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Nutrient removal as a soil fertility planning tool

By Lyndon Hicks PAg, Crops Extension Specialist, Yorkton

February 2019

Fall soil testing is a great tool to give producers a snap shot of the levels of nutrients remaining in their soil, but it is not the only tool. We can also consider using the nutrient replacement method, which involves replacing the nutrients removed by the crop. To obtain consistent high yields and maintain sustainability in our agricultural systems, we should be replacing those nutrients that are being removed from the field in the form of grain. In other words, we need to balance the inputs with the outputs.

How do we do this? Knowing which nutrients and how much each crop removes with the grain is the first step. Each crop differs in the nutrient content of the grain and therefore differs in the amount of nutrients removed with the grain. Canadian Fertilizer Institute has a great publication called “Nutrient Uptake and Removal by Field Crops,” and it gives an estimate of the nutrient uptake and removal rates based on typical nutrient concentrations found in crops grown in Western Canada under good growing conditions. Table 1 is a condensed version of the table and can be used as a guide.

High-protein crops such as peas and canola need a lot of nitrogen. These crops use approximately three pounds of nitrogen for every bushel of grain produced. However, it is not all removed in the grain. With canola, for every bushel of grain removed, two pounds of nitrogen are taken with it. In other words, a 50 bushel-per-acre canola crop uses 150 pounds of nitrogen, and 100 pounds of the nitrogen is removed with the grain. With the replacement strategy, to target a similar crop the following year, the 100 pounds of nitrogen that were removed should be replaced. Replacement strategy allows us to replace what we remove.

The obvious method of replacing nitrogen is through fertilizer application. However, using pulse crops is also a way to manage nitrogen on that field. Pulse crops can fix nitrogen from the air and do not need additional fertilizer nitrogen to produce high-yielding crops. In fact, seeding peas on fields where the most nitrogen was removed may be a good fertility management strategy and may save on fertilizer costs.

It is not only nitrogen that we can use the replacement strategy with but other nutrients, as well. Phosphorous is one nutrient that the replacement strategy works really well with, as it doesn’t move much in the soil. Oilseeds and grain legume crops take up and remove more phosphorous than cereals. With canola, every bushel of grain removes one pound of phosphorous. With 50-bushel canola, this year it means 50 pounds of phosphorous has been removed. Peas and cereals remove less phosphorous at approximately 0.7 and 0.6 pounds, respectively, for every bushel produced. Oats and barley remove even less phosphorous than wheat.

With phosphorous, the only replacement strategies are through fertilizer or manure applications. There are no quick fixes, like using pulse crops for nitrogen. Therefore, the replacement strategy works well in combination with soil tests and crop needs.

There are also other nutrients such as potassium, sulphur and possibly some micronutrients that we may want to consider. Soil tests are good to use in combination with crop removal rates to ensure we are not depleting our soil resources.

Using soil tests in combination with crop removal rates will help not only with calculating fertilizer needs next year, but also crop choice. A field where 50 bushels of canola was taken off means there will be little nitrogen or phosphorus left. Crop choice in this field should be one that is less reliant on phosphorus (ex. cereals and pulses) and one that may be able to fix their own nitrogen (pulses). Knowing the crop removal rates, as well as the needs of the crop (crop uptake rates), is important for choosing crops and fertility programs for next year.

In summary, when you are planning next years’ fertility program take into consideration the yields obtained this year and use the nutrient replacement strategy along with soil test results to most accurately predict needs for next year. Balancing the inputs with the outputs is a good step to sustainability and is one of many tools you can use.

For more information, contact your local Crops Extension Specialist or contact the Agriculture Knowledge Centre at 1-866-457-2377.

Table 1.  Rates adapted from Nutrient Uptake and Removal by Field Crops published by Canadian Fertilizer Institute for Western Canada 1998.

Crop

Average Uptake per Bushel

Average Removal per Bushel

 

lbs./bu.

lbs./bu.

 

Nitrogen

P2O5

K2O

Sulphur

Nitrogen

P2O5

K2O

Sulphur

Spring wheat

2.1

0.8

1.8

0.2

1.5

0.6

0.4

0.1

Winter wheat

1.4

0.6

1.5

0.2

1.1

0.5

0.4

0.1

Barley

1.4

0.6

1.3

0.2

1

0.4

0.4

0.1

Oats

1.1

0.4

1.5

0.2

0.6

0.3

0.2

0

Rye

1.7

0.8

2.4

0.3

1.1

0.4

0.4

0.1

Corn

1.6

0.7

1.3

0.2

1

0.5

0.3

0.1

Canola

3.2

1.5

2.3

0.5

1.9

1

0.5

0.3

Flax

2.9

0.8

1.8

0.6

2.1

0.6

0.6

0.2

Peas

3.1

0.8

2.7

0.3

2.3

0.7

0.7

0.1

Lentils

3.1

0.8

2.6

0.3

2

0.6

1.1

0.2

Faba beans

5.7

2

5.1

0.3

3.4

1.2

1

0.1

Soybeans

5.2

0.9

3.4

0.4

3.8

0.8

1.4

0.1

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