Performing Department
Agronomy & Plant Genetics
Non Technical Summary
Although organic agriculture has more than tripled in production value over the last decade, the number of acres certified organic is still only 7% of total crop acreage nationally (USDA NASS). From our ongoing interaction with many stakeholders interested in transitioning to organic systems (Principles for Transitioning - NIFA Project #MIN-13-G27), we have learned that farmers are faced with unique production, environmental, and economic challenges. Production challenges include weed control, adapting to new crops and complex crop rotations, and nutrient management. In turn, these factors contribute to environmental and economic challenges during transition. One of the primary tenets of organic agriculture is improving soil health, but if concerns about potentially lower yields and lack of organic premium during the transition period are not addressed, growers will not be able to give high priority to environmental benefits when choosing a rotation strategy for transition. Our research seeks to expand transitioning producers' options beyond row crops to perennial crops so that they can fulfill the organic mandate to improve the soil, even before they are certified. As a result, farmers will not only benefit from increased profits in the short term, but their soil function will be improved, leading to higher yields over the long term. Improving the environmental and economic outcomes that farmers can achieve during organic transition would in turn foster greater adoption of organic practices.Regardless of how ecologically beneficial a practice is, producers cannot ignore economic realities in managing the three years of transition. Organic farming can be as profitable as conventional farming (Mahoney et al., 2004; Chavas, et al., 2009), part of which may be attributed to the price premiums that farmers receive for organic products (Archer et al., 2007; Clark and Alexander, 2010). Farmers considering transitioning to organic often anticipate economic returns based on yields typically attained using conventional practices, while in fact, yields often decrease during transition, likely due to limiting N, weed pressure, and farmer inexperience with a new production system (Delbridge et al., 2015; Martini et al., 2004). Transitional crops cannot be marketed and sold as organic, therefore the price premiums that come with organic products are not available to offset the economic losses related to lower yields. These and other factors can lead to lower returns in transition (Dabbert and Madden, 1986). A recent study of organic and transitioning Minnesota farmers found that profitability for transitioning farmers fell dramatically in transition (Delbridge et al., 2015). Among the significant problems these same farmers experienced were lower yields and reduced fertility, and complications due to weeds (King et al., 2014). This clearly demonstrates the many risks farmers experience during transition and may also explain why some conventional producers choose not to convert to organic. We are proposing to examine transitioning rotation options - including a novel perennial grain crop - that may address both environmental and profitability concerns. Now is a critical time for this research because of low commodity prices that translateto difficult profit margins during transition, and current trends of declining organic prices due to imports from foreign nations (Bunge, 2017).
Animal Health Component
40%
Research Effort Categories
Basic
40%
Applied
40%
Developmental
20%
Goals / Objectives
Farmers interested in transitioning from conventional to organic systems are faced with unique challenges regarding weed control, fertility, improving soil health, and generating income during the transition period. Many transition systems rely on tillage to control weeds and annual crop rotations, which have been associated with soil carbon (C) loss. Intermediate wheatgrass (IWG) is a cool-season grass that is being bred for increased seed yields to become the first perennial grain crop. IWG could help producers overcome the challenges of organic transition, while also simplifying management, reducing tillage-associated C emissions, and improving soil health relative to annual crop-based organic transitions. This project will compare six organic transition systems that include IWG, summer and winter annuals, perennial legumes, and systems with various combinations of grain, forage, and cover crops. In each system, we will measure 1) agricultural output/profitability, 2) soil health (both biological and physical integrity), 3) C dynamics, and 4) weed supression. Our objective is to identify an organic transition cropping system that improves profitability, soil health, and C sequestration. Crop yields will be incorporated into enterprise budgets to determine profitability of each system. This project is driven by research and outreach that documented concerns of Midwestern farmers regarding reduced fertility and yields, complications due to weeds, and low profits during organic transition. Results will be shared through Extension and other outreach efforts. This project supports the Organic Transitions program's goal of increasing the competitiveness of transitioning