Economic and Environmental effects of Compost use for Sustainable Vegetable Production

Economic and Environmental effects of Compost use for Sustainable Vegetable Production

Summary

A comparison of the agronomic, economic and environmental effects of compost, poultry litter, and inorganic fertilizers on three organic farms demonstrated that soil chemical and physical properties, but not crop yields, were improved with agronomic rates of compost compared with low rates of compost, poultry litter or fertilizer. Accurately estimating nitrogen availability, not the source of nitrogen, was most critical to preventing groundwater contamination by nitrate-N.

Objectives/Performance Targets

The value of compost in improving soil properties and supplying plant nutrients has been documented, but transitional and conventional farmers are hesitant to substitute compost for inorganic fertilizers or manures because the agronomic and economic benefits have not been well quantified. The value of using compost may be further enhanced if environmental advantages over commercial fertilizer and manure can be demonstrated. The goal of this project is to compare the effects of compost, manure, and inorganic fertilizer on agronomic, environmental, and economic variables for sustainable vegetable production.

Specific objectives
Assess the effects of compost, manure, and fertilizer on:
1. Soil biological, chemical and physical properties indicative of soil quality;
2. Nutrient leaching and runoff;
3. Average yield levels, net economic returns, and the variability of both yield and net economic returns over multiple production periods.

Accomplishments/Milestones

Two years of field research investigating the effects of various combinations and rates of soil amendments for production of a rye cover crop-vegetable rotation has been completed. We have demonstrated that two years of annual agronomic N compost rates increased soil total and available nutrient concentration, organic matter, pH, and cation exchange capacity; reduced soil bulk density; and had no effects on soil water infiltration, water-filled pore space, or respiration rate compared to a control, an annual low compost rate, and commercial fertilizer applied annually (according to soil test laboratory recommendations). Improved soil properties after two years of annual agronomic N compost rate applications did not have any effects on crop yield compared to annual poultry litter application rates, and annual commercial fertilizer rates. There were no differences in leachable nitrate-N occurred during two years of continuous agronomic rates of compost, manure, and fertilizer and a control treatment, in which no amendments were applied.

Agronomic, environmental, and economic data will be collected and interpreted for at least one additional growing season in order to develop an economic value for compost as a soil amendment. This work will include: Collecting and analyzing soil samples for further soil chemical, physical, and biological indicators of soil quality; Harvesting and analyzing crop yield data for agronomic effects and development of economic assessment; and Collecting lysimeter samples for nitrate-N leaching data and runoff samples following rainfall simulation for the potential surface water contaminants nitrogen, phosphorus, and sediment.

We plan to extend the duration of the study with the availability of additional funding sources in order to develop long-term indicators of soil quality parameters. Possible collaboration from a vegetable horticulturist, a plant physiologist, a soil microbiologist and a plant pathologist from Virginia Tech and other universities will enable us to assess in more detail the effects of the soil amendments on crop quality, plant physiological function, soil microbial activity and disease prevalence. These comprise potential non-nutrient benefits of compost that require further examination.

Impacts and Contributions/Outcomes

The results are providing and should continue to provide definitive analysis of inorganic versus organic fertilizers (esp., compost), including the quantification of non-nutrient and environmental values, which will enable farmers to learn how to credit the value of compost. Field days demonstrating the agronomic value of compost have resulted in increased use of compost at more scientifically-based application rates among farmers throughout Virginia. We will continue to summarize and present results as SARE reports, fact sheets, scientific manuscripts, and at on-farm field days and agricultural and composting conferences. Eventually, compost rate recommendations will be incorporated into Virginia Cooperative Extension Soil Testing Laboratory recommendations.

Collaborators: