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Determination of biologically active components of the soil organic matter, such as soil microbial biomass carbon (C) and nitrogen (N) can be used as indicators for variations in soil productivity due to changes in soil management. Soil agronomic management practices bring about changes in the physical and chemical properties of the soil, resulting in variations in soil microbial biomass and microbial diversity. The effects of tillage, mulch and inorganic fertilizers on soil microbial biomass C and N, microbial populations and bacterial diversity were determined from the treatment combinations which had been applied for 5 years in Central Kenyan Highlands. The test crop used was maize (Zea mays L.). The study involved conventional and minimum tillage systems, mulching and inorganic fertilizers (120 kg N/ha). Tillage (P < 0.001), mulch (P < 0.001), and fertilizer (P = 0.009) significantly affected soil microbial biomass C and N whereby minimum tillage and mulch increased soil microbial biomass C and N. Interestingly, minimum tillage and mulch recorded the highest bacteria and fungi CFUs compared to conventional tillage and inorganic fertilizers. Only fertilizer and mulch (P < 0.001) had significant effect on actinobacteria CFUs. Amplified ribosomal DNA analysis (ARDRA) showed that the highest genetic distance of 0.611 was recorded between treatments conventional tillage + no mulch + no NPK fertilizer and conventional tillage + no mulch + NPK fertilizer. The results demonstrate that minimum tillage and mulching are attractive soil agronomic management practices since they increase soil microbial biomass and bacterial diversity in agricultural soils.

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Rose is the world’s most traded cut flowers with 74 % being produced in Kenya. Pests like spider mites, caterpillar, aphids, thrips, nematodes and diseases such as crown gall, downy mildew, powdery mildew and botrytis highly compromise rose production. Crown gall disease caused by Agrobacterium tumefaciens is the most problematic disease of roses in Kenya, causing a production loss of up to 60 % depending on the age and variety of rose. An experiment to determine the antibacterial effect of Artemisia and ginger extracts was carried out in vitro, where the inhibitory zones around filter discs soaked with extracts on Muller Hinton agar was established. The extracts were emulsified with dimethylsulfoxide (50 %) and minimum inhibitory concentrations of Artemisia (125 mg/ml), ginger (62.5 mg/ml) and mixture of Artemisia and ginger (31.25 mg/ml) were used to soak the filter discs whereas the commercial recommended rate of copper hydroxide of 6.25 mg/ml was used. Artemisia and copper hydroxide (commercial antibiotic) had highest inhibition zone of 12.80 mm compared to ginger 10.60 mm. A mixture of Artemisia and Ginger had a slightly lower inhibition zone (10.20 mm) though not significantly different from ginger (P> 0.001). An eight-month greenhouse experiment was also done to determine the efficacy of the extracts on inoculated rose plants. The results showed that crown gall incidence and gall weight were low but not significantly different from copper hydroxide and Artemisia. Crop vigor, which was indicated by stem length was highest for Artemisia treatment with an average of 73.54 cm followed by copper hydroxide (67.25 cm) while ginger and mixture of ginger and Artemisia had 53.44 cm and 64.70 cm respectively. From the results of this research, Artemisia and Ginger extracts are promising alternative to control crown gall and possibly other diseases in field crops. Artemisia performance compares well with copper hydroxide and therefore the best alternative to replace copper hydroxide.