“Soluble organic nitrogen sources suitable for fertigation in organic vegetable production are much needed,” said lead author of the study, Charles Ogles. Ogles and colleagues at Auburn University studied the effects of three different nitrogen sources during a two-year crop sequence of yellow squash and collards. The scientists used hydrolyzed fish fertilizer, inorganic nitrogen (N) source with secondary and micronutrients, inorganic nitrogen without secondary or micronutrients and a zero nitrogen control for the study. Nitrogen was applied at recommended rates for both squash and collards, 80 percent of the recommended rates and 60 percent of the recommended rates. The study design included a zero nitrogen treatment used as the control.
“To eliminate the rotation order effect, the crops were switched each year: yellow squash-collard in year one and collard-yellow squash in year two” said Ogles.
In the first year of the study, the researchers found that yellow squash had a 30 percent higher yield when grown with inorganic nitrogen as compared with squash grown in hydrolyzed fish fertilizer.
Collards showed a 21 percent higher yield when grown with inorganic nitrogen source with secondary and micronutrients as compared with collards grown in the hydrolyzed fish fertilizer.
“In the second year of the study, highest yields of collards were again produced with inorganic nitrogen source with secondary and micronutrients treatments, followed by those grown in the hydrolyzed fish fertilizer treatments,” the authors said. “Second-year squash grown in the inorganic N treatments produced highest yields, while squash grown in the fish fertilizer had a 16 percent lower yield as compared with those grown in the two inorganic N sources.”
Additional results revealed that inorganic nitrogen without secondary or micronutrients produced lower marketable collard yields than the other treatments, an outcome the authors attributed to sulfur deficiency.
After performing economic analyses, the authors concluded that if growers can obtain the price premiums associated with organic produce, the use of hydrolyzed fish fertilizer could be an economically feasible option in organic vegetable production. This study was originally published in HortScience and summarized in the May 2015 issue of Acres U.S.A.