Tillage and Cover Crop Management Influence Weeds, Insects, Soil and Crop Nutrients, Crop Development and Yield in Organically Managed North Carolina Sweetpotato Ipomoea batatas (L.) Lam. Systems.

Abstract

In 2004, North Carolina supplied 46% of the nations' sweetpotato and generated 79 million dollars for the state but of the 16,000 ha in production that year; only 405 ha were managed according to federal organic standards. A three-year field experiment was initiated in 2001 to evaluate organic sweetpotato 'Beauregard' production systems that varied in cover crop management and tillage. Three organic systems including 1) compost and no cover crop with tillage (Org-NC), 2) compost and cover crop incorporated prior to transplanting (Org-CI), and 3) compost and cover crop with reduced tillage (Org-RT) were compared to a conventionally managed tilled and chemical control (Conv) production system using a randomized complete block design with six replications. All sweetpotato tissue macro and micronutrient concentrations were within sufficiency ranges defined by North Carolina Department of Agriculture & Consumer Services. Sweetpotato N (4.6%), P (0.5%), and K (4.3%) tissue concentrations were greater in Org-CI compared to remaining systems at 60 DAP in 2004. Monocot and dicot weed density and biomass were similar between Org-NC and Org-CI each year, and with few exceptions were similar to Conv. In Org-RT, high monocot weed density limited sweetpotato vine above ground biomass (154 g m⁻²) and total yield 11.2 Mg ha⁻¹) in 2002. In 2001, the percentage of No. 1 grade roots was at least 19% greater in Org-CI (65 %) and Org-NC (62 %) than Conv (50 %). In 2002, the percentage of No. 1 roots was similar among Org-CI (74 %), Org-NC (71 %) and Conv (67 %) and similar among systems in 2004. Root quality was assessed based on degree of insect damage by wireworm-Diabrotica-Systena (WDS) complex. In 2001, Org-RT had the highest percentage of marketable roots (68 %) compared to remaining systems (19-43 %). The number of marketable roots was similar among systems in 2001 and 2004, but reduced in Org-RT (1.3 Mg ha⁻¹) compared to remaining systems. Means of wireworm (Melanotus and Conoderus spp.) densities per trap were significantly correlated with degree of root damage. Overall, organic systems performed as well as the conventionally managed system in at least one or more areas.