2019 ASHS Annual Conference

Cover crops have well-documented benefits for soil health, pathogen suppression, and crop yields in field cropping systems, but have been less utilized in year-round high tunnel systems due to short windows for cover crops and potential lost revenue. Conservation practices that provide ecosystem services but take land temporarily out of cash crop production create trade-offs, which we examined in an experiment integrating winter cover crop treatments into a continuously cropped tomato-lettuce rotation in Kentucky and Tennessee in 2017 and 2018. The four winter treatments included: a lettuce cash crop, a winter wheat monoculture, a crimson clover monoculture, and a biculture of wheat and clover. Services evaluated included several soil parameters, nitrogen leaching, weed seed bank management, and yields. Soil samples were taken at 0-6” and 6-12” depths. Soil data were analyzed separately by site, as soil type and baseline fertility conditions varied between the two. There were no cover crop treatment effects in Kentucky. Soil K declined every year at both soil depths. In the surface layer, soil K declined from 383 lbs/ac to 213 lbs/ac. Soil K varied by treatment over time, with the treatments incorporating wheat and the biculture decreasing at the 0-6” soil depth. Soil K in the other treatments (clover, lettuce) declined numerically but were not different over time. Like Kentucky, soil K content in Tennessee decreased in each layer over time, declining from 454 lbs/ac in the surface layer to 119 lbs/acre over the course of the experiment. Weed biomass was analyzed separately by state due to differences in background weed pressure. Both states had greater weed biomass in clover compared to wheat and biculture. In Kentucky, weeds accounted for 32-56% of the biculture biomass, 61-94% of clover monoculture, and 17-53% of wheat monoculture (2017 and 2018, respectively). Poorer cover crop performance in the winter of 2017-18, relative to weeds, could be explained by lower temperatures. In Tennessee, weeds accounted for a much smaller fraction of the biomass- 2-6% of the biculture, 9-12% of the clover monoculture, and 1-9% of the wheat monoculture (2017 and 2018, respectively). Tomato yields did not differ by treatment; however, yields were higher in 2017 than 2018 and higher in Kentucky than Tennessee both seasons. Unmarketable fruit (%) increased from 2017 to 2018 and was higher in Tennessee. Much of the unmarketable fruit was due to yellow shoulder disorder, likely due to the decline in K observed during the experiment.