Assessment of the effects of selective weed management strategies for the production of direct-seeded rice yield in Mwea, Kirinyanga county, Kenya.

Abstract

The use of Direct Seeded Rice (DSR) is on the rise due to its low input requirements, providing advantages such as reduced labor, water usage, reduced physical strain, early crop maturity, improved soil conditions, reduced methane emissions, and suitability for diverse cropping systems. However, DSR faces challenges from high weed infestation, limiting its adoption and productivity. The study assessed the effects of selective weed management strategies on DSR systems, aiming to enhance overall crop yield and sustainability in Mwea, Kirinyaga County, Kenya. The study was carried out in a randomized complete block design with three replicates. Eight quadrants were established for data collection in each treatment in which four of the quadrants were 0.5m x 0.6m and the other four were one meter running rows. Data on weed counts, biomass, plant phyto-toxicity, weed phyto-toxicity, crop counts, crop height and crop biomass were collected on the 0.5m x 0.6m quadrants. Data on tiller density and yield attributes was collected in the 1m running row. Various methods were used in data analysis including Shannon diversity index to analyze weeds diversity across the various treatments, a two-way ANOVA and Kruskal Wallis was used to evaluate the variations among the treatments and the means separated using LSD and Dunn test. The most dominant weed species in DSR field were Richardia grandiflora and Dactyloctenium aegyptium with a Shannon Weiner diversity index of 0.98 and 0.60 respectively. The maximum herbicide efficiency was observed under the application of combination of preemergence and post-emergence herbicide; Pendimethalin + Bispyribac sodium (>80%) and Pendimethalin + Florpyrauxifenbenzyl (>80). In contrast, Cyhalofop-butyl + penoxsulam + one hand weeding (<15%) demonstrated the lowest weed control efficiency. Treatments that either solely used or combined Bispyribac sodium recorded the highest phyto-toxic effects at 35 DAS (range between 2.80% and 2%). Other than the weedy free check the lowest phytotoxic effects was seen in treatments that had Pendimethalin and Florpyrauxifen-benzyl (1.08%). Based on yield results other than the weed-free treatment the combination of Bispyribac sodium + pyrazosulfuron + one hand weeding showed a high adjusted grain weights (1474 g). Thus, treatments that were mostly in combination, for example Pendimethalin + Bispyribac sodium and Bispyribac sodium + pyrazosulfuron + one hand weeding, consistently showed superior control across all weed types. Thus combination of herbicides (PRE-emmergence + POSTemmergence) and with a little boost from hand weeding is recommended for effective weed management practices in DSR.