GRAIN-SORGHUM SOYBEAN ROTATION AND FERTILIZATION INFLUENCE ON VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI

Vesicular-arbuscular mycorrhizal fungi (VAMF) can reduce plant stress resulting from nutrient deficiencies, drought, and other factors. he objective of this work was to measure the effect of soybean [Glycine mar (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] rotation and fertilization on plant response and VAMF root colonization and diversity, and relate effects to soil environment. Fertilizer treatments consisted of no fertilizer, N, and manure. Rooting densities correlated with previous crop, VAMF colonization, and soil NO3. Root colonization by VAMF was affected by previous crop, rooting density, N fertilization, soil P, and water-filled pore space. Root colonization by VAMF ranged from 93% at 15 cm to 15% at the 120-cm soil depth. Root density and VAMF colonization were least when soybean was grown the previous year and manure was applied. Root colonization by VAMF for control, N, and manure treatments were 54, 53, and 30%, respectively, for continuous soybean and 61, 55, and 44%, respectively, for soybean from rotation plots. Root colonization by VAMF for control, N, and manure treatments were 69, 59, and 54%, respectively, for continuous grain sorghum and 56, 48, and 31%, respectively, for grain sorghum from rotation plots. These agricultural soils contained a diverse mixture of 26 VAMF species, which is probably a major factor in the region's soil productivity. Plants stressed due to cropping system or fertilizer practice have greater VAMF colonization and VAMF activity. A diverse VAMF population could increase the ability of VAMF to respond to different stresses.