Strawberry
Fertilizer
Fertilizers
The objectives of a fertilizer program are:
- to promote rapid and early runnering of new plants
- to promote rapid growth, development and early runner formation before the end of July
- to maximize crown formation after late August of the establishment year.
Fertilizer rates must be based on sound data derived from soil testing and plant tissue analysis. Estimated nutrient levels or general recommendations are not sufficient for maximum yields. Growers should also pay careful attention to timing and application methods.
Soil Testing
Soil tests should be used to determine the suitability of a field for strawberry production and to guide the ongoing fertility program.
The quality of the laboratory results is as good as the soil sampling procedure used to obtain the sample. For detailed soil sampling instructions, contact your local agricultural office or provincial soil testing laboratory.
Key points to remember in soil sampling are:
- Use proper augurs and clean containers for sampling.
- Sample well before transplanting or renovating to provide sufficient time for the sample to be processed and recommendations returned.
- Sampling depths are 0 to 6 in. (0 to 15 cm) and 6 to 24 in. (15 to 60 cm).
- Do not sample in locations where fertilizers have been recently incorporated.
- Air dry the soil sample immediately after sampling. (This step is often overlooked by growers).
Field Description and Cropping History
This information enables the laboratory to maintain records for research purposes. More importantly, it helps the lab make sound fertilizer and management recommendations for the grower. Over time, individual growers can monitor the fertilizing history and levels of nutrients of their fields.
Soil Test Reports
The following information will help the grower understand and use the results of a soil test report.
Carbonate Content indicates the calcium carbonate content of the sample. High to very high calcium levels in the soil can restrict nutrient availability to the plants. Absence of calcium carbonate does not mean the fields require lime as most prairie soils have sufficient lime. Only very acid soils require additions of lime.
pH indicates the acidity or alkalinity level of the soil. Soils with a pH in the range of 5.5 to 7.5 are usually satisfactory for strawberry production.
pH is important because it influences the solubility or availability or mineral elements required for plant growth. Phosphorus, for example, becomes less available to plants at levels below pH 5.3 and above pH 5.7, while potassium solubility is hampered when levels are above 7.5. Nitrogen is available in the pH 5 to 8 range. Soil pH greater than 7.5 has been associated with yellowing of strawberries caused by the lack of iron uptake in the plant leaf tissue.
Conductivity measures the salinity (salt) level. A conductivity reading of less than 1 mS/cm is best for strawberries. Levels greater than 1 could result in growth problems and reduced yields. Adding lime or gypsum will not correct a soil salinity problem.
Texture indicates the relative amounts of sand, silt and clay. Loam soils are a good mixture of sand, silt and clay and are neither droughty nor difficulty to till.
Nitrogen
Nitrogen is one of the most important elements in strawberry production. Nitrate nitrogen, the form most readily used by plants, is indicated in lb/acre (kg/ha) in soil test results.
High nitrogen rates are likely to increase the number of runners. This could be a disadvantage because too many runners can create high populations and excessive competition. On the positive side, high nitrogen levels in the summer may increase branch crown formation and benefit overall production.
Generally, nitrogen is fairly mobile in the soil and can move into the plant quickly. It can be affected by a number of environmental factors, including rain or irrigation. In saturated soil conditions, nitrate nitrogen rapidly converts to a gas and is lost.
After a planting is established, nitrogen can be broadcast over the entire field or banded over the rows. Banding is a more cost-efficient application method, because the same amount of fertilizer can be used to cover twice as much field area. Nitrogen can also be applied through the irrigation system. (Follow guidelines in "Fertilizer Application" section.) Several applications of nitrogen are more effective than a large, single application.
