Microbial Husbandry: Nurturing Microbes to Capture Soil Ecosystem Services

Abstract

Soil microbes drive many agroecosystem functions that dictate crop productivity, environmental outcomes, and management costs. Chapter 2 introduces microbial husbandry, a framework to manage soil microbes by creating soil conditions that allow critical taxa to thrive. Subsequent chapters apply microbial husbandry to nutrient cycling under maize (Zea mays L.) using a model system, ridge tillage and rye cover cropping (Secale cereale L.). We tested hypotheses with Bayesian structural equation modeling. In Chapter 3, arbuscular mycorrhizal fungi (AMF) insured against early season phosphorus (P) deficiency: AMF contributed to 40% higher maize P uptake in ridge till, at a 7% growth cost. Managers may increase P uptake by reducing physical disturbance to increase AMF abundance, and by increasing bulk density beyond levels in chisel plow. For Chapter 4, we wrote pyroots, a Python computer vision module, to measure roots and fungal hyphae in environmental samples cheaply and reproducibly (Appendix A; www.github.com/pme1123/pyroots). We also reported the first AMF hyphal length density values at 60 cm depth. Hyphal growth was independent of maize root growth, which suggests roots and hyphae can be managed independently. In Chapter 5, filamentous fungi acquired as much mineral nitrogen (N) as maize roots over five weeks after planting. While most root N uptake occurred in rows, fungal uptake occurred in both rows and inter-rows. Managers may encourage fungal N uptake without competing with crop needs by concentrating crop residue in the inter-rows. Overall, microbial husbandry helped us manage competing microbial functions simultaneously: nutrient provisioning in rows, and fertility building in inter-rows. Context-appropriate management tools can create soil conditions that enable microbes to perform these functions.