Rice-husk mulch depth effects on weed pressure and yield of Brassica carinata

Abstract

Weed competition is a significant constraint to Rape/Ethiopian mustard (Brassica carinata) production. However, the optimum depth of readily available rice-husk mulch for simultaneous weed control and yield gain is undocumented. A field experiment was conducted from April to June 2024 at the Crop Museum, Sokoine University of Agriculture, Morogoro, Tanzania (6° 85? S, 37° 64? E; 568 m a.s.l.) using a Randomised Complete Block Design with five replications. Five management options were tested: unweeded control (0 cm mulch), rice-husk mulch at 5, 10 and 15 cm depths, and the farmer's practice of hand-weeding every two weeks. Weed density (0.25 m² quadrats), plant growth traits and marketable fresh-leaf yield (g plot?¹; 1.44 m²) were recorded and analysed by ANOVA (Tukey 5 %) and regression. Rice-husk mulch markedly suppressed weeds; 10 cm mulch reduced density from 83.4 ± 11.3 to 7.45 ± 1.34 weeds 0.25 m?², an average 91 % reduction relative to the unweeded control. Hand-weeding yielded the highest yield (449 ± 88 g plot?¹ ? 3.12 t ha?¹), but a 5 cm mulch produced a statistically similar yield (404 ± 31 g plot?¹) and 47 % more than the unweeded treatment. Leaf area emerged as the sole significant predictor of yield, with each additional cm² contributing 2.08 g (p = 0.008), explaining 39 % of yield variation. Treatment effects on yield were not significant at ? = 0.05, reflecting large within-treatment variance, yet clear biological trends were evident.