Transitioning to organic: fertility management in potato production

Abstract

An increasing demand for organic crops in the US represents a considerable opportunity for organic, as well as conventional growers interested in exploring the transition to organic production. Renewed interest in organic farming has resulted in a need for research involving organic fertilizers. Limited research has been conducted on organic vegetable production with previous research conducted primarily outside the Deep South US. Field studies were conducted at the Louisiana State University (LSU) AgCenter Burden Center to investigate the effect of three levels of pre-plant organic NPK fertilizer (8-5-5, Nature Safe) combined with a sidedress application of organic NPK fertilizer (13-0-0, Nature Safe), compared to fish emulsion (5-2-2, Agro-K) or no fertilizer control treatments on the growth and yield of “Red LaSoda” potatoes. Plant height, width, leaf area, and above and below ground biomass (dry weights) were determined 3 times (once a month) and marketable yield was evaluated at harvest for the fall 2006 and spring 2007 growing seasons. Plots were harvested 3 months after planting according to USDA guidelines. There were no differences in marketable yield due to fertilizer treatment for the fall growing season, but there were differences for the spring growing season. In the spring study, the recommended rate of nitrogen (100 lbs. N/A) had adequate yields, the double rate (400 lbs. N/A) had lowest yields and the fish emulsion (66 lbs. N/A) had the highest yields. The results of the study suggest that organic potato production in Louisiana is profitable. If compared, commercial organic fertilizer is more expensive than conventional fertilizer, as are labor costs, but due to price premiums ($20/50 lb. sack of conventional fresh market potatoes and $35/50 lb. sack of organic fresh market potatoes, as of 2007), the organic production systems had potentially 2 to 3 times higher gross and net benefits when compared to a conventional production system. In this study, the use of fish emulsion as the sole fertilizer was one of the most costly but profitable production systems, as yields and gross and net benefits were highest. Fish emulsion may have a beneficial association with plant growth regulators.