Soil nutrient analysis is like a balance slip from the bank. By checking the balance this fall, farms can set fertilizer rates specific to the needs and yield potential of each field.
The following article was written by Warren Ward, an agronomy specialist for the Canola Council of Canada in eastern Saskatchewan.
Sampling in late fall instead of just before seeding gives the advantage of time. With results in the fall, farms have more time for fertilizer planning. Fertilizer prices can also be lower in the fall, but not always. With fall soil test results, the general benefit is that farms can plan their blends and rates, and buy the right amount of fertilizer at a lower price.
The best time for fall sampling is after soils cool to below 10°C. Cool soils reduce the microbial activity that can mobilize nutrients. Soil samples collected after this activity slows down will more closely reflect spring nitrate contents. If farms plan to band fertilizer in the fall, sampling when soils drop to 10°C (but not too much lower) should allow for fall application – based on soil test results – before the ground freezes.
A custom-collected two-depth sample (0-6″ and 6-24″) plus lab fees will cost around $100. More samples collected should lower the cost per sample. Soil nutrient analysis may not provide a return on investment for every field tested – especially if results confirm that a farm is using the right rate to meet its yield target. However, soil test analysis may encourage a farm to use higher nitrogen rates to match yield goals or, in the case of high nutrient reserves, lower their rates. In these cases, profitability can go up with soil tests.
One sample or many?
One composite sample per field can provide a general impression of soil nutrient levels. For the composite, take 15-20 cores from the most productive areas – not hill tops, not low spots, not saline areas. Divide each core by depths and put them into separate pails. Suggested depths are 0-6” and 6-24”, or a three-way split of 0-6”, 6-12” and 12-24”. Submit a separate sample for each depth.
With composite samples, farms can create fertilizer blends specific to the needs for each field. If field-specific fertilizer blends are not logistically possible, a compromise is to apply the same blend at different rates to match the yield goal for each field.
Zone sampling increases precision. Instead of one composite sample per field, submit composites for each productivity zone within the field. Zones are generally based on productivity differences that can be fairly predictable based on soil characteristics, drainage or elevation. Three zones could be hilltop, mid-slope and low-lying areas. For each zone, follow sampling methods similar to the composite sample technique. This could mean six or more samples per field (two depths for three zones, for example), but this method can provide meaningful results for fields with higher levels of soil variability, and can point to the potential value of variable-rate fertilizer applications.
Canola 4R Advantage
The new Canola 4R Advantage program provides financial incentive to soil test fields that have not been sampled as part of a 4R Nutrient Stewardship plan in the past.
Canola 4R Advantage, funded by Agriculture and Agri-Food Canada through the Agricultural Climate Solutions – On-Farm Climate Action Fund (OFCAF), is a voluntary program that supports farmers in initiating or advancing 4R Nutrient Stewardship practices. Canola farmers can apply for funding to help pay for practices that can improve nitrogen management. Eligible practices include soil testing, enhanced efficiency fertilizer, preferred application timing and field zone mapping. Farmers can seek funding for up to two practices per year. Up to 85 per cent of eligible costs can be reimbursed – up to $12,000 per farm each year. For more on the program, including guidelines and application, visit canolacouncil.org/4r-advantage.
