Soil physical, biological, chemical, and carbon data and cover crop biomass data from Sac Valley almond orchard comparing multiple cover crop compositions with resident vegetation for effects on soil health and nematodes

Planted cover crops and naturally occurring resident vegetation in
orchards and agricultural fields belong to multiple functional groups
which differ in traits, growth dynamics, and ability to influence soil
health and biology. These different vegetation mixes may influence soil
food webs and ecosystems over a growing season as well as regulating
nutrient cycling outcomes. This study characterized soil organisms and
nutrients as well as physical and chemical indicators of soil health in an
almond orchard with three vegetation mixes: winter resident vegetation
(dominated by Vicia, Malva, and Hordeum weedy species), and two cover
crops mixes, one functionally diverse (brassica, legume, cereals) and one
functionally uniform (brassicas), all of which had been implemented for
four years. While physical soil health indicators differed seasonally,
only biological indicators differed among the vegetation. During the
winter and early spring growth period, both cover crop mixes increased
microbial biomass nitrogen compared to resident vegetation, while the
uniform mix supported greater numbers of nematodes overall, regardless of
trophic group. The diverse cover crop mix supported more complex nematode
food webs, as measured by the Structure Footprint, while nematode
communities overall were primarily influenced by cover crop biomass and
microbial biomass nitrogen. Soil nutrients increased after vegetation
termination by flail mowing in all treatments, and the resident vegetation
had the largest increase in dissolved organic carbon between the Cover and
Post-Cover time points. Nematode indicators of food web composition and
function decreased after termination, including the Structure Index,
Fungal Footprint and Bacterivore Footprint. In contrast, the relative
abundance of herbivores increased over time and, at the Post- Cover time
point, both the diverse mix and the uniform mix had a higher proportion of
root herbivores than resident vegetation, although these were primarily in
the genus Tylenchorhynchus and not considered economically damaging.
Increased processing of resources through generalist root herbivore
nematodes may have been due to nematodes feeding on the cover crops
themselves or on almond roots that foraged into soils with more nutrients.
These results suggest that cover cropping can influence soil food webs on
multiple fronts including root herbivores and predators. Greater knowledge
of how cover crops influence soil health and for how long, during a
season, will allow for the more efficient use of cover crops in
Mediterranean systems.