Table 1 Fertilizer Recommendations Based on Soil Test Results (lb/acre)
Nitrate Nitrogen Content (0-24 inches) |
Nitrogen Availability Category |
Nitrogen Recommended (lb/acre) |
0 - 4 |
VL- |
125 - 116 |
| Exchangeable Potassium (K) in Soil (0-6 inches) | Potassium (K) availability Category | Potassium (K) Recommended(lb/acre) |
| 0 -28 29 - 56 57 - 83 86 - 113 114 - 142 143 - 171 160 - 199 200 - 228 229 - 256 257 - 285 286 - 313 314 - 342 343 - 371 371 - 399 400 + |
VL- VL VL+ L- L L+ M- M M+ H- H H+ VH- VH VH+ |
200 - 190 190 - 179 168 - 158 158 - 147 147 - 136 136 - 125 125 - 115 115 - 104 104 - 93 93 - 83 83 - 72 72 - 61 61 - 49 61 - 49 0 |
| Exchangeable Phosphorus (P) in soil (0-6 inches) | Phosphorus availability Category | Phosphorus (P) recommended (lb/acre) |
| 0 -10 11-17 18 - 25 26 - 36 37 - 89 90+ |
VL L M H VH |
98 - 91 90 - 86 85 - 79 79 - 72 67 - 29 0 |
| Soil Sulphate Sulphur Content (0-24 inches) | Sulphur Availability Category | Sulphur (S) Recommended (lb/acre) |
| 0-10 9-20 21-29 30-39 40-59 50+ |
VL L M H VH VH+ |
27 27 27 0 0 0 |
Table 2 Fertilizer Recommendations Based on Soil Test Results (kg/ha)
| Nitrate Nitrogen Content (0-60 cm) | Nitrogen Availability Content | Nitrogen Recommended (kg/ha) |
0 - 4 |
VL- |
140 - 130 |
| Exchangeable Potassium in Soil (0-6 inch) | Phosphorus Availability Content | Phosphorus Recommended (kg/ha) |
| 0 -31 32 - 63 64 - 93 96 - 127 128 - 159 160 - 191 192 - 223 224 - 255 256 - 287 288 - 319 320 - 351 352 - 383 384 - 415 416 - 447 448 + |
VL- VL VL+ L- L L+ M- M M+ H- H H+ VH- VH VH+ |
225 - 213 213 - 201 201 - 189 189 - 177 177 - 165 165 - 153 153 - 141 141 - 129 129 - 117 117 - 105 105 - 93 93 - 81 81 - 69 69 - 55 0 |
| Exchangeable Phosphorus in Soil (0-15 cm) | Potassium Availability Category | Potassium (K) Recommended (kg/ha) |
| 0 - 11 12 - 19 20 - 28 29 - 40 41 - 100 101+ |
VL L M H VH |
110 - 102 101 - 96 95 - 89 88 - 81 80 - 35 0 |
| Soil Sulphate Sulphur Content (0-24 inch) | Sulphur Availability | Sulphur (S) Recommended (kg/ha) |
| 0 - 11 11 - 22 23 - 33 34 - 44 45 - 66 67 + |
VL L M H VH VH+ |
30 30 30 0 0 |
Rates and Timing for Nitrogen Applications
Timing of nitrogen application has a direct bearing on yield, fruit quality and plant development. Nitrogen applications in late summer often promote flower bud formation for the next year?s crop. However, nitrogen application in late fall may delay normal dormancy and cause increased risk of winter injury.
New Fields: Nitrogen should be applied and incorporated prior to planting at a rate based on soil test results. (See Table 2 for recommended rates.) When new plants have established their own root system, apply 15 to 20 lb/acre (17 to 22 kg/ha). Make another small application at the early stages of runnering.
Established fields: Nitrogen can be applied at 15 to 20 lb/acre (17 to 22 kg/ha) to an established planting early in the spring. This can be supplemented with foliar sprays, especially if the planting has shown some winter injury.
In most cases, nitrogen applications should be limited during the spring of the fruiting year. Excessive nitrogen in bearing plants favours the development of large, numerous leaves that may hide flowers and interfere with pollination. Also, larger leaves tend to maintain wet conditions near the ground, which promotes fruit rot.
