Improving Nitrogen Management in Agriculture: Opportunities Gleaned from Organic Systems
Open Access
- Author:
- Grantham, Alison Mills
- Graduate Program:
- Ecology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 10, 2015
- Committee Members:
- Jason Philip Kaye, Dissertation Advisor/Co-Advisor
Jason Philip Kaye, Committee Chair/Co-Chair
Marvin H Hall, Committee Member
David A Mortensen, Committee Member
Elsa Selina Sanchez, Special Member - Keywords:
- Nitrogen
Agriculture
Organic Agriculture
Sustainable Instensification
Ecology
Agroecology - Abstract:
- Achieving sustainable intensification goals for agriculture hinges on two essential and seemingly contradictory improvements in nitrogen (N) management: reducing N losses while increasing crop productivity. Conventional agricultural systems have attained prolific productivity, built upon tremendous inputs of inorganic N fertilizer. But, these production increases have largely stalled, and much of the N fertilizer used to achieve these yields escapes, polluting air and water. Organic agriculture takes a different approach to N management and productivity. Built on the philosophical foundation of systemic design, organic agriculture aims to use biological processes to provide N and other services necessary to support crop productivity. This organic approach results in systems with a fundamentally different structure than their conventional counterparts. In organic systems, these contrasting structural elements include: perennials, rotation diversity/complexity, legumes, and manure; which we hypothesized impart improvements in N retention and/or provisioning. Goals of this research were to: (1) determine whether annual or perennial forage systems better mitigated potential greenhouse gas (GHG) losses related to grazing and extreme rainfall events, (2) assess efficacy of alternative organic N management strategies in providing inorganic N and supporting forage yields, (3) evaluate the availability of organic N in soils of organic systems and to the crop species grown in them. I relied on a 2012-2014 organic forage systems experiment to characterize effects of N management practices employed in these systems in terms of the N they provided in the soil during the growing season (soil NH4+, NO3-, amino acids and other free primary amines), as well as the N that escaped (N2O losses, NH3 volatization, NO3- leaching). While N management in both conventional and organic agriculture aims to provide N in inorganic forms, emerging evidence suggests organic forms of N may also be plant-available, however quantifying the contribution of N compounds, especially organic ones, to plant N nutrition is methodologically challenging. I used a large greenhouse experiment to indirectly test the ability of 3 N environments to support growth of four forage crop species, and then directly test the capacity of plants from each of these 12 growth phase treatments to take up labeled forms of inorganic N and amino acids using 2 alternative tracer methodologies. I found perennial organic forage systems exhibit multiple N management benefits over annual systems: lower N2O fluxes, lower soil NO3- leaching, and greater inorganic N use efficiency, although annual systems exhibited higher absolute yields. Among annual organic systems, those that relied on a legume N provisioning strategy, rather than a manure N provisioning strategy, displayed superior inorganic and organic N availability and yields. All forage species demonstrated amino acid N uptake abilities that increased when the plants were grown in the presence of amino acids. Thus, the greater use of perennial and legume crops may increase amino acid N availability and facilitate direct crop plant utilization of this previously unrecognized soil N resource, reducing N losses while maintaining or increasing crop productivity.