An evaluation of alternative methods of P application for increased maize production under smallholder farmers' conditions in Kenya

Smallholder farmers in sub-Saharan Africa are confronted by low crop production due to phosphorus deficiency and a limited investment capacity in P inputs. Alternative P fertilizer types are being commercialized which aim at improved P use efficiency through specialized formulations. These products include, amongst others, leaf sprays, seed coatings and conditioners with humic acids. We evaluated these products in pot trials under greenhouse conditions and in multi-locational participatory field trials with farmer groups in three distinct agro-ecological zones in Kenya. The products were applied in conjunction with TSP fertilizer at half the recommended economic rate, as the P supplied through these products was insufficient to attain adequate crop yields. P response was assessed by including treatments without P addition, and TSP applied at half and full recommended rate. In the pot trial, none of the products significantly (P<0.05) increased the shoot dry matter yield of 6-weeks old maize. Seed coating, however, resulted in increased root yield and root-shoot ratio. In the field trials, responses to TSP application were observed in two agro-ecologies, with maize yield increases in the order of 1.4 – 2.6 t ha-1. However, none of the treatments with the different products significantly increased maize yields. Leaf spraying tended to result in yield penalties, particularly when rainfall was insufficient after application of the spray. Correlation analysis revealed that seed treatment has a small positive effect on yield when control yields are low, but not necessarily when response to P fertilizer was large, suggesting that the effect of the treatment way not be directly related to P nutrition. Possibly, seed treatment may have stimulated root development during early stages, which could entail benefits in drought-prone areas and will be further investigated. Our findings indicate that alternative methods of P application have limited benefits for maize production under smallholder farmers' conditions. (Texte intégral

Effect of cropping systems on accumulation of Fusarium head blight of wheat Inocula in crop residues and soils

Article PurchasedFusarium head blight (FHB) is an economically important disease of wheat, which causes reduction in grain yield both quantitatively through reduced seed weight and qualitatively by contaminating grains with mycotoxins. The effect of cropping systems on accumulation of FHB inocula in crop residues and soil was assessed at hard dough stage of wheat during the 2013 cropping season in three agro-ecological zones in Narok County, Kenya. A semi structured questionnaire was used to obtain information on wheat production practices. Fusarium spp. were isolated from crop residues and top soil, while incidence and severity of FHB were assessed at mid-anthesis. Majority of the wheat farmers were small scale producers who rotated wheat with maize, grew the two crops in adjacent fields, grew wheat in consecutive years, left wheat residues as standing hay for livestock and practiced simple land preparation methods. Prevalence of FHB was 100%, while mean incidence and severity were 20.7 and 28.4%, respectively. The most frequently isolated Fusarium spp. were F. chlamydosporum and F. graminearum in crop residues and F. oxysporum and F. proliferatum in soil. The incidence of Fusarium spp. in soil and crop residues was highly correlated to FHB incidence but not to severity of the disease. Wheat production practices affect the survival of Fusarium spp. in soil and crop residues between cropping seasons. It is therefore, recommended that after harvesting, wheat straw and maize stover should be removed from the field or be incorporated into the soil through tillage to allow faster decomposition. Inclusion of maize as a rotation crop in wheat production should also be avoided

Occurrence of Fusarium head blight of wheat and associated mycotoxins in Narok and Nakuru Counties, Kenya

Open Access JournalFusarium head blight (FHB) is an important disease of small grain cereals. This study assessed the incidence and severity of FHB of wheat at hard dough stage, and levels of deoxynivalenol and T2-toxin at harvest by direct competitive enzyme linked immuno-sorbent assay. Wheat ears were randomly sampled from 51 farms in Narok County and 51 farms in Nakuru County at hard dough stage while wheat kernels were sampled at harvest. Prevalence of FHB in both Counties was 100%. The mean incidence of FHB was 28.4% and 20.5% in Narok and Nakuru Counties, respectively with 16.9% and 11.7% corresponding severity. Over 14 Fusarium spp. were isolated from wheat ears and kernels with F. avenaceum, F. poae and F. graminearum being isolated in the highest incidence. Levels of DON in the kernels ranged from below limit of detection (<LOD) to 623 µg/kg while the concentration of T-2 toxin ranged from <LOD to 69 µg/kg. The levels of DON and T2-toxin in wheat kernels in the two Counties were within the limits set by the European Commission and the United States Food and Drug Administration. The relatively low incidence and severity of FHB correlated with the low levels of DON and T-2 toxin in harvested wheat grains. There is however need to continuously monitor occurrence of FHB and toxin levels in wheat which varies among seasons due to variability in climatic conditions

