Summer Cover Crop and Plant Back Timing Effects on Fall Cabbage Production

Farmers across the state of Iowa have expressed interest in more sustainable practices to supply nutrients, suppress weeds, and boost yield in vegetable production.  This study conducted at the Horticulture Research Station, Ames, IA, investigated the effect of: buckwheat, cowpea, oats, and sorghum-sudangrass cover crops on soil chemical and biological properties and cabbage (Brassica oleraceaL. ‘Caraflex’) yield.  A no-cover crop plot was established as a control treatment. The study was a split plot design with cover crops as the whole plot factor and transplanting date as the sub plot factor (planting immediately after cover crop termination or eight days later).  Data was collected on: cover crop biomass, nitrate leaching, leaf chlorophyll concentration, yield characteristics, and soil microbial biomass carbon. Cover crop biomass in 2013 ranged from 5,388 kg∙ha^-1 in sorghum-sudangrass to 2,961 kg∙ha^-1 in cowpea. In 2014 cover crop biomass was lower with the amounts ranging from 2,575 kg∙ha^-1 in sorghum-sudangrass to 1,160 kg∙ha^-1 in cowpea.  Nitrate leaching was measured below the rooting zone using lysimeters.  In both years cowpea had one of the highest readings for nitrate loss indicating more nitrate was available to the crop as compared to other cover crop treatments.  Between the other four treatments data was inconclusive as to any relationship between them.  Chlorophyll content of the cabbage had a significant interaction between the cover crop treatments and planting date in 2014 only.  Chlorophyll content was highest in both years with the early planted cowpea treatment. There were no measureable differences in soil microbial biomass between any of the treatments in both years.  Marketable cabbage yield for 2013 was significant between cover crops, planting date, and interactions.  In 2014 cabbage yield was significant only between treatments.  The highest yields in both years were in the early planted cowpea and late planted cowpea.  Marketable head count followed the same significance patterns between treatment, planting date, and the interaction between treatments and planting date as the marketable yield.