Effects of organic and inorganic fertilization on soil bacterial and fungal microbial diversity in the Kabete long-term trial, Kenya

The effects of crop manure and inorganic fertilizers on composition of microbial communities of central high land soils of Kenya are poorly known. For this reason, we have carried out a thirty-two-year-old long-term trial in Kabete, Kenya. These soils were treated with organic (maize stover (MS) at 10 t ha(-1), farmyard manure (FYM) at 10 t ha(-1)) and inorganic fertilizers 120 kg N, 52.8 kg P (N(2)P(2)), N(2)P(2) + MS, N(2)P(2) + FYM, a control, and a fallow for over 30 years. We examined 16S rRNA gene and 28S rRNA gene fingerprints of bacterial and fungal diversity by PCR amplification and denaturing gradient gel electrophoresis separation, respectively. The PCR bacterial community structure and diversity were negatively affected by N(2)P(2) and were more closely related to the bacterial structure in the soils without any addition (control) than that of soils with a combination of inorganic and organic or inorganic fertilizers alone. The effect on fungal diversity by N(2)P(2) was different than the effect on bacterial diversity since the fungal diversity was similar to that of the N(2)P(2) + FYM and N(2)P(2) + MS-treated. However, soils treated with organic inputs clustered away from soils amended with inorganic inputs. Organic inputs had a positive effect on both bacterial and fungal diversity with or without chemical fertilizers. Results from this study suggested that total diversity of bacterial and fungal communities was closely related to agro-ecosystem management practices and may partially explain the yield differences observed between the different treatments

Do commercial biological and chemical products increase crop yields and economic returns under smallholder farmer conditions?

During recent decennia, new commercial products have appeared on the market as alternatives to common fertilizers. While some of these products are based on well-established technologies, such as rhizobium inoculation, others have not been subjected to scientific scrutiny. During 3 years, we evaluated over 80 of these new products, including microbial inoculants and chemical products on major legume, cereal and banana crops across diverse agro-ecological conditions in Ethiopia, Nigeria and Kenya in the laboratory, greenhouse and field conditions. Amongst the rhizobial inoculants, several products from different companies were found very effective in increasing nodule biomass on soybean and increasing grain yield by up to 30 %, and benefit-cost ratio of up to 5.0 realized. Except for tissue cultured bananas, the effect of arbuscular mycorrhizal fungal (AMF) inoculants was less evident with optimal yield of legumes realized with co-inoculation with P solubilizing bacteria and when supplemented with inorganic fertilizer such as DAP. Other products containing Trichoderma or Bacillus spp. improved growth under field conditions, soil-dependent growth improvements of over 40% in tissue culture bananas. The potential of products to reduce soil pathogenic rhizosphere organisms, particularly Fusarium, was also observed. Chemical products evaluated, special attention was given to alternative P fertilizers such as leaf sprays, seed coatings and conditioners with humic acids. The effect on cereals depended on the crop, the soil and accompanying agronomic measures. Benefit-cost ratios were favorable for seed P coating Teprosyn, because this is a fairly inexpensive treatment (US $3 ha 1). Results demonstrate economic returns of US$ 4 for every dollar invested for soybean production and US $4.6 for every dollar invested in maize production. The Net benefit of US$ of 5,265 for Rhizatech matches benefits of US $5,115 derived from Conventional practice with half investment of US$ 62 compared to US $ 135. The potential for biological and chemical commercial products is evident and the need for continued evaluation. Smallholders may benefit from good quality products that are correctly applied to the appropriate crop under appropriate soil and crop management