West Nipissing Field Info Day

Written by Emily Seed, on behalf of the Northern Ontario Farm Innovation Alliance

Northeastern Ontario Soil & Crop Improvement Association Regional Communications Coordinator

The West Nipissing/East Sudbury Soil & Crop Improvement Association held a field day in August focused on soil fertility. The day featured Colin Elgie, OMAFRA’s Field Crop Soil Fertility Specialist, followed by presentations on precision and variable rate equipment and a demo on variable rate manure application.

Elgie began at the basics, taking the audience through a breakdown of soil. Soil is 45% minerals, 20-30% water, 20-30% air, and 5% organic matter. Air and water are the components that allow soil to have life. The organic matter is what supports nutrients in cycling through the soil.

When looking at soil fertility, it is important to understand the crop intended to be grown. The most important plant nutrient is whatever nutrient is needed most. For example, adding more nitrogen to soil already high in nitrogen won’t necessarily help yields. A gain in crop yields will only be seen when the limiting nutrient (the one with the lowest nutrient level) is taken care of.

Nutrients in the Soil:

Understanding nutrients is key to understanding soil fertility. Primary (or macro) nutrients include Nitrogen, Phosphorus, Potassium, Carbon, Hydrogen and Oxygen. These nutrients are required by plants in the highest amounts. Secondary nutrients include Calcium, Magnesium and Sulphur. Micronutrients include Boron, Chlorine, Copper, Iron, Manganese, Molybdenum and Zinc. These micronutrients are not any less important, just required at much smaller amounts.

These nutrients in the soil need to be accessible to plants, and so looking at nutrient mobility in the soil will help to understand the availability of nutrients. Nitrogen can have a medium to high mobility in the soil, which means that it can easily leach from the soil. This is why nitrogen applied in the fall usually doesn’t last all the way to spring.

Mobility of nutrient within the plant itself also needs to be considered. Nitrogen, phosphorus and potassium are highly mobile in the plant. If there is a deficiency, the plant could take stored nutrients from the bottom leaves and move them up higher to concentrate them at the top of the plant for grain development. There can be real issues in grain development if there are deficiencies in nutrients that are less mobile within the plant.

Nutrient mobility also affects where the nutrients should be placed. For example, if a field is low on phosphorus (which has an incredibly low soil mobility level), the phosphorus should be applied in bands where the plant roots can actually access it. There is a very small chance that phosphorus applied more broadly would move to where the roots can access it.

Soil Testing

“Soil testing is the most important dollar you’ll spend”, says Elgie. There are many different methods of soil testing, including composite sampling (the most traditional method), grid sampling, zone sampling, and sensor-based sampling. Typically, 6’ cores are taken. 20+ cores are mixed together to create one 1-lbs sample to be sent to the lab. Soil sampling should be done at a minimum of every 3-4 years. The soil sampling method used should be matched to the field variability.

Field variability can be identified by looking at what changes across the field, such as soil type, nutrient levels, water holding capacity and yield potential. Variation in a field can be caused by:

Field variability can also be identified by:

Composite or bulk sampling is the simplest method of soil sampling and can be done very easily across a consistent field. Point or grid sampling divides a field boundary into sections of 5 acres or so, taking samples in each “grid” square and GPSingwhere that specific sample was taken. This provides you with a geo-located sample that can be used to help create a map showing differences in the soil for variable rate applications when applying lime, fertilizer, seeding, etc. Zone or polygon sampling uses sources of data to create zones that are similar (e.g. high-yielding, low-yielding, problem spots, etc.), which provides the field’s natural variability for variable rate application.

Finally, sensor-based sampling is a newer method that is still being learned about. The sensor can measure electrical conductivity, topography and slope. Using this information, a soil core approximately 3 feet deep is taken to look at the soil type and identify the texture. Other variations of sensor-based sampling use the earth’s natural gamma radiation based on the breakdown of nutrients and use this data to take a 6’ sample at various locations to help gauge what the soil is like compared to the radiation. The advantage of sensor-based sampling is that it provides incredibly fine-tuned results, obtaining one data point every 5 square feet, for example. However, this is currently way more data than most planting or fertilizing equipment can handle at this point. If you have extremely variable ground, sensor-based sampling will provide you with the most accurate picture.

Soil sampling results can be used for variable rate applications, such as lime, manure, nutrients, seeding populations and tillage.

Target Soil Fertility Levels:

Target soil fertility levels may differ based on the crop, yield goals, management (e.g. tillage, planting, crop protection, soil type, economics, and the short-term vs. long-term outlook).

Moderately high fertile soils typically have a soil pH of 6-7.5, a phosphorus level of 15-20 ppm and a potassium level of 100-120 ppm.

Nitrogen and Sulphur Fertilizer Approach:

Nitrogen and sulphur are highly mobile nutrients in the soil, so soil reserves cannot be built up by fertilizing. It is important to soil test for nitrogen and sulphur, but there is no real benefit to doing this test in the fall, as the levels will not be the same in the spring. Because it is difficult to know the exact levels, nitrogen and sulphur fertilizers should be applied based on desired crop response each year to get the best “bang for your buck”. A dollar more of nitrogen will typically result in a dollar more in crop yield to a certain extent.

Phosphorus, Potassium and Magnesium Fertilization Approach:

For phosphorus, potassium and magnesium, the sufficiency approach can be used. Ask yourself, “will I get a response to additional fertilizer this year”? Rented ground or a crop that may not see a big response may change your answer to the question.

The other approach is to build up and maintain soil nutrient levels. This focusses on more of a long-term outcome that can allow you to cut back on fertilizer in future years when prices are high. By applying fertilizer, you can build to a responsible level to maintain the highest yield potential. Building soil test levels requires a lot of inputs, as the added nutrients needs to be greater than the nutrients lost during crop removal.

Soil pH & Neutralizing Soils:

Soil pH is an indication of how acidic or basic the soil is (or the hydrogen concentration of the soil). The pH level impacts soil organism activity, performance and breakdown of pesticides, nitrogen fixation by legumes and the availability of nutrients.Nutrients are most available around a pH of 6-7.5. Crops also have varying sensitivities to soil pH levels.

Raising soil pH is relatively easy and cheap, whereas lowering soil pH is difficult and very expensive. When applying lime, it is important to consider the product, as there are several products but not all have the same effectiveness.

If using wood ash, the rate of application would need to double to have the same effectiveness as calcitic lime. Any lime source should will have an ag index to indicate it’s ability to neutralize the soil.

A trial exploring soil pH on canola yields in Manitoba showed that there is a 200 kg/hectare yield difference when applying lime to low-pH soils. When looking at alfalfa, when the pH is less than 7, the crop will only have half of it’s yield potential. Oats, on the other hand, are much less susceptible to soil pH variation.

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By taking into consideration soil test results, field variability and nutrient interactions, soil fertility can be managed using the 4R approach – right source, right place, right time, right rate.