Measuring soil evaporation from a cropped land in the semi-arid Makanya catchment, Northern Tanzania: Methods and challenges

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Estimating soil water loss from cropped land is vital for sustainable management of water resources in semi-arid and hot regions. Soil evaporation (Es) is an important process in these regions but hard to quantify. The study aimed at quantifying Es in maize field under three treatments using micro-lysimeters (MLs). It also aims to identify sources of challenges in the method. The treatments were; flat cultivation with mulching (FCM), without mulches (FC) and double digging (DD, manual tillage practice), were replicated trice. In each plot, two micro-lysimeters were installed, one containing soil samples to measure soil evaporation and an empty one to measure throughfall (Ʈr) under the maize canopy. The 24-hr soil samples weight change and throughfall records were used to estimate soil evaporation for each plot. The estimated mean daily soil evaporation was 3.4 mm/day in FC, 2.1 mm/day in FCM and 3.0 mm/day for DD. There was a challenge in the method during the rainfall period which lead to both negative and high Es values during rainfall period. Less throughfall from empty MLs than in soil containing MLs caused the negative Es and the opposite was true for higher Es during rainy period. We urge the method to be improved by measuring throughfall simultaneously with soil weight changes immediately after rainfall events and minimize random errors by using many MLs. To have more results on reducing water losses while increasing available water for crop growth in this water scarce environment, we suggest FCM to be combined with DD treatment.