Soil Gases and Temperatures: A Beef Cattle Feedlot Compared to Alfalfa

Dry wells or caissons were used in an alfalfa field and at two locations in a feedlot pen to insert instrumentation and sampling devices to characterize the soil profiles. Soil gas compositions and temperatures studied for a 9-yr period were strikingly dissimilar among the three sampling sites, yet each location had certain consistent properties unique to it. Two distinct areal-wise soil-zones had developed in the feedlot pen—one anaerobic and one aerobic. Only the anaerobic, feedbunk site produced methane (CH₄). High soil carbon dioxide (CO₂) and low oxygen (O₂) contents were found there and at the pen center. Dinitrogen (N₂) content at the feedbunk site was consistently less than in air which was attributed to a positive CO₂ and CH₄ pressure from biological sources. The main effects of location and year interacted with either depth or season for the common gases O₂, N₂, and CO₂ at the three caisson sites. The main effects of depth, season, and year on O₂ and CO₂ were separated at the feedbunk site by excluding the other locations from data analysis. A first order interaction of season by year for N₂ and CH₄ showed the dependence of those gases on seasonal temperature change modified by years. A significant influence of the caissons on nearby soil temperature gradients was not detected. There were significant positive correlations between soil gas compositions and temperatures for CO₂ at all locations and for CH₄ at the feedbunk site. Soil N₂ content was negatively correlated with soil temperature at both the feedbunk and center sites. These and other complementary results indicate that anaerobic soil conditions beneath a continuously-maintained, intact, moist manure pack would minimize possible nitrate nitrogen (NO⁻₃-N) formation and contamination of soil and groundwater.