FIELD RESPONSE OF MAIZE TO A VAM FUNGUS AND WATER MANAGEMENT

Mycorrhizae improve plant nutrient uptake and are known to affect the water relations of plants grown in growth chambers and greenhouses. This paper summarizes a 3-yr field study that tested the effects of mycorrhizae and water management on the growth and grain yield of maize (Zea mays L.). In each year, two inoculation treatments (inoculated or not with Glomus etunicatum Becker and Gerdemann) and three water-management treatments (fully irrigated, moderate stress, and severe stress) were applied to fumigated and fertilized Millhopper fine sand (loamy, siliceous, hyperthermic Grossarenic Paleudult). Inoculum was placed in a furrow 10 cm deep at an average rate of 1500 propagules per meter of row. Six to 7 wk after planting, colonization ranged from 0 to 6% of total root length on noninoculated plants and from 10 to 61% on inoculated plants. Twelve to 13 wk after planting, colonization ranged from 2 to 30% on noninoculated plants and from 21 to 56% on inoculated plants. Water stress had little effect on root colonization. By 52 d after planting, one more leaf had appeared and one additional leaf had formed a collar on inoculated plants. Inoculation increased the concentrations of P and Cu in both shoots and grain on all measurement dates. Overall, grain yields (0.306) and total above-ground biomass yields (0.458 Mg ha-1 cm-1 of water) increased linearly with irrigation. A positive response to mycorrhizal inoculation was constant across irrigation levels (0.802 for grain and 1. 170 Mg ha-1 for biomass). Therefore, the proportional response of maize to inoculation with G. etunicatum increased with increasing drought stress.