“Soil testing in the fall, rather than in the spring, gives more time for collecting samples and planning fertilizer programs,” says Mark Cutts, crop specialist at the Alberta Ag-Info Centre. “It also allows producers to take advantage of lower fall fertilizer prices, and reduces spring workload.”
Soil sample collection can occur once soil temperatures are below 7 C.
“Waiting until soil temperatures are cooler means soil nutrient levels determined in the fall should closely reflect spring nutrient levels,” he adds.
Cutts says that it is important to ensure sample collection occurs in a consistent manner from representative areas of the field.
“For example, if there are small areas of poorly drained low spots in a field, these areas should not be included in the sample collection. The non-representative areas can be sampled separately to determine their fertility status.”
Sampling at the appropriate depths is also important. Recommended sampling depths are 0 to 15 cm, 15 to 30 cm and 30 to 60 cm.
“The 0 to 15 cm depth will capture crop available soil phosphorous and potassium. However, for mobile nutrients such as nitrate nitrogen and sulphate, sampling to a depth of 60 cm gives a more reliable measure of the amount present in the soil profile.”
Applying fertilizer in the fall is another practice that producers may want to consider.
“The most common method for applying fall fertilizer is to band nitrogen either as urea (46-0-0) or anhydrous ammonia (82-0-0),” he says “Since nitrogen makes up the biggest volume of applied fertilizer, a fall application will enhance efficiencies during spring seeding. Fall nitrogen fertilizer applications can be made once soil temperatures are below 7 C.”
Applying urea or anhydrous ammonia fertilizer at cooler soil temperatures will help maintain nitrogen in the ammonium (NH4+) form.
“The ammonium form of nitrogen is preferred as it is protected from denitrification or leaching losses,” he adds. “However, there is no real advantage to a fall application of seed-placed plant nutrients such as phosphorus and potassium.”
“Ultimately, by evaluating soil nutrient levels and applying nitrogen fertilizer in the fall, producers can gain efficiencies in time management and cost of production.”