Soil Moisture Patterns under Sesame Straw Mulch in an Uncropped Vertisol of Eastern Sudan

Abstract

Rainfed farming in eastern Sudan depends on rainfall that occurs within a short and uneven season. In the cracking Vertisols of Gedaref, soil moisture after wetting can decline quickly, especially when the surface remains exposed. This study examined whether observed soil moisture differed among sesame straw mulch rates after a standardized wetting event in an uncropped Vertisol containing 76% clay, 14% sand, and 10% silt. The field experiment was arranged in a randomized complete block design with three replications and five mulch rates: 0, 1.39, 2.78, 4.17, and 5.56 t ha −1 , equivalent to 0, 0.5, 1.0, 1.5, and 2.0 kg per 3.6 m 2 plot. Each plot received 100 L of water, equivalent to 27.78 mm. Mulch was applied four days after wetting, and soil moisture was then measured weekly for eight weeks at 0 - 30 and 30 - 60 cm depths. No soil-moisture measurement was taken before mulch application. A repeated-measures linear mixed-effects model showed that soil moisture increased by 0.592 percentage points for each additional t ha −1 of sesame straw mulch, while it declined by 0.482 percentage points per week. The mulch treatment × sampling week interaction was not significant (F = 0.33, p > 0.99), so treatment-specific slopes were treated only as descriptive summaries. Across depths and weeks, mean soil moisture was 23.27% under the 5.56 t ha −1 treatment and 19.69% in the control, giving an observed difference of 18.2%. The results show that observed soil moisture differed among sesame straw mulch rates after a standardized wetting event under uncropped conditions. Evaporation, soil cracking, crop emergence, and yield were not measured. The findings should be treated as preliminary field dry-down evidence and tested under cropped conditions before field recommendations are made.