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

View the project final report

• 2006 annual report
• 2007 annual report

Commodities

• Agronomic: potatoes
• Vegetables: sweet potatoes, beans, broccoli, cabbages, eggplant, garlic, greens (leafy), onions, peas (culinary), peppers, sweet corn, tomatoes
• Additional Plants: herbs, ornamentals

Practices

• Crop Production: agroforestry, nutrient cycling, organic fertilizers
• Education and Training: extension, networking, on-farm/ranch research, participatory research
• Natural Resources/Environment: hedgerows, hedges - woody
• Soil Management: green manures, organic matter

Building soil organic matter (SOM) is critical for organic farmers, particularly in the Southeast where the hot, humid climate results in rapid SOM decomposition. Annual cover cropping is becoming more common as a way to build up SOM and its associated nutrients. However, winter cover crops alone are usually insufficient to supply the nutrients needed throughout the summer growing season. Additional amendments are needed, but they can be very expensive to buy or logistically difficult to process. For several years, the Agroecology Lab of the Univ. of Georgia has been experimenting with perennial legumes as a source of organic matter and nitrogen in an organic farming system. The legumes are planted in hedgerows, 4 meters apart, and the crop is planted in the “alley” between the hedges. The hedges are pruned regularly during the growing season. Results have shown an increase in soil N and P available to the crop growing in the alley. We hypothesize that root sloughing caused by a physiological imbalance following pruning results in a major nutrient and organic matter input into the cropping system. An alley cropping system may be particularly beneficial in restoring degraded or fallow fields by providing a nutrient primer, while allowing the hedges proper time to be established. Once the hedges are established and cropping begins or is renewed, the hedges supply nutrients and organic matter to the soil. Of the several perennial legumes that we have investigated, Amorpha fruticosa (false indigo) has proven preferable. It is native to Eastern U.S.; its structure is that of a shrub; it sprouts prolifically; the stems are slight, and when pruned do not interfere with cultivation operations.The objectives of this project are: to evaluate a strategy of soil organic management for organic farming systems that includes perennial leguminous shrubs in an alley cropping system as a sustainable source of nutrients; to analyze the contribution of root sloughing to soil organic matter and nutrient concentration; to develop an outreach component that will critically assess current management approaches, establish on-farm trials, disseminate research results, provide feedback to researchers, and conduct workshops and internships.Field experiments will compare total crop yield, and soil physical and chemical properties in an alley cropping system with a system that relies on traditional inputs (composts and green manures) for nutrients. The contribution of root sloughing to soil fertility in an alley cropping system will be quantified with stable isotopes. To develop an outreach and education component, the Agroecology Lab has enlisted five commercial organic growers as an advisory group for a proposed network of organic farmers. Georgia Organics, the umbrella organization for organic farmers in Georgia, will cooperate in forming this network, and sponsor workshops for intensive discussions and feedback on techniques of organic matter management. The proposed research and outreach will significantly enhance current education activities, which include annual visits of over 1500 University of Georgia and regional students, an intensive ecological agricultural field course, a seasonal internship program, and grower workshops.

1. Research Objectives 1. 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. 2. To measure the time and effort needed to manage the two systems. 3. To determine whether pruning of above ground biomass of a perennial legume causes an increase in root sloughing, and if so, to quantify the contribution of root sloughing to soil organic matter and nitrogen. Outreach and Educational Objectives: 1. To develop an outreach component that will disseminate research results, establish on-farm trials, conduct workshops and internships, and provide feedback to researchers; 2. To continue, expand, and integrate the Agroecology Lab's current educational program for undergraduates and graduate students into the outreach program. Performance Targets To assess and develop viable strategies to restore SOM to degraded agricultural lands throughout the region in a socially attractive and financially viable manner. Specifically, we will: assess the viability of a theoretically sustainable organic vegetable production system that is specifically designed to meet the management challenges facing growers in the Southeast; refine its application on working organic farms; research the ecological mechanisms underlying the sustainable system; share our results on a regional basis; obtain feedback from growers as to the extent that perennial legumes, winter cover crops, conservation tillage, and other techniques can help them solve their organic matter management challenges. Outreach programs will be a two-way street, through which the Agroecology Lab and Georgia Organics will obtain feedback as to success of the program and guidance as to which direction future research should take, and how to improve the effectiveness of the outreach program.