Mycorrhizal colonization and nutrient uptake of dry bean in manure and compost manure treated subsoil and untreated topsoil and subsoil

Abstract

Eroded or leveled Portneuf silt loam soils (coarse‐silty mixed mesic Durixerollic Calciorthid) have been restored to topsoil productivity levels by manure application, but not by other organic sources such as cheese whey. In dry bean (Phaseolus vulgaris L. cv. Viva), only soil organic matter and Zn concentration of leaf tissue correlated with improved yields. Manure application could potentially increase or decrease mycorrhizal colonization depending on which factors dominate. Manured and unmanured soils from a long‐term field experiment were sampled and mycorrhizal spores were quantified, but there was no significant manure treatment effect on spore numbers. A greenhouse study was conducted to see if manure or composted manure freshly applied to subsoils would facilitate mycorrhizal colonization in dry bean roots compared to untreated topsoil or conventionally fertilized subsoil. Low level colonization (< 5%) was observed 21 days after planting and that increased to 58% by 56 days after planting. Roots grown on subsoil treated with manure or composted manure showed higher percent colonization than roots from untreated subsoil, but roots on topsoil had highest colonization. This increase in colonization was statistically significant for the last two sampling dates. Topsoil promoted the greatest percent colonization in early bean growth and this was reflected in greater Zn uptake during early growth stages. By day 56, plants grown in manured subsoil absorbed Zn equal to topsoil and at higher levels than the subsoil control. However, this increase in Zn uptake was not seen in plants grown in compost manured subsoil. A decrease in root and shoot weight was observed in the composted manure treatment and this seemed to decrease mycorrhizal efficiency. Uptake of other nutrients was either not related or was negatively related to mycorrhizal infection. The higher percent colonization of roots by mycorrhizal fungi stimulated by manure could explain the field observations of higher bean yield and Zn contents in dry bean in manured than in untreated subsoils.