Developing crop recommendations is a multi-step process, taking into account field history, hopes for the coming year, and, of course, soil test results
While making crop plans with farmers this winter, we tried to build a complete crop nutrition solution for each crop. Our initial plans focused on macronutrients — mainly, fertilizer rate recommendations based on what was left in the soil and what we needed to add to achieve 2012 yield targets.
To get an overview of the 2011 growing season for our trading area (in the Peace River region of northern Alberta) we checked the Government of Alberta’s AgroClimatic Information Service (ACIS) website (at www.agric.gov.ab.ca, type “acis” in the search box). We saw that rainfall recorded by nearby weather stations during the 2011 growing season was 2.5 to 3 times the previous three-year average.
Next, we looked at the Agriculture Financial Services Corporation (AFSC) publication “Alberta Yield”, and found that cereal crops in Risk Area 19 in 2011 yielded about 40 per cent above the previous three-year average, and canola crops yielded about 25 per cent higher.
Based on the nutrient uptake and removal rates required to grow those heavy crops and nutrient losses due to saturated soil, we knew we had to take soil samples to see just how low our nutrient levels were.
Soil sampling conditions were almost ideal last fall. We sampled fields to a depth of 24 inches, separating the top zero to six inches and the lower six to 24 inches. We recorded all the locations of the sample sites with GPS co-ordinates to ensure year-to-year consistency.
Once we had the soil sample reports, one of the first things we looked at was the cation exchange capacity (CEC) value. These numbers give us an indication of the nutrient holding capacity of the soil.
Next we compared the organic matter (OM) percentage for each soil sample with previous years’ information and trend lines. Organic matter percentages help determine the amount of nutrients that become available from soil mineralization and microbial nutrient cycling. The mineralization rate in the soil can be quite variable due to factors such as moisture, temperature, compaction, type of residue and management practices.
For our recommendations, we estimate only a conservative amount of nitrogen coming from the organic matter as compared to other regions, because of the shorter growing season and relatively cooler temperatures in the Peace country. We are also on the conservative side on the uptake and removal values for each crop.
Soil sample results
Soil sample results for nitrate confirmed what we expected. Nitrogen (N) levels in the soil are very low compared to accumulated reserve levels of nitrogen seen in previous years’ samples. The lower levels of nitrate nitrogen were true in both the zero- to six-inch depth and the six- to 24-inch depth.
Nitrogen recommendations start with yield targets and what is required to achieve them. We account for the nitrogen that should be available to the crop and apply the difference. With a high proportion of the fields in the Peace country planted to canola, our strategy for sulphur fertilization is to apply sulphur (S) based on an N:S ratio of 5:1.
The majority of the fields we sampled this year were tested with a complete lab analysis, including micronutrients. Here is where a clearer picture of the nutrient levels of the soil became obvious.
Phosphorous (P) levels seem to be maintaining, on average, a level trend.
On evaluation of the pH levels of the soil, some results are giving us a cause for concern. The majority of the sample results ranged between the ideal 6.0 to 7.0 pH but there were a number of samples less than 6.0 pH, and some at the other end of the spectrum with a pH greater than 7.0. As soil nutrient availability is affected by pH, we’re concerned about the interaction of phosphorous at low pH with higher amounts of available aluminum and iron. When the pH is at the high end of the scale, we recognize phosphorous availability is limited by calcium and magnesium in the soil. The placement and rates of phosphorous we recommend is based on the soil test results and limitations to plant availability.
Soil potash (K) levels are, on average, lower than previous years. Potash fertilizer application has been cut back or skipped by farmers for the past few years, since prices spiked in 2008. The straw material grown in 2011 was also significantly greater than in previous years. Over time, shorting the crop on potassium and mining the soil will negatively influence yield potential. For lower testing fields, we recommend applying at least crop removal rates of potassium, and we build recommendations for potassium deficient fields.
This year, we decided to examine soil test micronutrient levels in depth. In the past we have disregarded these measurements, and were hesitant to make product recommendations. Of the fields we sampled, 48 per cent tested low for copper (Cu), 50 per cent tested low for manganese (Mn), 30 per cent tested low for zinc (Zn) and 70 per cent tested low for boron (B). Our strategic approach is to provide these nutrients by targeting those fields and crops with the greatest probability for response.
This year, we followed a strategy of building complete crop nutrition solutions for each crop and field on the farm. I believe we’re on target to provide the crop a little bit more of what it needs to achieve yield objectives. †