Mycorrhizal colonization and nutrition of wheat and sweet corn grown in manure‐treated and untreated topsoil and subsoil

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Abstract
Dry bean yields (Phaseolus vulgaris L.) were raised to similar levels as the topsoil by manure application to eroded or leveled Portneuf silt loam soil (coarse‐silty mixed mesic Durixerollic Calciorthid). Only soil organic matter and zinc (Zn) content of leaf tissue were correlated with improved yields. Manure application increased mycorrhizal colonization and Zn uptake in pot experiments with dry bean which would explain the increased yields in the field. A field study was conducted to see if similar effects of manure and mycorrhizal colonization could be observed in field grown spring wheat (Triticum aestivum L.) and sweet corn (Zea mays L.). This study was conducted on existing experiments established in the spring of 1991 at the USDA‐ARS farm in Kimberly, Idaho, to study crop rotation/organic matter amendment treatments on exposed subsoils and focused on mycorrhizal colonization as related to topsoils and subsoils treated with conventional fertilizer (untreated) or dairy manure. Mycorrhizal root colonization was higher with untreated than with manure‐treated wheat and sweet corn. Root colonization was also higher in subsoil than in topsoil for wheat, but there were no differences between soils for sweet corn. Shoot Zn and manganese (Mn) concentrations generally increased with increased root colonization for both species (except between soils with corn Mn contents). Wheat shoot potassium (K) concentration was increased by manure application, but the affect declined with time, was the opposite of colonization and was not observed with sweet com. Phosphorus (P), calcium (Ca), magnesium (Mg), iron (Fe), and copper (Cu) concentrations either were not influenced or were erratically affected by mycorrhizal colonization. Yields of wheat were highest for manure‐treated subsoil and topsoil compared to untreated soils. Mycorrhizal colonization was different between conventional and manure‐treated soils and between topsoil and subsoil and these differences increased Zn and Mn uptake, but they did not explain the improvement in wheat yields obtained with manure application.