Managing VAM in a semi-arid agroecosystem

Abstract

Field studies were conducted during the 1994 and 1995 growing seasons on Olton loam soil in Texas, USA to determine the impact of a terminated wheat cropping system on vesicular-arbuscular mycorrhizal colonization of cotton cv. Paymaster HS-26. Conventional tillage, intact herbicide-sprayed wheat, simulated treatment (cotton sown in a conventional cropping system but with wheat shoots inserted without roots into the soil to form a windbreak), and cotton sown into herbicide-sprayed wheat but with the aboveground portion of the wheat plants removed. VA mycorrhizal inoculation potential and colonization levels were measured as well as crop yields. The presence of the winter wheat root systems did increase VA mycorrhizal colonization levels at specific times during the growing seasons. Decreases in VA mycorrhizal activity during the first part of the growing season may have been due to a disruption of any established hyphal network as a result of early tillage practices in preparation for sowing. Yearly differences in colonization patterns and VA mycorrhizal inoculation potential as well as in final yields were also observed. These differences may have been due in part to differences in soil moisture levels as well as to other environmental stresses that mycorrhizal colonization could not impact. The management of VA mycorrhizae in an agroecosystem may be feasible when the effects of agricultural practices and abiotic constraints on the mycorrhizae inoculum dynamics and plant responses are fully understood.