Nutrient Recycling in Urban Agriculture

Nutrient Recycling in Urban Agriculture

Summary

The Re-Vision Urban Agriculture Project is using SARE funds to support a project that demonstrates two systems that recycle nutrients for enhanced energy efficient plant production: 1) compost heating and enrichment of soil for off-season, greenhouse production of mesclun salad mix, seedlings and other crops; 2) aquaponic plant production that links bio-filtration of fish wastes from a recirculating Tilapia system to nutrient-rich, hydroponic basil production. Both of these technologies serve growers who need to maximize production and income in limited space and who want to recycle on-farm waste products for sustainable cropping. Compost heating and enrichment systems as well as integrated aquaponic systems will be evaluated at Re-Vision Urban Farm and at additional sites that will be added during the three-year project period.

Objectives/Performance Targets

• Compost Heating Systems will be operational at Re-Vision Urban Farm and at 5 other sites in MA during the 3-year period.

  An Integrated Aquaponic System will be operational at Re-Vision House to produce fish and plants for sale through nutrient recycling/plant filtration. Aquaponic systems at 2-4 other sites will come on-line by the end of the project period.

  Four to six women from Re-Vision House will be trained annually in aquaculture, aquaponics and greenhouse production. They will gain research skills and work experience by collecting and analyzing data from the compost and aquaponic systems and by producing and marketing crops.

  Extension and technical assistance will be provided to other groups and individuals through workshops, site visits and a project website.

Accomplishments/Milestones

1. Bruce Fulford, of City Soil & Greenhouse, has been working with Re-Vision Urban Farm to manage the compost system on site and to monitor heat and CO2 output in the greenhouse growing beds. During December of 2003 a 16”x 40”plastic hoop-house greenhouse was constructed to house the compost pile. This compost greenhouse is designed to improve heat generation from the decomposition of organic materials and minimize heat loss during the cold winter months. The heating system insures that losses of odor and nutrients are controlled using passive and forced air biofiltration. In addition, the new greenhouse increases year-round growing capacity, as cold tolerant crops, such as spinach and lettuces, can be grown directly in a soil layer on top of the compost pile while benefiting from a heated root zone and heat escaping into the air. In the winter of 2004, organic materials were brought in late, as we were waiting for the greenhouse to be completed and for access to raw organic materials for composting. It was late February by the time materials were brought in and the system was operational. The compost pile contained a mix of horse manure from the park stables and leaves from Franklin Park. Although air temperatures were not as severe, we were able to monitor temperatures in the two growing beds in the original greenhouse for a couple months and have good comparison data. We also were able to plant a crop of spinach on the top of the compost pile and utilize the warm space for seedling production.
   This winter (2005) we should have more compost heat during the coldest months, when the plants can benefit most and we will be less reliant on our back-up gas heating system. In late November, 2004, compost produced in the aerated static pile in RHI’s 800 square foot composting enclosure was unloaded and 140 cubic yards of blended manure and leaves was brought in. Leaves, horse manure and bedding from Boston’s waste stream were mixed prior to delivery to ReVision’s composting enclosure. We focused on optimizing moisture in the incoming material and will investigate delivery systems for supplemental moisture during the composting process. Over the winter months we will track temperature data and CO2 levels, along with labor and equipment costs associated with materials handling and ongoing operations. In both 2004 and 2005, heat from the pile is transferred to the growing beds in the first greenhouse through pipes running from the center of the pile into the greenhouse, and then moved by a blower through two pipes running 18 inches under the soil surface in the growing beds. To evaluate the system, we disconnected the pipes in one of the beds and monitored soil temperatures and plant production in the two, side-by-side beds. The results of the 2004 data are provided in the outcomes section of this report.
   Compost projects initiated by Bruce Fulford at three other sites in 2004 are described below:
   Seeds of Solidarity Farm Orange, MA- Bruce Fulford met with nearby dairy farmers to coordinate blend ratios, equipment use, and plan delivery of late winter heating supply of manure, bedding and leaves. Solar (photovoltaic) powered blower will be used for the air delivery system that moves compost heat and CO2 to the greenhouse beds from a compost pad 30 feet away. The PV system, inverter and battery bank are functional and a new in-line blower has been selected. The insulated subterranean air delivery system will be installed in January of 2005.
   Massachusetts Audubon Society’s Drumlin Farm. Lincoln, MA- Drumlin Farm plans to proceed this winter and spring with an improved manure management system for the demonstration and educational farm’s livestock manure. The biothermal heating system for seedling production will utilize manure and bedding from poultry, sheep and cows which will be stored under cover to prevent leaching and runoff..
   Yale University, New Haven CT- There are now conceptual and schematic drafts of a compost heated, biofiltration greenhouse that would be integrated into a proposed composting facility. The facility would compost food waste and manure from Yale University’s Sustainable Food Program, landscape maintenance, and equine facilities. The University is addressing site permitting requirements prior to moving forward with facility development.
   VanGaurden CSA, Dover, MA- The farm is planning for winter and spring composting in tunnels and cropping in a thin soil layer on top of compost. The farmer will be making passive composting piles/growing beds of locally produced leaves, poultry and horse manure with bedding.