Changes in fungal population and aflatoxin levels and assessment of major aflatoxin types in stored peanuts (Arachis hypogaea Linnaeus)

Peanut kernels of Homabay Local, Valencia Red, ICGV-SM 12991 and ICGV-SM 99568 cultivars were storedfor six months in jute, polypropylene and polyethylene bags to assess the effect of storage bags, temperature andR.H. on fungal population and aflatoxin contamination. Moisture content (M.C.), fungal population and aflatoxinlevels were determined before storage and after every 30 days during storage. Isolates of Aspergillus flavus andA. parasiticus were assayed for production of aflatoxin B1, B2, G1 and G2. The correlation between MC,population of A. flavus and A. parasiticus and aflatoxin levels in peanuts was also determined. Six fungalpathogens were commonly isolated from the peanut samples and occurred as follows in decreasing order:Penicillium spp. (106.6 CFU/g), A. flavus L-strain (4.8 CFU/g), A. flavus S-strain (2.9 CFU/g), A. niger (2.6CFU/g), A. parasiticus (1.7 CFU/g) and A. tamarii (0.2 CFU/g). The overall population of A. flavus L-strain was66% higher than that of A. flavus S-strain. Ninety one percent of A. flavus and A. parasiticus isolates produced atleast one of the four aflatoxin types assayed, with 36% producing aflatoxin B1. Total aflatoxin levels rangedfrom 0 - 47.8 μg/kg with samples stored in polyethylene and jute bags being the most and least contaminated,respectively. Eighty nine percent and 97% of the peanut samples met the EU (≤ 4 μg/kg) and Kenyan (≤ 10μg/kg) regulatory standards for total aflatoxin, respectively. Peanuts should be adequately dried to safe moisturelevel and immediately packaged in a container - preferably jute bags - which will not promote critical increasesin fungal population and aflatoxin contamination

Occurrence of Aspergillus species and aflatoxin contamination in raw and roasted peanuts from formal and informal markets in Eldoret and Kericho towns, Kenya

Published Online: August 2013.The population and diversity of fungal species and levels of aflatoxin contamination were investigated in 228 marketed peanut samples; 140 from formal and 88 from informal markets, in Kericho and Eldoret towns of Kenya. Ground pea- nut samples were cultured on Modified Dichloran Rose Bengal (MDRB) agar while aflatoxin level was quantified based on indirect competitive ELISA. Correlation between the incidence of major aflatoxin-producing fungal species and aflatoxin levels was also established. Fungal species commonly isolated from the peanut samples included Asper-gillus flavus L strain, A. flavus S strain, A. parasiticus, A. tamarii, A. caelatus, A. alliaceus (all of Aspergillus section Flavi) and A. niger. Fungi isolated in low frequency included Fusarium spp., Penicillium spp., Mucor spp. and Rhi- zopus spp. Aflatoxin levels in peanut products ranged from 0 to 2345 μg/kg in raw peanuts, 0 to 382 μg/kg in roasted coated peanuts, and 0 to 201 μg/kg in roasted de-coated peanuts. Overall, levels of total aflatoxin were higher in sam- ples from informal (mean = 97.1 μg/kg) than formal (mean = 55.5 μg/kg) market outlets. There was a positive and sig- nificant correlation (R2 = 0.63; p ≤ 0.05) between aflatoxin levels and the major aflatoxin producing fungi in raw pea- nuts from formal markets in Eldoret town. Additionally, total aflatoxin in raw peanut samples from informal markets in Kericho was positively and significantly correlated (R2 = 0.81; p ≤ 0.05) to the population of A. flavus (L and S strains). In roasted coated peanuts sampled from formal market outlets in Eldoret, aflatoxin levels correlated positively and sig- nificantly (R2 = 0.37; p ≤ 0.05) with A. flavus S strain. There is need to create awareness among peanut traders and con- sumers on proper handling of peanuts and health risks associated with consumption of unsafe peanut products

