Economic and Environmental effects of Compost use for Sustainable Vegetable Production

Economic and Environmental effects of Compost use for Sustainable Vegetable Production

Summary

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 fertilizers for the production of vegetables on economic, agronomic and environmental variables.

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.

Approach
Pumpkins (cv ‘Magic Lantern’) were grown in 2000 on two organic farms (Bracketts Farm, Voyager Foundation Farm) and Virginia Tech’s Northern Piedmont Agricultural Research and Education Center (NPAREC). Each site was planted with a rye winter cover crop that was disced into the soil in the spring prior to applying the soil amendment treatments: 1) control, 2) 5 tons compost/acre annually, 3) 5 tons compost/acre plus supplemental fertilizer annually, 4) 50 tons compost/acre annually, 5) 50 tons compost/acre – one time application, 6) 50 tons of compost/acre – one time application plus supplemental fertilizer annually, 7) agronomic N rate of poultry litter annually, and 8) recommended fertilizer annually. Weed control was achieved with tillage and a 4-inch straw mulch. Armicarb 100 (potassium bicarbonate) was used to control powdery mildew. All plots sites were set up to provide trickle irrigation as needed.

Results
Few yield differences among treatments occurred during the initial season, which was probably due to the higher than normal rainfall and the high residual soil fertility at each site. The average yields of marketable pumpkins at each site were 51.6 MT/ha (NPAREC), 86.45 MT/ha (Bracketts), and 83.6 MT/ha (Voyager). Post-harvest soil analysis revealed higher nutrient contents (P, K, and Mg), pH and CEC and lower bulk density in the high compost treatments than in the control, inorganic fertilizer, and low rate compost treatments. Soil respiration was higher with the high compost rate than in the control and higher when commercial fertilizer was applied with the low rate of compost than with the low compost rate alone. No treatment differences were observed for infiltration or % water-filled pore space. There were also no treatment differences in the amounts of nitrate-N that leached through the soil horizon through September.

Results indicate that compost, despite eliciting little effect on yield, soil water-holding capacity, and soil respiration, increased soil nutrient availability, pH and CEC, and decreased soil bulk density. It is expected that bulk density will decrease with high compost application rates over time, but seeing evidence of it within the first cropping season was not expected. We discussed the research expectations with 150 farmers, agricultural consultants, educators, and researchers at the annual NPAREC Field Day held in August, 2000.

Future plans
A minimum of two additional seasons of vegetable crop production will be used to develop further data on yield responses, soil properties, water quality, and economic value of compost, manure, and fertilizer. The results will provide the most definitive analysis of inorganic versus organic fertilizers to date, including the quantification of non-nutrient and environmental value, in the interests of enabling farmers to learn how to credit the value of compost and promoting compost use among farmers. We will summarize and present results as SARE reports, fact sheets, scientific manuscripts, and at on-farm field days and agricultural and composting conferences.

Collaborators: