Potassium management
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to the run up in the cost of potash, many farmers cut back on the
amount of potash they applied for crop production, especially in 2008
and 2009. Due to adequate levels of potassium (K) in the soil or the
ability of soils to supply K, crop biomass and grain yields may not have
been seriously affected. However, applying less than crop removal over
several years will gradually reduce the reserve amounts of K in the
soil. Some summaries of soil test values over the past few years
indicate available K levels have been drawn down. Fields where the whole
crop biomass has been removed (corn silage, forages, straw removal) are
the ones where the most change may have occurred and need attention
first. It is important to be applying at least what will be removed from
the field in the harvested portion of the crop (see table). With the
price of potash coming down to a more reasonable level, now is the time
to look at improving the K level of field soils used for crop
production. The first step is sampling the soil in your fields and
having it tested to determine the available K status and need for
additional K.
For improving the potassium (K) status of the soil broadcast and
incorporation of potash is the best approach. On no-till soils,
broadcasting the potash as far ahead of planting is desirable. This will
provide more time for the potash to dissolve and move downward into the
soil root zone. Banding some potassium (20 to 40 lbs K2O/a) at planting
is a way to improve potassium use efficiency, improve early plant
growth and improve crop yield under certain situations or soil
conditions. Banding potassium at planting is most likely to be
beneficial under no-till and heavy residue situations, and in soils
having low to moderate levels of available K. Sandy soils are more
likely to have inadequate potassium. In recent years, there have been a
number of cases where soybeans growing on sandy soils have developed
potassium deficiency, which undoubtedly ultimately reduced crop yield.
On these sandy soils banding or broadcasting potash may be essential for
soybeans as well as corn.
Amounts of K2O removed from the field in the harvested portion of the crop.
_______________________
Alfalfa 50 lbs/ton
Clover-grass hay 39 lbs/ton
Corn 0.27 lbs/bu
Corn silage 8.0 lbs/ton
Soybeans 1.4 lbs/bu
Wheat, grain 0.37 lbs/bu
Wheat, straw 23 lbs/ton
