Effects of Organic and Inorganic Fertilizers on Weed Diversity and Population in Tobacco (Nicotiana tabacum L.) Farms in Migori County

Abstract

Tobacco (Nicotiana tabacum L.) is a significant cash crop in Migori County, Kenya, and plays a vital role in the local economy. However, the cultivation of tobacco is not without its challenges, one of which is weed infestation. Weeds in tobacco farms can compete with the crop for essential resources, such as water, nutrients, and sunlight, leading to reduced crop yields and quality. Effective weed management is crucial to maintain the productivity and profitability of tobacco farming in the region. Therefore, the study objective was to analyze the effects of inorganic fertilizer (DAP fertilizer) and organic manure on population density of weed species, as well as the species diversity of the weed population under tobacco crop. A study was conducted in Migori county, employing a randomized complete block design, with four locations (Masaba, Mabera, Kakrao, and Bondo) and three different treatments, each of which was replicated three times. These treatments comprise of various types of fertilizers, including inorganic and organic variants, along with a control group receiving no fertilizer. The study's primary focus was on assessing weed population, leaf yield, and alterations in soil physico-chemical properties. During the second weeding phase, Malva verticilate was counted, with a mean value of 10.42, in both Mabera and Masaba. However, no instances of Malva verticilate were recorded in the other two sites. Sida alba acuta and Richardia brasilium R. brasiliens were counted in all four locations, with mean values of 6.22 and 28.21, respectively. The data obtained was subjected to statistical analysis using the General Linear Model (GLM) and analysis of variance (ANOVA) within the GENSTAT 12, 2012 statistical software package. To determine significant differences, means were separated using Tukey's test at a 5% level of significance. Results of the study showed that the dominant weed flora among monocot weeds were Eleusine indica L., Cynodon dactylon L., Digitaria sanguinialis L. and Chloris barbata L. Among dicot weeds, Phyllanthus niruri L., Amaranthus viridis L., Euphorbia hirta L., Heliotropium indicum L., Gynandropsis pentaphylla L., Launaea nudicaulis L. and Oldenlandia umbellata L. were found as major weeds. Cyperus rotundus L. was the only sedge found associated with tobacco crop across the four sites. This was common under inorganic fertilizer treatments, indicating that TF treatment suppressed growth and development of sedges. Results indicate that weed distribution and population under inorganic and organic fertilizer is related not only to the soil nutrient and physical content, but also to competition from the crop for water and light. Therefore, it is recommended to consider a combination of inorganic fertilizer and organic manures to optimize weed control and soil health in tobacco farming.