Soil Inorganic Nitrogen Content and Indices of Red Raspberry Yield, Vigor, and Nitrogen Status as Affected by Rate and Source of Nitrogen Fertilizer

Abstract

The single‐year response of soil inorganic nitrogen (N) content and indices of red raspberry (Rubus ideaus L.) yield, vigor, and N status to rate and source of fertilizer N were determined. Twenty‐nine trials were conducted in commercial plantings from 1994 to 1996. Treatments were 0, 55, or 110 kg N ha⁻¹ as ammonium nitrate or 55 kg N ha⁻¹ as a slow‐release fertilizer product containing 60% polycoated sulfur‐coated urea and 40% urea. Soil nitrate (NO₃) content frequently increased during the growing season, indicating that soil N supply was nonlimiting. The plant indices were generally insensitive to fertilizer‐N rate under these high‐N fertility conditions. Soil nitrate content measured after berry harvest was frequently excessive even at the recommended N rate and can be used to identify fields with excess N fertility. The slow‐release N fertilizer provided limited benefits compared with use of ammonium nitrate.

Keywords:

• Ammonium
• floricane
• primocane
• Rubus ideaus
• slow‐release fertilizer
• nitrate

Acknowledgments

The assistance and cooperation of all the growers who allowed us to work on their fields is gratefully acknowledged. Funding for the project was provided by the Canada‐British Columbia Green Plan for Agriculture, the B.C. Raspberry Growers Association, Green Valley Fertilizer, Coast Agri Ltd., and the Fraser River Action Plan of Environment Canada. The assistance of Bill Peters in developing the crop‐vigor rating system is gratefully acknowledged. Laboratory and field assistance was provided by D. Chapple, L. Birston, M. Levesque, G. Telford, C. Watson, and M. Younie.