Cover crops enhance resource availability for soil microorganisms in a pecan orchard

Authors: RODRIGUEZ-RAMOS, JEAN - University Of Oklahoma; Scott, Natalie; MARTY, JAYMEE - National Center For Appropriate Technology; KAISER, DANIEL - Environmental Defense; Hale, Lauren

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2022
Publication Date: 6/10/2022
Citation: Rodriguez-Ramos, J.C., Scott, N.M., Marty, J., Kaiser, D., Hale, L.E. 2022. Cover crops enhance resource availability for soil microorganisms in a pecan orchard. Agriculture Ecosystems and the Environment. 337. Article 108049. https://doi.org/10.1016/j.agee.2022.108049.
DOI: https://doi.org/10.1016/j.agee.2022.108049

Interpretive Summary: Alley cover crops will impact soils in tree and vine cropping systems, but the on-farm variation in soil chemical and biological properties associated with cover crops is unclear. Our evaluations of a pecan orchard with alley cover crops revealed that the alley soils contained greater soil microbial biomass, nutrients, and moisture than adjacent tree rows. The microbial communities supported under the cover crops are indicative of nutrient rich conditions and dominance of two groups of beneficial mycorrhizal fungi were differentially supported under the tree rows and cover crops. Altogether, this study reveals that variance in soil conditions created by the cover crops stimulated unique soil microbial communities, which may have resource availability implications for tree crops with long-reaching lateral roots, like pecan.

Technical Abstract: Currently, there are substantial knowledge gaps on the impacts of cover crops on soil resources in tree cropping systems, wherein they are typically planted in interrow alleys and maintained for multiple years. While cover crops immobilize soil nutrient and uptake soil water, they can also prevent soil water evaporative losses and return nutrients to soils via decomposition of plant residues and stimulation of microbial nutrient cycling. This study evaluated soils beneath a mixture of cover crop species and beneath adjacent pecan trees in 5- and 7-year-old orchards. To evaluate impacts of cover on the soil biota, nutrients, carbon, and their dynamics across a production season, we employed routine soil chemical analyses, phospholipid fatty acid analysis, and high throughput sequencing of 16S rRNA genes and ITS regions for soils collected at four time points. We revealed that in the cover cropped alley soils contained higher relative abundances of microbes that use labile soil substrates in resource rich conditions. Soil chemical analyses provided additional evidence that the cover crops did not deplete soil nutrients and reduce soil moisture, but rather, enhanced soil nutrient and moisture contents during many of the sampling time points. Notably, cover crop plant species correlated with soil nutrients and plant beneficial microbes, which may warrant consideration when selecting cover crop species. The tree row and cover cropped alley soils had different proportions of plant-beneficial mycorrhizal fungi. The tree rows supported higher numbers of ectomycorrhizal (ECM) fungi and alleys had higher relative abundances of arbuscular mycorrhizal (AM) fungi, suggesting potential benefits for tree species like pecan, which support dual colonization by AM and ECM fungi. Altogether, the cover crops enhanced soil carbon, nutrients, and microbial populations in a pecan orchard and these impacts were frequently greater in a 7-year-old versus 5-year-old orchard.