Developing Soil Fertility Systems for Urban Agriculture in the Upper Midwest

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2012: $7,239.00
Projected End Date: 12/31/2013
Region: North Central
State: Minnesota
Project Coordinator:
Alexander Liebman
Stone's Throw Urban Farm

Annual Reports


  • Vegetables: broccoli, greens (leafy), peppers, tomatoes


  • Crop Production: cover crops, intercropping, nutrient cycling, organic fertilizers
  • Education and Training: demonstration, networking, on-farm/ranch research
  • Farm Business Management: budgets/cost and returns, agricultural finance
  • Production Systems: agroecosystems
  • Soil Management: green manures, organic matter, soil analysis, soil microbiology, soil quality/health
  • Sustainable Communities: local and regional food systems, urban agriculture

    Proposal summary:

    Urban farming faces significant challenges in developing soil fertility due to initial
    degraded soil quality, years of neglect and mismanagement, and intense weed pressure.
    Conversion of vacant lots frequently requires significant inputs to raise soil organic
    matter levels, stimulate beneficial microorganisms, and improve soil structure and
    aggregate stability. Due to spatial constraints it is often quite challenging to integrate
    an adequate cover-cropping regime to adequately maintain and develop the soil. Urban
    farming land is at a premium and the costs of experimentation are quite high. Also,
    on-site food waste composting and animal integration at a level needed to significantly
    enhance fertility is prohibited under local regulation. In addition, the transport of
    food waste in Minnesota needed to produce significant amounts of compost is strictly
    regulated. Therefore, we believe cover cropping must play a vital role in long-term
    soil fertility. Other SARE recipients have addressed the profitability of urban farming
    in general (Susana Moua, grant FNC08-704), but have not addressed the soil biology
    barriers specific to transforming degraded urban land into space capable of production
    agriculture. We believe this is an intrinsic part of developing urban farm systems that are
    profitable over the long-term.

    This experiment will evaluate the interactive effects of several cover crops and compost
    application upon soil health, crop yield, and farm economics in degraded urban soils.
    We seek to develop a small-scale cover-cropping regime that will be directly applicable
    to urban farming. This process will require management systems that function across

    highly variable soil qualities and the use of plant varieties that operate effectively as
    intercrops or short-season annuals. We seek to develop fertility systems that will create
    healthy, productive soils to ensure long-term ecological health and financial success for
    our operation. We will explore the optimal ways to simultaneously increase soil fertility
    and crop yield in low-input urban farming systems. Despite large start-up challenges,
    urban agriculture presents a unique opportunity to develop productive cropping systems
    on marginalized land in immediate proximity to population centers. Urban farming
    is especially apt to develop profitably due to market proximity and increased market
    preference for food grown locally with non-synthetic inputs. Also, farming in highly
    trafficked areas ensures ample opportunities for education across a wide breadth of socio-
    economic, racial, cultural, and educational backgrounds.

    The development of sustainable practices in urban farming can be extrapolated to rural
    market gardens, school gardens, food production on marginalized land and low-input
    agriculture in general. Many city centers throughout the Upper Midwest face problems
    with food insecurity and decentralized land use including Cleveland, Milwaukee,
    and Detroit. Urban farming projects in these cities will benefit greatly from better
    understanding of urban soil fertility improvement. Youth education regarding local
    food has burgeoned recently and knowledge from our experiment could be used to help
    maintain and develop school gardens. Our research to discover economically efficient
    and ecologically necessary methods for long-term soil fertility in small, marginalized
    lands across a variety of soil types will help rejuvenate vacant areas throughout the

    Midwest, helping to turn them into food-producing places. Pockets of plant biodiversity
    provide habitat for bird and insects amidst large segments of paved space. Lastly, as
    population levels continue to rise, increasing the demands placed upon agricultural lands,
    developing methods for long-term, sustainable food production on marginal lands will
    become increasingly important.

    Project objectives from proposal:

    Cover cropping is a main component of soil fertility yet is difficult to incorporate into
    crop rotations due to the spatial and temporal constraints of urban farming. Available
    land can rarely be devoted solely to cover cropping, as we must constantly maximize
    food production. To achieve this goal, our farm often plants three or four succession
    crops during the season. Depending on the timing of frost, it may be difficult to
    establish cover crops late in the season, posing an additional financial risk. However, we
    understand that over the long-term soil fertility maintenance and improvement is vital
    to achieving high yields and healthy plants. Therefore it is essential that urban farms
    accurately assess the efficacy of cover cropping as part of their overall fertility plans.
    We will experiment with three legume-grass and sole legume plantings that we hope
    will improve soil organic matter, fix atmospheric nitrogen, and decrease soil erosion
    during the late fall, winter, and early spring. All cover crop effects will be compared
    to a sole compost and compost + cover crop trial. As composting is a common method
    for our farm and the majority of other small scale, especially urban, operations it is
    important to measure if cover cropping can replace or enhance the effects of compost.
    Metrics for evaluation will be: succeeding cash crop yield, amount of nitrogen and cover
    crop biomass produced, change in soil bulk density, soil organic matter and available
    nutrients, and seed and establishment cost. All legume species will be inoculated with
    Rhizobia bacteria following standard agronomic procedures.

