Effects of NPK10-20-10 Chemical Fertilizer and Arbuscular Mycorrhizae on the Response of Common Bean (Phaseolus vulgaris L.) in an Acidic Soil of Lubumbashi Region

Most soils in the Lubumbashi region are acidic (pH 4 to 6) and poor in available phosphorus. The production of crops such as common beans requires large amounts of chemical fertilizers, generally up to 200 kg ha⁻¹ of NPK10-20-10 compound fertilizer, recommended for good production, but which are not affordable for most of smallholder farmers. More over the pH range is not optimal for fertilizer efficiency. Under this circumstances fertilizers use efficiency can be made effective by arbuscular mycorrhizae (AMF) even when applied at low doses. In this study, four types of AMF inoculum (Acaulospora, Gigaspora, Glomus and Acaulospora-Gigaspora-Glomus) and an uninoculated control were selected and combined with two levels of NPK10-20-10 application, by bringing a quantity of products of 100 kg ha⁻¹, 200 kg ha⁻¹ and unfertilized plot as control. Application of NPK 200 kg ha⁻¹ reduced colonization frequency and AMF spore density with 28.5 to 41.8%, respectively. Plants that received 200 kg NPK ha⁻¹ associated to Acaulospora-Gigaspora-Glomus were less sensitive to bean fly than others. Application of 200 kg NPK ha⁻¹ as well as inoculation with Acaulospora-Gigaspora-Glomus or association of mycorrhiza with NPK fertilizers offered the similar number of pods per plant (8 to 10). Treatment with low doses of NPK (100 Kg NPK ha⁻¹) combined with Acaulospora-Gigaspora-Glomus inoculum yielded well (15%) compared to the control and reduces the quantity of chemical fertilizers to be applied. NPK alone or inoculation with Acaulospora-Gigaspora-Glomus AMF inoculum improved bean yield by 12%.