Field Crop Response to Potassium on Soils with High Extractable Potassium and Varying Soil Supply Rates of Potassium

Crop responses to K on many western Canadian soils, even on soils testing high in K, have many people questioning the soil testing procedures used and/or the method by which K varies within fields. Using the Plant Root Simulator (PRS) probe, an ion exchange membrane system for measuring soil nutrient supply rate, a project was initiated in the semi-arid region of Saskatchewan to evaluate crop responses to fertilizer K on soils which are regarded as non-responsive using traditional K extraction methods.

IPNI-1999-CAN-SK23

01 Mar 2000

1999 Annual Interpretive Summary

Field Crop Response to Potassium on Soils with High Extractable Potassium and Varying Soil Supply Rates of Potassium, 1999

Crop responses to K on many western Canadian soils, even on soils testing high in K, have many people questioning the soil testing procedures used and/or the method by which K varies within fields. Using the Plant Root Simulator (PRS) probe, an ion exchange membrane system for measuring soil nutrient supply rate, a project was initiated in the semi-arid region of Saskatchewan to evaluate crop responses to fertilizer K on soils which are regarded as non-responsive using traditional K extraction methods.

Using PRS probes, the K supply rates of three fields were determined using grid sampling. Maps generated from this grid-sampling pattern indicate large areas of the field that were both deficient and adequate in K supply. These fields were planted to spring wheat, canola and flax in 1999 with 90 foot wide strips of 0, 19 and 37 lb K2O/A applied at seeding. Unfortunately, hail damage resulted in loss of the canola and wheat field tests. However, preliminary results from the flax field indicate a positive (+50 percent) grain yield response to added K relative to the check in certain landscape positions, while no response was observed in others. Further evaluation of the data will require an overlay of topographic information from the field so that specific landscape elements can be identified for their responsiveness to K fertilizer additions. SK-23F