Phosphate and Potassium Decline

Rethinking P & K Fertility.

Soil surveys conducted in a number of provinces across Canada are revealing a general decline in soil P and in potash. This has come as a surprise to many growers that have fertilized based on the ‘replacement approach’ of applying amounts of nutrients removed by the crop. Growers and agronomists also have questioned the sufficiency approach recommended by many government extension services. Rightly so, crop yields are much higher than when many of these fertility research trials were done. Then came the ah-ha moment.

Provincial sufficiency approach does not include an adjustment for current or expected yields. The sufficiency approach is based on many years of university research that produced yield response curves for P & K for various soil test levels (figure 1).  Fertilizer recommendations were then based on [...]