The effects of soil health management practices on soil organic carbon persistence and accrual in vineyards

Abstract

Context and purpose of the study. Climate change is already threatening California vineyards, as they grapple with increasing extreme weather events and drier growing seasons. As vineyards adopt soil health management practices to bolster their adaptation to these threats, there is potential for these same practices to contribute to climate change mitigation. In particular, cover crops, reduced/no-tillage, livestock integration, and compost application can all increase soil organic carbon (SOC), which prevents carbon (C) from being released into the atmosphere and accelerating climate change. However, SOC is a dynamic soil property, as SOC is continually undergoing transformations via decomposition, so it’s crucial to understand better not just how the total C pool changes in response to soil health management, but also how organic matter is allocated between the mineral-associated carbon (MAOC) and particulate organic carbon (POC) fractions. While MAOC can remain in the soil for decades to centuries, POC has a mean residence time of a few years to decades, thus making MAOC a more stable form of soil C. Thus, our study aims to examine the effects of soil health management practices, adopted alone or in combination, on total SOC, MAOC, and POC concentrations in vineyards.

Material and methods. In summer 2023 and 2024, we collected soil samples at 24 vineyard blocks in Napa County, California, USA. The vineyard blocks reflect a gradient of soil health management practice adoption, with each site utilizing from one to four practices (maybe list out practices here?; unless it’s the same as you mentioned in the previous section), so we have an even distribution of six vineyard blocks along each bin within the gradient. Due to their geographic proximity, all vineyard blocks experience similar annual temperatures and precipitation, but there is variation in their soil textures, with sites having either loam, silt loam, or clay loam soils. At each site, we collected bulk soil samples from 0-40 cm, subdivided into 10 cm depth increments, within five vine inter-rows. We used air-dried, 2-mm sieved soil for all SOC, MAOC, and POC measurements. We separated MAOC and POC by physical fractionation (MAOC < 53 μm). We measured the C content within each fraction and analyzed bulk samples for total SOC by combustion using an Elementar Vario MAX Cube CN elemental analyzer.

Results. In the surface soil depths (0-20 cm), we expect that total SOC concentrations will increase with the number of soil health management practices adopted, while the relative allocation of C between MAOC and POC will vary with the kinds of practices utilized. We expect that sites that implement reduced/no-tillage will have a greater proportion of POC, since the lack of cover crop residue incorporation into the soil slows the decomposition of plant material. In contrast, we expect that sites that apply compost and incorporate sheep grazing will have a greater proportion of MAOC due to the provision of more labile C forms for microbial decomposition.