Browsing by Subject "Nutrient Management"

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    Microbial Husbandry: Nurturing Microbes to Capture Soil Ecosystem Services
    (2018-09) Ewing, Patrick
    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.
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    The Timing of Winter Application of Dairy Manure and its Placement Within the Snowpack Affect Nutrient Loading to Snowmelt Runoff
    (2022-03) Allen, Luis
    Runoff from agricultural fields can contribute to the degradation of surface waters when not adequately controlled. Application of manure in the winter is practiced in the upper Midwest of the USA, where seasonally frozen soils reduce or eliminate infiltration from precipitation events and can result in greater nutrient losses from overland runoff. While extensive research exists on the hydrological conditions that interact with manure nutrient losses from runoff during spring, summer, and fall, winter manure best management practices need further investigation. Further research is also needed due to the changing hydrological conditions from the effects of climate change, such as the increased number of freeze-thaw cycles and the shortening of the snowfall period during the winter season. Two studies evaluated whether the timing of winter manure application and its placement within the snowpack affect the nutrient content and loading of snowmelt runoff. In the first study, two dairy manure application timings were assessed under field conditions: early manure (applied in December or January and over frozen soils in the absence of snow) and late manure (applied in February or March and over a snowpack). In the second study, three manure placements were assessed within a 30-cm snow column under laboratory-based conditions: manure under snow (US), manure between snow (Mid), and manure over snow (OS). The timing of winter manure application showed a statistically significant lower nutrient loading to snowmelt runoff from the early manure treatment, regardless of the hydrological and climatic variations between years. Manure placement within the snowpack showed a significant treatment effect on nutrient loading for nitrate-N, ammonium-N, and dissolved reactive phosphorus. A significant placement treatment effect was not observed for total nitrogen (bound), total phosphorus, dissolved carbon, and dissolved organic carbon. These studies suggest that while nutrient loading to snowmelt runoff may be reduced, results may vary depending on hydrological conditions and the type of nutrient studied. This research may inform winter manure and water quality best management practices. Producers may better assess the timing of manure application to reduce nutrient losses. Goals can also be assessed depending on the nutrient of concern.