farmers.The following is an overview of the proposed treatments:Transition system 1: Transition system 1 is a monoculture stand of the perennial grass IWG that will be fertilized with an organic N source, be harvested annually for grain, and then harvested to remove residual straw annually. This system will be tilled during the last year of the transition just prior to planting the corn/soybean crop and will provide winter cover for all three years of the transition period.Transition system 2: Transition system 2 is an intercropped bi-culture of intermediate wheatgrass and alfalfa where the IWG will be harvested for grain and the alfalfa will function as a green manure for N fertility. Alfalfa could also affect C cycling by increasing N content of litter inputs, and reduce weed competition by increasing ground cover. This system will be tilled during the last year of the transition just prior to planting the corn/soybean crop and will provide winter cover for all three years of the transition period.Transition system 3: Transition system 3 is an alfalfa monoculture. Organic alfalfa is a valuable commodity for the rapidly growing organic dairy industry (Greene and McBride, 2015), and therefore is one of the more important organic crops for farmers in the Upper Midwest. Alfalfa does not require N fertilizer or annual tillage, which improves the carbon footprint of this system. This system will be tilled during the last year of the transition as described in system 2.Transition system 4: This system includes a rotation of forage/green manure and high-value food crops including summer and winter annuals and a perennial. The perennial forage crop red clover is frost seeded into winter wheat and then overwinters between the first and second year, therefore preventing two tillage events. Red clover is followed by a high-value, food-grade soybean that is eligible for a non-GMO premium, even during transition (Kowalski, 2017). This system includes both grasses and legumes during different periods of the transition, and will require two tillage events and provide winter cover for all years during the transition.Transition system 5: This system is a commonly used corn/soybean rotation with a mixture of hairy vetch and winter rye as a winter cover crop. The system will require annual tillage, which may reduce the C storage potential, but will provide winter cover to conserve topsoil and its role in C sequestration.Transition system 6: This system includes a rotation of corn and soybeans managed without a winter cover crop. This treatment serves as a check as it is a common non-organic rotation in the Upper Midwest.
Project Methods
Duplicate transition experiments using the treatments described above will be conducted at two contrasting transitioning sites in Minnesota. One site will be located in west-central MN at Madison (45.00 °N, -96.15 °W) on a Webster Clay Loam. The second site will be located on a Waukegan silt loam near Farmington (44.64 °N, -93.14 °W) in south-central MN. Average annual rainfall at Madison and Farmington is 45 and 70 cm, respectively. Each site is currently conventionally farmed. Sites will be selected so that phosphorus, potassium, or other nutrients are not limiting.The experimental design for each experiment is a randomized complete block with four replications. In the third year of the experiment, we will employ a split-plot design by establishing corn and soybean following each of the main transition systems. Each plot will be 12 x 20 m. Intermediate wheatgrass, alfalfa, winter wheat, and winter rye-vetch cover crops will be seeded in September 2017, while other crops will be seeded in May 2018. At both locations, the crop in the season preceding the experimental period will be spring-seeded wheat that will be harvested for grain by mid-August 2017. We will use organically produced IWG seed and commercially available crop varieties.In spring of 2020, each plot will be divided into two 6 x 20 m subplots for seeding of corn and soybean. In all experiments, plant nutrients (P, K, S, and B) will be supplied to non-limiting levels using composted manure as recommended for each species based on early spring soil testing in 2017. Soil pH will be adjusted as necessary according to Minnesota recommendations. For IWG and corn monocultures, N fertilizer will be applied in April of 2018 and 2020 using composted poultry manure.Weed assessment: The population density and biomass of weed species will be assessed in spring of 2018, 2019 and 2020 at two and four weeks after seeding of annual crops before each tillage by sampling four 0.5 m2 areas within each plot along the center rows of each plot. We will use the same timing for the weeds in the perennial crops. We will also measure weed seedbank in fall 2017 and in spring of 2020 in early May before the first tillage using a sampling procedure adapted from Forcella (1992).Carbon budget: The carbon budget of each cropping system will be calculated using a comprehensive analysis of carbon inputs and outputs from the system, as described by Cheng et al. (2000), but modified for measurements appropriate for our field scale agronomic system. We will calculate both flux-based and pool-based carbon budgets. Carbon inputs: The flux based calculation compared to the