Vesicular-arbuscular mycorrhizas and the soil-disturbance-induced reduction of nutrient absorption in maize.

This study was designed to test the hypothesis that disruption of the macrostructure of a previously zero-tilled soil is capable of reducing vesicular arbuscular (VA) mycorrhizal infection to a degree such that phosphorus (P) absorption is reduced. Undisturbed soil cores (within plastic cylinders) were excavated from long-term, zero-tilled plots. Soil removed from these plots, which was first subjected to structurally disruptive forces and then packed into identical cylinders, formed the disturbed comparisons. Maize (Zea mays L.), wheat ( Triticum aestivum L.), spinach (Spinacea oleracea L.) or rape (Brassica napus L.) were grown in the cores and P and zinc (Zn) absorption patterns monitored. Soil disturbance significantly reduced P and Zn absorption by maize grown in soil originating from three sites differing in local geography and/or texture Disturbance also reduced mycorrhizal infection in the three soils. A significant effect of disturbance upon the VA mycorrhizal infection of both maize and wheat roots (both mycorrhizal) and also upon the P absorption by these species was observed. None was found with respect to spinach and rape comparisons (non-mycorrhizal). Injection of benomyl, a potent inhibitor of mycorrhizal fungi, into the soil surface significantly reduced the influence of soil disturbance upon P absorption. No significant differences were found in VA mycorrhizal infection within fungicide-treated cores. We accepted our hypothesis based upon the above evidence. [ABSTRACT FROM AUTHOR]