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