   Integrated aquaponic production continues at Re-Vision House, although we have faced endless challenges in producing fish for sale. Last winter a number of different integrated systems were operational and although the fish were problematic, due to a wide range of variables that are hard to control, the plants thrived in all of the systems we tested. .Basil was grown in two systems that connect the fingerling tanks (2 shallow tanks holding 500, 1-3” fish each) in the second floor greenhouse to aquaponic plant production (500 basil plants growing in organic media sitting in either shallow tubes or floating on rafts) in the third floor greenhouse. This system seemed to function well- in 2004 we grew 2,500 fingerlings to 3” size (gave away half of those) and harvested approximately 100 lbs of basil (most of which was processed into pesto). In the first floor greenhouse, three 420 gal. tanks, which hold 250 fish each, from fingerling size to harvest at 1 lb weight, were not connected to hydroponic systems, but did have basil plants (about 100) growing on top of the tanks on floating rafts. Water in these three tanks was circulated through a rotary drum filter and bio-filter before returning to the fish tanks. Unfortunately, we experienced major fish loss in these tanks due mostly to electrical (power going off) and mechanical (drum filter breaking down and working inconsistently) problems. If nothing else, aquaculture and aquaponics has been a huge learning experience for us and a test of our perseverance. It is an evolutionary process that hopefully will lead to a balanced, healthy and reliable aquaponic system. In the latest incarnation, we have rebuilt the first floor systems to follow the design used by Growing Power in Milwaukee, Wisconsin. This more low-tech, and less energy dependent system should better reflect the needs and capacity of a grassroots project and women’s shelter such as ours, and many others who might want to duplicate this food production model. This fall, with support from Heifer Project International, and the help of a team of volunteers, we built two systems that connect two of the first floor tanks to three-level structures. The wooden structures have biofiltration on the bottom and plants growing on the next two levels. The water from the fish tanks moves via gravity into the bio-filter (a plastic-lined trough filled with bio-balls) and is pumped from there to two levels of shallow trays where plants grow in porous pots that sit in the shallow water. The water moves through the trays and falls back into the tanks, adding oxygen to the fish water as it does. These two systems should be up and running and productive in 2005. We did not alter the integrated system on the second and third floors, since it works well, but we have eliminated one of the two systems in an effort to downsize a bit, emphasize plant production, lessen energy input and mechanical dependence and increase self-reliance. Hopefully, by the end of the project period, next fall, we will have good data, good news and valuable expertise to share with the SARE program and others.

   The internship program in the Re-Vision Urban Agriculture Project has been on-going through the project period. In 2004, ten (2-4 at a time) women from the shelter participated in the project as interns, working 20 hours per week in the agriculture and aquaculture programs. Most of these women worked from 3 to 6 months, but one woman has been working with us more than a year and another has continued to work with the agriculture project even after leaving the shelter. During the internship these women became proficient in many areas of fish and plant care as they gain a general understanding of and appreciation for the ecological processes affecting growth and system health. Each group of interns receives training in the compost heat and aquaponic systems and they then have monitoring duties related to both SARE projects at Re-Vision Farm. These include collecting temperature data for the compost heat system- recording daily temperatures in the compost pile and in the growing beds. They also do water quality testing (measuring o2 and nutrient levels along with bio-organisms in the fish tanks, plant beds and biofilters) at various points in the aquaponic system. This fall, the interns were very involved in creating the first-floor, integrated systems, from design through construction, and therefore they have a more complete understanding of how they work, how to troubleshoot them and how to maintain them.

