Influence of soil fertility amendment practices on ex-situ utilisation of indigenous arbuscular mycorrhizal fungi and performance of maize and common bean in Kenyan highlands

Abstract

Arbuscular Mycorrhizal Fungi (AMF) are important in agriculture and have received attention as they are considered a part of an active and diverse soil biological community essential for increasing the sustainability of agricultural systems. However, most of agricultural practices have a negative impact on AMF association and agricultural soils are AMF impoverished. Interventions to replenish AMF include re-introduction through inoculation or manipulation of existing AMF to increase density. A major problem with inoculation is that there is possible competition with native (indigenous) AMF species. Indigenous AMF will be more adapted to the soil environment than introduced strains but with conflicting results on the effects of AMF inoculation on crop yield, more field studies for different ecological areas are required. The objective of the study was to compare the effect of inoculating crops with indigenous AMF applied applied singly or combined with other Soil Fertility Amendment Practices (SFAP) on root colonisation and subsequent performance of maize (Zea mays L.) and common bean (Phaseolus vulgaris L.). Analysis was also done on the best soil amendment practice that encourages crop colonisation by AMF. This was tested under field experiment and compared with control treatment (no soil amendment practice) and three other soil fertility amendment practices used singly or in combination with AMF; (1) MAVUNO (macro- and micronutrients and secondary nutrients) fertilizer, and (2) Calcium Ammonium Nitrate (CAN) and Triple Super Phosphate (TSP) (3) cattle manure. Maize and bean performances were determined and compared between the treatments for a period of two consecutive seasons with the experiment replicated in two benchmark sites of Embu district (highlands of central Kenya) and Taita-Taveta district (coastal highlands). Soils at Embu have high soil pH than at Taita which results in low phosphorus levels and possible micronutrients deficiencies. Even though no significant differences were observed from root colonisation by AMF with application of SFAP, significant differences were observed at the crop yield. Bean crop was more responsive to AMF inoculation than maize in terms of yield. Combination of AMF inoculant with other organic and inorganic fertilizers resulted in higher crop yield compared to AMF applied singly. Thus, utilisation of indigenous AMF species has potential to constitute an environmentally friendly method of soil fertility amendment over time to improve maize and bean production potential of small-scale holders but consideration should be done on the local soil nutrients conditions, other soil fertility amendment practices in use and the targeted crop.