Perennial legumes as a sustainable source of soil organic matter in Southeastern organic farming systems

Perennial legumes as a sustainable source of soil organic matter in Southeastern organic farming systems

Summary

Field plots: There was no significant difference in soil carbon between alley cropped plots (plots with leguminous hedgerows) and plots without hedgerows. However, soil nitrogen was higher in the plots with hedgerows.

Pot experiment: 160 seedlings of Amorpha fruticosa were potted and labeled with 13C and 15N in June, 2007. Half were periodically pruned, and soil and plant samples were taken through the spring of 2008.

Outreach: A workshop entitled “Managing the Southeastern Organic Farm: Establishing Priorities for an Organics Research and Development Program”was held as part of the Georgia Organics annual conference at Dalton, Georgia, on Feb. 29th, 2008.

Objectives/Performance Targets

Field plots objective: To compare crop yield, soil organic matter, and soil properties of an alley cropping system plus winter cover crops with a more conventional organic farming system that uses composts plus winter cover crops but no perennial leguminous shrubs, and to measure the time and effort needed to manage the two systems.

Pot experiment objective: To determine whether pruning of above ground biomass of a perennial legume causes an increase in root sloughing, and if so, to use 13C and 15N to quantify the contribution of root sloughing to soil organic matter and nitrogen.

Outreach objective: To develop an outreach component that will disseminate research results, establish on-farm trials, conduct workshops and internships, and provide feedback to researchers; To continue, expand, and integrate the Agroecology Lab’s current educational program for undergraduates and graduate students into the outreach program.

Field Plots: Trials were carried out to test the effectiveness of perennial legumes in an alley cropping system to supply nutrients to crops compared with other organic and conventional systems of cultivation. In 2006, three varieties of chili peppers were grown, and in 2007, a combination of corn and squash was used.
Alley cropping alone was not sufficient to maintain soil C levels over the 0-15 cm soil depth, but addition of compost at 10 tons/ha was sufficient to maintain soil total C, while semi-annual additions of 10 tons/ha (total 20 tons/ha/y) slightly increased soil total C. ). Alley cropping without additional compost maintained total soil N, and with the addition of composts, increased soil %N slightly, from .1% N to .2% N at 0-5cm depths. In the plots without alley cropping, treatments receiving no compost additions decreased in soil N, whereas those with compost additions increased slightly in soil N.
There was no difference in soil physical properties between plots.
Analysis still pending: NH4/NO3 from 0-30 cm (mineral N remaining after cover crop and summer crop seasons); Microbial biomass in 0-5 and 0-20 cm soil depths in winter and spring; Yields.

Pot experiment: Trials conducted in the summer and fall of 2006 were carried out to determine the most effective technique for isotopic enrichment of plants. In January of 2007, 160 seedlings, 1.8 years old were transplanted to 5 gallon pots occurred. In June, 2007 these plants were prepared for labeling by covering the soil with plastic to prevent direct contact of soil with the label solution. Plants were kept in hoop houses that were kept closed for the 24 h immediately after spraying but otherwise were kept open. Dual labeling (13C and 15N) started on June 7. Labeling was done by spraying the leaves with a urea solution prepared by dissolving 2 g 99 atom % 13C urea and 4 g 99 atom % 15N per liter of D.I. water. Plants were sprayed every 7 days for 9 weeks. Control unlabeled plants were also sprayed with non-enriched urea solution of equal concentration. On August 3rd, after the final spraying, half of the plants were pruned. Pruning was repeated on September 6 and November 3. A set of unlabeled control pots was only pruned one time. Beginning on August 14th we destructively sampled 5 replicate pots of each treatment twice after first pruning, twice after the second pruning and once after the third pruning. Destructive sampling involved separating the soil from the plant material. Plant material from each pot was separated into roots, leaves and stems, freeze-dried and weighed. Soil was homogenized and a sample was collected to be processed within 24 h for dissolved carbon and microbial biomass carbon and nitrogen by chloroform fumigation extraction in K2SO4. Remaining soil was freeze-dried within 24 h of collection. Liquid extracts have been sent for isotopic analysis of C. For obtaining nitrogen isotopic ratios, an aliquot of the liquid extracts was digested through persulfate oxidation to convert all forms of nitrogen into nitrate. Digested and undigested extracts were subjected to a diffusion method to capture nitrate in solution into acidified glass fiber disks and have been sent for analysis.