   Numerous outreach activities have been undertaken by project staff and collaborators. A major accomplishment for Re-Vision Urban Farm was the creation of a website (www.re-visionfarm.org) where we can reach and network with many organizations and individuals. The farm also had many groups and individual visitors come to tour, learn and volunteer at the farm, including the NOFA Garden Tour, the Urban Agriculture Conference organized by the Food Project and the Heifer Project Fall Training. Project staff members also gave talks at the Community Food Security Conference, at community gardens, and at community organizations. We also exchanged ideas with interested individuals through e-mails, list-serves and the web. Bruce Fulford attended Meetings on site with one of the largest composters in Vermont (Adam Sherman of Intervale Compost).He was a speaker at the MIT Sustainable Design Conference, Cambridge MA (October 2004) focusing on urban watershed protection and nutrient management strategies. He also developed draft designs for compost-greenhouses on Massachusetts farms in Lee MA., and has had ongoing discussions with a NY state composter for possible application of large scale greenhouse enrichment and heating systems.

Impacts and Contributions/Outcomes

Temperature data was collected for the compost heating system at Re-Vision House for two months- from the beginning of March, 2004, just after the compost pile was made, through April, 2004. Temperatures were taken every morning in 4 spots in the compost pile and 3 locations along the length of each of the two growing beds (one with compost heat under the soil and one without). Outside and inside air temperatures were also recorded, along with the max and min temperature for the day. Since the coldest part of winter was behind us at that point, air temperatures averaged in the low 40s, but ranged from 22 to 60 degrees at 8 am. We found that the compost pile maintained a temperature (taken at 3’ below the top surface) above 100 degrees for the entire two month period. There was some variation over time and also between the front and back of the pile. Generally the front of the pile was warmer than the back by 20 to 30 degrees. The difference between the two spots was small at the onset, but grew wider over time, so that by the second month (April) the back of the compost pile was well below 100 degrees, about 70, while the front section was well above 100 degrees, at about 110 degrees. Over time the readings also dropped. Temperatures were about 137 degrees soon after the organic material was brought in, were generally between 115-120 degrees by the end of March, and remained at about 110 in the warmer part of the pile through the month of April. Inside the hoop house, where soil temperatures were measured in both growing beds, we found consistently higher soil temperatures (taken 6-8 inches below the surface) in the bed with the compost heat. It seemed to take a week or two from the time we started taking the temperatures and recording data until we saw some variation between the two beds, but from about March 7 on, there was about a 5 degree difference between the soil temperatures in the heated and unheated beds. Again, I believe the impact of the compost heat would have been more dramatic if the air temperatures had been colder because on colder (20 degrees to freezing) mornings, or periods of cold, the compost bed was significantly warmer. Soil temperatures in the unheated bed were generally in the lower 50s, while temperatures in the heated bed were in the upper 50s to lower 60s. The average difference between the two beds was about 5 degrees, but it was interesting to note that the growing bed with heat was significantly warmer at the end nearer to the blower, and soil temperatures grew cooler as you moved towards the other end. This variation was not evident in the unheated bed. Comparing temperatures in the middle of each bed, you find readings mostly between 52 and 54 degrees in the unheated bed and 58 to 60 degrees in the heated bed. This difference is greatest at the beginning of the period and seems to disappear by the second month (April). Since compost temperatures remained reasonably consistent, it is possible that mechanical failure was responsible. In 2005 we will be able to collect temperature data in January and February and compare this data with that collected last year. We have also made some modifications the compost materials and compost management which might result is greater heat and co2 generation, which, in turn, would translate into better plant growth. This year we will also collect nutrient data from the aquaponic systems at Re-Vision House, so we should have more outcomes to report on nutrient levels and plant/fish production in our final report.

Collaborators: