MYCORRHIZAL DEVELOPMENT AND PHOSPHORUS ABSORPTION IN MAIZE UNDER CONVENTIONAL AND REDUCED TILLAGE

Arbuscular mycorrhizae participate in P uptake by maize (Zea mays L.). Previous studies using pot-grown plants have shown that P uptake by maize is greater when soil is not disturbed between cropping and planting. This study was conducted to determine if mycorrhizal colonization and shoot P absorption in the field are higher under reduced tillage, under conditions of soil fertility and tillage management representative of commercial farming. Maize was sampled in 1990 and 1991 from plots maintained under no-till (NT), and ridge tillage (RT). These were contrasted with maize from plots given moldboard plow (MP) tillage each year, which disturbs the soil to a greater extent. Plots were fertilized at recommended rates. In the early part of both years, shoot P concentration in NT and RT were significantly greater than under MP. These differences in shoot P did not persist after the six-leaf stage. Greater development of mycorrhizae in the early season was seen in the RT and NT systems relative to that in MP. There were no significant effects of tillage on final yield, possibly due to the relatively high soil P levels. Under NT and RT, arbuscular colonization had a maximum at 48 d after planting (DAP) of 55% and 60%, respectively, followed by a linear decrease to near 10% at 166 DAP. Under MP, a plateau of 45% arbuscular colonization was sustained between 48 and 97 DAP, followed by a linear decrease similar to that in NT and RT.