Publication 360, Fruit Production Recommendations: Nitrogen

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

1. Introduction
2. Nitrogen and the environment
3. Sources of nitrogen
   • Synthetic fertilizer
     • Table 3-10. Fertilizer Materials: Primary Nutrients (PDF 108 kb)
       • Nitrogen
       • Phosphate
       • Potash
   • Products that modify the release of nitrogen
   • Manure nitrogen
     • Table 3-11. Average Fertilizer Replacement Values for Different Types of Manure (PDF 75 kb)
   • Manure and food safety
   • Legumes
     • Table 3-12. Nitrogen Contribution of Plowed Down Legumes (PDF 69 kb)
   • Other organic nutrient sources
   • Avoid fertilizer burn!
4. Other topics in Soil Management, Fertilizer Use, Crop Nutrition and Cover Crops
   • Assessing Nutrient Needs
   • Soil Organic Matter
   • Soil pH and Liming
   • Phosphorus
   • Potassium
   • Calcium
   • Magnesium
   • Micronutrients
   • Cover Crops
5. Ch.3, Soil Management, Fertilizer Use, Crop Nutrition and Cover Crops (PDF 189 kb)
6. Related Links

Introduction

Nitrogen is an important element for the growth and development of all crop plants. Nitrogen is naturally present in all soils. As soil microbes feed on crop residues and soil organic matter, they release nitrogen into the soil. As soil organic matter levels increase, so do the levels of naturally available nitrogen. Management practices which maintain and increase soil organic matter will also help to enhance soil fertility and crop productivity. Legumes, such as alfalfa and red clover, build soil fertility by capturing atmospheric nitrogen and releasing it slowly into the soil.

Nitrogen deficiencies usually first appear on older leaves. These leaves will turn light green or yellow as nitrogen is relocated from older, less productive leaves to the newest growth. Cool growing conditions in early spring often cause plants to develop a temporary nitrogen deficiency. This is usually due to poor growing conditions, and not necessarily a lack of nitrogen in the soil.

Nitrogen and the environment

The level of nitrogen in the soil changes constantly. Processes like leaching and denitrification result in the loss of nitrogen from the soil. Denitrification occurs when the soil is waterlogged. Anaerobic microbes convert nitrate and ammonia into nitrous oxide. This gas can contribute to air pollution and is approximately 300 times more potent than carbon dioxide as a greenhouse gas.

The nitrate form of nitrogen, while being readily available to plants, moves easily in water through the soil. As a result, it has the potential to pollute groundwater and surface water.

When the amount of nitrogen supplied to the crop meets the crop's growth requirements, the risk of loss to the environment is greatly reduced. The potential for nitrogen loss is highest during the late fall and early spring. The application of nitrogen according to the crop's need reduces residual soil nitrogen at the end of the season and leaves little available for losses.

It is important to account for fertilizer, manure and other sources of nitrogen when you assess a crop's fertility requirements. Other management practices to reduce the risk of nitrate losses include:

• use of cover crops
• timing nitrogen applications close to crop nitrogen uptake
• reduction of total nitrogen applications
  

Sources of nitrogen

Synthetic fertilizer

The most common nitrogen fertilizer sources are outlined in Table 3-10. Fertilizer Materials: Primary Nutrients, below. Generally, all nitrogen sources are effective in providing a crop with nitrogen. Cost, crop management and ease of application will largely determine the selection of one source over another.

If nitrogen is to be applied early in the spring when soils are below 10°C, urea may help prevent leaching losses. Under these conditions, it takes 3-6 weeks for urea to convert to the plant-available ammonium and nitrate forms. As only nitrate-nitrogen is susceptible to leaching losses, early spring rain will not result in leaching. By the time the nitrate conversion has occurred, the crop is entering its rapid growth phase and minimal downward percolation of water will make leaching less likely.

Table 3-10a. Fertilizer Materials: Primary Nutrients (Nitrogen) (PDF 73 kb)

¹ Liquid under pressure.

See also:

• Fertilizer Materials: Phosphorus
• Fertilizer Materials: Potassium

Products that modify the release of nitrogen

Slow-release fertilizers have granules that have been coated in sulphur or a polymer to control the release of the nitrogen over an extended period of time. Nitrification inhibitors are added to nitrogen fertilizers to help delay the chemical conversion of urea into the plant available forms. Depending on the weather conditions, the delayed release of these products may not necessarily coincide with peak nitrogen demand.

