Who can tell me how much phosphorus (P2O5) and potassium (K2O) was removed by crops over the last three growing seasons?  This question was posed to the audience at the SouthWest Ag Conference by Peter Johnson with little response.  Fertilizer is a large production expense and the ability to monitor its use is becoming more important as margins tighten and public awareness heightens.

An annual tool to estimate fertilizer application is to calculate previous crop removal (Table 1).  As yields increase, the amount of P2O5 and K2O removed from the soil also increases.  Below is an estimate of the crop removal for both P2O5 and K2O under average and above average crop yields (Example 1 and 2). 

Yields for some producers have escalated in recent years, similar to the second example.  Ontario soil test levels of P2O5 and K2O are declining due to higher crop yields without nutrient replacement.   A 25-30% increase in yield has demanded a 25-30% increase in nutrient removal from the soil.  

Consider calculating a nutrient removal budget and compare it to the nutrients applied.  If there is a large difference, it is strongly recommended to increase the fertility applied.  The reverse is also true – if crop yields did not remove the nutrients applied, this may be a good year to adjust nutrient application to save costs in the short term.

Shawn Winter, CCA-ON, Maizex Seeds Product Development Manager
Twitter: @SWinter_Maiz