This summary is intended as a brief overview and as a supplement to the nutrient management guides available online at Oregon State University: Nutrient Management for Blueberries in Oregon, EM 8918; Caneberries: Nutrient Management Guide, EM 8903-E; and Strawberries. Fertilizer Guide, FG 14). I encourage everyone working with commercial berry crops to access these and other publications on soil sampling, modifying soil pH etc.
Key questions that need to be answered with regard to any nutrient management program are: How much nutrient should be applied? When is the best time to apply the nutrient? What source of the nutrient or what material is best to apply? And what method of application is best?
How much nutrient should be applied is often estimated using soil and plant tissue testing, experience, observations of plant growth, and information on the amount of nutrient generally required for good growth and production. Nutrient availability and plant nutrient status are assessed by soil and tissue testing. I will focus most on this aspect of developing and adjusting a nutrient management program.
Soil testing is commonly the only method used to adjust nutrient management programs in annual crops – in these crops there is not enough time to adjust fertilizer programs based on tissue analysis.
In perennial crops, soil testing is important to adjust soil nutrient status prior to planting. This not only gets plants off to a good start, but is the only way to effectively increase soil pH. Pre-plant incorporation of nutrients that are immobile or do not move readily into the rooting zone with a surface application (e.g. phosphorus, potassium) is very effective.
Prior to planting get a representative sample of the field/block. Taking soil samples to the tillage depth (where any pre-plant application of nutrients would be incorporated) is recommended. You may also choose to take a tillage depth sample (e.g. to 6 inches deep) but also a deeper one (from 6 inches to 1.0 or 1.5 ft) to get an idea of stratification of soil pH and nutrients. Take soil samples well in advance of planting so that pH can be adjusted (e.g. sample in early fall for spring planting of caneberries or strawberries or a year in advance for blueberries) – it takes time for incorporated lime or sulfur to react and change soil pH.
Base nutrients to be incorporated prior to planting on target or recommended soil levels (Table 1). In blueberry, be conservative on addition of sulfur to acidify the soil, as raising the pH to the target range if too much sulfur (S) was incorporated is difficult. Be aware that standard fertilization programs lead to acidification of the soil in the row – the pH will thus decrease over time in all perennial berry crops. Generally, for every 100 lb N/acre/year applied (as urea), soil pH will decrease 0.1 unit per year in our soil. For these reasons the target pH for newly planted berry crops should be at the top of the recommended range (Table 1).
|Nutrient||Deficient at less than|
|Phosphorus (P; Bray)||25-40 ppm||20-40 ppm||45 ppm|
|Phosphorus (Olsen)||10-20 ppm||10-20 ppm||20 ppm|
|Potassium (K)||100-150 ppm||150-350 ppm||75-175 ppm|
|Calcium (Ca)||1000 ppm||1000 ppm||1000 ppm|
|Magnesium (Mg)||60 ppm||120 ppm||120 ppm|
|Boron (B)||0.5-1.0 ppm||0.5-1.0 ppm||1.0 ppm|
|EC||2 dS/m||2 dS/m||2 dS/m|
Annual soil sampling is not needed in perennial berry crops unless you are correcting a problem. We recommend soil samples be collected every two to three years to monitor changes in soil nutrient status. In established fields, sample at the same time of year (e.g. late winter or fall) so that years can be more easily compared. Collect soil samples in the plant row (where the fertilizer is applied) and, in drip irrigated fields, sample at a similar distance from the emitter and plant in all sub-sample locations. The irrigation wetting front, fertigation, and band applications of fertilizer affect soil sample results. Do not collect soil samples in spring right after fertilization has occurred. If mulch is present, remove the mulch layer before taking the soil sample. How deep should the soil sample be? You can take soil samples so that the depth reflects where the most active berry crop roots are: soil surface to 0.5-1 ft deep in strawberries and 1.5-2 ft deep in caneberries and blueberries. However, nutrients and soil pH are often stratified – fertilization over time leads to varying soil pH and nutrient content with soil depth. If you take a sample from the soil surface to 1.5 ft deep, the reduced soil P and K and the higher soil pH at the lower depths will reduce the average soil P and K and increase the soil pH relative to what is found in the fertilizer “zone” nearer the soil surface. This should be kept in mind when interpreting soil analysis results and planning nutrient management programs. You can take soil samples at two depths (e.g. 0 to 3 in. and 3 in. to 1 ft) to better understand the level of stratification occurring in your farm.Note. Recommended levels may change in the future from local research findings.
Testing soil to predict nitrogen (N) application rates in berry crops is not advised. Note that high soil N concentration in late summer/fall can be an indicator of excessive N fertilization.
