Flax Tips: Fertility Requirements for Flax
This document will review the current research on the effects of fertilizer practices and crop rotation on flax yield. To accurately manage soil fertility in your rotation, soil testing and consultation with your local agronomist is recommended.
Nutrient Uptake and Removal
Table 1 shows nutrient uptake and removal of macronutrients by flax. ‘Uptake’ refers to nutrients taken up by roots into the plant over the growing season. While ‘removal’ refers to the nutrients in the harvested seed portion of the crop removed from the field and exported off the farm. The difference in uptake and removal is straw/stubble left in the field.
Table 1. Estimated Macronutrient Uptake and Removal by Flax (Pounds/Bushel)
| Nitrogen (N) | Phosphorus (P2O5) | Potassium (K2O) | Sulphur (S) | |
|---|---|---|---|---|
| Uptake | 2.6 – 3.2 | 0.75 – 0.92 | 1.6 – 2.0 | 0.5 – 0.6 |
| Removal | 1.9 – 2.3 | 0.6 – 0.7 | 0.5 – 0.7 | 0.2 – 0.3 |
Estimates are calculated from the Nutrient Uptake and Removal by Field Crops. Western Canada 2001. Canadian Fertilizer Institute.
Table 2 shows the difference in nutrient removal at three different target yields: 22 bushel/acre, 32 bushel/acre and 42 bushel/acre. For example, a 32 bushel/acre flax crop will remove (i.e. export off the farm) 80 lbs. of nitrogen per acre.
Flax yield opportunities vary on the Prairies depending on year, region and farm-specific conditions like available soil moisture and prevalence of lodging. Soil test and apply fertilizer according to a realistic target yield. Excess nitrogen levels may predispose your flax crop to lodging.
Table 2. Estimated Macronutrient Removal by Flax Based on Target Yield
| Target Yield | |||
|---|---|---|---|
| 22 bushel/acre | 32 bushel/acre | 42 bushel/acre | |
| — Nutrient Removal* — | |||
| Nitrogen | 55 lbs./acre | 80 lbs./acre | 105 lbs./acre |
| Phosphorus (P2O5) | 15 lbs./acre | 22 lbs./acre | 29 lbs./acre |
| Potassium (K2O) | 15 lbs./acre | 19 lbs./acre | 25 lbs./acre |
| Sulphur | 6 lbs./acre | 6 lbs./acre | 8 lbs./acre |
*Estimated nutrient removal for flax grain using the International Plant Nutrition Institute web-based calculator (http://www.ipni.net/article/IPNI-3346). Rates are slightly higher than estimates from the Canadian Fertilizer Institute (Table 1).
Right Source, Right Rate, Right Time, Right Place!
The 4R principles of nutrient stewardship provide a framework for maximizing crop yield and improving economic efficiency by reducing environmental losses. Below you will find what we know about the 4Rs as they relate to flax fertility.
Nitrogen
Placement
Flax seed is extremely sensitive to fertilizer damage. For this reason, nitrogen (N) fertilizer should not be placed with the seed. Optimum placement of N in the Canadian prairies is spring before fall and banding before broadcast. Studies have found little difference in side-band vs. mid-row band. Incorporating N fertilizer can be a time saver, but environmental loss is the trade-off. Nitrogen leaching is a concern since flax has a relatively shallow root system. Flax may be a good candidate for split-applications due to N sensitivity and since it can be susceptible to mid-season N deficiencies.
Rate
Flax can show good response to fertilizer N when soil N is low. Soil testing prior to applying N fertilizer is highly recommended, as flax can be limited by both insufficient and excess N. Studies show that N deficiency can reduce the production of tillers, fruiting branches and capsules produced per plant, while excess N can increase the incidence of lodging and delay maturity. Without a soil test, 31 to 98 lbs./acre of actual N is recommended for flax seeded on stubble. Be careful to consider the environmental conditions and N supplying capacity of your soils. For example, if conditions are dry or excessively wet, flax growth and uptake may be limited. As well, N will be subject to losses to the environment, through denitrification and leaching.
Fertilizer Source and Timing
There has been limited research on optimum fertilizer types and timing for flax. A study in Saskatchewan found there were very few differences in agronomic performance of urea vs. anhydrous ammonia and side-banded vs. mid-row banded, but other studies have found that urea can be more damaging to seeds than anhydrous ammonia. Due to environmental losses, fall-banded N was less effective than spring-banded N.
Phosphorus
Rate
Phosphorus (P) is a very important nutrient for flax growth, however, flax has generally shown an inconsistent response to P fertilization. Some research in Western Canada shows positive responses to P2O5 fertilizer placed below or side-banded with the seed, at rates between 13 and 36 lbs./acre, on soils with low background P. However, the impact of crop rotation frequently has a more significant effect on flax yield than P fertilization. This is due to flax forming associations with mycorrhizal fungi, a symbiotic relationship between plant root and fungi to obtain P. To better manage P for flax, manage soil P throughout your rotation, ensuring an adequate soil residual supply for flax and do not grow flax after a non-mycorrhizal crop like canola.
Placement and Source
There is very little work on differences in fertilizer P sources on flax yield, but similar to nitrogen fertilizers, P fertilizers can also cause seed damage when placed in the row. As little as 13 lbs./acre of seed-placed P2O5 (MAP) has been shown to have negative effects on crop establishment. To ensure crop emergence, P fertilizer should be placed away from the seed either below the seed row, side-banded or broadcasted. Controlled release P fertilizers may be a good option for preventing seedling burn while ensuring adequate P rates when soil P is very low.
Potassium and Sulphur
Flax is a moderate user of both K and S nutrients. K deficiency is unlikely to occur in clay-textured soils, but could be an issue in sandier soils. For rotations with high S use crops like canola or peas, S applications may be beneficial if soils are below 22 lbs./acre in the top 60 cm.
Iron and Zinc Chlorosis
Most soils in Western Canada are generally moderately high in calcium and magnesium. However, high levels of these nutrients can influence the availability of others. Flax is more sensitive to zinc deficiencies than other crops, and may cause “chlorotic dieback” or zinc chlorosis (yellowing of leaves). If plants recover, they will usually have delayed maturity. Excessively wet, calcareous soils are more susceptible to zinc and iron chlorosis.
Look for irregular patterns of chlorosis in the field (Figure 1). If you know that your soil conditions can cause zinc chlorosis, consider soil testing and the use of fall applications of zinc. Adding zinc once symptoms have shown up in the field has not been shown to remedy zinc chlorosis.
Flax can grow out of iron chlorosis if wet conditions are alleviated. Prevention of iron chlorosis may be achieved by better drainage. AC Emerson, if commercially available in your area, is more tolerant to iron chlorosis than other varieties.
Figure 1. Chlorosis in Flax
For further information on soil fertility, please visit:
Saskatchewan Ministry of Agriculture: http://www.saskatchewan.ca/business/agriculture-natural-resources-and-industry/agribusiness-farmers-and-ranchers/crops-and-irrigation/soils-fertility-and-nutrients
Alberta Ministry of Agriculture and Forestry: https://www.agric.gov.ab.ca/app21/infopage?cat1=Soil%2FWater%2FAir&cat2=Soil%20Fertility
Manitoba Agriculture, Food and Rural Development: http://www.gov.mb.ca/agriculture/crops/soil-fertility/
Canadian Fertilizer Institute: http://fertilizercanada.ca/
Flax Council of Canada Flax Growers Guide: https://archive.flaxcouncil.ca/wp-content/uploads/2015/02/FCOC-growers-guide-v11.pdf
