Prescribed defoliation strategies influence soil carbon and nitrous oxide potential in pastures

Abstract

Cool‐season perennial grasslands are commonly used for livestock pasture. However, understanding of the belowground effects of forage defoliation (selective pressure applied by grazing) management is nascent. We investigated how defoliation management affects aboveground (forage productivity) and belowground processes (soil C/N), microbial nutrient cycling, and potential nitrous oxide [N2O] emissions). We hypothesized that rotational (moderate frequency) defoliation at low severity will increase soil organic matter (SOM) storage and microbial capacity to cycle C, N, and P, but that these changes would also lead to greater soil N2O emission potential. Data were collected from organically (OF) and conventionally managed (CF) farms with differing botanical composition in West Virginia, where three frequencies and two severities of forage defoliation were imposed. At OF, more severe defoliation decreased labile soil C content (–26%), while moderate defoliation resulted in a 39% reduction in microbial enzymatic capacity to cycle C, but not at CF. The N2O emission potential (ratio of nirK/nosZ functional gene abundance), was differentially affected by defoliation treatments at both sites. At OF, defoliation severity altered N2O emission potential, whereby low severity resulted in an 82% decrease in potential N2O emissions compared with high severity treatments. At CF, continuously defoliated plots exhibited a 71% lower N2O emission potential relative to less frequent defoliation. Belowground microbial parameters were more responsive to defoliation at OF, suggesting past management may influence how grazing management asserts belowground changes. Results suggest that defoliation management could enhance soil C storage, but potentially at the risk of increased N2O emissions.

Early production of switchgrass (Panicum virgatum L.) and willow (Salix spp.) indicates carbon accumulation potential in Appalachian reclaimed mine and agriculture soil

“…Future work should also examine how shallow soil, such as those in the mine sites with a very shallow layer of topsoil, interacts with soil C processes. As increased accessible C can lead to increased N 2 O production potential, exploring the consequences of switchgrass and willow production on the emissions of greenhouse gases such as N 2 O would help understand the environmental sustainability of these systems (Kelly et al., 2022). Lastly, future work would benefit from a biochar treatment derived from switchgrass or willow feedstock as to consider biochar itself as a bioproduct and apply it using rates commensurate with feedstock and biochar yield.…”

Tree Species Influence Nitrate and Nitrous Oxide Production in Forested Riparian Soils

“…All plasmid-transformed genes were sequenced by Sanger sequencing using M13 primers to confirm the identity of each insert (Genomics Core Lab at West Virginia University). Standard curves for nirK and nosZ were determined using the cloned products via real-time quantitative PCR (qPCR) following the protocol outlined in [82]; a qPCR was run with a 10 µL final volume containing 2 µL PCR grade water, 0.5 µL each forward and reverse primers (total primer concentration = 500 nM), 5 µL of SYBR qPCR 2× master mix, and 1 µL template using the following conditions: Stage 1: 95 C for 15 s for 1×. The qPCR samples were run in triplicate.…”

“…The qPCR samples were run in triplicate. Using the same conditions, a qPCR was then run for each soil sample DNA extraction, and using the respective standard curve equations, the gene copy number was calculated [82]. All the calculations were corrected for soil moisture content so that gene copy numbers were standardized to g of dry soil.…”