Fertility and Agronomic Interactions


Soil sampling and soil testing is essential to measure soil nutrient levels and other chemical and physical soil properties that will influence crop growth. Soil testing should be used to determine fertilizer applications on specific fields. Where soil tests are not available, general recommendations may be followed. However, field history, cultural practices and inherent fertility of the field must be considered when using general recommendations.


Water is a critical nutrient for crop growth. The soil available water at planting is critical for seed germination, stand establishment and early plant growth but precipitation during a growing season plays a greater role in determining oat yield than soil available water at seeding. Available soil moisture also interacts with nitrogen levels to affect lodging in oat. Under irrigation, growing season water demands are slightly lower for oat than for spring wheat (17 inch or 430 mm for oat compared to 18 inches and 460 mm for spring wheat) (Irrigated Crop Recommendations, Agri-Facts, Alberta Agriculture).

As stated above, oat is well suited for no-till or reduced tillage where water retention is maximized by snow trapping and enhanced water infiltration into the soil profile.

Fertility and Agronomic Interactions


In most fields in western Canada, nitrogen (N) is the most yield limiting nutrient.

The amount of N fertilizer required to achieve optimum yield depends on:

  • soil nitrate-N (NO3-N) levels
  • N mineralization potential of the soil during the growing season
  • soil moisture at the time of seeding
  • expected precipitation during the growing season
  • oat variety

These conditions can vary greatly from year to year and with the previous rotational crop. Requirements for N fertilizer increase when the soil test nitrate level is low or when soil moisture or in-season precipitation is high.

Soil test for nitrate-N to a depth of 24 inches (60 cm) and measuring the amount of stored soil moisture are required when determining optimum fertilizer nitrogen rates. The more moisture that is received, the higher the yield potential and a higher requirement for nitrogen is needed to achieve that yield.

Generally, a100 bushel/acre (3584 kg/ha) oat crop will require total nitrogen (soil N plus N fertilizer) of 97-117 lbs/acre (110-131 kg/ha). Soil test recommendations will provide nutrient recommendations specific to target yields, location and moisture levels.

Nitrogen rates above optimum levels may cause increases crop lodging and decrease yield (May et al. 2017). Increasing nitrogen rates also resulted in statistically significant declines in test weight, kernel weight and the percentage of plump kernels, all detrimental crop quality measurements. In studies conducted in eastern Canada, Yan et al. (2017) reported that yields increased with nitrogen rates up to 134 lb/acre (150 kg/ha) and that varieties responded differently to nitrogen. Location (environment) also influenced the results. However, in Yan et al. (2017), test weight, kernel weight and the percentage of plump kernels was not measured, but they noted that β-glucan content was not affected by nitrogen levels.

Research conducted by Ma et al. (2017), and May et al. (2017) both concluded that optimum oat yields, without reductions in kernel weight and plumpness, were achieved when the soil + fertilizer N level were approximately 89 lbs/acre (100 kg/ha) (Figure 3.5).

Fertility and Agronomic Interactions
Fertility and Agronomic Interactions
Figure 3.5. On the right are oat with a total of 71.4 lb/ac (80 kg/ha) soil + fertilizer nitrogen, while on the right are oat grown with 110 kg/ha soil + fertilizer nitrogen (photo courtesy of Dr. Chris Willenborg).

Ma et al. (2017) reported that variety choice was critical to both yield potential and susceptibility to lodging. High yielding varieties with lodging resistance are most likely to respond favorably to increased nitrogen rates.

Nitrogen for organic production can be added to the soil by producing crops that are able to “fix” their own nitrogen (legume crops such as alfalfa, clovers or pulses) and working the crop residue into the soil (plowdown). Livestock manure is also a good source of nitrogen.


About 80% of prairie soils are considered phosphorus (P) deficient. Soil P availability to plants can be assessed by soil sampling and testing to determine plant available soil P. However, response to phosphate in oat (increase in yield) is inconsistent and often does not correspond to soil test levels.

