Organic farmers in the Southeastern US face a myriad of management challenges, a combination of the subtropical climate and land degradation from centuries of tillage-intensive monocultures. Soils in the region are often highly eroded, largely devoid of topsoil, nutrients and soil organic matter. This 3 year field study examines the effects of 10 experimental cropping systems on agronomic soil quality (SQ), and the tradeoffs between soil restoration and production economics. This work was conducted on a highly degraded soil in the north Georgia Piedmont, and included systems comprised of techniques observed to increase SQ when used individually, but that are rarely studied in combination. These include organic practices, conservation tillage and alley cropping (AC) with perennial legumes. The SQ parameters studied include bulk density, soil carbon and nitrogen levels, pH, as well as above- and below-ground plant production and crop yields. Data were analyzed using a mixed model. Production economics were studied by constructing enterprise budgets for 3 vegetable crops. A second degree stochastic dominance (SDSD) analysis was conducted to compare yields, net returns and changes in soil C levels over the course of the experiment, which provided “rankings” of the systems’ performance over the duration of the study.
Results/Conclusions
Compost additions were required to maintain soil C, N and pH. AC systems with compost maintained soil C, and increased in soil C when mulch was not applied. Soil bulk density decreased significantly in AC systems without mulch (p<0.10). Crop yields did not differ significantly by treatment, but were lower than typical conventional yields in Georgia due to the degraded soil on the study site. Despite low yields, net returns on organic vegetable crops were over $15,000 per acre in some systems. SDSD analysis found the AC system receiving10 tons/acre of compost and no mulch dominated the other systems in yield, net return and soil carbon rankings. The conventional system ranked the lowest. The SDSD analysis also demonstrated the tradeoff between moderate application of composts and mulch for weed suppression. While mulch reduced weeding labor by an average of 23%, mulched AC systems, regardless of compost quantity, had among the lowest soil C rankings. This was a non-additive effect that emerged from a systems level study, probably due to increasing decomposition rates under the mulch. This study demonstrates that organic, conservation tillage systems can restore SQ and command high returns if labor requirements can be met.
