Managing VAM in a semi-arid agroecosystem

Abstract

Effective management of mycorrhizae in agriculture should provide benefits to production systems by improving seedling establishment and reducing adverse effects due to abiotic stresses. It has been observed that cotton seedlings grown on the Southern High Plains in association with terminated wheat may be better able to survive many abiotic stresses. Protection from the impact of sand particles is an obvious result of the presence of the wheat, but another advantage of this cropping system may be to enhance the colonisation of cotton roots by VA mycorrhizae which, in turn, could improve early seedling development. Therefore, field studies were conducted during the 1994 and 1995 growing seasons to determine the impact of the terminated wheat cropping system on VA mycorrhizal colonisation of cotton. Four treatments were initiated that consisted of 1) conventional tillage system; 2) intact terminated wheat treatment; 3) simulated treatment (cotton planted in a conventional cropping system but with wheat shoots present with no roots); and 4) cotton planted into terminated wheat but with the above-ground portion of the wheat plants removed. VA mycorrhizal inoculation potential and colonisation levels were measured as well as crop yields. The presence of the winter wheat root systems did increase VA mycorrhizal colonisation 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 planting. Yearly differences in colonisation 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 colonisation 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 inoculwn dynamics and plant responses are fully understood.