Preparing the Soil for Berry Production: The Basics
Successful berry production depends on careful attention to every aspect of production. Most important is proper land preparation, long before strawberries, raspberries or other berry crop is planted. If mistakes are made during the preplant process, the effects can be felt for the life of the planting, and the economic potential of the crop becomes limited. The best management and cultural practices cannot compensate for soil problems that should have been corrected before planting.
Plant strawberries and raspberries on sandy loam or loam soil that is 60 - 120 cm deep. Other soil types may be acceptable with good management. However, heavy soils tend to be too cold and wet, while sandy to gravely soils have a poor water holding capacity. A good site for berry production will have good air drainage and wind protection, minimal land slope, an available water supply, physical separation from wild berry plants, and no harmful herbicide residues. Assuming the site is suitable for berry production, the main soil management considerations include the organic matter, fertility, pH, drainage, soil compaction and soil pests.
Soils for berry crops should have an organic matter (OM) content of 3% or more. The OM can fluctuate considerably up or down according to good or bad management practices. OM serves as a source of energy for helpful micro-organisms, and acts like a sponge, holding nutrients so they dont leach but remain available to the plant. OM helps to build better soil structure; keeping heavy soils open and helping to bind together lighter soils. OM also facilitates air movement and the entrance and percolation of water into and through the soils. OM improves the water-holding capacity of the soil. In a dry year, plants growing in soil with low OM will not do as well as those in soils with adequate OM.
There are several ways to increase the OM content of soils. The most traditional has been with the use of manure. However, for most horticultural producers a ready supply of manure is not available. Weed-free cattle or swine manure applied at 25-40 tonnes/hectare is beneficial especially if it contains bedding material. Poultry manure could be used but it does not contribute that much to the soil OM. Where poultry manure is used, apply no more than 7tonnes/hectare the fall before planting strawberries. Fresh poultry manure can burn the tender strawberry and raspberry roots. Well composted manure can be applied in the spring; otherwise it should be applied in the previous fall and worked in. Do not apply manure in the spring if berries will be harvested that same year.
A substitute for manure is hay or straw applied at 7 tonnes/hectare in the spring a year before planting. Unless the residue contains at least 1.5% nitrogen, the soil organisms will actually remove nitrogen (about 30 kg/ha) from the soil to break the residue down. Legume based hay materials have enough nitrogen but for non-legume hay or straw, apply 4 kg N per tonne of hay or straw (20 lbs/ton) at the time of application. As the residues break down, most of the nitrogen will be slowly released and made available to the plants.
A third strategy for improving the soil OM content is to plant a cover crop and work it into the soil the year before strawberries are planted. The cover crop will help to improve soil structure and added needed organic matter as the residue decomposes. Cover crops are most beneficial where the soil texture, soil structure or soil organic matter content is not ideal for berry production. Cover crops cannot replace all the benefits that come from manure but when manure is not available, they are a good substitute.
Cover crops include sorghum-sudan grass, pearl millet, winter rye or oilseed radish.
Sorghum-sudan and forage pearl millet
Sorghum-sudan and forage pearl millet are excellent choices for growing as cover crops for soil improvement. The root growth is extensive and the top growth lush. A pre-plant herbicide treatment is recommended for crop establishment. Plant after all threat of frost is past; mid-June. The crop will benefit from the warm temperatures of early to mid-summer. Approximately 50 kg/ha of N will help the crop achieve maximum top growth.
Mow these grasses before they are 1metre in height, in order to encourage tillering and to ensure that stalks are not woody and will break down readily. Allow at least 15 cm of growth to remain in order to encourage the plant to re-grow.
Winter rye is seeded from late August into mid-October, often following field or vegetable crops. It grows until freeze-up, and then commences growth again in March - early April (slightly earlier than winter wheat). Growth rate is very rapid during May. The stand is generally killed in late April or early May by tillage or herbicide use. Rye can produce significant root and top mass for return to the soil. A rye cover crop suppresses winter annual weeds effectively. Winter rye can be seeded later than any other crop and still survive over winter. For good ground cover and erosion protectiprotection, seed winter rye at least a month before freeze-up.
