The Potash Development Association (PDA) has recently updated its nutrient recommendations for maize crops in 2023. This update is crucial for farmers, as appropriate fertilisation is vital to the success of the maize crop, whether it’s grown for animal silage, anaerobic digestion (AD), feedstock, or grain. Nutrition greatly influences not only the yield of the crop and its nutritional content, but also growing costs.
Potassium (K) is the nutrient required in the greatest amount by maize, with an average 40t/ha crop taking up around 360kg/ha of potassium oxide (K2O) by early August. The demand for K is particularly large in the period of rapid growth, when the crop needs to take up about 8kg/ha of K2O/day. The soil must be able to supply both the total and daily requirement of K without any hindrance. This requires an adequate level of readily plant-available soil nutrient. During maximum periods of growth, the maize plant will contain more K than nitrogen (N). Maize crops also remove large amounts of K, typically 4.4kg K2O/t fresh yield. This amounts to 175kg/ha for a 40t/ha crop. However, these amounts must be replaced to maintain soil fertility. Nutrient off-take is dependent on yield; a 30t/ha crop removes 130kg K2O and a 50t/ha crop removes 220kg/ha K2O.
Potassium has several 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. The nutrient is also essential for the transport of sugar from the leaves to the storage organs where the sugar is converted to starch. Potash also plays a major role in maintaining the turgor (i.e. rigidity) of plant tissue.
Magnesium (Mg) is an essential element in chlorophyll and hence for photosynthesis. Crop removal, with regard to maize, is 40kg/ha of magnesium oxide (MgO). The total requirement, to be supplied from manure and fertiliser, should be related to soil Mg levels. Additional Mg is only justified at soil Index 0 when 50-100kg MgO/ha should be applied every three to four years. If both K and Mg soil levels are below the optimum, then growers should apply up to 100kg MgO/ha.
Sulphur (S) is a constituent of protein together with nitrogen and the supplies of these nutrients in plants are highly inter-related. Studies have shown that one nutrient will accumulate in plants when the other is deficient. When this deficiency is corrected the accumulated nutrient is then used in protein synthesis. Therefore, a shortage in the availability of S will reduce the efficiency of nitrogen use. Sulphur deficiencies are possible in areas where the soil level is below optimum. The nutrient is available in animal manures, but much of this is unavailable.
Maize is not very sensitive to trace element deficiencies, but boron, copper, zinc, manganese and iron may occasionally be deficient on soils where manure is not applied regularly. This updated nutrient recommendation by the PDA will help farmers in ensuring the appropriate fertilisation of their maize crops and ultimately improve their crop yield and quality.