Manure nitrogen

In addition to nutrients and micronutrients, manure also supplies valuable organic matter that helps to build and maintain soil structure. Adjust fertilizer rates to account for the nutrients in manure.

50-60% of the nitrogen available in manure is available to the crop during the first growing season after application. The remaining organic nitrogen becomes available in small, diminishing quantities in successive years. Up to 10% of the total nitrogen in manure can be available for the following year. Where manure is applied regularly to the same field, there may be a significant amount of residual nitrogen available for a crop.

The quantities of nutrients contained in manure can vary greatly. The type of livestock, ration, bedding, added liquids and storage system all affect the final nutrient analysis. Table 3-11. Average Fertilizer Replacement Values for Different Types of Manure, provides the approximate amount of crop-available nitrogen in manure. A manure-analysis, available from several laboratories in Ontario, provides the most accurate assessment of the nutrients contained in a specific source of manure. Refer to Appendix C. Accredited Soil-Testing Laboratories in Ontario, for a list of laboratories providing this service.

Table 3-11. Average Fertilizer Replacement Values for Different Types of Manure (PDF 111 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.

Use manure responsibly:

Manure and food safety

Fruit can become contaminated in the field if it comes into contact with pathogens that cause human illness. These pathogens may come from manure and manure-based composts. The lifespan of these pathogens in manure is not well known. Proper composting of manure, which results in the compost being heated to a specific temperature for a specific period of time, will reduce the level of most pathogens. Manure application within 120 days before harvest is not recommended.

Legumes

Legume crops are able to capture atmospheric nitrogen. As the legume crop residue decomposes, this nitrogen becomes available for subsequent crops. When fruit crops are planted following alfalfa hay, or a legume cover crop such as red clover, the rate of fertilizer nitrogen should be decreased according to Table 3-12. Nitrogen Contribution of Plowed Down Legumes.

Table 3-12. Nitrogen Contribution of Plowed Down Legumes (PDF 69 kb)

¹ Applies where the legume stand is thick and over 40 cm high.

Other organic nutrient sources

Biosolids derived from paper mill fibre have been used in orchards and vineyards to maintain soil organic matter. However, before this material can be applied to land, you must have a Certificate of Approval issued by the Ontario Ministry of the Environment (MOE) for the site. Rates depend upon the nitrogen content of the material and can be in the range of 25-30 dry tonnes/ha. However, MOE has final approval of the material and the applied rate. Any application restrictions are included as conditions on the Certificate of Approval.

Biosolids from sewage treatment plants or paper mill waste can be a useful source of nutrients and organic matter. Guidelines for their use are available from OMAFRA and MOE. A Certificate of Approval for land application is required and is available from MOE. An analysis of nutrients applied should be given by the applicator to the landowner whenever biosolids are applied. Always consult with your processor, packer or broker before applying municipal sewage biosolids on ground intended for vegetables anywhere in the rotation.

Note: Municipal sewage biosolids must not be applied to tree fruits and grapes within three months of harvest. For small fruit (strawberries, raspberries and blueberries) application may not occur within 15 months of harvest.

Avoid fertilizer burn!

Many nitrogen and potash fertilizer materials contain high amounts of salts. If a germinating seedling or young transplant comes into contact with a concentrated fertilizer band, the tender roots may become seriously damaged. For this reason, it is important to ensure that the correct fertilizer and the appropriate rate are selected for each application.

Urea is an effective, economical source of nitrogen for broadcast applications but it has a relatively high salt index. It is not suitable for use in starter fertilizers or banded applications. If low soil moisture conditions exist at the time of planting, urea burn may occur on coarse sandy-loam soils and growers should consider switching to a different nitrogen source. Anhydrous ammonia also has a relatively high salt index. It is an effective source for side-dress applications that must be injected into the soil.

Ensure that starter or transplant fertilizers contain only as much nitrogen as necessary to get the crop started. Fertilizers that contain more than half as much nitrogen as phosphate frequently contain urea and may cause crop damage.

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