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Potash for maize

June 2019

Following the recent heavy rainfall, some spring sown crops will have quickly gone from a state of moisture stress to waterlogging, not ideal in the early stages of production! Some of the later sown spring crops, such as maize have been slow to get going due to the dry soil conditions. The rainfall will help these to take up nutrients from the soil and improve, but in some cases there are some short term waterlogging issue to be resolved first.

To produce a good crop, maize plants need to grow very rapidly once they have germinated. They will do this if the soil moisture and structure are good, the temperature is warm and nutrition is adequate. Maize can easily produce 50 t/ha in a period of four months. To support this rapid growth it has a large demand for nutrients and any shortage will restrict early growth and final yield.

Potash is the nutrient required in the greatest amount by maize. An average 40 t/ha crop takes up around 360 kg/ha K2O by early August. The demand for potash is particularly large in the period of rapid growth and the crop needs to take up about 8 kg/ha K2O per day. The soil must be able to supply both the total demand of 360 kg/ha and the daily requirement of 8 kg/ha without any hindrance. This requires an adequate level of readily plant available soil potassium. During maximum periods of growth the maize plant will contain more K than N.

Maize crops also remove large amounts of potash, typically 4.4 kg K2O/t fresh yield which amounts to 175 kg/ha for a 40 t/ha crop. This quantity must be replaced to maintain soil fertility. Nutrient offtake is dependent on yield; a 30 t/ha crop removes 130 kg K2O and a 50 t/ha crop removes 220 kg/ha K2O.

Potassium has a number of diverse roles in plants. It plays an important role in regulating the water content of the plant and with an adequate supply of K, plants can survive drought stress more easily. It is essential for the transport of sugar from the leaves to the storage organs where the sugar is converted to starch. It plays a major role in maintaining the turgor (i.e. rigidity) of plant tissue. Leaves need to be turgid to remain fully extended to maximise the surface exposed to sunlight that provides the energy to convert carbon dioxide in the atmosphere to sugars in the leaves. Plants well supplied with K also seem to be less susceptible to fungal and pest attacks.