In the last issue of Grainews, I discussed agronomic management of growing mustard. In this issue we’ll discuss nitrogen requirements; in the next issue, we’ll discuss the other nutrients mustard needs to achieve optimum production.
Mustard grown on cereal stubble almost always needs nitrogen fertilizer, frequently needs phosphate fertilizer and occasionally needs sulphur fertilizer. Soil testing to 24 inches is important to develop a sound fertilizer management program.
All mustard types are very sensitive to insufficient nitrogen (N) and are very responsive to N fertilization when plant available soil N levels are low. On continuously cropped land, mustard responds well to the addition of N fertilizer, and yield gains in the range of 30 to 70 per cent are common. Our field research in Alberta concluded that N fertilizer application was the most influential agronomic factor controlling the yield and quality of mustard. Adequate N promotes vigorous plant growth, large leaf area with a deep green colour, branching, flowering and pod development.
Mustard takes up N from the time the roots begin to function until all uptake of nutrients and water ends with maturity. Under normal growth conditions, the amount of N taken up is greatest during the early stages of growth, and then, N is translocated within the plant from leaves and stem to pods and seeds during flowering and maturity.
The primary soil N source taken up by mustard roots is nitrate-N (NO3-). To achieve optimum yield, an adequate supply of plant-available N is required. Soil N comes from mineralization of soil organic matter. The amount and rate of mineralization of soil organic matter is affected by soil temperature, moisture, pH, aeration, amount of soil organic matter.
Nitrogen in older leaves is redistributed to younger leaves to maintain growth. As a result, when N is deficient, the older leaves first show a characteristic lighter green to yellow colour; then, they will wither and drop by flowering.
The amount of nitrogen fertilizer required depends on four factors:
- The level of soil nitrate-nitrogen (NO3-N) at the time of planting;
- The mineralization potential of the soil during the growing season;
- Stored soil moisture at planting; and,
- Expected precipitation during the growing season.
The lower the soil N level, the greater the need for nitrogen fertilizer. As stored soil moisture increases and/or growing season precipitation increases, the need for additional nitrogen fertilizer increases. The optimum N fertilizer rate is a function of soil N, stored soil moisture (SSM) in spring and expected growing season precipitation (GSP). Therefore, soil testing for nitrate-N to 24 inches and determining the amount of stored soil moisture before seeding are critical to aid in determining optimum fertilizer N rates.
Our Alberta research was used to develop general fertilizer recommendation tables for the brown and dark brown soil zones based on three soil moisture conditions.
Application timing and placement
Ideally, N fertilizer should be applied at the time of seeding, using a direct seeding system. Mustard is extremely sensitive to seed-placed N fertilizer, so it is best to place all N in a side-band or mid-row band at the time of seeding. Side-banded N should have at least 1-1/2 inch of separation between the seed row and fertilizer band.
One option is to band N prior to seeding. The disadvantage of spring banding N fertilizer is that the seedbed is disturbed and valuable seed bed soil moisture can be lost. Therefore, it is generally a better option to band N fertilizer in very late fall.
For farmers who want to place N fertilizer with the seed using a single shoot, direct seeding system, an option is to use coated, slow release urea such as ESN (Environmentally Smart Nitrogen). Polymer coated urea will release the coated urea fertilizer slowly over a period of up to 60 days. Recent Alberta Agriculture research suggests that rates of up to 40 lbs. N/ac. can be safely seed-placed with a 10 per cent seedbed utilization.
In my next article, I’ll continue on this theme with recommendations for phosphorus, potassium, sulfur and micronutrients.