Pending tasks:
The last two destructive samplings to be carried out in late February and late March.
An assessment of the ratio of death to live roots in plants that have never been pruned, plants pruned only once and plants pruned three times will be carried out in April 2008.
Once all sampling dates have occurred we will plant rye seeds in re-hydrated freeze-dried soils from the seven sampling dates and from pruned and unpruned plants. Rye plants will be collected two and three weeks after planting and analyzed for isotopic enrichment levels.

Outreach:
On Feb. 29th, 2008. a workshop entitled “Managing the Southeastern Organic Farm: Establishing Priorities for a UGA/Georgia Organics Research and Development Program” was held as part of the Georgia Organics annual conference at Dalton, Georgia
There were about 40 participants divided into four focus groups: researchers, extension agents, and two groups of experienced organic farmers. Their objective was to conduct a strategic assessment of the needs of organic farmers, and produce a prioritized list of recommendations that will be the basis of a program for a regional Program for Organic Agriculture with integrated capabilities of research, education, and outreach. Each group first came up with their own list of priorities, and in a second round, results from each group were pooled into a list of top five priorities.
The top five were: Place-based research (research specific to the problems of Georgia organic growers);Establishing regulations that would permit small scale farmers to legally process fruit, vegetables, and animal products; Developing of new organic markets, organic products, and packaging for organic products; Increasing net profit, determining the most profitable crops, and demonstrating profitability of organic versus conventional agriculture; Improving methods for soil building and increasing soil fertility.
During the past year, a website (www.springvalleyecofarms.org) was established in part to publicize the results of research and outreach sponsored by SARE. An article on the Georgia Organics workshop appears in the Home Page, while more detailed reports on the field and pot experiments are given on the Site Projects page.

Accomplishments/Milestones

Field Plots: Trials were carried out to test the effectiveness of perennial legumes in an alley cropping system to supply nutrients to crops compared with other organic and conventional systems of cultivation. In 2006, three varieties of chili peppers were grown, and in 2007, a combination of corn and squash was used.
Alley cropping alone was not sufficient to maintain soil C levels over the 0-15 cm soil depth, but addition of compost at 10 tons/ha was sufficient to maintain soil total C, while semi-annual additions of 10 tons/ha (total 20 tons/ha/y) slightly increased soil total C. ). Alley cropping without additional compost maintained total soil N, and with the addition of composts, increased soil %N slightly, from .1% N to .2% N at 0-5cm depths. In the plots without alley cropping, treatments receiving no compost additions decreased in soil N, whereas those with compost additions increased slightly in soil N.
There was no difference in soil physical properties between plots.
Analysis still pending: NH4/NO3 from 0-30 cm (mineral N remaining after cover crop and summer crop seasons); Microbial biomass in 0-5 and 0-20 cm soil depths in winter and spring; Yields.

