# Optimizing Water and Nitrogen Management Strategies to Unlock the Production Potential for Onion in the Hexi Corridor of China: Insights from Economic Analysis

## TL;DR

This study finds optimal water and nitrogen management for onions in China's Hexi Corridor to maximize yield and economic benefits while minimizing environmental impact.

## Contribution

A novel water-nitrogen economic benefit coupling model is developed to optimize resource use for onion cultivation in arid regions.

## Key findings

- Medium-to-high water-nitrogen combinations improve onion quality but excessive inputs reduce economic benefits.
- The N2W3 treatment (264 kg·ha−1 nitrogen and 100% ETc irrigation) consistently provided the highest yield and economic returns over four years.
- A bivariate quadratic regression model accurately predicts economic benefits based on irrigation and nitrogen inputs.

## Abstract

Water and nitrogen are the key factors restricting the productivity improvement of onion in the Hexi Oasis. Unreasonable water and fertilizer management not only increases input costs, but also causes environmental pollution of farmland soil, thereby affecting the sustainable development of agriculture. To explore the effects of the water–nitrogen interaction and optimized combination schemes on onion yield, water–nitrogen use efficiency, and economic benefits under mulched drip irrigation in the Hexi Oasis, a four-year (2020–2023) water–nitrogen coupling regulation experiment was conducted at the Yimin Irrigation Experimental Station in Minle County, Hexi Corridor. The onion was used as the test crop and three irrigation levels were established, based on reference crop evapotranspiration (ETc): low water (W1, 70% ETc), medium water (W2, 85% ETc), and sufficient water (W3, 100% ETc), as well as high nitrogen N3 (330 kg·ha−1), medium nitrogen N2 (264 kg·ha−1), and low nitrogen N1 (198 kg·ha−1). Meanwhile, no nitrogen application N0 (0 kg·ha−1) was set as the control at three irrigation levels. This study analyzed the effects of different water and nitrogen supply conditions on onion quality, yield, water–nitrogen use efficiency, and economic benefits. A water–nitrogen economic benefit coupling model was established to optimize water–nitrogen combination schemes targeting different economic objectives. The results revealed that medium-to-high water–nitrogen combinations were beneficial for improving onion quality, while excessive irrigation and nitrogen application inhibited bulb quality accumulation. Both yield and economic benefits increased with the increasing amount of irrigation, whereas excessive nitrogen application showed a diminishing yield-increasing effect, simultaneously increasing farm input costs and ultimately reducing the economic benefits. In the four-year experiment, the N3W3 treatment in 2020 achieved the highest yield, economic benefits, and net profit, reaching 136.93 t·ha−1, 20,376.3 USD·ha−1, and 14,320.8 USD·ha−1, respectively, with no significant difference from the N2W3 treatment. From 2021 to 2023, the N2W3 treatment achieved the highest yield, economic benefits, and net profit, averaging 130.87 t·ha−1, 28,449.5 USD·ha−1, and 21,881.5 USD·ha−1, respectively. Lower irrigation and nitrogen application rates mutually restricted the water and nitrogen utilization, resulting in low water use efficiency, irrigation water use efficiency, nitrogen partial factor productivity, and nitrogen agronomic use efficiency. The relationship between the irrigation amount, nitrogen application rate, and the economic benefits of onion fits a bivariate quadratic regression model. This model predicts that onion’s economic benefits are highly correlated with the actual economic benefits, with analysis revealing a parabolic trend in economic benefits as water and nitrogen inputs increase. By optimizing the model, it was determined that when the irrigation amount reached 100%, the ETc and nitrogen application rate was 264 kg·ha−1, and the economic benefits were close to the target range of 27,000–29,000 USD·ha−1; this can be used as the optimal water and nitrogen management model and technical reference for onion in the Hexi Oasis irrigation area, which can not only ensure high yield and quality but also improve the use efficiency of water and nitrogen.