Keep soil pH in the range considered ideal for the berry crop (Table 2). In blueberry, if soil pH is too low then we see problems with manganese (Mn) and aluminum (Al) toxicity to plants. When soil pH is too high we can see problems with less iron (Fe) and zinc (Zn) being available. If pH is below or above recommended levels, plant symptoms of nutrient deficiencies or toxicities often occur; in such situations the problem is best fixed by correcting soil pH.
Soil pH affects nitrification – or the rate an ammonium-N fertilizer is nitrified to nitrate-N. At a soil pH of 6.0, fertilizers containing ammonium-N (e.g. urea, ammonium sulfate) are rapidly nitrified to nitrate-N (80% converted in 6 weeks). In contrast, at a pH of 5.5, nitrification is much slower (30 to 40% in 6 weeks) (see figure 4 in caneberry nutrient management guide for data). Caneberries and strawberries take up the nitrate form of N – keeping soil pH closer to 6.0 allows for use of less expensive fertilizers containing ammonium as they would be rapidly nitrified allowing for efficient plant uptake. Blueberry plants take up ammonium-N; keeping soil pH at 4.5 to 5.5 delays nitrification, keeping the ammonium fertilizer in a form that can be taken up by the plants.
Leaf tissue analysis provides information on the nutrient content of the plant – sometimes even when soil nutrient content is adequate, the plant is not able to take up the nutrients required (e.g. soil pH is incorrect; dry or saturated soil; weather; cultural issues such as overcropping, irrigation, etc.).
Tissue standards have been developed using results from research experiments and estimated from large databases that relate tissue nutrient levels to good yielding fields for each crop (OSU). Well- designed research experiments are needed in many berry crops to improve tissue standards.
In all berry crops, tissue nutrient concentration changes throughout the season; for example, leaf N concentration (%N) is always highest in the early season and lowest before leaf fall in autumn. The recommended time of sampling leaves for tissue analysis is related to a period of time when the leaf nutrient concentration is most stable.
Tissue nutrient levels will also change with location or age of the leaf and what type of leaf it is. For example, in caneberries results from floricane leaves will be different than primocane leaves; in strawberry, results from leaves during fruiting will be different than leaves after renovation; in blueberry, leaves from whips will have different nutrient levels than those from lateral shoots. Always sample the recommended tissue at the recommended time (Table 3).
|Crop||Sample time||Tissue to sample||Comments|
|Strawberry||After renovation (~ mid to late August)||Most recently fully-expanded leaves||Soil sampling best for short-term field plantings|
|Floricane-fruiting blackberry & raspberry||Late July to early August||Primocane leaves approx. 1 ft from tip||Standards are based on Marion and Meeker|
|Primocane-fruiting raspberry & blackberry||Late July (raspberries), from bloom - early red fruit (blackberry)||Most recently fully expanded primocane leaf||Standards for primocane raspberry need modifying. Standards are being developed|
|Blueberry||Late July to early August||Most recent fully-expanded leaves||Avoid whips (sample from laterals). Standards developed from Bluecrop.|
When collecting tissue samples:
- Sample at the correct time for the crop; published tissue standards are NOT correct if sampled at any other time of the season.
- If you are seeing problem plants at any time of the year, collect leaves from affected and “normal” looking plants and compare tissue analysis results for clues as to the cause.
- Collect the right tissue; for example, there are no standards for fruiting lateral leaves in caneberries.
- Do not wash leaves as some nutrients can be leached with washing. Note that any micronutrients in fungicide applications, foliar nutrient applications, and dust on leaves can lead to “higher” than typical nutrient results (keep records).
- Sample cultivars separately. While there is little data on cultivar specific standards, we do know that cultivars differ – one reason may be fruiting season. Research is underway to try to address this.
- Keep excellent records on crops and blocks sampled, time of year sampled and any associated yield or fruiting season information. It will be important to look for trends over time.
- In perennial crops, tissue analysis and observations of plant growth are best used to plan for and adjust nutrient management programs for the following year.
- Do not use just tissue N concentration to adjust N fertilizer programs. Use recommended fertilizer application rates as a starting point and adjust programs based on observations of plant growth and tissue N.
- Be aware that tissue nutrient concentrations that are below or above the recommended levels (Table 4) may indicate a soil problem (e.g. high tissue Mn may mean soil pH is too low).
