Publication 360, Fruit Production Recommendations: Potassium

Excerpt from Publication 360, Fruit Production Recommendations 2010-11,
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Table of Contents

1. Introduction
2. Sources of potassium
   • Table 3-10c. Fertilizer Materials: Primary Nutrients (Potassium) (PDF 108 kb)
   • Table 3-11. Average Fertilizer Replacement Values for Different Types of Manure (PDF 75 kb)
3. Potassium application methods
4. Potassium recommendations
• Table 3-14. Potassium Requirements for Berries, Tree Fruits and Grapes (PDF 74 kb)
5. Other topics in Soil Management, Fertilizer Use, Crop Nutrition and Cover Crops
   • Assessing Nutrient Needs
   • Soil Organic Matter
   • Soil pH and Liming
   • Nitrogen
   • Phosphorus
   • Calcium
   • Magnesium
   • Micronutrients
   • Cover Crops
6. Ch. 3, Soil Management, Fertilizer Use, Crop Nutrition & Cover Crops - PDF 189 kb
7. Related Links
   

Introduction

Potassium is an important component of plant cells. It also influences the uptake of water by the roots and plays a role in both respiration and photosynthesis. The sugar and starch content of crops like potatoes and tomatoes may be affected by potassium levels. Most crops require equal amounts of potassium and nitrogen.

Potassium deficiency usually appears on the older leaves first. It can cause yellowing or burning of the leaf margins.

Sources of potassium

Mineral fertilizers

The most common potassium sources are outlined in Table 3-10. Fertilizer Materials: Primary Nutrients.

Table 3-10c. Fertilizer Materials: Primary Nutrients (Potassium) (PDF 73 kb)

See also:

• Fertilizer Materials: Nitrogen
• Fertilizer Materials: Phosphorus

Manure

Manure is an excellent, inexpensive source of potassium. It also supplies the soil with valuable organic matter and micronutrients. Table 3-11. Average Fertilizer Replacement Values for Different Types of Manure, provides the approximate amount of crop-available potash contained in manure.

Table 3-11. Average Fertilizer Replacement Values for Different Types of Manure (PDF 75 kb)

Nutrient values based on average analysis results for over 3,000 samples.There are large variations between manures, so a manure analysis is your best guide to nutrient availability.¹

Table 3-11a. Liquid Manure

Table 3-11b. Solid Manure

¹ Data from manure analysis provided from Ontario Labs collected between 1992 and 2007.
² Nitrogen based on spring application, incorporated within 24 hr. Unincorporated manure will have less N due to ammonia losses.
³ Phosphate from manure or biosolids is assumed to be 40% as available in the year of application as that in commercial fertilizer (another 40% of the phosphorus is available the following year).
⁴ Potassium from manure is assumed to be 90% as available in the year of application as that in commercial fertilizer.

Unlike nitrogen, the potassium found in manure can be held by the soil over a considerable period of time. Regular application of manure over time may result in a build-up of potassium which should be monitored with a soil-testing program.

Manure can pose a food safety risk on many fruit crops. Ensure at least 120 days between manure application and harvest.

Potassium application methods

The mobility of potassium fertilizers is limited and falls between that of nitrogen and phosphorus. It is not prone to leaching losses, with the possible exception of very sandy soils low in organic matter. Potash should be broadcast and incorporated prior to planting. After establishment where a drip irrigation system is used, up to half of the potassium requirement can be applied by fertigation. At least half of the potassium should be applied in the spring as a broadcast or band in the drip-line of the crop or in the herbicide strip. Potassium can be blended with nitrogen and applied in one pass.

Foliar applications can be made in grapes and should be considered in dry years when soil uptake is reduced. Foliar application at veraison may improve yield of grapes.

Potassium recommendations

Use a soil test from an OMAFRA-accredited lab in conjunction with Table 3-14. Potassium Requirements for Berries, Tree Fruits and Grapes, below. For crop specific details see:

• Apple Nutrition
• Berry Crop Nutrition
• Grape Nutrition
• Tender Fruit Nutrition

Excessive potassium applications reduce a crop's ability to take up magnesium from the soil. Where potassium levels are high, magnesium deficiencies are more likely to occur, particularly if magnesium levels are already low.

Potassium is important for fruit colour, winter hardiness, tree growth and disease resistance in tree fruits. In apples and tender fruits, do not exceed 3 kg of potash per tree even in cases of severe deficiency.

Do not use muriate of potash (0-0-60) in blueberries, currants and gooseberries due to their sensitivity to chloride.

Table 3-14. Potassium Requirements for Berries, Tree Fruits and Grapes
Potash (K20) required (kg/ha) (PDF 74 kb)

Probabilities of profitable crop response to applied nutrient HR = high response, MR = medium response, LR = low response, RR = rare response, NR = no response
* 1 M ammonium acetate extract
† For established tree fruits and grapes, plant analysis is used to estimate requirements.
‡ Apply only every second year.

Related Links

• OMAFRA Publication 611, Soil Fertility Handbook
• Soil Management
• Soil Fertility & Crop Nutrition
• Soil Water Management
• Best Management Practices: Soil Management
• Cover Crops
• OMAFRA Publication 505: Ontario Weeds
• OMAFRA Publication 75: Guide To Weed Control