4Rs for Nitrogen Management in Berry Crops

Author: Tejendra Chapagain, PhD, PAg

Nitrogen (N) is one of the primary limiting elements in most Ontario soils. However, nitrogen use efficiency (NUE) is low, with only about 40-65% of the total applied fertilizer N is utilized by the crop. Therefore, effective N management provides opportunities for enhancing nitrogen use efficiency and for reducing the environmental footprint of crop production, which minimizes fertilizer requirements and saves input costs. This is possible by using 4R nutrient stewardship.

The 4R’s are all about making the right decisions on fertilizer products (right sources) along with the right timing, right placement, and right rates of application. And high fertilizer nitrogen prices are providing an incentive to manage N as efficiently as possible.

Because berry crops have shallow root systems and high moisture demands, precise nitrogen (N) management is critical to balance crop growth with the need to prevent nitrate leaching from the root zone by excessive spring rains or irrigation. Over application also reduces yield and delays fruit maturity. The following provides suggested 4R Nutrient Stewardship guidelines for Ontario berry production:

Right Source

Selecting the proper form of nitrogen depends heavily on the specific berry crop, soil type, and soil pH.

• Blueberries: Always choose an ammonium-based source like ammonium sulphate (if soil pH is above 5.0) or urea (if soil pH is below 5.0). Blueberries cannot efficiently process nitrate forms of nitrogen, and muriate of potash must be avoided due to chloride toxicity.
• Strawberries and Raspberries: Nitrate or balanced ammonium-nitrate forms work best. However, avoid excessive ammonium forms of nitrogen if anthracnose fruit rot or angular leaf spot are active in your strawberry fields, as it can worsen disease pressure.
• Organic Amendments: Soil organic matter is the driving force in making N management decisions. In general, each 1% organic matter content in the soil releases about 10-15 pounds of nitrogen per year. Therefore, a soil with 4-6% organic matter may release a significant amount of nitrogen from the soil and can often tolerate reduced synthetic fertilizer rates.

Use well-composted manure but it must be factored into the overall nitrogen budget to prevent late-season release. Also, account for nitrogen credit if a large amount of mulch is incorporated during renovation. Be cautious with high carbon-to-nitrogen mulches like sawdust, straw, or wood chips. These can induce temporary nitrogen deficiency by tying up available soil nitrogen as they decompose.

• Enhanced Nitrogen Fertilizers: Blueberries also respond well to slow-release nitrogen fertilizer which allows for less frequent fertilizer applications. In fact, some types can be applied just once a year. The price per pound is expensive, but labor costs are greatly reduced. More Ontario specific research is required on the use of slow-release fertilizers, controlled release fertilizers and those containing nitrification or urease inhibitors to minimize N losses and improve crop nitrogen use efficiency in berry crops.

Right Rate

The target rate must balance crop removal against existing soil nutrients to avoid soft fruit, excessive canopy growth, and disease.

Establishment Year:

Strawberries: Apply 50 kg of actual nitrogen per hectare just prior to or 2–3 weeks after planting.

Blueberries: A total of 12-18 g of actual nitrogen per bush in a split application. They are often killed by over fertilization with nitrogen or the use of the wrong type of fertilizer since they are a salt sensitive plant. This is especially true under non-irrigated conditions.

Raspberries: 30–40 kg/ha of actual nitrogen as a side dressing 2-3 weeks after planting (i.e., once the soil has settled). Do not apply nitrogen before planting.

Mature Crops:

June-bearing strawberries generally require 75-90 kg N/ha annually, largely split between renovation (i.e., 50 kg N/ha in late June or July) and late summer (i.e., 25-40 kg N/ha in mid-August).

Mature highbush blueberries (6+ years) may require increased amounts each year until it reaches 36–48 g of actual nitrogen per bush.

Raspberries: Nitrogen rate slightly increased to 40-60 kg N/ha in year 2, and 50-75 kg N/ha in year 3 and the subsequent years.

Right Time

Timing applications with high crop uptake minimizes environmental losses though leaching, volatilization and nitrous oxide emission.

• Strawberries (June-bearing): Do not apply nitrogen in early spring to established fields, as it causes soft fruit and dense, disease-prone canopies. Instead, apply the largest portion at renovation immediately after harvest, followed by a smaller application in late August to feed developing fruit buds for the next year. The day-neutral varieties, however, are fertilized in the spring when leaves first appear, and again in the summer when berries begin to grow.
• Blueberries: Apply just prior to budbreak in the spring. On typical Ontario sandy soils, split this into two-thirds at budbreak and the remaining one-third at petal fall to increase nitrogen-use efficiency.
• Raspberries: For established plantings, apply about half of the total annual nitrogen early in the spring (late March to early April) to support budbreak and early leafy growth, and the remaining half roughly four to six weeks later (i.e., late May to June).

Fall Restriction: Never apply nitrogen fertilizer late in the fall to prevent leaching or late-season plant growth that is highly susceptible to Ontario’s winterkill. Also, Ontario’s autumn rains easily leach late-season nitrogen out of the shallow root zone before or after the plants go dormant.

Right Place

Placement ensures shallow berry roots can access nutrients before they volatilize or wash away.

• Fertigation: For day-neutral strawberries and crops grown on plastic mulch, deliver nitrogen in small, weekly increments through drip irrigation. This places water-soluble N directly into the active root zone.
• Banding and Side-Dressing: For matted-row system strawberries, bush berries and raspberries, place granular fertilizer in a narrow band roughly 30 cm out from the base of the plant or around the drip line of the bush. Avoid broad broadcasting into the alleyways, which only feeds weeds and wastes money. The nitrogen in urea can be lost as ammonia gas if it is applied to the soil surface and not incorporated. The ammonia can cause strawberry leaves to blacken. Incorporation or banding of urea prevents this problem.
• Setbacks: Maintain mandatory environmental setback distances from any open surface water or tile drainage inlets according to Ontario nutrient management regulations.

Variable Rate Technology (VRT)

VRT is a tool that allows farmers to apply fertilizers, water, chemicals, and seed at different rates across a field. There are two types of VRT: map-based and sensor-based. Map-based VRT adjusts product application based on a pre-generated map of the field. However, sensor based VRT uses mounted sensors that measure soil properties or crop characteristics in real-time.

Diagnostic Tools

Optimum N rates vary significantly by crop type. The most accurate application plans rely on annual leaf tissue analysis (late June to early August) paired with an accredited OMAFA soil test taken to a depth of 30 cm for nitrate tracking. Investing in soil testing every three years and plant tissue testing annually will provide an accurate assessment of nutrient needs and ensure you apply the right rate at the right time and match application to production improving your bottom line.  

Dr. Chapagain is Soil Fertility Specialist with Ontario Ministry of Agriculture, Food and Agribusiness (OMAFA) based in Guelph.