3 Key Ways Grid Sampling Helps Your Input Dollars Go Further

Ben Schapelhouman, Certified Crop Advisor, Founder TECC Agriculture Ltd.

Grid sampling chart from a field in Northern Ontario shows the range between high pH and low pH in a field that might otherwise be assumed to be ‘average’ without grid sampling. Without grid sampling you might assume you don’t need to use very much lime. However, you can see there are serious problem areas that need action. © TECC Agriculture Ltd

When it comes to crop inputs sometimes guessing is the best that farmers can do, but it is an expensive and inefficient way to grow crops. While there are some fascinating technological advances under development which will likely change the way farmers manage crop fertility by the end of the decade, there is already an inexpensive, time proven, and effective solution – grid soil sampling.

When it comes to selecting crop inputs, it’s important to know which nutrients are already available in the soil and which are not. This article will break down how grid soil sampling can reduce the guesswork involved in input decisions, and how related best management practices can benefit both your crop yield and your bank account.

Grid sampling involves laying a grid of a pre-determined size over the field and taking a series of 8-12 cores (usually collected in a Z pattern) inside each grid box. The size of the grid is often set at about 3 acres; however, grids of 5 acres can be used as a cheaper alternative. The larger the grid size is, the less useful the data is for variable rate product application later on. Grid sampling is a good way to get a picture of what’s going on in the soil. It allows you to see the variation in soil properties across the field and plan accordingly. If you lay a yield map over your grid sampling data it can also give an indication of what soil properties are the most closely correlated with yield. The alternative to grid testing is whole-field sampling, where soil cores from across an entire field are mixed together and tested. However, since results are averaged across the field, it can lead to much less efficient input applications.

It Makes Dollars and Sense

Cost is often the driving force behind grid sampling versus whole-field sampling, or indeed no sampling at all. Farmers routinely spend upwards of $100/acre per year for fertilizer, compared to only about $3.50/acre annually for grid sampling. Grid soil sampling allows for the creation of detailed fertility maps, which can be easily used by agronomists to make variable rate lime or fertilizer application plans for specific field zones. This has become much more relevant now that most input suppliers and a growing number of farmers are equipped with variable-rate application equipment. Large farms with staff agronomists or small to medium growers with access to an independent or sales agronomist and a variable rate fertilizer applicator are best able to take advantage of grid soil sampling to save money on crop inputs.

Soil in the Limelight

Soil pH levels are often overlooked in northern Ontario because, in the past, whole-field sampling often indicated suitable ‘average’ levels. Grid sampling, however, can reveal a great disparity between high and low pH levels across the field. Lime costs about $25 – $45 per tonne, depending on location and quality, so farmers really want to be applying it exactly where it’s needed, and not over-applying it where it is not needed. Remember, applying lime on high pH soils can exacerbate existing nutrient availability problems too.

Solving for N

After soil pH, the next most economically beneficial use of grid soil sampling is management of nitrogen in cereal and canola crops. This is simply accomplished by looking at differences in soil organic matter (OM) levels – high OM means more mineralized nitrogen available for the crop. Without grid soil sampling and variable-rate applicators, farmers were forced to apply an average nitrogen rate on an entire field. The result of this practice is often low yields in the low organic matter zones, and lodging in the higher organic matter zones. Lodging often reduces yields by as much as ½ tonne/acre, or about $100/acre, not to mention time delays and quality discounts. It does not need to be like this. With high definition soil organic matter maps, farmers may not use less nitrogen, but they will almost certainly distribute it differently, producing a far more even and better standing crop at harvest.

Potash is Your Friend

Finally, the last significant way to save money on nutrient inputs or boost yields using grid soil sampling is soil potassium management. Unlike many parts of western Canada, northern Ontario’s grey, forested soils are often deficient in soil potassium. Organic, or muck soils, have a particularly high requirement for potash applications. Important benefits of potassium are that it strengthens cereal straw (for reduced lodging) and contributes to higher soybean yields. Fall is a great time of the year to take advantage of variable rate potash applications so that some of the pressure is off when spring seeding rolls around again. Farmers make significant investments in crop nutrient inputs every year, but more is not always better. Effectively managing soil pH helps maximize these investments – this is especially true of starter phosphorus, which is less available at low soil pH. Smart management decisions made this fall and next spring will have an impact on next fall’s cereal harvest and on overall farm profitability.

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