The management of populations of vesicular-arbuscular mycorrhizal fungi in acid-infertile soils of a savanna ecosystem: I. The effect of pre-cropping and inoculation with VAM-fungi on plant growth and nutrition in the field

A field trial was conducted at two sites in the savanna ecosystem of eastern Colombia to compare the effects of inoculation with vesicular-arbuscular mycorrhizal fungi (VAMF) of Brachiaria dictyoneura (a tropical grass), cassava (Manihot esculenta), the tropical forage legume kudzu (Fuerana phaseoloides) and Sorghum sp., and two phosphate sources. The second stage of the trial studied the effect of these pre-crop treatments on the subsequent growth, nutrition and VAM status of cowpea (Vigna unguiculatd) and Stylosanthes capitata in the following season, compared with both crops sown in native savanna. Inoculation significantly increased the levels of VAM and plant yields in the early growth stages of all crops during the first season, particularly with the rock phosphate (RP) source. The most significant increases were observed in the mycorrhiza-dependent cassava and kudzu crops up to 15 weeks after sowing, and were associated with increased foliar uptake of P and Mg. The effectiveness of the introduced inoculum was greater at the field site with a sandier soil. In the second season the levels of VAM in roots of cowpea and S. capitata were all increased significantly in pre-cropped plots compared with a savanna control. The increased presence of VAM was associated with significantly increased yields on plots previously sown to cassava, kudzu and Sorghum sp. The data support the idea that increasing the VAMF inoculum potential of these acid-infertile soils by inoculation or pre-crops can greatly increase the rate of establishment of mycorrhiza-dependent host plants.