Rye should be killed in the fall or early spring to avoid loss of soil moisture, and difficulties in incorporation. Full season rye is an excellent host for root-lesion nematode, while cover crop or short term rye is no different than wheat.
Oilseed radish is commonly seeded in August or early September. It is unaffected by early frosts, can grow to a height of 50 to 90 cm and blooms in October. The plant has a thick but short taproot, varying between carrot and turnip shaped. It is killed by severe frosts in late November or December. Oilseed radish provides a reasonably rapid soil cover and excellent erosion protection over winter and returns moderate amounts of organic matter to the soil. For good growth, this crop must have a large amount of available nitrogen, either applied as fertilizer or manure left from a previous crop. Some oilseed radish varieties release compounds which are toxic to nematodes, but only when large amounts are tilled green into the soil.
Growth will be poor if soil nitrogen levels are low or if soil compaction is severe. Scattered volunteer plants may appear in the following crops.
For more information on growing cover crops, consult OMAFRA publication #811, Agronomy Guide or the cover crop section on the OMAFRA website.
Soil Fertility and pH
The most reliable way to determine fertility and lime requirements for strawberries and raspberries is to take a soil test preferably a year before but no later than the fall before planting.
Where manure has been added, it is advisable to take a soil test, since manures provide a number of nutrients, particularly phosphorous and potassium. Publication #360, Guide to Fruit Production, provides tables to indicate the reduction in fertilizer where manure has been applied.
Most fertilizer requirements can be added just prior to planting. The recommended rate for nitrogen at that time is 50 kg of actual nitrogen per hectare. Nitrogen fertilizer should not be applied in the fall since it could be lost through leaching. Where phosphorous is required, incorporate at least 20 cm. into the soil. Phosphorous does not move very readily through the soil and if it is not incorporated properly the plants will not be able to use it.
Magnesium (Mg) levels should be between 40 - 100 ppm on the soil test. If the levels get below this, yields may be affected because Mg is essential for chlorophyll which produces the food for the plants. If Mg levels get below 40 and if the pH is below 6.5 then add dolomitic limestone (which contains 11 - 22% Mg). If the levels are below 30 ppm and the pH is higher than 6.5 then apply 30 kg/ha of soluble Mg to the soil as one would apply potash. Many fields have potash levels that are too high. In the presence of excess potash, plants will not take up enough Mg even though the soil levels are apparently adequate. Apply additional Mg if the Mg levels are between 31 - 39 ppm and the potash levels are greater than 250 ppm.
Manganese and zinc are part of the suite of soil tests that are accredited by OMAFRA. On your soil test report, the results will be expressed as both ppm and as an index; the index allows for the influence of pH on the nutrient availability. If either of these two micro-nutrients drop below 8 ppm then crop deficiencies may occur. These nutrients are not soil applied but can be applied as foliar sprays if deficiency symptoms show up in the leaves.
The optimum pH for raspberries and strawberries is slightly acidic (around 6.0 - 6.5). In Ontario, if the level gets below 6.1 then lime is recommended for coarse and medium textured soils. On fine soils lime is recommended if the pH dips down to 5.6. At a low pH calcium, magnesium and possibly phosphorous may not be readily available to the plant. If Mg levels are low then dolomitic lime can be used to correct acid soils otherwise calcitic lime is suitable. Apply lime in the fall and preferably one year before planting to allow time for the soil chemistry to change.
If the soil pH is high it usually is not economical to bring it down with sulfur. In most cases the crops will grow well enough at a higher pH. Several micronutrients such as iron may become limiting if the pH gets too high. These deficiencies are best corrected through foliar sprays.
Strawberries and raspberries cannot tolerate poorly drained soils. Optimum production will never be achieved if the crop has wet feet, even for a short time. Near perfect drainage is required. Actively growing roots will begin to suffocate and die within 24 hours of being submerged. In addition, wet conditions favour the occurrence of soil borne diseases. Strawberries can be severely damaged by black root rot or red stele. Raspberries are susceptible to Phytophthora root rot. Advice on drainage requirements can be obtained from a drainage contractor.
