Black Soldier Fly-Composted Organic Fertilizer Enhances Growth, Yield, and Nutrient Quality of Three Key Vegetable Crops in Sub-Saharan Africa

Worldwide, French beans (Phaseolus vulgaris L.), tomato (Solanum lycopersicum L.), and kales (Brassica oleracea L. var. acephala) are considered economically important food crops. There is a rapid decline in their yield due to severe soil degradation. Thus, high commercial fertilizer inputs are crucial, though they remain expensive and inaccessible to resource poor farmers. We investigated the comparative performance of composted black soldier fly frass fertilizer (BSFFF), conventionally composted brewer's spent grain (BSG), commercial organic fertilizer (Evergrow), and mineral [nitrogen, phosphorus, and potassium (NPK)] fertilizer on growth, yield, N use efficiency, and nutritional quality (crude protein, crude fiber, crude fats, ash, and carbohydrate concentrations) of tomatoes, kales, and French beans under greenhouse and open-field conditions for two seasons. The fertilizers were applied at rates equivalent to 371 kg of N ha−1. For each crop, the plots were treated with sole rates of BSFFF, BSG, Evergrow, and NPK to supply 100% of the N required. Additional treatments included a combination of BSFFF and NPK, and BSG and NPK so that each fertilizer supplies 50% of the N required. The control treatment consisted of unfertilized soil. Results show that vegetable yields achieved using a combination of BSFFF and NPK were 4.5, 2.4, and 5.4-folds higher than the yield from the control treatment for tomatoes, kales, and French beans, respectively. The combined application of BSFFF and NPK produced 22–135%, 20–27%, and 38–50% higher yields than sole NPK for tomatoes, kales, and French beans, respectively, under both greenhouse and open-field conditions. The highest agronomic N use efficiency was achieved in sole BSFFF-treated plots compared to sole BSG and Evergrow. The N taken up by the vegetables was significantly higher when BSFFF and NPK were integrated. Vegetables grown using a combination of BSFFF and NPK had the highest crude protein and ash concentrations. Our findings demonstrate that the integration of BSFFF and NPK in vegetable cropping systems at the recommended rate of 1.24 t ha−1 BSFFF and 322 kg ha−1 NPK would improve soil health, boost yield, and nutritional quality of vegetable crops.

Analysis of Pesticide Residues in Tomatoes and French Beans from Murang’a and Kiambu Counties, Kenya

Poor Pesticide-handling practices during production of tomatoes and French beans pose adverse health and environmental effects. This study was conducted to determine the concentrations of pesticide residues in tomatoes and French beans grown and sold in Murang’a and Kiambu counties, Kenya. Samples were collected in farms and markets during the wet and dry seasons. Pesticide residues were extracted using the QuEChERS method and quantified using GC-MS/MS and LC-MS/MS. The recoveries of pesticides from spiked samples were within the acceptable range (70-120%) for quantitative pesticide residue methods. The concentration range of pesticides residues in tomatoes were: profenofos, <LOQ to 0.18 mg/Kg; omethoate, <LOQ to 0.03 mg/Kg; indoxacarb, <LOQ to 0.05 mg/Kg; chlorantraniliprole <LOQ to 0.11 mg/Kg; spirotetramat <LOQ to 0.01 mg/Kg; and metalaxyl < LOQ to 0.02 mg/Kg. The concentration range of pesticides residues in French beans were: imidacloprid <LOQ to 0.29 mg/Kg; chlorantraniliprole <LOQ to 0.37 mg/Kg; spirotetramat <LOQ to 0.01 mg/Kg; indoxacarb <LOQ to 0.05 mg/Kg; and metalaxyl <LOQ to 0.02 mg/Kg. The concentrations of pesticide residues in tomatoes and French beans were below the Maximum Residue Levels set by the Joint FAO/WHO Food Standards Programme and the European Union except for concentrations of omethoate in tomatoes, which were higher in 29% of analyzed samples. The presence of omethoate in tomatoes, whose use in vegetables is banned, suggests poor pesticide handling practices by some tomato farmers in the two counties.

