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Effect of Long Term Compost Application in a Certified Organic System on Soil Quality and Vegetable Yields
In 1999, West Virginia University, established an organic farming systems project with an agronomic, animal and horticulture component. The organic farm became certified organic in 2002 and has been operated under organic certification for the past 13 years. In the market garden section of the 63 acre farm, 32 plots measuring 5 meters by 15 meters were established. Sixteen of these plots were managed as high input and sixteen as low input plots. High input plots received 22 tons of composted dairy manure per hectare and a rye-vetch cover crop during each winter season since the inception of the farming systems. Fertility in low input plots was managed solely with a rye-vetch cover crop. A four year rotation of legumes, cucurbits, solanaceous, and leafy crops was established in 1999 and has been maintained ever since. Soil organic matter in the top 15 cm of the soil profile has remained unchanged in low input plots at 5.2% in 2004 to 5.4% in 2014. Dramatic increases in soil organic matter from 6.4% in 2004 to 8.7% in 2014 were observed. Over this period yearly compost application improved yields by 22% in all crops combined, however individual crops responded quite differently. Peas only showed a yield gain of 4% in high versus low input plots, whereas pumpkin yield was increased by 57% in high input plots when compared to low input plots. The yield was 11%, 15%, 18%, 23%, and 25% higher in high input plots than for low input for tomato, peppers, zucchini, green beans, and lettuce respectively. Additional data from concurrent experiments with differing rates of compost (11 to 88 ton per hectare) showed that over-application (more than 22 tons of composted dairy manure per hectare) can lead to nutrient leaching and phosphorus build up in soils, despite incremental improvements in yield.