Nitrogen Management and the Effects of Compost Tea on Organic Irish Potato and Sweet Corn

Supply and synchronization of plant-available nitrogen (N) to the soil is a major challenge for organic farmers, especially when growing crops in soils that are in transition from conventional to organic systems. This research evaluated the effects of site produced cover crops and application of soil amendments on N uptake and crop yield of organic Irish potato (Solanum tuberosum) and sweet corn (Zea mays). Cover crops were crimson clover (Trifolium incarnatum) and forage radish (Raphanus sativus). Soil amendments included in-row application of commercially produced dehydrated compost tea absorbed on charcoal (Soil Biology Innovations) and post-plant sidedressing with organic N fertilizer. Irish potato and sweet corn were grown at the Kentland Agricultural Research Farm near Blacksburg, VA in an organic transition soil during the summers of 2006 and 2007. Nitrogen uptake and crop yield were not affected by cover crop species in either year. SBI increased yield of sweet corn, but not Irish potato for both years; SBI had no effect on N uptake of either crop. Post-plant N sidedressing increased N uptake and crop yield of Irish potato and sweet corn in 2007, but had no effect on crop yield in 2006, presumably because pre-plant organic fertilizer was applied at planting in 2006, but not in 2007. This study shows that the combination of site produced cover crops and applied soil amendments may be required to produce high marketable yields of organic Irish potato and sweet corn in the transition soil used in these experiments.