    We will compare oats/peas, hairy vetch/rye, and red clover as late-season cover crops
    sown after harvest of the main crop. We will test levels of nitrogen fixation and soil
    improvement by soil testing in the fall (between harvest and cover-crop planting) and
    spring (before spring planting). Oats/peas and hairy vetch/rye are two comparable

    legume-grass mixtures planted in crop rotations throughout the Upper Midwest. Peas
    and vetch fix comparable amounts of nitrogen, 90-150 lbs N/A and 90-200 lbs N/A,
    respectively (SARE, Managing Cover Crops Profitably, 3rd Edition, 2007). Red clover
    is a commonly used legume, fixing up to 110 lbs. N/A (Penn State, Using Organic
    Nutrient Souces, online PDF, 2009). It overwinters, maturing the following June. Oats/
    peas winter kill while hairy vetch/rye commonly overwinter. This may lead to variable
    conditions for spring planting. Therefore, in addition to the metrics described above, we
    will document ease of planting among the three systems. Despite significant research and
    usage of these cover crops, their viability and impact in urban farming systems is, to our
    knowledge, unknown.

    We will plant 81 100’ beds in this experiment. 18 beds each will be planted into hairy
    vetch/rye, oats/peas and red clover. ½ these beds will receive compost in addition to
    cover crop. The beds will be subdivided into 3 crop groups the following spring: brassica
    transplants, salad greens mix, and nightshade transplants. We picked these three crop
    divisions because they have different cultural and nutrient specifications. Therefore
    they will provide us with a nuanced understanding of the impact of our soil management
    techniques. Cover crops will be planted fall 2012 and succeeding cash crops planted
    spring 2013. Lastly, compost will be applied to 27 100' beds in fall without cover crop.
    These will also be subsequently planted with each of the succeeding crop varieties.
    These 27 beds will serve as an experimental control.

    We will use several parameters to assess our project’s results.

    1. We will employ soil tests to evaluate the effect of cover cropping and its
    interactions with compost application on soil organic matter, soil nitrogen levels,
    available nutrients and pH. We will take soil samples before and after compost
    application and cover crop trials for proper comparison. Replicates of treatments
    will be pooled into a single soil test to account for differences in original soil

    2. Cover crop biomass will be compared among all treatments. Procedure will
    follow protocol in Managing Cover Crops Profitably, SARE, 3rd Edition:
    Yield (lb.)/Acre = Total weight of dried samples (lb.) / # square feet sampled x
    (43560 sq ft./1 acre)
    In addition to data received from soil samples, % N in cover crop biomass will also
    be calculated.

    3. We will measure yield for all crops succeeding cover crops. Yields, measured in
    pounds, will be compared among all treatments.

    4. We will measure soil bulk density before and after cover cropping. As soil
    organic matter content may not change over the short duration of the experiment,
    tracking density changes will be an important marker of cover crop success. As
    compaction is a severe problem in urban soils, a decrease in soil bulk density
    will indicate that cover-cropping methods have increased pore space thereby
    improving water movement, root penetration, and seedling germination. We will
    use USDA methods (Soil Quality Test Kit Guide, Chapter 4,
    assessment/files/chpt4.pdf) for determining soil bulk density.

    5. We will document ease of planting and residue breakdown among treatments.
    This will be most important in discerning the importance of winterkill cover
    crops. This will be recorded qualitatively.

    6. We will keep a photographic journal to track cover-crop germination, growth, and
    disease and/or insect pressures.

    7. We will conduct financial analyses to determine the economic feasibility of these
    practices. Yield increases will be compared to implementation and maintenance
    cost of cover cropping. Costs will include labor, seeds, and the opportunity cost
    of foregoing planting the same space into a late fall or early spring cash crop.

    8. Adoption of our techniques by other urban and small-scale vegetable growers
    throughout the Upper Midwest will signal that our project has contributed to the
    larger sustainable agriculture community.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.