Nitrogen Fertilization of Berry Crops

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

Part II: Strawberries

We have been studying uptake and use of fertilizer nitrogen in red raspberry and strawberry, and are presently looking at blueberry. In the last issue I reported on the results of our research on raspberry. 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

Strawberries:

We studied the June-bearing variety 'Totem' (15" single matted row on 40" centers) from the first through the third fruiting season. Some of our treatments included the following granular (broadcast band) applications: 1) no added fertilizer N; 2) 25 lb N/a in April + 50 lb N/a at renovation; and 3) 50 lb N/a at renovation. In addition, we added the following foliar treatments (5% solution of urea in 75 gallons of water per acre, amounting to about 14 lb N/a per application); all foliar treatments were in addition to a 50 lb N/a granular application at renovation: 1) foliar at pre-bloom in April; 2) foliar at green fruit in early June; 3) foliar at early post-renovation in early August; and 4) foliar at late post-renovation in early September. We did not study N needs in the planting year.

We monitored the amount of fertilizer N taken up, where it moved in the plant and what happened to it (stored or lost).

• Plants grew quickly in the spring increasing total plant dry weight over four fold from April to early July. Renovation or the physical act of mowing off leaves after harvest, led to a 65 to 70% decline in total plant dry weight. After renovation, plants grew slowly increasing dry weight to just above spring levels before entering dormancy.
  
• Plant dry weight decreased as the planting aged. Also how the plants "looked" changed: weight of crowns increased whereas the weight in the leaves decreased from the first to the third fruiting season.
  
• There was no effect of nitrogen rate or method of application on plant growth (dry weight), total plant nitrogen, yield, or fruit quality (rot, firmness, sugar concentration) from the first through the third fruiting season. There was a trend for increased fruit rot in the high spring N treatment. Unfertilized plants did not suffer a yield loss. Why? (see below)
  
• Strawberry plants did take up a large quantity of the 25 lb N/a applied as a granular in the spring, 63% of the fertilizer applied. Very little of the spring fertilizer N went to the roots or the crown, but rather was taken up and moved into the leaves and fruit. When plants were renovated, all of the spring FN was lost!
  
• About 42% of the 50 lb N/a applied at renovation was taken up by the strawberry plants. This fertilizer initially went into the leaves, but then accumulated in the crown and roots. About half of the FN taken up was lost as leaves senesced going into dormancy.
  
• Still, about 40% of the total N stored in the strawberry plant in late winter came from the fertilizer applied at renovation the year before. This stored fertilizer was used for new leaf growth and fruiting in spring.
  
• Plants that were not fertilized at all had the same total amount of N in the plant as those that received 50 lb N/a at renovation. The needed N in these plants likely came from mineralization in the soil in late summer.
  
• In the spring, about 46% (6 lb N/a) of the foliar N fertilizer applied was taken up whereas the post-renovation foliar applications were less efficient (15% taken up) likely due to increased volatilization of urea in the hotter summer temperatures.
  
• The accumulation of fertilizer N in the foliar treatments increased well after the foliar fertilizer was applied, indicating that most of the uptake was through the roots rather than the leaves.
  
• Any N obtained from foliar fertilization in spring was lost when plants were renovated.
  
• None of the foliar applications benefited yield or strawberry plant growth.

In summary, strawberry plants do take up fertilizer N when it is provided. Fertilizer N initially goes to the leaves and the fruit (if present during application) and moves into the crown and roots late in the season. Any fertilizer N applied in the spring is lost when leaves are mowed at renovation. I wouldn't recommend spring fertilizer N unless a planting is very weak; it did not benefit yield in this study and the added leaf growth can increase fruit rot. Since strawberry plants need most of their fertilizer after renovation to supply the new flush of growth, they can rely on mineralized N available in the soil when they do not get any fertilizer. Our unfertilized plants did just as well as those that received 50 lb N/a at renovation.

Soil OM, soil type and growing conditions will affect how much N is required on your farm. If you have doubts about how much fertilizer your plants need or whether there would be enough mineralized N available in your soils without the addition of N fertilizer , then leave a small section of your field unfertilized after renovation and compare it to a normally fertilized section. I'd appreciate hearing from you.

Editors note: This article provides great information on when strawberries use nitrogen most efficiently. It also confirms our thoughts about foliar-applied N.

However, this research was conducted on clay loam soils with 3-4% organic matter. We are not changing our recommendations for fertilizing berry crops just yet. Ontario growers can find information in OMAFRA publication #360, Fruit Production Recommendations, Chapter 8, Berry Crops.

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