COMPARING SOIL HEALTH AND WEED SUPPRESSION WITHIN ORGANIC ANNUAL AND PERENNIAL ROTATIONS

One of the challenges faced by farmers how to control weeds and also build soil health. Tillage remains a key tool for controlling weeds, especially in organic systems, yet it disrupts soil aggregates and oxidizes soil organic matter, thereby having detrimental effects on soil health. This project addresses two key questions relevant to organic farmers:1) Does a rotation with both annual and perennial crops improve soil health and weed suppression compared to an annual-only rotation with cover crops?2) Does the species diversity of perennials and annual cover crops influence soil health and weed suppression?Our long-term goal is to improve our understanding as to how perennial phases of organic crop rotations can be improved to maximize soil health and weed suppression benefits, as well as overall farm profitability. To meet this goal, we plan to address the following objectives. Objective 1: Evaluate the forage yield and quality of a diverse set of perennial species grown within an organic farming system. The perennial rotation will be phased into our Penn State research station site beginning in the spring after growing corn followed by a cereal rye cover crop. Monocultures of six perennial species will be planted (two legumes, two grasses, and two forbs) along with mixtures of those species, with the most diverse mix including all six species. The perennial species will be harvested for hay for two years and be followed by corn. The perennial diversity gradient distinguishes this proposal from most prior research, and the establishment, yield and quality of these forage species and mixtures will provide material for outreach meetings and extension articles. In addition, the establishment of the diverse perennial rotation at the research station will provide the foundation for accomplishing Objectives 2-4.Objective 2: Evaluate the potential for perennial forage crops to improve soil health as a function of species diversity and length of establishment. At the research station, we will compare soil health within corn-perennial (including simple and diverse perennial stands) and corn-soybean-wheat rotations (with simple and diverse cover crops). We will measure soil carbon levels (partitioned into particulate and mineral-associated organic carbon), soil physical properties (wet aggregate stability and infiltration rates) and soil biological health (microbial biomass and daily respiration rates). Baseline metrics will be collected at the beginning of the project and repeated two years after perennials are established. These data will allow us to evaluate the short-term impacts of diverse perennial forage crops on soil health.At the on-farm sites, we will make the same soil health measurement in established perennials. On-farm sites will be selected for their long history of rotational perennial use, to assess the long-term impactof perennials on soil health. The research station and on-farm soil health datadata will support farm tour and grower meeting discussions about relationships between perennial species, rotations and soil health as well as the development of a webinar about perennial forage crops and soil health.Objective 3: Compare weed suppression by annual cover crops and perennial forage crops across a plant diversity gradient. A diverse group of winter cover crops including six species (two legumes, two grasses and two brassicas) are grown in monoculture and mixtures (2-6 species) between wheat and corn at the Penn State research station. Establishing perennial treatments with a similar diversity gradient (both in number and types of species) will allow us to make a series of comparisons of weed suppression by annual and perennial species. We will sample weed biomass in the annual cover crops and perennial crops in both fall and spring. At these times, we will measure both counts and biomass of Canada thistle, a perennial weed that is problematic at this site and particularly difficult to control in organically managed systems. We will also measure weed biomass in corn following the annual cover crops and the perennial forage crops. Finally, we will assess the weed seedbank in the annual and perennial rotations both in the field and through greenhouse soil seedbank studies. The data generated by the research in this objective will detail the weed suppression benefits of constructing more diverse crop rotations that include perennials, which will be disseminated to farmers at outreach events and through extension publications.Objective 4: Quantify corn yields and overall profitability of a perennial-annual rotation compared to an annual rotation with cover crops across a plant diversity gradient. We will use structural equation modeling to compare how these rotations and embedded cover crop and perennial plant diversity gradients affect corn yields either directly or indirectly through their influence on soil health metrics and weeds. In addition to comparing corn yields, the overall profitability of these two rotations at the research station will be assessed using partial budget analyses. These analyses will help farmers decide whether and how to incorporate perennials into annual cash-crop rotations. Also, they will guide farmers who are considering planting different perennial species or changing their rotation. The yields and profitability analyses will be published in an extension article and incorporated into outreach presentations.