Potato growers using a controlled release fertiliser (CRF) in preference to a standard programme are seeing higher yields and environmental benefits.

Such fertilisers are being increasingly employed to support potato crops, according to Scott Garnett, from ICL Speciality Fertilisers. “They play an important role in improving yield, reducing nutrient losses and simplifying fertiliser application. Using them has been shown to reduce leaching by 55% in comparison with a normal nitrogen fertiliser.

“Nitrogen is often applied once at a 100% rate, but plants actually need it on a little and often basis. A great analogy I often use to explain this is that you wouldn’t feed a baby an adult sized three course meal, before it’s fully grown,” he said.

“They have a range of different release periods – ranging from one to two months, and even up to five to six months, depending on requirements.” But, he added, this is based on an optimum soil temperature of 21°C, so, realistically in the UK climate, farmers will find a one to two-month product lasting for three to four months.

“Using a CRF limits the need for top dressings and the fact that the fertiliser remains available to the plant over a longer period, offers vital nutritional support to the crop throughout the whole of the growing cycle,” he pointed out.

The way the technology works is simple, but effective. The fertiliser granules have a special coating, a semi-permeable layer that controls the release of the nitrogen to the growing plant.

“As the granule takes in moisture and the soil temperature increases, the coating expands, forming fissures for water to move into the granule. The water movement happens via osmosis, which works like a pump. As the water moves in, nitrogen moves out for the plant to uptake,” he said.

The volume and speed of it being released into the soil is directly related to soil temperature and moisture content, with more available as the soil warms up. If the temperature drops, the coating condenses and stops the flow of nutrients, as plants are not actively growing at lower temperatures.

Jersey Royals get benefit of new fertiliser

SUCH fertilisers have boosted the Jersey Royal Company’s yields and its technical manager, Ryan Stone, managed independent CRF trials across a 6 ha area of the famous early cropping potatoes.

These demonstrated a significant opportunity for the company, he said, pointing out that it is responsible for 65% (1400 ha) of the island’s total potato area, with 20,000 tonnes of the early variety exported to the UK mainland annually.

“Last year we applied Agromaster CRF, to half of the field trial area. The other half received a standard fertiliser, with both being applied two days before planting,” said Mr Stone. "It was applied from mid-March until the end of April, 2016 at a rate of 180 kg of nitrogen per ha.

“When we monitored the crop, the early digs didn’t show much of a difference between the untreated control and the CRF-treated potatoes, but after 12 weeks, the difference was clear and we saw up to 8% yield increase in some fields,” he added.