Assessment of French Beans Production at Kariua in Kandara, Murang’a County- Kenya

A sample survey research was conducted in November 2017 to January 2018 at Kariua area in Murang’a county, Kenya, with a sole aim to assess the current situation experienced by the French bean farmers in the area as well as form basis for further research, in which 43 farmers were interviewed. The parameters of interest were the average input levels of various factors (manure, fertilizers and water), average spacing of the crops in the field, the average output of the beans, the general plants’ health- all these were per crop point, land sizes under French beans cultivation as well as the demographic factors like age, gender and family size. The questionnaire was the main data collecting tool. Analysis of the data collected was carried out using both descriptive and inferential statistics: Using both R software and Ms-Excel. The results showed that farmers are experiencing very low yields at peak on average and poor plant health (harvest=13.4 g, infected leaves= 8 and immature pods= 15, all per crop point). Average land size under French beans farming, D.A.P and C.A.N fertilizers applied, manures applied, crop spacing and water for irrigation were found to be approximately 79.80 m2, 4.75 decigrams, 2.49 decigrams, 24.69 grams, 9.81 cm by 27 cm and 4.38 litres respectively. Low yields and poor crop health, scarce resources, pests, infections, diseases and intercropping and were also evident in the region.

Efficacy of Neem, Tithonia and Tephrosia Leaf Extracts in Management of Root-Knot Nematodes in French Beans (Phaseolus vulgaris L.)

Root-knot nematodes (Meloidogyne spp.) are a major problem in French bean production within the smallholder farming systems. Control of root-knot using synthetic nematicides is not viable due to environmental concerns relating to their toxic residues. There is need to develop alternative control options that will promote soil health and reduce parasitic nematode densities. A study was conducted to determine the efficacy of Neem (Azadirachta indica A. Juss), Tithonia (Tithonia diversifolia) and Tephrosia (Tephrosia purpurea) leaf extracts in management of root-knot. Controlled lath house and field trials were conducted where the treatments were extracts from Neem, Tithonia and Tephrosia at different concentration levels of 25 ml/L, 50 ml/L and 100 ml/L). Vydate (Oxamyl 10%) a synthetic nematicide served as a standard positive control while treatments with no extracts application and no nematode application served as negative controls. The treatments in the lath house were arranged in completely randomized design while the field trials were arranged in randomized complete block design. Fench beans were planted on nematode infested soils and data on root galling indices and yield components was collected. Data collected was subjected to analysis of variance and significantly different means separated using Tukey’s Studentized Range Test at P=0.05. The extracts evaluated reduced root galling with their efficacy being similar to that of Vydate® (Oxamyl 10%) which was used as a positive control. Neem extracts treatments had the lowest mean galling index of the extracts, followed by Tithonia. Root-knot nematode galling indices were highest in the untreated control at 10 both in trial I and trial II. Treatment trials from Neem and Tithonia at concentration levels of 100 ml/L resulted in highest yield of French beans while yield from the untreated plants were the lowest. The results indicate extracts can be adopted to suppress root-knot nematodes.

Assessment of the Potential of Eco-Friendly Nematicides in the Management of Root-Knot Nematodes on French Beans in Kenya

Root-knot nematodes (RKN) (Meloidogyne spp) are a serious pest causing heavy economic losses in a wide range of agricultural crops. A trial was carried out to evaluate the effectiveness of various eco-friendly nematicides in the management of RKN affecting French bean. The field trial was carried out in two seasons with the following treatments; Rigel-G (salicylic acid), Phyto Protect (Sesame oil extract), Mytech (Paecilomyces lilacinus), Neemraj 0.3% (Azadirachtin), Vydate® (Oxamyl) as a positive control and an untreated control. Various rates; Rigel –G (2.5 ml/l), Phyto Protect (10 l/ha), Mytech (125 g/ha) Neemraj 0.3% (3L/ha) and Vydate® (6 l/ha) of treatments were administered and damage on plants was assessed based on galling indices, crop biomass and yield whereas nematode reproductive potential was assessed based on the J2 counts. There was no significant difference (P ≥ 0.05) in the nematode population densities and galling indices observed among the eco-friendly nematicides and the conventional nematicide (Vydate®). Eco-friendly nematicides had a significant (P ≤ 0.05) reduction of RKN J2 population densities compared to the negative control. The negative control had the highest mean of root-knot nematode densities (240 RKN/200 cc soil) and a galling index of 3.77 while Vydate and Neemraj had the lowest mean density (40 RKN/200 cc soil) in the first season. Similar results were observed in the second season with control having the highest RKN J2 population densities (285 RKN/200 cc soil) and a galling index of 3.89 and Vydate had the lowest (23 RKN/200 cc soil). The results of this study clearly indicate that eco-friendly nematicides can be fully adopted to suppress RKN in French beans as alternatives to conventional nematicides.