Investigating unproductive water losses from irrigated agricultural crops in the humid tropics through analyses of stable isotopes of water

Abstract

Abstract. Reliable information on water flow dynamics and water losses via irrigation on irrigated agricultural fields is important to improve water management strategies. We investigated the effect of season (wet season and dry season), irrigation management (flooded and non-flooded), and crop diversification (wet rice, dry rice, and maize) on soil water flow dynamics and water losses via evaporation during plant growth. Soil water was extracted and analysed for the stable isotopes of water (δ2H and δ18O). The fraction of evaporation losses were determined using the Craig–Gordon equation. For dry rice and maize, water in shallow soil layers (0 to 0.2 m) was more isotopically enriched than in deeper soil layers (below 0.2 m). This effect was less pronounced for wet rice but still evident for the average values at both soil depths and seasons. Soil water losses due to evaporation decreased from 40 % at the beginning to 25 % towards the end of the dry season. The soil in maize fields showed stronger evaporation enrichment than in rice during that time. A greater water loss was encountered during the wet season, with 80 % at the beginning of the season and 60 % at its end. The isotopic enrichment of ponding surface water due to evaporation was reflected in the shallow soils of wet rice. It decreased towards the end of both growing seasons during the wet and the dry season. We finally discuss the most relevant soil water flow mechanisms, which we identified in our study to be those of matrix flow, preferential flow through desiccation cracks, and evaporation. Isotope data supported the fact that unproductive water losses via evaporation can be reduced by introducing dry seasonal crops to the crop rotation system.

Soil moisture variability affected by sand mulch: An isotope‐based assessment of irrigated farmland in Northwest China

“…Affected by precipitation infiltration and soil evaporation, the topsoil is often in the process of a dry wet alternation. Therefore, the parameter n in this paper takes the average value of 0.75, which represents the average dry‐wet condition of the soil (Mahindawansha et al, 2020).…”

“…As an addition to the traditional ecological methods, the hydrogen and oxygen stable isotope technology has greatly improved the understanding of the water movement within the soil‐plant‐atmosphere continuum (Sprenger et al, 2016). The stable isotopes of hydrogen and oxygen in soil water can reveal precipitation, irrigation water infiltration process, soil water movement mechanism, soil evaporation, and so on (Deng et al, 2013; Goldsmith et al, 2012; Ji et al, 2021; Kleine et al, 2020; Mahindawansha et al, 2020; Yang et al, 2016; Zhao & Wang, 2018). Although the soil moisture regime under sand mulch has been highlighted in previous studies in arid land (Jiménez et al, 2005; Li, 2003; Sharma & Bhardwaj, 2017), the isotope‐based assessment is still limited, and the isotopic variability before and after irrigation was not well understood.…”

Can a Crop Rotation and Fallow System Reduce the Carbon Emission Intensity of Agriculture?

“…Secondly, providing water for crops consumes a large amount of water resources but also leads to a serious depletion of freshwater resources in China. Reducing the over-absorption of water by crops promotes a rise in the surface water table, which increases soil wetness and reduces the need for crop irrigation [40]. Thirdly, prolonged labour increases the morbidity rate of the agricultural workforce and even reduces the life expectancy of the workforce, thus lowering the quality and supply of labour.…”

Flushing or mixing? Stable water isotopes reveal differences in arctic forest and peatland soil water seasonality

“…The macropore findings of the study by (Renée Brooks et al, 2010) have been confirmed to some extent in many biomes across the globe (Evaristo et al, 2016; Javaux et al, 2016). Other studies revealed that under a rainy temperate (Herve‐Fernandez et al, 2016), humid subtropical (Luo et al, 2019), tropical savanna (Mahindawansha et al, 2020) or subalpine (Langs et al, 2020) climate these interactions may be seasonally limited and dependent on soil moisture conditions. Bowling et al (2017) examined whether snowmelt water can create a unique pool of tightly bound water that is used by plants in seasonally snow‐covered areas during the growing season.…”