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Commercial Blueberry Production in Minnesota and Wisconsin

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Selecting and Preparing a Site

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Blueberries require moist but well-drained acidic soil. Choose a frost-free, level or gently sloping site in full sun with good air circulation. Blueberries must have a consistent moisture supply, yet only a few hours of standing water can kill the plants, so surface and internal soil drainage are essential.

Soils

Open, porous soils such as sandy loams, loamy sands, and coarse sands with a high organic matter content will best provide the aeration needed. To improve the likelihood of successful establishment on most soils, add one and one-half to two cubic feet of peat per plant to the soil. Be sure to mix peat thoroughly with the soil. Clay soils that are acidic and high in organic matter may also be used for blueberry plantings. However, aeration and drainage are often poor and plants on these soils may develop root problems.

Peat and muck soils should be avoided. These soils are wet and cold in the spring, and often are located in low-lying areas, subjecting the plants to spring frost damage and standing water. In late summer, the soil releases a large amount of nitrogen, which delays the plants' hardening before winter and increases chance of winter injury.

pH

Always use soil testing to assess and adjust soil pH. A soil pH of 4.5 to 5.5 is optimum for blueberry production. A pH higher than 5.8 may cause iron chlorosis, characterized by interveinal yellowing of the leaves. If the pH is too high, add acid peat or sulfur to the soil according to soil test results. Fine-textured soils with pH values above 7.0 should not be used unless the top 18" of soil are amended with an equal volume of acid peat moss and further acidified if necessary. The peat moss will break down over time; organic mulch materials should replenish the level of organic matter in the soil as they decompose.

Elemental sulfur can be used to lower pH. Because it reacts slowly with the soil, elemental sulfur should be applied and incorporated to plow depth the year before planting. The soil type, present pH, and the desired pH are used to determine the amount of elemental sulfur needed. Table 3 provides guidelines for elemental sulfur use. Test soil pH again three to four months after initial application. If soil pH is not in the desired range, reapply according to Table 3.

Table 3. Elemental sulfur application rates to change soil pH to 4.5

initial pH	sand or loamy sand		sandy loam or loam
	lb./1000 ft2	lb./acre	lb./1000 ft2	lb./acre
7.0	19	800	58	2500
6.5	15	650	46	2000
6.0	12	525	35	1500
5.5	8	350	24	1000
5.0	4	170	12	500

Iron sulfate also can be used to lower soil pH. This material reacts faster than elemental sulfur but is more expensive. Multiply the rate of elemental sulfur needed by seven to determine the amount of iron sulfate needed. Although aluminum sulfate also lowers pH, it can be toxic to roots and is therefore undesirable as a soil acidifying amendment.

Acid sphagnum peat incorporated prior to planting at the rate of one to two cubic feet per plant will provide a favorable root environment for establishing blueberries in soils with a high pH. The positive effects of acid peat will last six to ten years. Unless other measures are used, the pH of the soil will eventually increase.

Use of ammonium sulfate or urea as the nitrogen source will also help maintain a low soil pH. Refer to Table 4 for application rates of nitrogen. Do not use ammonium sulfate at rates higher than those recommended for supplying nitrogen. Excessive nitrogen available late in the growing season can increase winter injury potential.

Table 4. Nitrogen recommendations for blueberries

age of planting	amount of nitrogen (N) to apply 1 in lb./acre
first year	30
second year	40
third year 2	50

¹Amount in table is for mineral soils. For high organic-matter soils lower rates by ten to 20 lb./acre.

²Base subsequent N fertilizer applications on leaf analysis and plant vigor.

Pre-Planting Weed Control

The year before planting, control perennial weeds, such as quackgrass, nutsedge, and Canada thistle, by fallow planting, repeated tillage, or with applications of non-residual herbicide. It is extremely difficult to control perennial weeds after the blueberries have been planted, so it's important that the field be free of perennial weed infestations before planting.

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