It has been a roller-coaster ride for most prairie growers this year.
The season started with April temperatures of 20 C and higher, which was a welcome change. As well, the lack of rain seemed like a blessing at the time as crops were planted into what was described by many as the best conditions seen in close to a decade.
These weather conditions revealed bad habits that producers had fallen into in recent years.
I saw fields that were affected by too much fertilizer in the seed row and placing anhydrous ammonia too close to the seed.
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Problems like this tend to be hidden when you get a half an inch of rain every time you pull out of a field. There were also problems with planting too shallow and poor emergence, and that was when everything started to crumble.
There was a period of 10 days where I think frost was reported somewhere on the Prairies every night. This, accompanied by severe flea beetle populations, resulted in the reseeding of a large number of canola acres.
And then the lack of rain began to manifest itself as an all-out drought in many areas.
I don’t have to remind growers in western Saskatchewan and central and eastern Alberta about what happens when little to no rain falls in the critical May-July period. When precipitation did come, it often came as thunder storms accompanied by devastating hail.
However, harvest is now well underway. Yields are variable, but I have already had reports that yields are better than anticipated in some dry areas.
All of these variable conditions will affect this year’s soil test results.
For starters, large yield variability in drier areas will play havoc with nutrient requirements.
A 40 bushel, 13.5 percent protein wheat crop, which may have occurred in better producing areas of a field, will remove 65 pounds of nitrogen, 25 lb. of phosphorus, 20 lb. potassium and five lb. sulfur, while 20 bu. yields in other parts of the same field will remove half that amount.
As well, there is the mineralization rate of nutrients to think about, especially nitrogen.
Three major factors will affect the amount of nitrogen mineralized from a given area of soil in a season: organic matter, which is the feedstock for the process; temperature and moisture.
Temperature does vary, but it doesn’t significantly affect mineralization rates in the soil.
This leaves moisture.
Rigas Karamanos’s VST Handbook — A Guide to Understanding Virtual Soil Testing and AgroMax II Agronomics says that approximately five lb. of nitrogen will be mineralized for each one percent of organic matter present under dry conditions such as we had this year.
This rises to nine lb. under normal conditions and 11 lb. under moist conditions.
These numbers are for the dark brown soil zone and vary depending on soil type.
We need to only think back to the record crop of 2013, when yields significantly surpassed expectations based on general fertilizer rates. This was caused by almost perfect conditions for the critical May–July period for mineralization.
All these factors tend to lead to a high degree of variability of nutrients in the field, which can be predicted only by soil sampling or using sophisticated modelling programs such as the VST.
Areas where hail has terminated crops should also be considered.
The amount of nutrients that have been taken up by these crops will depend on the stage when they were hailed.
As well, the amounts available for the following crop will depend on the weather following the storm and how the residue was managed: was it grazed, baled or turned under?
All of these factors make a good argument for why soil testing should be high on a grower’s list of things to do after harvest this fall.
