Forage Maize Fertiliser Requirements

Soil preparation and sowing

The aim when sowing maize is to achieve quick germination and rapid unhindered early growth. The seedbed should be prepared with this in mind. If there is any soil compaction below plough depth the field should be subsoiled when conditions are suitable. Maize fields will normally be ploughed followed by seedbed preparation leaving a reasonably fine surface tilth at least 7.5 cm deep. Below this the soil should be firm but open, preservation of moisture in the seedbed is important.

		Reasonably fine tilth
		Germination level of uniform depth
		Firm but well structured layer
		Well shattered subsoil

Seed should be sown on to a firm base at 4-6 cm depth, shallower depths are preferred unless the soil is dry. Sow when the soil temperature reaches 8-10°C, usually the third week in April to early May. Too early sowing will hinder germination and establishment and set back the crop, too late will miss a few days of growth and may result in lower yields.

Soil analysis

As maize is a valuable crop with a high demand for nutrients it is important to know the soil pH and available nutrient levels in order to apply the necessary lime and fertiliser to ensure good crops. When the maize field has been chosen a soil sample should be taken for analysis unless the field has been tested within the last 3 years. (See PDA leaflet 24 'Soil Analysis' for guidelines on soil sampling).

Lime

Maize needs a pH of 5.8 - 7.0. The field should be limed if the pH is 6.0 or lower. If the soil magnesium index is 0 or 1 the use of magnesian limestone should be considered.

Target soil potassium level

For a crop such as maize, which has a high demand for K, it is important to maintain soil K at not lower than Index 2- (121-180 mg K/litre) on fields on which maize is grown regularly. Maintaining this level of K is particularly important because at this level the soil can meet the large demand of the crop for K. To maintain this level of soil K, potash should be applied in amounts equal to the removal in the harvested crop to maintain soil fertility. If soil levels are lower than this, extra potash is needed to build up reserves and to make sure there is sufficient for the crop. If soil K levels are very much higher than 180 mg/litre then potash applications can be reduced but care should to taken to ensure that levels do not fall much below 180 mg K/litre. It is difficult to build up soil K levels on sandy soils and adequate amounts of K in manure or fertiliser should be applied for each crop.

Total potash recommendations

The amount of K₂O that should be applied is related to the soil K level as shown below. This is the total to be supplied from manures and fertilisers.

Potash recommendations, kg K₂O/ha