Science-based decision support for formulating crop fertilizer recommendations in sub-Saharan Africa

Open Access Article; Published online: 31 Jan 2020In sub-Saharan Africa, there is considerable spatial and temporal variability in relations between nutrient application and crop yield, due to varying inherent soil nutrients supply, soil moisture, crop management and germplasm. This variability affects fertilizer use efficiency and crop productivity. Therefore, development of decision systems that support formulation and delivery of site-specific fertilizer recommendations is important for increased crop yield and environmental protection. Nutrient Expert (NE) is a computer-based decision support system, which enables extension advisers to generate field- or area-specific fertilizer recommendations based on yield response to fertilizer and nutrient use efficiency. We calibrated NE for major maize agroecological zones in Nigeria, Ethiopia and Tanzania, with data generated from 735 on-farm nutrient omission trials conducted between 2015 and 2017. Between 2016 and 2018, 368 NE performance trials were conducted across the three countries in which recommendations generated with NE were evaluated relative to soil-test based recommendations, the current blanket fertilizer recommendations and a control with no fertilizer applied. Although maize yield response to fertilizer differed with geographic location; on average, maize yield response to nitrogen (N), phosphorus (P) and potassium (K) were respectively 2.4, 1.6 and 0.2 t ha−1 in Nigeria, 2.3, 0.9 and 0.2 t ha−1 in Ethiopia, and 1.5, 0.8 and 0.2 t ha−1 in Tanzania. Secondary and micronutrients increased maize yield only in specific areas in each country. Agronomic use efficiencies of N were 18, 22 and 13 kg grain kg−1 N, on average, in Nigeria, Ethiopia and Tanzania, respectively. In Nigeria, NE recommended lower amounts of P by 9 and 11 kg ha−1 and K by 24 and 38 kg ha−1 than soil-test based and regional fertilizer recommendations, respectively. Yet maize yield (4 t ha−1) was similar among the three methods. Agronomic use efficiencies of P and K (300 and 250 kg kg−1, respectively) were higher with NE than with the blanket recommendation (150 and 70 kg kg−1). In Ethiopia, NE and soil-test based respectively recommended lower amounts of P by 8 and 19 kg ha−1 than the blanket recommendations, but maize yield (6 t ha−1) was similar among the three methods. Overall, fertilizer recommendations generated with NE maintained high maize yield, but at a lower fertilizer input cost than conventional methods. NE was effective as a simple and cost-effective decision support tool for fine-tuning fertilizer recommendations to farm-specific conditions and offers an alternative to soil testing, which is hardly available to most smallholder farmers

Morphological Variation in the Wild-Weedy Complex of Sorghum bicolor In Situ in Western Kenya: Preliminary Evidence of Crop-to-Wild Gene Flow?

Crop wild relatives are important components of agroecosystems and have over the years been exploited in breeding programs as sources of genes for novel traits. Information on the extent and patterns of variability is important in formulating effective conservation and utilization strategies for existing crop wild relative populations. We conducted surveys and collections of wild and weedy accessions of Sorghum bicolor (L.) Moench in Lambwe Valley in western Kenya in order to investigate occurrence, distribution, and morphological variability in the wild-weedy complex of S. bicolor under local agroecological conditions. We also attempted to understand the role, if any, of crop-to-wild gene flow in structuring variability within and among populations. The morphological data presented here showed wide variability within wild-weedy sorghum populations with respect to habitats and morphotypes. True wild sorghum populations in national parks and the sugarcane belt were clearly distinguishable from the putative hybrids or intermediate forms found in sorghum fields, in sorghum field margins, and, to some extent, by the roadside near sorghum fields. The existence of these intermediate forms is empirical evidence of introgression between cultivated sorghum and its wild-weedy relatives. Extensive introgression, especially within in situ conservation areas and/or in areas of high diversity, would lead to genetic erosion and possible depletion of these important wild sorghum genetic resources