COPPER REQUIREMENTS FOR ONIONS GROWN ON ORGANIC SOILS IN NEW YORK

In replicated field experiments at 49 sites during a 5-year period in New York, broadcast applications of 42 kg/ha of CUSO₄ (25% Cu) did not have a measurable effect on onion bulb yield or bulb quality (color of outer, dry scale and dry scale retention). Cu soil test levels (O.1 N HCl extractant) at the sites prior to CUSO₄ applications ranged from 0.2 to 9.0 ppm.
Most of the sites had routinely received annual applications of Cu fertilizer because growers had felt that Cu was required for production of good quality bulbs.
At one site, with a Cu soil test level of 0.2 ppm, onion leaf Cu level was increased from 4.5 to 7.0 ppm by application of 42 kg/ha CUSO₄. At all other sites, soil CUSO₄ application did not affect onion leaf Cu levels.
One year after application of 84 kg/ha CuSO₄, total Cu levels in soils in 7 different fields were increased by amounts ranginf from 37 to 175 ppm.
Differences in amount of Cu increase were attributed to varying bulk densities and soil management practices.
Application of 84 kg/ha CUSO₄ in April generally caused an increase in Cu soil test levels the following spring.

I International Symposium on Edible Alliaceae

L.A. Ellerbrock

https://doi.org/10.17660/ActaHortic.1997.433.64