Nitrogen use and management in red raspberry

Graduation date: 2003The effects of ¹⁵N-labeled fertilizer applied to mature summer-bearing red\ud raspberry (Rubus idaeus L.) plants were measured over two years. Four nitrogen (N)\ud treatments were applied singularly at 0, 40, or 80 kg·ha⁻¹ of N in early spring\ud (budbreak), or split with 40 kg·ha⁻¹ of N (unlabeled) applied at budbreak and\ud 40 kg·ha⁻¹ of N (¹⁵N-labeled) applied 8 weeks later. Plants were sampled six times per\ud year to determine N and ¹⁵N content in the plant components throughout the growing\ud season. Soil was also sampled seven times per year to determine inorganic N\ud concentrations within the four treatments as well as a bare soil plot. There was a trend\ud for the unfertilized treatment to have the lowest and for the split-N treatment to have\ud the highest yield in both years. N application had no significant effect on plant dry\ud weight or total N content in either year. Dry weight accumulation was 5.5 t·ha⁻¹ and\ud total N accumulation was 88-96 kg·ha⁻¹ for aboveground biomass in fertilized plots in\ud 2001. Of the total N present averaged over two years, 17% was removed in prunings,\ud 12% was lost through primocane leaf senescence, 13% was removed through fruit\ud harvest, 30% remained in the over-wintering plant, and 28% was considered lost or\ud transported to the roots. Peak fertilizer N uptake occurred by July for the single N applications and by September for the last application in the split-N treatment. This\ud uptake accounted for 36-37% (single applications) and 24% (split application) of the\ud ¹⁵N applied. Plants receiving the highest single rate of fertilizer took up more fertilizer\ud N while plants receiving the lower rate took up more N from the soil and from storage\ud tissues. By mid-harvest, fertilizer N was found primarily in the fruit, fruiting laterals,\ud and primocanes (94%) for all fertilized treatments; however, in the split application,\ud the majority of this fertilizer N was located in the primocanes (60%). Stored fertilizer\ud N distribution was similar in all fertilized treatments. By the end of the second year,\ud 5-12% of the fertilizer acquired in 2001 remained m the fertilized plants. Soil nitrate\ud concentrations increased after fertilization to 10.6 g·sampled volume⁻¹, but declined to\ud an average of 4.8 g·sampled volume⁻¹ by fruit harvest. Seasonal soil N decline was\ud partially attributed to plant uptake; however, leaching and immobilization into the\ud organic fraction also contributed to the decline