Effect of Organic Fertilizers on the Growth, Yield, and Nutritional Quality of Kale (Brassica oleracea L)

Abstract

Kale (Brassica oleracea L) is widely grown by Kenyan smallholder farmers, but its production is hindered by declining soil health from prolonged inorganic fertilizer use. With rising interest in sustainable farming, commercial organic fertilizers like Bokashi and Safi Sarvi are emerging in regions such as Mwea and Githunguri. However, their effectiveness and farmers’ attitudes toward them remain underexplored. This research evaluates the effect of Bokashi and Safi Sarvi on the growth, yield, and nutritional quality of kale and also investigates smallholder farmers' attitudes toward their use. Greenhouse and open-field trials were conducted at JKUAT to assess the effects of Bokashi and Safi Sarvi on kale growth, yield, and nutritional quality. The experiment consisted of four (4) treatments as follows: T1 = (Bokashi1), T2 = (Safi Sarvi), T3 = CK1 (NPK ), T4 = CK2 (no fertilizer). Growth and yield parameters measured were plant height (cm), leaf count, leaf width (cm), fresh and dry weights (g/plant). Nutritional analysis included ash, crude protein, fiber, fat, protein, carbohydrates, and minerals (Ca, P, K, Mn, Mg, Fe, Zn). A completely randomized Design (CRD) was used in the greenhouse and a randomized complete block design (RCBD) in the field, with three replications per treatment. Data were analyzed using ANOVA (p ≤ 0.05) in R software, employing Fisher's Least Significant Difference (LSD) test for mean separation. Attitudes were measured using 14 statements on a Likert scale in a face-to-face survey of 109 randomly selected smallholder farmers in Githunguri and Mwea (Sept–Oct 2023). Data were analyzed descriptively (percentages) using SPSS v23. Greenhouse experimental results indicated that at week 10, Bokashi-treated kale grew tallest in the (27.23 cm), had more leaves (13.13), and broadest leaf width (26.61cm), including fresh leaf weight (1492.77g, 1499.45g and 1500g), and dry weight (143.43g, 143.90g, and 143.66g) at harvests 2, 3, and 4 respectively compare to NPK though statistically insignificant from Safi Sarvi. No significant difference was noted in the growth and yield parameters among fertilizer treatments during the field experiment. Nutritional analysis revealed that NPK-treated kale had the highest ash concentration (13.20%), while Safi Sarvi-treated kale recorded the highest crude fat (3.88%) and crude protein (13.09%) levels, though not significantly different from Bokashi or NPK. The crude fat (1.82%) and crude protein (6.37%) were observed to be lowest in non-treated kale (Control). Bokashi-treated kale leaves recorded the highest concentrations of P(354.15 mg/100g), K (394.23 mg/100g), and Mg (60.97 mg/100g), while Safi Sarvi produced the highest Ca (394.20 mg/100g) and Zn (1.83 mg/100g) levels. Survey findings revealed that 58.7% of the interviewed farmers were women, 99.1% relied on farming as the main source of income, and 82.6% were married. The study results show a high (100%) utilization rate of organic fertilizer. Likert scale rating of attitudinal statements revealed vast majority (97.2%) use organic fertilizers for health reasons, and 99.1% derive personal satisfaction from using them. 93.6% believe organic fertilizer is cheaper than inorganic alternatives, 95.4% report better yields with its use, and 87.2% expressed the need for government support to increase organic fertilizer use. The study showed that Bokashi and Safi significantly influenced kale growth, yield, and nutrient quality. A highly positive attitude was demonstrated by farmers in the study area towards organic fertilizer use. The study suggests Bokashi and Safi Sarvi can be used for enhancing kale production. Further research on nutrient combinations and application rates may help optimize crop yields across environments. Also, the need for government support (subsidize organic fertilizer) to promte the continuous use of organic fertilizer among farmers in the study regioins.