Release of ‘locked-in’ soil phosphorus could help potato growers reduce phosphate inputs

Potato growers could reduce phosphate applications by up to 40kg/ha, equivalent to a phosphate saving of £51/ha, by using a soil complexing agent that helps unlock nutrient reserves already present in the soil, according to Agrii trials.

Across three seasons and a range of soil textures, crops treated with Agrii-Start Release pre-emergence have delivered a positive yield response, with improvements seen in marketable fraction and tuber bulking.

Tom Land, Agrii National Fertiliser Manager, says phosphorus uptake is often influenced by factors including soil calcium content, pH and temperature.

“Regardless of these, the use of Agrii Start-Release has been overwhelmingly positive in our latest trials, with increases to the marketable fraction and tuber bulking.”

Making more soil phosphorus available to the crop

Phosphorus is vital for crop development, but its availability can be limited by soil chemistry. Even where phosphorus is present in the soil, it may not always be available to the crop when it is needed.

Agrii Start-Release uses proven technology to free phosphorus particles from positively charged cations that bind with them, making them immobile and unavailable to the plant.

In high pH soils, calcium and magnesium can interfere with phosphorus availability. In low pH soils, aluminium and iron ions can have a similar effect. Agrii Start-Release helps free phosphorus from these bonds, typically involving calcium, aluminium and magnesium, making more of the soil’s existing nutrient reserve available to the crop.

Positive results across potatoes and field vegetables

The latest potato results build on experience seen in earlier Agrii trials with field vegetables and salad crops.

Agrii Start-Release has delivered yield increases across a range of crops, including:

• Spinach
• Onion
• Leek
• Carrot
• Cabbage

Trial sites were intentionally selected across both high and low pH levels, as pH affects different ions but has the same overall impact on phosphate availability.

In potatoes, even where no phosphate was applied, crops treated with Agrii Start-Release delivered a significant yield increase. This demonstrates its ability to release previously unavailable soil nutrients.

Across a range of growing conditions, Agrii Start-Release delivered yield increases of 17-30%, alongside improvements in tuber bulking.

Potential phosphate savings

Agrii estimates an average saving of 30-40kg P/ha from a 4-litre/ha application of Agrii Start-Release.

Based on phosphate purchased as TSP at £590/t, the fertiliser saving is estimated at up to £51/ha.

Tom says these fertiliser savings alone help justify its use, before any additional benefit from improved marketable yield is considered.

“Any improvement in the marketable yield fraction arising from increased soil availability further supports these gross margin benefits.”

Flexible application options

To avoid the need for a standalone spray application, Agrii has investigated the tank-mix compatibility of Agrii Start-Release with a range of products typically applied at this timing.

It can be applied:

• In-furrow with Rhizoctonia solani treatments such as azoxystrobin or fluxapyroxad
• Across the ridges with pre-emergence herbicides
• Across the ridges with post-emergence herbicides
• With liquid fertilisers

A single application will be active for about 60 days post-application.

Supporting fertiliser management this season

Agrii Start-Release could offer a practical way for potato growers to improve phosphorus availability and make better use of nutrients already in the soil.

It may be particularly useful where phosphate levels could be limiting, or where existing soil levels do not allow further phosphate applications.

With input costs still under pressure, improving access to locked-in soil phosphorus could help growers reduce unnecessary phosphate use while supporting crop performance and marketable yield.