By: John Ippolito, PAg., Regional Crops Specialist, Kindersley
Soil testing is always recommended prior to making fertilizer application and purchase decisions. However, the majority of fields are not soil tested. If soil testing for the purpose of making purchasing decisions is not a big enough incentive, here are 5 scenarios that may provide the incentive you need to test some of your fields.
Wheat yields are okay but protein content is low. Wheat plants use nitrogen to build yield first and then protein as shown in the graph below. If desired protein levels have not been reached, that indicates there may not have been sufficient nitrogen to meet the crop requirements for yield. Yield and protein could have been increased through more nitrogen being applied.
Canola flowers were pale yellow and possibly yields were not as high as anticipated. These would be indicators of insufficient sulphur fertility or sulphur levels are not in balance with nitrogen and phosphorus.
Phosphorus application rates have remained the same for a number of years. The 2015 survey of soil labs conducted by the International Plant Nutrition Institute indicated that over 80 per cent of samples from Saskatchewan were below the critical level. Phosphorus removal in grain from a 35 bushel per acre canola crop is 33 to 40 pounds per acre. If annual application rates were only 20 to 25 pounds per acre, you have been falling behind for a number of years. Phosphorus fertilizer efficiency also decreases as less is available in the ground.
Perennial forage fields have recently been converted back to annual crop production. Forages harvested as hay result in removal of relatively large amounts of nutrients. There may be a higher requirement for sulphur, phosphorus and potassium in these fields.
Biomass in the form of silage or straw is removed regularly. The majority of potassium taken up by plants remains in the straw so actual removal by a grain crop is small. Regular removal of the biomass as silage or straw may contribute to potassium deficiencies on these fields over time.
Soil testing is a time-consuming job but testing to address specific situations may provide a benefit beyond what is normally achieved with representative field testing. For more information on soil testing and fertility, contact your regional crop specialist.