Soil that is compacted can have dramatic affects on the productivity of berry plantings. A hardpan will restrict the movement of water down through the soil resulting in poor drainage. Root development will also be restricted. To break up hardpans, sub-soil before planting. The depth of subsoiling should be no more than a few centimeters below the zone of compaction because any deeper uses more energy and risks the potential of deeper compaction. The best time to subsoil is when the soil is dry, (e.g. August) so that the hardpan shatters. If subsoiling is done when the soil is too moist the hardpan will not be properly disrupted. A cover crop should be established after subsoiling to ensure that roots stabilize the cracks created. Every effort should be made to reduce tillage and traffic operations to prevent re-establishment of the compacted layer.
The final consideration for preparing the soil is to control pests such as weeds, insects and diseases.
The primary weed concerns are perennial weeds such as quackgrass, Canada thistle, bindweed, etc. If these weeds are not controlled before planting then they can become a real problem, and will limit the life of the planting.
In the season before planting it is possible to reduce the perennial weeds through intensive cultivation of fallow land. However, this approach is expensive and severely reduces the soil OM. Herbicides are the most common approach to eradicating these weeds.
The weed that seems to cause the most problems is quackgrass. An approach to controlling quackgrass is to apply glyphosate in the spring before planting when the grass is a minimum of eight inches high with 3-4 leaves. If the field was not fall plowed, an application around May 15 - 20 is probably the earliest application date or else there will not be enough leaf growth to ensure net movement down into the roots for adequate kill. If the field was fall plowed, an early spring application will not be successful because the quackgrass will emerge sporadically. For fallow fields, make two applications, one in May and another in September. For heavy infestations use the high rate on the label.
For broadleaf perennials a suitable herbicide applied over the cover crop could be selected. If a cover crop is not grown, a broad spectrum herbicide such as glyphosate can be used. Timing is crucial for proper control as outlined in OMAFRA publication #75, Guide to Weed Control under the heading Special Methods of Weed Control - Site Preparation.
In some cases it may be advisable to rotate into a row crop where a vigorous herbicide program can be implemented. In all cases avoid herbicide residues that can hurt berry plants.
White grubs and wireworms are two serious soil-borne pests that are common in sod and pasture crops. Berry crops should not be planted within two years of any type of sod. A row crop such as corn or pumpkins could be grown for at least one year prior to planting to help reduce the incidence of grubs, wireworms and other soil insects.
Diseases and Nematodes
Crop rotation is important to prevent the build-up of certain diseases. Strawberries or raspberries should never be planted back to back. Pythium and Rhizoctonia are known to build up in strawberry plantings. The main soil borne disease encountered in both strawberries and raspberries is Verticillium wilt. In addition to infecting strawberries and raspberries, this fungus is also the cause of wilt in solanaceous crops such as tomatoes, potatoes, peppers and eggplants. Therefore strawberries and raspberries should not be planted (preferably within 4 years) after one of these crops. Similarly, lambs quarters, pigweed and nightshade are known to harbour Verticillium so weeds should be controlled.
Nematodes are soil borne pests common in both raspberries and strawberries. These are small eel-like worms invisible to the naked eye but easily seen under a microscope. They can be a problem on sandy soils but usually not on heavier soils. Nematode numbers can be determined through analysis of a soil sample.
If the numbers are high, fumigation is a proven and effective means of control. Some cover crops, such as pearl millet, hot mustards, and marigolds, will suppress nematodes. In contrast, legume crops encourage nematode populations.
In summary, optimum production throughout the life of a strawberry or raspberry planting can only be achieved if the soil is properly prepared before planting. Proper preparation includes building up the organic matter content, fertility, appropriate pH, ensuring good drainage and control of pests such as weeds, insects, and diseases.
Adapted from a presentation by Frank Louws, Ontario Horticultural Crops Conference, 1989. Revised August 1998, March 2009, and April 2013.
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