Nutrient removal with drought-stressed corn
For P, the removal rate by harvesting biomass will most likely be lower than what is normally removed when only grain is harvested. If a low yield of 4 tons of dry biomass/acre is harvested at 5 lb P2O5/ton, the removal would be 20 lb P2O5/acre. Even if we use a higher value of 40 lb P2O5/acre (the amount accumulated in vegetative tissues by R1 under normal conditions), these removal values are lower than the 77 lb P2O5/acre removed when harvesting 180 bushels of grain per acre.
For K, however, removal rates can be much higher than the normal removals with grain harvest. Using the same low yield of 4 tons of dry biomass/acre, if the material contains 20 lb K2O/ton, the crop would remove 80 lb K2O/acre; if the material contains 30 lb K2O/ton, then 120 lb K2O/acre would be removed. The estimates can be higher still if we use 170 lb K2O/acre, which is the accumulation in vegetative tissues by R1-R2 under normal conditions. Whichever estimate is used, they are all much higher than the normal removal rate of 50 lb K2O/acre for a grain yield of 180 bushels an acre.
On the other hand, if grain yields are low and biomass is not harvested, the removal rates will be lower than normal. Whatever your particular situation, it is very important to correctly account for removal rates in order to appropriately manage fertilizer applications this fall.