There are exceptions to this rule. For example, heavily mulched plants can lack nitrogen since the nutrient is used by organisms that break down the straw. Under such conditions, applying up to 10 lb/acre (11.2 kg/ha) of nitrogen may increase berry size and yield, provided adequate fertilizers are used at renovation.
Winter injury: Fields that have undergone severe winter injury or that are generally lacking in vigor will respond to a band or broadcast application of ammonium nitrate at 80 lb/acre (90 kg/ha) early in the season.
Renovation: A nitrogen application of 50 to 80 lb/acre (56 to 90 kg/ha) is recommended at renovation time. This key period of "renewal" and fruit bud initiation takes place in mid summer. An additional 15 to 20 lb/acre (17 to 22 kg/ha) can be applied in mid August, the time of flower bud initiation. Applying nitrogen too late in the growing season may delay the plant hardening process, which could result in winter injury.
Phosphorus
This value describes the ability of the soil to supply phosphorus to plants. It is measured in lb/acre (kg/ha). Phosphorus and potassium are measured only at a depth of 0 to 6 in (0 to 15 cm).
Phosphorus moves slowly in the soil. Its availability to plants depends on soil pH as well as the actual phosphorus content of the soil. Most prairie soils tend to be alkaline, which results in low levels of available phosphates.
This nutrient is especially important for root and seed development so pay special attention to phosphorus requirements when preparing fields for planting. Adequate supplies are needed to promote early production of daughter plants, good vegetative growth and runnering. (See Table 2 for recommended rates.)
Potassium
Potassium readings are measured in lb/acre (kg/ha) and are a measure of the soil?s ability to provide potassium to the plant.
Potassium is associated with strong leaf petioles, sturdy fruit stalks and increased winter hardiness. It is also needed for good fruit colour and sugar content.
Sandy soils below 2% organic matter require higher applications of potassium.
Many prairie soils have sufficient potassium to meet plant needs. (See Table 2 for recommended rates.)
Sulphur
Sulphur is measured in lb/acre (kg/ha). The value indicates the amount of sulphate - sulphur in the top 2 ft (60 cm) of soil.
Sulphur is mobile in the soil. For most prairie soils, sulphur-containing fertilizers like super phosphate and ammonium sulphate provide adequate levels for good plant growth. Higher levels have been found beneficial to lower the pH in some alkaline soils on the Prairies. Some growers use fertilizers containing sulphur so that the equivalent of 50 lb/acre (56 kg/ha) is used at renovation. These higher rates also provide a slight acidifying affect to the soil. (See Table 2 for recommended rates.)
Table 3 - Plant Analysis Values for Determining the Mineral Status of Strawberries
| Nutrient | Normal Range | Nutrient | Normal Range |
| Nitrogen | 2.0 - 3.0% | Sulphur | 0.15 - 3% |
| Phosphorus | 0.25 - 0.4% | Zinc | 20 - 250 ppm |
| Potassium | 1.3 - 2.5% | Manganese | 50 - 250 ppm |
| Calcium | 0.8 - 1.8% | Iron | 60 - 250 ppm |
| Magnesium | 0.25 - 0.5% | Boron | 25 - 50 ppm |
Micro-nutrients
Micro-nutrients (zinc, copper, manganese, boron, chlorine, iron and molybdenum) rarely affect plant growth. However, the availability of micro-nutrients can be affected by imbalances in soil pH or by uneven application of major nutrients like nitrogen, phosphorus, potassium, and sulphur. These deficiencies may affect plant vigor and berry quality. Field trials have shown yield reductions of 15% where iron is deficient in plants.
Nutrient problems can be overcome through the use of foliar sprays containing the required nutrients. However, nutrient levels should first be verified with plant tissue testing.
