Nitrogen is important for the production of organic vegetables, yet can be quite costly to manage.
Nitrogen management is even more challenging when production practices call for the use of polyethylene mulch combined with fertigation.
"Soluble organic nitrogen sources suitable for fertigation in organic vegetable production are much needed," said lead author of the study, Charles Ogles.
Mr Ogles and colleagues at Auburn University studied the effects of three different nitrogen sources including hydrolysed fish fertiliser, during a two year crop sequence of yellow squash and collards.
The other treatments were an inorganic nitrogen source with secondary and micronutrients, an inorganic nitrogen without secondary or micronutrients, and a zero nitrogen control.
Nitrogen was applied at 100, 80 and 60 per cent of recommended rates for both squash and collards.
In the first year of the study, the researchers found that yellow squash had a 30 per cent higher yield when grown with inorganic nitrogen as compared with squash grown in hydrolysed fish fertiliser.
Collards showed a 21 per cent higher yield when grown with inorganic nitrogen source with secondary and micronutrients as compared with collards grown in the hydrolysed fish fertiliser.
Results in the second year of the study were similar, with squash and collards grown on the fish fertiliser again showing lower yields than those on inorganic nitrogen.
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.
However, after performing economic analyses, the authors concluded that if growers can obtain the price premiums associated with organic produce, the use of hydrolysed fish fertiliser could be an economically feasible option in organic vegetable production.
"Although yields were reduced in the crops grown in hydrolyzed fish fertilizer treatments, the premium price and resultant profit associated with organic products were enough to offset the reduced yield," the authors said.
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