Evapotranspiration and its components over a rainfed spring maize cropland under plastic film on the Loess Plateau, China

Xiang Gao,Fengxue Gu,Haoru Li,Daozhi Gong,Weiping Hao,Jianmin Chu

doi:10.5424/sjar/2020184-16370

Abstract

Aim of study: To determine seasonal variations in evapotranspiration (ET) and its components; and ascertain the key factors controlling ET and its components in a rainfed spring maize field under plastic film.Area of study: Shouyang County in Shanxi Province on the eastern Loess Plateau, ChinaMaterial and methods: Eddy covariance system combined with micro-lysimeters and meteorological observing instruments were used in the field. The manual method was used to measure the green leaf area index (GLAI) during the growing season.Main results: In 2015 and 2016, the growing season ET accounted for 80% and 79% of annual ET, respectively. Soil evaporation (E) accounted for 36% and 33% of the growing season ET in 2015 and 2016, respectively. The daily crop coefficient increased with increasing GLAI until a threshold of ~3 m2 m−2 in the canopy-increasing stage, and decreased linearly with decreasing GLAI in the canopy-decreasing stage. At equivalent GLAI, daily basal crop coefficient and soil water evaporation coefficient were generally higher in the canopy-increasing and -decreasing stages, respectively. During the growing season, the most important factor controlling daily ET, T, and E was net radiation (Rn), followed by GLAI for daily ET and T, and soil water content at 10-cm depth for daily E; during the non-growing season, daily ET was mainly controlled by Rn.Research highlights: The daily crop coefficient and its components reacted differently to GLAI in the canopy-increasing and -decreasing stages.

Highlights

The evapotranspiration (ET) is coupled with photosynthesis, and plays a key role in the energy balance of land surface (Wu & Shukla, 2014), thereby affecting many biological and physical processes that occur at the ground surface (Sen, 2004)
Soil evaporation (E) and crop transpiration (T) constitute most ET in agricultural ecosystems; understanding these two components is important for optimizing agricultural management to increase plants water use efficiency (Kool et al, 2014)
The period from seed-sowing date (1 May in both years) to canopy dying date (7 October in 2015; 4 October in 2016) was defined as the growing season, and the green leaf area index (GLAI) peak marked the end of the canopy-increasing stage and the beginning of the canopy-decreasing stage

Summary

Introduction

The evapotranspiration (ET) is coupled with photosynthesis, and plays a key role in the energy balance of land surface (Wu & Shukla, 2014), thereby affecting many biological and physical processes that occur at the ground surface (Sen, 2004). More than 80% of total cultivated land is rainfed cropland (FAO, 2011), which plays a vital role in maintaining stable ecosystems and agricultural productivity (Zhang et al, 2016). It is critical, to study ET in rainfed agricultural ecosystems to model crop production and to elucidate the mechanisms for the hydrological and biogeochemical cycles. The eddy covariance system is regarded as the standard method for observing turbulent fluxes between the surface and atmosphere (Taylor et al, 2013) This technique has been widely used for accurate measurements of water vapor fluxes in different terrestrial ecosystems (Wu & Shukla, 2014; Yang et al, 2016). ET in the non-growing season influences the annual water balance (Suyker & Verma, 2009; Zhang et al, 2016), as this period usually lasts more than half a year, but few studies have paid attention to this period in single-cropping systems in the drylands of northwest China

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Conclusion