Ed Brown, Hutchinsons' agronomist, says using a foliar urea treatment can offer potential benefits for cereal crops. Wendy Short reports.

Replacing a percentage of soil-applied nitrogen with a foliar urea treatment offers several potential benefits, according to Hutchinsons agronomist, Ed Brown.

A 10kgs/hectare foliar application of urea to supply nitrogen to a cereal crop can produce a 30-40kgs/ha saving on soil-applied nitrogen and reduce the farm’s carbon footprint, said Mr Brown. The practice has been trialled on a number of farm sites around the country for the past three years and it offers a potential cost saving of about £40-plus/ha, depending on market prices.

“Soil-applied nitrogen is only 30-50 per cent efficient and its efficacy can be influenced by the weather at the time of application,” said Mr Brown. “However, a foliar urea application will produce a response independent of weather conditions. It is 100 per cent efficient, as it is not subject to the losses associated with soil-applied nitrogen. In addition, the urea is applied much further along the plant’s nitrogen conversion process, so less energy and water are required for conversion into protein.

“The calculation that shows the opportunity for a £40-plus/ha cost saving on nitrogen inputs is a direct comparison of the price of the ingredients that are used in the foliar mix, versus 40kgs/ha of soil-applied nitrogen. It excludes a cost allocated to an additional pass with the sprayer, but cutting down on soil-applied nitrogen and partially replacing the treatment with foliar urea will produce a worthwhile return on investment. It can be achieved without the risk of a yield penalty.”

The Northern Farmer: Ed Brown, Hutchinsons agronomist

The foliar urea is applied as a liquid, but growers can purchase a solid urea product which can be dissolved in water on-farm, he added.

“The foliar urea application rate will depend on whether the grower has used an off-the-shelf product, or has dissolved the urea on farm,” he said. “A standard rate would range between 50 and 80 litres per hectare. In terms of nitrogen value, I would recommend setting a maximum rate of 10kgs/ha, to avoid leaf scorch. Up to three foliar urea treatments can be applied throughout the growing season."

Foliar urea can be applied from the flag-leaf stage onward, he said.

"We do not have precise trial results to indicate the optimum plant growth stage for the application that will produce the best response to date, but a large crop biomass will result in greater uptake. The weather conditions at the time of application are important – the best times are early morning or evening. Very warm weather should be avoided, because it will lead to the closure of the leaf stomata. This will restrict the plant’s ability to take up the product and increase the risk of scorch.”

The rate of soil-applied nitrogen should not be determined in isolation as a baseline for working out foliar urea rates, he advised.

“A base amount of soil nitrogen will always be required by the plant, to build adequate biomass. Foliar urea is not intended to fully replace soil-applied products, as it will not supply sufficient quantities of nitrogen as a stand-alone treatment. Ideally, a programme will include more than one application, in order to maximise the total rate of foliar urea used in the spray regime over the growth period.”

Mr Brown pointed out that new guidelines are expected to be introduced in spring 2024. They will restrict the use of urea-based fertilisers, with the aim of reducing ammonia emissions and protecting the environment. The rules will require a urease inhibitor to be used from April 1. However, warm, dry conditions in March, for example, could lead to significant nitrogen losses from urea.

He said growers who have reduced their soil-applied nitrogen rates and used a foliar urea application have given favourable reports.

“The use of a small volume of foliar urea to replace a greater amount of soil-applied nitrogen is a well-proven concept. It is a highly effective way of maintaining nitrogen supply to the plant during dry periods, when the uptake of soil-applied nitrogen is limited. Bypassing the soil and supplying a source of nitrogen that is safe, as well as being highly efficient, provides growers with the chance to minimise their reliance on conventional, soil-applied sources.

“The foliar application of nitrogen has traditionally been linked with maize and oilseed rape crops and it has not been widely utilised for cereals, largely because the ingredients used in the mix were expensive. However, experimentation with the inclusion of a range of cheaper ingredients to produce the same effect have been successful.

“My research into the system was partly driven by the weather patterns in recent years, which have seen late-season dry spells hindering the uptake of soil-applied nitrogen and led to a check in plant growth rates. The fact that the system can also save money and can help to reduce the farm’s carbon footprint further contributes to its potential value to farm businesses,” said Mr Brown.