Fertility and Nutrients
Ontario wheat harvest provides opportunity to improve soil health
July 24, 2020 By OMAFRA Field Crop Team
Harvested wheat fields offer the perfect opportunity to focus on improving soil health. Planting cover crops and/or applying manure or other organic amendments provides soil microbes with the carbon compounds that help create a more porous soil structure, which improves water, air and nutrient cycling.
Here are a few common questions that come up every year regarding the application of manure or other organic amendments:
Which field needs the nutrients or organic matter most?
Spring and fall manure applications generally occur when there are time or weather restrictions. After cereal harvest, soil conditions are generally less prone to compaction and the time restrictions of spring. This mid-summer timing allows the time to get manure to fields further away from the source that are often bypassed in the early spring rush. The value of manure is maximized when applied to fields or portions of fields that need the nutrients and organic matter most.
Should the straw be removed or incorporated?
Straw adds revenue value to a cereal crop, but also contains nutrients and organic matter – whose removal has a cost. Removing straw does not remove all the organic matter, since there is significant benefit in the stubble and root mass that remains. The addition of cover crops and/or manure will compensate for the removal of straw. Whether removing or keeping straw, ensure combines are effectively spreading chaff well across the width of the header. Uneven spreading leads to a greater need for tillage. If the straw is removed, it might lessen the need for tillage, which further protects the organic matter and nutrients from the cereal stubble and roots. This year straw is more plentiful than last year, and demand and prices are lower.
Should manure be applied before or after planting a cover crop?
The decision will depend on the purpose of, and type of cover crop, manure type (liquid or solid) and application timing. There is no right answer, but there are a few considerations. In dry soil conditions, incorporating nutrients can be difficult. Applying manure, incorporating it and then planting a cover crop results in delay of cover crop growth, but allows for incorporation of nutrients and an opportunity for weed control and residue management. Cover crops can be seeded in conjunction with manure application, but this requires attention to seed placement relative to manure placement.
Manure applied into an established cover crop, such as red clover, is generally surface-applied. It will provide nutrients quickly and the crop cover will provide protection from nutrient loss (volatilization) and runoff. Liquid manure can be injected, but, depending on depth and degree of soil disturbance, there can be some damage to the cover crop. Shallow injection with use of straight coulters will minimize damage while accelerating cover crop growth. When manure is applied into standing cover crops, uniform application is important, as is wide application swath, to minimize damage to the cover crop from wheel traffic. Composted manure applied into a standing cover crop is a low risk for nutrient loss compared to application of manure with high nutrient concentrations, where it is generally better to incorporate.
When is the best time to take a manure sample?
To obtain the most accurate estimate of nutrients applied, manure samples should be collected when manure is being applied to a field. Manure database numbers provide a good estimate and are a practical place to start but having actual values from the manure applied enables fine-tuning of fertilizer requirements. A sample from an agitated storage or from various loads taken over the application time will provide an opportunity to determine available nutrients for the next crop. An analysis should include dry matter, total nitrogen, ammonium nitrogen, total phosphorus and total potassium. In addition, testing for some of the micronutrients – such as sulphur, zinc and manganese – will provide information on potential fertilizer savings. C:N ratio in solid manure will provide insight into nitrogen availability. pH, especially for liquid manure, will help determine how quickly incorporation should occur to minimize N volatilization losses.
Using the New Manure Calculator
Using actual manure sample lab analysis or database averages, the Organic Amendment Calculator (available for mobile, tablet or computer) provides a quick estimate of available nitrogen, phosphorus, potassium and micronutrients, including dollar value of manure (after application). It is part of OMAFRA’s new AgriSuite software tools, which include Crop Nutrient, Organic Amendment, Fertilizer and PLATO calculators.
For the weather data for July 13-19, and to keep up with the latest field crop news in Ontario, visit the OMAFRA Field Crop News website.