Plant Tissue Testing
Plant tissue testing can determine if soil nutrients are being taken up in adequate amounts by the strawberry plant. Even when nutrients are in adequate supply, a plant?s ability to use available nutrients can be affected by several factors, including soil temperature, root development, drought, high temperatures, soil saturation with water, fertilizer application methods and timing.
Tissue testing results can help growers avoid long term nutrient problems. Occasionally, severe nutrient problems are encountered early in the growth of a crop. A tissue analysis may allow time for corrective measures to be taken in the same season, thereby reducing the potential loss.
Normal nutrient levels in strawberry tissue vary with plant growth stages such as flowering, fruiting and after fruiting. Tissue values may also be affected by time of sampling, the age of the leaves and the cultivars sampled. However, deficiency levels are reliable indicators that nutrients must be added.
As in soil sampling, the correct procedures for tissue test sampling are important. Key points to remember are:
- Take care to ensure cleanliness in sampling and handling.
- Use proper sampling equipment.
- Take the plant part at the proper time of growth.
- Take a representative sample and immediately clean and dry it with a dry cloth or soft brush.
- Avoid non-typical plants and areas in the field.
- Do not wash the sample.
Avoid samples that have fertilizer contamination, pesticide residues or soil particles.
- Collect samples in a clean brown paper bag, not a metal container.
- Select the youngest expanded mature leaf as a sample.
- Take 25 to 30 leaves from a reasonable number of typical plants throughout the field.
- Dry the sample at room temperature.
Send these sample to provincial or private tissue testing laboratories. (See section on soil fertility).
Application of Fertilizers
Foliar Application of Fertilizers
Fertilizers may be sprayed on the leaves as a supplement to soil applications. Foliar application brings about a quicker response than soil feeding. It is very useful in "perking up" plants during renovation, or when roots systems suffer from severe winter injury. Generally, any stand that is poor or lacking in vigor may benefit from this procedure. This is particularly the case in third and fourth year fields.
Foliar application has been found to be more successful on lighter soils than on heavier soils that are high in organic matter.
Foliar spraying can be used to apply nutrients like nitrogen or supplementary trace elements such as iron, magnesium, boron and calcium.
Foliar applications are most effective during early growth. The use of surfactants or spreaders, such as soap solutions, can enhance nutrient uptake through leaf tissue.
To avoid leaf burn, nutrient sprays should not be applied during hot weather. Never apply pesticides and nutrients together.
Fertilizer Application Through the Irrigation System
Uniform water application is essential when an irrigation system is used for fertilizer application. Sprinkler operating pressure uniformity can be checked by inserting a pressure gauge in the nozzle. The minimum pressure should be 30 lb/sq in. (200 kPa). Pressure from nozzle to nozzle should not vary more than 20%.
Fertilizers that can be spread by irrigation include ammonium sulphate, ammonium nitrate, calcium nitrate, ammonium phosphate, muriate of potash, urea and borax. Do not use irrigation to apply phosphoric acid (a corrosive element), anhydrous ammonia (solutions will be lost to the air), or superphosphates and lime (cannot be dissolved in water).
To apply, fertilizer is dissolved in a drum, then introduced into the irrigation line through a valve - either by suction or by pressure - over a 10 to 15 minute period.
After application is completed, continue irrigating for 30 minutes. To avoid burning the foliage, the system must be run until the plants are rinsed with water free of fertilizers.
Do not fertilize at the beginning of an irrigation because nutrients may be leached out of the root zone by water applied after the fertilizer injection.
Calculating the Rate
To determine the amount of fertilizer that should be injected into the irrigation system, multiply the area covered by the sprinklers by the prescribed fertilizer rate. For example: At a 40 x 60 ft. (12 x 18 m) sprinkler spacing, 0.05 acres (0.02 ha) are covered by each sprinkler. Twelve sprinklers cover - 0.6 acres (24 ha). To apply 50 lb/acre (56 kg/ha) of fertilizer for this 12 sprinkler setting, inject 0.6 x 50 = 29.6 lb (13.44 kg) of fertilizer into the system.