Nitrogen Fertilization of Berry Crops

This article was reviewed by the editor of The Ontario Berry Grower for technical accuracy and appropriateness.

Part 1: Raspberries

We have been studying uptake and use of fertilizer nitrogen in red raspberry and strawberry, and are presently looking at blueberry. I will report here and in the next issue, on N fertilizer uptake and needs of all but blueberry, because we are not yet done with the blueberry work. Thanks to professor Tim Righetti at OSU, student Hannah Gascho Rempel, and Research Assistant, Gil Buller, for assistance in these projects. We appreciate the support of the Oregon Strawberry Commission, the Oregon Raspberry and Blackberry Commission, the Agricultural Research Foundation, and the NCSFR. If you would like more information on any of the following please contact Bernadine at strikb@science.oregonstate.edu

Red raspberry:

We studied the uptake of fertilizer nitrogen (FN) in a mature summer-bearing 'Meeker' planting. The treatments were: 1) no added nitrogen; 2) 80 lb N/a in mid-March; 3) 40 lb N/a in mid-March; and 4) 40 lb N/a mid-March + 40 lb N/a in mid-May (we followed the uptake of FN in the second half of this split application only). No primocane suppression was done in either year and floricane prunings were removed from the field. Fruit was machine harvested. The soil type was a clay loam with a 3 to 4% organic matter content.

• Nitrogen rate or timing had no effect on plant growth (dry weight) or total plant nitrogen content over the two-year study.

• There was a trend for the unfertilized plants to have the lowest yield and for the split, 40+40, plants to have the highest yield. This was likely because, primocanes were longer in the fertilized plants than in the unfertilized plants - 20 to 31" longer.

• From 36 to 37% of the fertilizer nitrogen applied in the spring (80 and 40 lb N/a in March) was taken up by the plants. When 40 lb N/a was applied in May (second half of the split application), 26% of this fertilizer was taken up by the red raspberry plants.

• We found that plants treated with higher rates of FN relied more on FN, while plants in the lower fertilizer rate treatments probably took up a higher percentage of their N from the soil and from recycled or stored N from the previous year.

• When fertilizer was applied in mid-March, more of the fertilizer initially went to the fruiting laterals and fruit. Later in the season, fertilizer that was taken up went primarily to primocanes. Fertilizer applied in mid-May went primarily to primocanes - in the last half of a split application, most of the value of the fertilizer is thus for the following year, not for the current season.

• The peak total nitrogen in the plant was 100 lb N/a. About 16 lb N/a was lost in harvested fruit, 16 lb N/a in leaf fall, and 14 lb N/a in removal of floricanes at pruning time in September. The remaining nitrogen in the plant overwintered in the above- or below-ground portion of the plant.

• Based on our study, if pruning or removal of dead fruiting canes is done in mid-September, on average, 13 lb N/a are lost (assuming prunings are taken out of field). However, if pruning is done in mid-August, on average 25 lb N/a are lost in the prunings. Prunings left in the field would slowly recycle their N back into the system.

• Data on soil nitrate and ammonium levels indicated that soil nitrate was available through mineralization in late summer, but this was not enough for plant needs. Thus, yield of the unfertilized plants declined over the two-year study. Higher rates of N fertilization led to levels of nitrate in the soil beyond plant needs; some of this may have been tied up in the organic matter fraction of the soil rather than leaching out of the root zone.

Our study showed that red raspberries require annual applications of fertilizer nitrogen to maintain growth and yield. Lower rates (40 to 50 lb N/a) than previously recommended here in Oregon would likely provide the best balance of improving efficiency of fertilizer uptake, providing for plant needs and reducing risk of nitrate leaching. Less nitrogen per acre is "lost" if growers delay pruning of dying floricanes until September rather than in August.

Related Links

• Nitrogen Fertilization of Berry Crops, Part 2

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