Soil microbial biomass alterations during the maize silage growing season relative to tillage method

Tillage method can significantly alter soil microbial populations and activities. Although considerable literature exists on microbial and soil chemical alterations under various tillage methods, little information exists on soil microbial biomass C (SMB) alterations during the growing season, and especially on the relationship of SMB to crop N use. The objective of this study was to determine the effect of no‐tillage (NT) or conventional tillage (CT), and soil location, on SMB during the growing season. A maize ( Zea mays L.) silage/ 15 N field experiment, under NT or CT for 3 yr before this study, was used during the fourth growing season. Averaged over sampling times and location (within‐row or between‐row), SMB in the 0‐ to 3.8‐cm and 3.8‐ to 7.5‐cm soil layers under NT was 87 and 33% greater, respectively, than under CT. Linear regression of soil surface layer (0–3.8 cm) SMB on day‐of‐year revealed a significant ( P ≤ 0.10) relationship only within‐row and under NT, with a 29% SMB decrease during the growing season. Similar regressions for the other layers and treatments were insignificant ( P > 0.10) or had small seasonal differences. SMB was consistently higher in the between‐row locations under both tillage methods. Despite substantial tillage method‐induced differences in SMB (50% overall, accompanied by small differential seasonal differences) in the more surficial layers, these alterations appear to have been of little practical consequence, since previous work on these plots revealed essentially no differences in silage utilization of either fertilizer N or soil N relative to tillage method. Thus, the importance of SMB in significantly affecting crop N use in this within‐row, banded, maize silage system is questioned.