Nutrients in the plant move in either the xylem (with water – this tissue is dead) or the phloem (with “food” – this tissue is alive). Nutrients that move in the xylem are not mobile within the plant as they simply move with water to the leaves (not from leaves to the fruit or from old leaves to new leaves, for example). Nutrients that move in the phloem are mobile within the plant. The nutrients that are mobile in the plant are: N, P, K, Mg, and Cl. The ones that are immobile are: S, Fe, Mn, Cu, Zn, Ca, and B.
|Manganese (ppm Mn)||30-350||50-300||50-650|
|Boron (ppm B)||30-80||30-70||25-45|
|Iron (ppm Fe)||60-200||60-250||60-200|
|Zinc (ppm Zn)||8-30||15-50||20-50|
|Copper (ppm Cu)||5-15||6-20||6-20|
Berry crops require adequate amounts all nutrients to grow and produce fruit. This will vary by plant age and perhaps by type or cultivar – particularly as yields and vigor differ.
Nutrients that are removed in harvested fruit and prunings, depending on the crop, in addition to the nutrients needed for plant growth need to be considered when planning nutrient management programs. Our research has shown that nutrient removal in fruit harvest varies with berry crop and yield (Table 5). For example, an estimated 15 lb N/acre is removed in a 5 ton blackberry crop (Table 5). In raspberry and blackberry, flailing the prunings (from caning out) between the rows returns these nutrients to soil making them available to the plant roots. However in blueberry, nutrients from flailed prunings are not returned to the plant over time because there are no blueberry roots in the row middles. The estimated nutrient content removed (per acre) when pruning mature blueberry plants is shown in Table 5.
|Fruit||Prunings (per acre)|
|Red raspberry4||Trailing blackberry5||Blueberry6||Blueberry7|
Efficiency of plant uptake of a fertilizer is affected by plant age (depth and width of root zone), presence of a surface mulch, amount of coverage of the in-row area (plants that fill the row space have a greater efficiency of uptake than those that do not), method of application (efficiency varies with granular, liquid, or foliar applications), and the amount and timing of fertilizer applied. Recommended rates thus may vary among application methods, not to mention plant age (Table 6). Applying higher than recommended rates of fertilizer can have adverse effects on plant productivity, fruit quality and the environment.
Table 6. Recommended nitrogen fertilizer rates for berry crops (adapted from OSU nutrient management guides referenced above)
|Crop||Planting year (lb N/acre)||Mature (lb N/acre)||Comments|
|June-bearing strawberry||30-60 (soon after planting); 20-30 (late July/early August)||50||Apply at renovation; spring N not recommended unless planting weak|
|Floricane-fruiting blackberry & raspberry||30-50 (soon after planting) (split applications)||50-80||Split applications starting at just before primocane emergence (or fertigate)|
|Primocane-fruiting raspberry & blackberry||30-50 (soon after planting) + 20 at bloom||50-80 (soon after planting) + 20 at bloom||Split applications starting at just before primocane emergence (or fertigate)|
|Blueberry||0.8 oz/plant; hand fertilization of granular recommended. Adjust for inefficiency if broadcast band or fertigated||N rate increases as planting ages 100 to 165 from year 5 to 8+||Split applications starting at bloom emergence (or fertigate). Add 25 lb N/a in year fresh sawdust added|
Research is underway to determine optimum collection sample times for various blackberry, raspberry, and blueberry cultivars and whether standards should differ among cultivars. In addition, we are learning more about nutrient uptake (all nutrients) to provide better recommendations on time and rate of nutrient application. Finally, we are measuring the nutrient removal from pruning in blueberry and caneberries to learn more about nutrient budgets. All of this information should be very useful to help growers better manage their berry crop nutrient programs.
I appreciate the contributions of John Hart, Extension Soil Specialist, Dept. Crop and Soil Sci., OSU, the graduate students in my program who have contributed to this body of work (Paula Mohadjer, Hannah Rempel, Renee Harkins, Javier Fernandez-Salvador, Emily Dixon, Pilar Bañados, and Denise Nemeth), Gil Buller (Senior Research Assistant), research colleagues (David Bryla, USDA-ARS, HCRU; Tim Righetti, formerly OSU; and Dan Sullivan, OSU), and grower collaborators.
- 1. a. b. Note. Recommended levels may change in the future from local research findings.
- 2. a. b. Note. Recommendations may change in the future from local research findings.
- 3. Note: Results will likely be adjusted as research on crop removal is underway.
- 4. Red raspberry cultivar was 'Meeker'
- 5. Blackberry cultivars were 'Marion' and 'Black Diamond' (no cultivar effect)
- 6. Blueberry range is for 'Elliot' (lower values) and 'Bluecrop'
- 7. Pruning data are for mature 'Elliott'