pool based calculation will give us an understanding of variation in the carbon budget over each growing season versus the total C sequestration per growing season. GPP flux will be determined with leaf area index measurements made every three weeks throughout the growing season using a portable LI-COR 6400. ANPP will be determined by measuring the dry matter yield and C content of each crop, plant litter, or other living residue, before crop termination. These aboveground biomass components will be measured from 3 randomly sampled 0.5 by 0.5 m quadrats in each plot for all crops within all systems. BNPP will be determined using a 90 cm deep soil core 4 cm in diameter that will be evacuated from each quadrat immediately after aboveground sampling. The three cores will vary in proximity to plant crowns; one adjacent to crowns, one in the center of the inter-row space (furthest distance from crowns), and one in between. Total root biomass will be separated and processed using the methods described for the root ingrowth cores below. All above- and belowground biomass will be dried, weighed, ground, and analyzed for C and N using a combustion analyzer (Jungers et al., 2017b). A second more detailed measurement of BNPP will be measured annually at the beginning and end of all annual crop phases, and during the spring, summer, and fall of all perennial transition systems. We will use root ingrowth cores to determine BNPP following the methods described by Steingrobe et al. (2001). Carbon outputs include measurement of CO2 and CH4 emissions every three weeks in each plot throughout the growing season (Venterea et al. 2005), using a Gasmet gas flux analyzer available.Soil biological and chemical properties: Soil carbon-related data will include measures of various carbon (C) and nitrogen (N) pools to help understand nutrient cycling and C accrual under each system at each site. Abiotic measurements of soil C include permanganate oxidizable C (POX-C) and dissolved C and N (DOC, DON). The POX-C pool of soil C is a highly active and labile pool of C that is known to be sensitive to management changes due to its accessibility to soil microbes, and thus likely to be a predictor of long-term soil C storage. Because microbial growth and activity strongly mediate nutrient cycling and either accumulation or degradation of soil C, we will measure microbial biomass, microbial enzyme activities (decomposition potential), and soil respiration, to determine soil C gains and losses of CO2 to the atmosphere.Soil physical properties: Soil infiltration, aggregate size, and stability are important physical properties that mediate C dynamics. These metrics will be measured in spring of year 1 and fall of year 3 of the study using the methods advised by the NRCS (Soil Quality Institute, 2001). We will also measure soil bulk density using the core method (Blake and Hartge, 1986) at the beginning and end of the study in each transition system in order to express soil C on a mass basis.Statistical analysis: Data will be analyzed using suitable modern parametric and non-parametric methods based on the distributions they follow. Most response variables will be analyzed by location. When appropriate, location will be treated as a fixed effect and tested alone and as an interaction with treatments to determine if treatments affect soil and yield variables similarly across locations. In response to the American Statistical Association's recent published statement on the use of P-values (Wasserstein and Lazar, 2016), we will use a combination of confidence and prediction intervals, in conjunction with P-values, to determine statistical significance of our University of Minnesota Project findings. A priori comparisons of yields across treatments will be made using analysis of variance within years. For example, we will compare IWG grain yields in transition system 1 and 2 for each year to test the effect of alfalfa on IWG grain yield. Yield data will also be used in economic analyses.Soil data analysis: Some soil variables - such as total organic C, bulk density, particle size distribution, and mineral concentrations - will be measured once in the beginning of each transition system and once at the end. We will compare the change in these variables across transition treatments to account for any initial spatial variation. Other soil data - such as POX-C, microbial C, and root biomass, will be measured annually. Comparisons will be made both within and between years among treatments using analysis of variance. We will test for time related trends in annually measured variables within each treatment using time-series analyses, with methods that account for potential autocorrelation in both space and time.Crop enterprise budgets: To aid in producers' financial understanding of the rotation treatments we are comparing, we will create crop enterprise budgets using the recommended standard practices for generating costs and returns estimates (American Agricultural Economics Association Task Force, 2000). Crop enterprise budgets include revenue (product revenue and government payments) and costs (seed, organic fertilizer, machinery operation costs, labor, management, rent and insurance) to generate net returns per acre (Lazarus, 2015; Chase and Delate, 2015).