Residual Effects of Fresh and Composted Dairy Manure Applications on Potato Production

Potato growers in Idaho and other dairy producing regions often grow potatoes on fields that have had a history of fresh and composted manure applications. Growers remain uncertain of the impacts that previous manure applications will have on tuber yield and quality, as well as diseases, physiological disorders, and contamination by human pathogenic bacteria such as E. coli. The focus of this study was to determine the long term effects of manure, compost, and chemical phosphorus (P) fertilizer applications on tuber yields, tuber quality, nutrient uptake, tuber disorders and diseases, and soil nutrient concentrations. Russet Burbank potatoes were grown in 2008 and 2009 on plots that had received dairy manure, dairy compost, P fertilizer, or no P source (control) at the same target P rate in 2003, 2004, and 2005. Compared with the P fertilizer treatment, applications of manure and/or compost significantly increased total yields, soil potassium (K), soil nitrate (NO 3 -N), early season petiole P, and late season petiole K in at least one year of the two-year study. There were no significant differences between P fertilizer, manure, and compost treatments on soil test P, late season petiole P, early season petiole K, E. coli populations on tuber surfaces, common tuber diseases and disorders, and tuber quality. Based on our findings, tuber yields significantly increased three years after applications of fresh and composted dairy manure, while tuber diseases, disorders, and quality were not affected.