Vegetable Yield and Soil Quality as Affected by Organic Cropping Systems

An organic vegetable cropping system experiment was initiated in sandy soils at Citra, FL, in Spring 2011. Different organic management practices were evaluated with respect to their influence on vegetable yield and on soil quality. Six vegetable production systems were established including two polyethylene mulch systems with or without cover crops, two unmulched bed systems with or without cover crops, and two reduced-tillage systems with cover crops and varying fertilization rates. Two crop sequences, i.e., spring yellow squash ‒ fall broccoli and spring tomato ‒ fall lettuce, were also evaluated. The experiment was arranged in a split-plot design, four replications, with crop sequences as the whole plots and production systems as the subplot treatments. Hairy vetch and cereal rye were grown prior to the spring vegetables in the cropping systems with cover crop incorporation and reduced tillage. Sunn hemp and sorghum-sudangrass were used as summer crops before planting the fall vegetables. Soil samples (0-15 cm) were collected before seeding cover crops in Spring 2011 and after the final harvest of fall vegetables in late winter. A wide range of soil quality parameters were measured, including pH, electrical conductivity (EC), bulk density, soil organic carbon (SOC), total soil nitrogen (TN), particulate organic matter carbon (POMC), potentially mineralizable nitrogen (PMINN), microbial biomass carbon (MBC), and Mehlich-extractable P, K, Ca, Mg, S, Fe, Mn, Cu, and Zn. Overall, the plastic mulch treatments resulted in the highest vegetable yields while cover crops did not show any significant effect. The yield reduction in the reduced tillage systems and tilled plots without mulches varied with the vegetable crops. The plots without cover crops showed the lowest level of root-knot nematode infestations despite the use of plastic mulch. There were no consistent treatment differences in soil quality among the 6 production systems across the two cropping sequences. At the end of the 2011 production cycle, Mehlich-extractable Mg was significantly higher under reduced tillage compared to the other production systems. The reduced tillage system also showed the highest level of soil EC. Temporal changes in soil quality parameters were greater than production system and cropping sequence comparisons. Total soil N, PMINN, Mehlich-extractable P, Ca, and Mn trended higher compared to data collected before spring cover crop planting. These results suggest that improvement of soil quality in sandy Florida soils will be challenging, warranting future research to evaluate the long-term effects of organic vegetable cropping systems on the soil.