Optimizing Irrigation Strategies to Improve Water Use Efficiency of Cotton in Northwest China Using RZWQM2

Xiaoping Chen,Haomiao Cheng,Shaoyuan Feng,Matthew W Sima,Fanjiang Zeng,Hao Wu,Lanhai Li,Zhiming Qi

doi:10.3390/agriculture12030383

Abstract

Irrigated cotton (Gossypium hirsutum L.) is produced mainly in Northwest China, where groundwater is heavily used. To alleviate water scarcity and increase regional economic benefits, a four-year (2016–2019) field experiment was conducted in Qira Oasis, Xingjiang Province, to evaluate irrigation water use efficiency (IWUE) in cotton production using the Root Zone Water Quality Model (RZWQM2), that was calibrated and validated using volumetric soil water content (θ), soil temperature (Tsoil°) and plant transpiration (T), along with cotton growth and yield data collected from full and deficit irrigation experimental plots managed with a newly developed Decision Support System for Irrigation Scheduling (DSSIS). In the validation phase, RZWQM2 adequately simulated (S) topsoil θ and Tsoil°, as well as cotton growth (average index of agreement (IOA) > 0.76). Relative root mean squared error (RRMSE) and percent bias (PBIAS) of cotton seed yield were 8% and 2.5%, respectively, during calibration, and 20% and −10.3% during validation. The cotton crop’s (M) T was well S (−18% < PBIAS < 14% and IOA > 0.95) for both full and deficit irrigation fields. The validated RZWQM2 model was subsequently run with seven irrigation scenarios with 850 to 350 mm water (Irr850, Irr750, Irr700, Irr650, Irr550, Irr450, and Irr350) and long-term (1990–2019) weather data to determine the best IWUE. Simulation results showed that the Irr650 treatment generated the greatest cotton seed yield (4.09 Mg ha−1) and net income (US $3165 ha−1), while the Irr550 treatment achieved the greatest IWUE (6.53 kg ha−1 mm−1) and net water production (0.94 $ m−3). These results provided farmers guidelines to adopt deficit irrigation strategies.

Highlights

Optimizing agricultural irrigation scheduling contributes to alleviating competition for water, especially in regions where groundwater resources are limited
Thorp et al [47] and Li et al [36] reported that the DSSAT model could effectively simulate cotton growth processes (LAI, canopy height, and biomass) under various deficit irrigation conditions
The RZWQM2 tended to slightly overestimate cotton seed yield and plant height achieved under the Decision Support System for Irrigation Scheduling (DSSIS) for both full and deficit irrigation

Summary

Introduction

Optimizing agricultural irrigation scheduling contributes to alleviating competition for water, especially in regions where groundwater resources are limited. Cotton (Gossypium hirsutum L.) is the most important natural fiber, food, and fuel crop in the world. China is the world’s largest producer and consumer of cotton. Cotton irrigation in the XUAR consumes 12.4 billion m3 y−1 of water, roughly a quarter of total agricultural water use in the region. Groundwater use in the XUAR reached 11.8 billion m3 y−1 , exceeding recommended levels of use by 57%, and resulting in a significant decrease in groundwater table [1]. Despite the implementation of water-saving practices (e.g., drip irrigation) and policies (e.g., raising water prices), the water use efficiency (WUE) for cotton remains between 0.43 and 0.73 kg m−3 [2], which are low values compared to those for other regions. The irrigation water use efficiency (IWUE) of cotton varied between 1.0 to 1.2 kg m−3 in the Texas High Plains (THP) region, USA [3]. Maintaining a sustainable irrigation strategy is important in arid northwest China

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Conclusion