Pot experiment: Trials conducted in the summer and fall of 2006 were carried out to determine the most effective technique for isotopic enrichment of plants. In January of 2007, 160 seedlings, 1.8 years old were transplanted to 5 gallon pots occurred. In June, 2007 these plants were prepared for labeling by covering the soil with plastic to prevent direct contact of soil with the label solution. Plants were kept in hoop houses that were kept closed for the 24 h immediately after spraying but otherwise were kept open. Dual labeling (13C and 15N) started on June 7. Labeling was done by spraying the leaves with a urea solution prepared by dissolving 2 g 99 atom % 13C urea and 4 g 99 atom % 15N per liter of D.I. water. Plants were sprayed every 7 days for 9 weeks. Control unlabeled plants were also sprayed with non-enriched urea solution of equal concentration. On August 3rd, after the final spraying, half of the plants were pruned. Pruning was repeated on September 6 and November 3. A set of unlabeled control pots was only pruned one time. Beginning on August 14th we destructively sampled 5 replicate pots of each treatment twice after first pruning, twice after the second pruning and once after the third pruning. Destructive sampling involved separating the soil from the plant material. Plant material from each pot was separated into roots, leaves and stems, freeze-dried and weighed. Soil was homogenized and a sample was collected to be processed within 24 h for dissolved carbon and microbial biomass carbon and nitrogen by chloroform fumigation extraction in K2SO4. Remaining soil was freeze-dried within 24 h of collection. Liquid extracts have been sent for isotopic analysis of C. For obtaining nitrogen isotopic ratios, an aliquot of the liquid extracts was digested through persulfate oxidation to convert all forms of nitrogen into nitrate. Digested and undigested extracts were subjected to a diffusion method to capture nitrate in solution into acidified glass fiber disks and have been sent for analysis.

Pending tasks:
The last two destructive samplings to be carried out in late February and late March.
An assessment of the ratio of death to live roots in plants that have never been pruned, plants pruned only once and plants pruned three times will be carried out in April 2008.
Once all sampling dates have occurred we will plant rye seeds in re-hydrated freeze-dried soils from the seven sampling dates and from pruned and unpruned plants. Rye plants will be collected two and three weeks after planting and analyzed for isotopic enrichment levels.

Outreach:
On Feb. 29th, 2008. a workshop entitled “Managing the Southeastern Organic Farm: Establishing Priorities for a UGA/Georgia Organics Research and Development Program” was held as part of the Georgia Organics annual conference at Dalton, Georgia
There were about 40 participants divided into four focus groups: researchers, extension agents, and two groups of experienced organic farmers. Their objective was to conduct a strategic assessment of the needs of organic farmers, and produce a prioritized list of recommendations that will be the basis of a program for a regional Program for Organic Agriculture with integrated capabilities of research, education, and outreach. Each group first came up with their own list of priorities, and in a second round, results from each group were pooled into a list of top five priorities.
The top five were: Place-based research (research specific to the problems of Georgia organic growers);Establishing regulations that would permit small scale farmers to legally process fruit, vegetables, and animal products; Developing of new organic markets, organic products, and packaging for organic products; Increasing net profit, determining the most profitable crops, and demonstrating profitability of organic versus conventional agriculture; Improving methods for soil building and increasing soil fertility.
During the past year, a website (www.springvalleyecofarms.org) was established in part to publicize the results of research and outreach sponsored by SARE. An article on the Georgia Organics workshop appears in the Home Page, while more detailed reports on the field and pot experiments are given on the Site Projects page.

Impacts and Contributions/Outcomes

Spring Valley Farm (the site where the SARE project is being conducted) continues to host over 1500 undergraduate students per year from the Athens and Gwinnett campuses of the Univ. of Georgia, as well as the Watkinsville campus of Gainesville State College. These students carry out lab exercises in which they learn more about organic agriculture.
Spring Valley Farm is the site of the Univ. of Georgia accredited course in Organic Agriculture, given each May to about 20 students. Several of the students in the course have become interns at “Full Moon Farm”, the commercial organic farm that comprises part of the Spring Valley research farm. The course is also part of the new UGA program in “Certificate in Organic Agriculture”.
Examples of other groups that also visited the farm include those from the State Botanical Garden, the Univ. of Georgia’s Environmental Ethics Certificate Program, and the “Outstanding in the Field” Program to honor chefs specializing in organic preparations.
An article featuring the educational work at Spring Valley Ecofarms was published in the Spring edition of Georgia Magazine, an official publication of the University of Georgia. A link to the article appears in the Spring Valley Ecofarms website (in the news).
A summary of the workshop held in conjunction with the Georgia Organics conference is available at the Spring Valley website (www.springvalleyecofarms.org)

Collaborators: