This month’s Maize Matters looks at the role of fertiliser and advice on application rates, as well as tips on seedbed preparation.
Potash is the nutrient which is required by maize in the greatest quantities and at some growth stages, plants will contain more potash than nitrogen, says Peter Hoey, of the Potash Development Association (PDA).
Potash is essential for the plant when taking up nitrogen, so when crops are growing fast, soil potash availability is paramount, he stresses. Deficiency will restrict growth and reduce final yields, so he recommends a soil K index of 2-.
This target can be difficult to achieve on light sandy soils, which would benefit from an application of manure. “The most important contribution made by potash is to regulate water content and maintain water pressure in the cell walls, which increases the crop’s standing power,” says Mr Hoey. “This, in turn, helps to maximise the exposure of leaves to sunlight, thereby increasing photosynthesis. “Potash is also involved in the transportation of sugars around the plant, before their conversion into starch.
It will aid plant survival in times of drought and adequate levels will enhance resistance to fungal diseases and pest attack. One sign of potash deficiency is poor cob fill and this is obviously a feature growers are most anxious to avoid.
White tips may also be seen on the end of the leaves at the start of the growing season.” An average, maize crop will have taken up roughly 360kg/ha of potash by early August and in the period of most rapid growth, uptakes can reach 8kg/ha/day, although offtake levels will also be significant.
“Offtakes of potash on maize fields are generally very high, especially where crops are harvested early. An average 40 tonnes/ha crop will remove about 176kg/ha of potash and the figure will be increased, for higher-yielding varieties.
These large amounts mean fields which grow maize should receive an annual application of the nutrient, to maintain the index for future crop growth. Potash can be applied as fertiliser, as organic manure, or as a combination of both.”
Meanwhile, KWS maize product manager John Burgess says crops should receive a total of 70-90kg/ ha of phosphate, to ensure photosynthesis is allowed to continue uninterrupted.
“After drilling, the plant quickly uses up the phosphate that is supplied to the seed, in order to develop new root structure,” he says. “It must then access reserves in the soil and these must be adequate, otherwise phosphate deficiency can occur just below the soil surface in the days following. Therefore, it is essential to maintain the phosphate index of the soil at 2 to 2+ as a minimum standard.”
Considerations for heavier soils
Considerations for lighter soils
KWS offers a free temperature service, to help with decisions on drilling date. Growers enter their postcode, to find the current soil temperature at 10cm at the five closest weather stations to the farm. The service also provides soil surface temperatures, to highlight the risk of frost. It can be found at www.kws-uk.com