Advice on early nutrition for forage maize crops

Top of the to-do list when planning this year’s forage maize crops should be to check soil pH and correct where necessary.

Maize needs a pH of 5.8-7, and outside this range, many key nutrients will not be available to the plant, advises nutrition agronomist Guillaume Franklin of Origin Soil Nutrition.

“If the basics aren’t right, the crop will be limited,” he says. “The Potash Development Association [PDA] recommends liming fields with a pH of 6 or less.”

See also: Benefits of undersowing maize for soil, water and grazing

Having addressed this, growers should refer to the Nutrient Management Guide (RB209) when calculating fertiliser requirements, says Guillaume.

While this gives application rates of nitrogen, phosphate and potash (according to soil indexes) for forage maize, there is no recommendation for sulphur. Yet it is just as important as nitrogen, he argues.

“If you’re not applying sulphur when you’re applying nitrogen, you’re really not helping the crop. Sulphur increases nitrogen-use efficiency, reducing the risk of leaching or mineralisation into unavailable forms of nitrogen.”

Crops with optimum sulphur perform better overall, he says, with increased dry matter (DM) yield, protein content and digestibility when fed as silage.

Maize plants deficient in sulphur have a yellow striped pattern on the leaves and yellowing between the veins. At advanced stages of deficiency, they become stunted.

“Sulphur is very mobile in the soil, so it leaches out easily. This means deficiency is greater with heavy rainfall in the winter months.

“After a wet winter, there will be nothing left from the previous season,” says Guillaume.

Sources of sulphur

Crop needs for sulphur used to be met by emissions from burning coal, he explains. Since the 1970s, these have declined steeply.

According to the PDA, while slurries and manures all contain sulphur, the amount can vary considerably, depending on the type of storage and what the livestock are fed.

This makes it difficult to rely on slurry or manure alone to supply the crop’s sulphur requirement “unless soils have had regular applications of manures over a long period of time.

Therefore, it is very likely sulphur will be required this year by most crops”.

Sulphur can be applied as ammonium sulphate, polysulphate or kieserite (magnesium sulphate monohydrate), Guillaume explains.

He points to a trial by Dorset-based Pearce Seeds, which showed an uplift in yield of 0.57t/ha in the crop receiving a starter fertiliser of di-ammonium phosphate (DAP), compared with none.

When DAP plus polysulphate was applied, yield was boosted by a further 0.55t/ha DM, to 16.6t/ha.

Polysulphate is mined in Yorkshire and provides sulphur, calcium, magnesium and potash.

“It benefits a fast-growing crop because it has a sustained release.

“It’s giving a continuous feed, not a sudden hit,” he says, adding that research at the University of Nottingham showed a 50-day-plus release of sulphur from polysulphate, compared with six days for ammonium sulphate.

Zinc

Zinc is also important for early development of the maize plant, he says. “It improves yields and brings harvest date forward. [That means] we can have less of a hard time getting that crop off.”

Guillaume points out that zinc becomes locked up in soils with high organic matter and high pH, as well as those with a high level of phosphate – such as soils where maize has been continuously grown.

He says one way to tackle this is with an application of zinc that adheres evenly, via electrostatic charge, to a starter fertiliser of DAP, which helps the plant in the first four to six weeks.