Estimation of soil water evaporative loss after tillage operation using the stable isotope technique

Abstract

A b s t r a c t. Application of stable isotopes in soil studies has improved quantitative evaluation of evaporation and other hydrological processes in soil. This study was carried out to determine the effect of tillage on evaporative loss of water from the soil. Zero tillage and conventional tillage were compared. Suction tubes were installed for soil water collection at the depths 0.15, 0.50, and 1.0 m by pumping soil water with a peristaltic pump. Soil water evaporation was estimated using stable isotopes of water. The mean isotopic composition of the soil water at 0.15 m soil depth were -1.15‰ (d 18 O) and -0.75‰ (dD) and were highly enriched compared with the isotopic compositions of the site precipitation. Soil water stable isotopes (d 18 O and dD) were more enriched near the surface under zero tillage while they were less negative down the profile under zero tillage. This suggests an occurrence of more evaporation and infiltration under conventional then zero tillage, respectively, because evaporative fractionation contributes to escape of lighter isotopes from liquid into the vapour phase leading to enrichment in heavy isotopes in the liquid phase. The annual evaporation estimated using the vapour diffusion equation ranges from 46-70 and 54-84 mm year -1 under zero and conventional tillage, respectively, indicating more evaporation under conventional tillage compared with zero tillage. Therefore, to reduce soil water loss, adoption of conservation tillage practices such as zero tillage is encouraged.K e y w o r d s: evaporative loss, tillage, isotopic fractionation, isotope technique INTRODUCTIONTillage is mechanical manipulation of the soil for the purpose of crop production and it affects significantly soil characteristics such as soil water conservation, soil temperature, infiltration and evapotranspiration processes. As tillage is known to cause soil surface disruption, fractionation of stable isotopes following soil tillage has been documented (Angela et al., 2009). Although tilled plots may have very high initial infiltration rate values, these rates rapidly decline with time (Guzha, 2004) probably due to intense alteration of the top centimetres of the soil (Josa et al., 2010) and rapid structural deterioration caused by slaking and dispersion. However, due to the effect of increased soil organic matter (Lipiec et al., 2006) and soil surface protection, high infiltration under zero tilled (ZT) plots have been documented (Shukla et al., 2003). According to Gupta et al. (2004) less intense tillage keeps the crop residue at the soil surface, thereby increasing the activity of surface-feeding earthworms, leaving the root channels undisturbed, leading to the presence of numerous surface-connected macro-pores and inter-pedal, hence higher infiltration. It has been reported that lower soil temperature due to higher water content in the topsoil and more plant residues on the soil surface under ZT usually result in reduced evaporation, whereas the opening of topsoil enhances evaporation from the tille...

Conservation Agriculture Effects on Soil Water Holding Capacity and Water-Saving Varied with Management Practices and Agroecological Conditions: A Review

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Conservation tillage and residue management improve soil health and crop productivity—Evidence from a rice-maize cropping system in Bangladesh

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Differences in soil evaporation between row and interrow positions in furrowed agricultural fields

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