Nutrients leave the paddock with the grain. A good yield means more nutrients go out and less remain in the soil. Some nutrients may need topping up to maintain yields.
How much topping up?
Different grains contain varying amounts of nutrients. The table below gives estimates of the nutrients removed in harvested grain. The numbers come from the Canola best practice management guide for south-eastern Australia. Ideally, analyse a sample of grain from your paddocks to calculate the actual amounts of nutrients removed.
|Crop||Nutrient (kg/ha of grain)|
Crop nutrition for next season
Factor nutrient export in the grain into your crop nutrition plan for next season:
- Calculate the nutrient removed in harvested grain for a paddock.
- Estimate nutrient levels by subtracting the nutrients removed from a pre-crop soil test.
- Use yield estimates to predict nutrient demand for the next crop.
- Identify likely nutrient deficits where soil nutrients may not meet crop demand.
- Correct these to support yield potential for the next season.
Long-term paddock fertility
Nutrient replacement models consider how to maintain soil nutrients within target ranges. Nutrient application strategies are usually longer-term. You can use nutrient performance indicators to track changes in paddock nutrients.
When soil nutrients are already in target ranges:
- match fertiliser applications with the nutrients lost in harvested grain
- correct deficiencies to meet crop demand based on yield potential.
When nutrients are below target ranges:
- apply fertiliser to meet current crop demand plus extra to build up nutrients in the soil.
Check your grain nutrients
Grain nutrient levels vary within and between paddocks. If possible, test grain from a few different paddocks. Phosphorus levels in grain can vary a lot from the reference values. Low protein in grain is a sign that not enough N was available to meet the water limited yield potential.
Test your grain to know how much nutrients were actually removed. This will give numbers more accurate nutrient budgets than reference values.
Tissue testing grain will also tell you if the crop
- had any other nutrient deficiencies
- produced grain suitable to use for seed next season.
Confirm with soil tests
Soil tests assess current paddock fertility levels. This improves estimates of next season’s fertiliser needs. Regular soil tests can track paddock fertility and watch for long-term declines in:
- nutrient levels,
- organic matter
- soil pH.
Don’t forget about stubbles
Some nutrients from crops remain in the stubbles. These also affect next seasons fertiliser budget. Account for any nutrient tie-up in stubble in your nutrient budgets.