Crop response to applied P fertilizer depends on the level of plant available P already in the soil, as well as soil moisture and temperature conditions early in the growing season.

Previously, an application of phosphate at 18-28 lbs/acre (20-30 kg/ha) with half this amount applied with the seed, was considered adequate to produce optimum yields.

Chris Holzapfel, from AAFC, Indian Head, was quoted as saying “research has shown that oat response to phosphorus fertilizer application can be inconsistent, but maintaining P levels is important from a long-term soil quality perspective. The crop in his demonstration presumably removed over 44 lbs P2O5 per acre (49 kg/ha) in the highest yielding treatments.

“When you are removing that level of phosphorus from the soil (Table 3.4), you need to be replacing it or you will be drawing down the soil residual phosphorus reserves. You are fertilizing the soil as much as you are trying to feed the crop.”

Situations where oat yields may respond to phosphate fertilizers include:

  • Fields that have not received phosphate fertilizers in past 5 years
  • Fields newly broken or broken from legume forage production
  • Crops grown on fallow
  • Cold, wet soils
  • Sandy or gravelly soils

Phosphate for organic production can be added to the soil by applying rock phosphate. Rock phosphate has a very low solubility, so it is not readily available. Therefore, it should be used as a part of a long-term program.

Another strategy is to include using buckwheat as a plough-down crop. Buckwheat has been shown to have the ability to accumulate phosphate and make it available following a plough-down. Livestock manure is also a very good source of phosphate.


Potassium helps in the building of protein, photosynthesis, grain quality and reduction of diseases. It also may increase straw strength. The response of oat to potassium usually occurs when soil test levels are below 280 lbs/acre (250 kg/ha). Potassium deficient soils tend to be light textured (sand to sandy-loam), alkaline, carbonated and imperfectly to poorly drained in their natural state. Organic soils are also frequently deficient in potassium.

An application of 15 lbs/acre (17 kg/ha) of potassium chloride (0-0-60), seed row applied may result in a positive crop response in cold, wet soils even when soil test levels are sufficient. Applications made at levels higher that 18 lbs/acre (20 kg/ha) should be side-banded or broadcasted to avoid damage to seedling plants.

Potassium for organic production can be added from a number of sources including wood ash, greensand (glauconite), and potassium sulphate, which will also add sulphur to the soil. Livestock manure is also a very good source of potassium.


Sulphur is essential for production of protein and oil. It promotes activity and development of enzymes and vitamins as well as helping in chlorophyll formation.

The oat crop requires sulphur in a fairly high level in comparison to other crops. It is required at lower levels that canola but about the same per acre levels as wheat.

Deficiencies of sulfur appear similar to nitrogen deficiencies as pale, stunted plants. Often sulphur deficiencies appear as isolated spots in a field due to extreme variability across a field. This may also result in misleading results from soil tests if a high-sulphate area is inadvertently sampled.

An application of 9–15 lbs/acre (10-18) kg/ha of a sulphate fertilizer will be sufficient in most soils, especially if it is part of a well-balanced sulphur program. Applications of elemental sulphur may not provide adequate levels of sulphur, especially if applied in the seed-row.

Sulphur for organic production can be added from a number of sources including some 33 sources of potassium sulphate. This will also add potassium to the soil.

Other sources include gypsum (calcium sulphate) and some sources of elemental sulphur. Livestock manure may be a good source of sulphur.


There are a number of nutrients classified as micro-nutrients that are essential to plant growth. When deficient, these may cause a reduction in crop productivity. Normally, micronutrients are not deficient in western Canadian soils.

Of all the micronutrients, oat is most susceptible to a deficiency of manganese. Manganese deficiencies mainly occur in organic soils, high-pH soils or sandy soils low in organic matter. A manganese deficiency in oat results in a disorder known as Grey Speck (Figure 3.6). Oat show manganese deficiency as a general yellowing and stunting, occasionally with grey specks on the leaves. A foliar application of manganese will cure a manganese deficiency where it occurs.

