Labor Day has come and gone. Though most farmers focus on harvest this time of year, it's also a time to be thinking more specifically about potassium from several forage crop fronts.
One of the primary factors to good alfalfa stand persistence is adequate soil fertility, especially potassium. Even though on many livestock farms we see phosphorus levels that are off the charts from repeated manure applications, such is not the case for potassium. Alfalfa removes copious amounts of potassium, 50 to 60 pounds (as K2O) per dry matter (DM) ton; nearly 100 pounds per acre of 0-0-60 fertilizer for every DM ton harvested per acre. That's what is needed just to maintain current soil fertility, not increase it. Exact fertility recommendations are available from extension offices in every state.
Bottom line: If you want productive, persistent alfalfa stands, supplying adequate potassium fertility is foundational and fall is a good time of year to make sure that happens as plants prepare for winter.
As tons and tons of corn silage are now being removed from fields across the country, realize that tons and tons of potassium are also leaving the field. Most of the potassium in a corn plant is in the stalk and this makes removal far greater for silage corn than for a grain-only harvest where stover is left in the field. How much greater? It depends on grain and silage yields, but at least 100 pounds of K2O equivalent per acre is not uncommon. Again, consult with your state's extension recommendations. If proper removal rates are not taken into account, soil potassium levels will suffer along with the performance of subsequent crops.
Bottom line: Harvesting corn for grain and harvesting corn for silage are very different from a nutrient removal standpoint, especially potassium. This difference needs to be accounted for through applied commercial fertilizer or adequate amounts of livestock manure.
In this era of high yielding forage crops, knowing soil fertility levels has never been more important. As has been stated many times, fall is a great time to soil test. It's impossible to make an informed application decision without knowing the inherent soil fertility level. This certainly is true for potassium, and a history of soil test data will tell you if your fields are holding fertility, trending down or trending up. In other words, a soil test will confirm or put into question your current crop fertilization program.
Bottom line: Soil test regularly if you're not doing so already.