis confirmed W3N1 as the optimal treatment for balancing yield, water use efficiency, and nitrogen productivity.

## Abstract

Optimizing the coupling effect between irrigation and N fertilizer to balance mung bean (Vigna radiata L.) production and the effective utilization of water and fertilizer resources is an important challenge for sustainable agricultural production. In this study, a field drip irrigation experiment was conducted on Mollisols in Northeast China, and twelve treatments were performed: four levels of soil water content (W1, 80~100% of field capacity; W2, 70~90% of field capacity; W3, 60~80% of field capacity; W4, rainfed condition) and three N application treatments (40 (N1), 80 (N2), and 120 (N3) kg/ha). We analyzed the coupling effects of water and N levels on mung bean growth, yield and yield components, water consumption, water use efficiency (WUE) and N partial factor productivity (PFP) in 2021 and 2022 and screened the optimal water and N regulation by the TOPSIS method. The results showed that the amount of N application dominated the regulation of water and N. In the first year, plant height, stem diameter, number of seeds per pod, 100-seeds weight, yield, aboveground dry matter accumulation, WUE, and PFP in mung bean decreased with increasing N applications at the same irrigation treatment. Furthermore, except for WUE, all results of the W3N1 treatment reached the highest levels, at 79.14 cm, 13 mm, 12.4, 6.2 g, 1430.45 kg/ha, 79.27 g (the drumming stage), and 35.76 kg/kg, respectively. The second year, plant height, stem diameter, yield and WUE had an increasing trend with increasing N applications at the W1. Based on the TOPSIS method, the W3N1 treatment could obtain the optimal comprehensive benefits of yield, WUE and PFP. This study can provide a most suitable water and N regulation model for guiding mung bean cultivation in the Mollisols region of Northeast China.