Agronomic Interactions

Cultivar choice and agronomic decisions are closely linked. Varieties respond differently to nitrogen levels (Yan et al 2017) but increasing nitrogen can be detrimental to test weight and may increase lodging which can increase harvest difficulties and is detrimental to crop yield and quality. The environment, especially available moisture influences all outcomes.

In areas with adequate moisture, a lodging resistant variety should be chosen, but in some cases, favored varieties may not have sufficient ß-glucan to meet quality standards (see comments on AC Morgan above).

High yielding varieties that are disease and lodging resistant will only perform well when sufficient nutrients, including water, are available.

The interactions of agronomic, variety choices and environment can be confusing but scientific research addresses the probability of success by conducting multiple trials, in multiple years and location. Some practices are usually the best.

Variety choice is key, Early seeding and increased seeding rates make oat more competitive and reduce tiller numbers.

These practices can reduce wild oat competition while avoiding harvest management difficulties.

Figure 3.6 Grey speck symptoms on oat. From Producing milling oat in western Washington: Guide to grain quality optimization and marketing. Winkler and Murray (2017).
Figure 3.6 Grey speck symptoms on oat. From Producing milling oat in western Washington: Guide to grain quality optimization and marketing. Winkler and Murray (2017).

Research Paper (2004): Canadian Journal of Plant Science (2004) 84: 1025-1036
“Effect of nitrogen, seeding date and cultivar on oat quality and yield in the eastern Canadian prairies”

William E. May, Ramona M. Mohr, Guy P. Lafond, Adrian M. Johnston, and F. Craig Stevenson.

As the portion of the oat crop increases for the human consumption segment, yield and quality, especially test weight, are important production parameters for a profitable oat crop. “The grower has to strike a balance between test weight and yield when optimizing N rate because the value of the oat is a function of both grain yield and quality.”

In this study, conducted from 1998 to 2000, 4 locations were used; one in Manitoba and three in Saskatchewan. The locations were: Brandon, Indian Head; Canora; and Melfort. Three seeding dates were used, early May, mid May and early June, along with the two cultivars AC Assiniboia and CDC Pacer. The four nitrogen rates used were 15, 40, 80 and 120 kg N/ha.

Results And Discussion:
Panicles per plant was the yield component that accounted for most of the yield increase achieved from increasing rates of nitrogen. Kernel weight was the yield component that decreased with increasing N. Physical seed quality tended to be highest with early seeding and low N rates.

Across site-years, the overall grain yields increased with increasing N supply, but the increase levelled off at the rate of 100 kg N ha-1. The optimum N rate was found to involve a trade-off between yield and quality.


The total amount of plant nutrients removed from the soil by a crop depends on the yield.

The greater the yield, the more nutrients are utilized. Removal of nutrients has implications for the subsequent crops. Based on equal seed yields per unit area, whole barley, wheat and oat plants extract about the same combined quantities of nitrogen (N), phosphorus (P2O5), potassium (K2O), and sulphur (S) from the soil, but considerably less than canola. When only the seed is removed, and all straw is left on the field, oat removes the least amount of nutrients from the soil (except for sulphur) compared to barley, wheat or canola (Table 3.4).

Table 3.4. Nutrients used by crops* in lb/acre.
(To convert to kg/ha by multiplying by 1.12. Canola yield is extremely high, but in order to make the comparison, it was left at the same weight as the other grains).
Wheat (48 bu/ac) Seed 70.5 28.5 18.7 4.5
Straw 28.5 6.2 57.1 7.1
Total 99.0 34.8 75.8 11.6
Barley (60 bu/ac) Seed 58.0 21.4 19.6 4.5
Straw 30.3 8.0 65.1 7.1
Total 88.3 29.4 84.8 11.6
Oat (84 bu/ac) Seed 51.7 21.4 15.2 7.1
Straw 35.7 13.4 62.5 8.9
Total 87.4 34.8 77.6 16.1
Canola (57 bu/ac) Seed 107.1 50.9 25.9 18.7
Straw 62.5 23.2 108.0 15.2
Total 169.5 74.1 133.8 33.9
*Source: Western Canada Fertilizer Association.