POTATO growers could cut phosphate applications by up to 40 kg/ha through the simple use of a soil complexing agent that releases reserves held in the soil, according to trials by Agrii.
Phosphorus is an essential macro-nutrient but often occurs at low concentrations in solution, even when applied as a soluble fertiliser owing to its fixation by positively charged minerals in soil. These positively-charged minerals, known as cations, bind with the phosphorus particles rendering them immobile and unavailable to the plant.
A complexing agent, such as that in Agrii-Start Release is specifically formulated to free the phosphorus particles from their entanglement with the major cations, typically calcium (Ca), magnesium (Mg) and potassium (K), and thereby make them available to the crop.
The use of complexing agents in agriculture is not new. Many water conditioners employ the same technology to treat hard water and support the performance of susceptible herbicides, such as glyphosate and clethodim.
Across three seasons and variable soil textures, crops that received Agrii-Start Release pre-emergence, delivered a positive yield response, according to Tom Land, Agrii’s National Fertiliser Manager.
“Phosphorus take-up is often influenced by a range of factors such as the soil’s calcium content, pH and temperature. Regardless of these, the use of Agrii-Start Release was overwhelmingly positive with increases to the marketable fraction and tuber bulking,” Tom said.
The result builds on experience seen in earlier trials with field vegetables and salads where the use of Agrii Start-Release delivered yield increases in a range of crops including spinach, onion, leek, carrot and cabbage.
Agrii’s trials targeted sites with both high and low pH levels because pH affects different ions but the effect on phosphate availability is the same. In high pH soils, calcium and magnesium have been shown to interfere with phosphorus availability while on low pH soils it is aluminium and iron ions. Even without any applied phosphate, crops that received Agrii-Start Release delivered a significant yield increase demonstrating its capacity to increase the crop available portion.
“Across variable seasons and soil textures and at sites with varying soil reserves Agrii-Start Release delivered yield increases of 17-30% and improvements in tuber bulking. We conservatively estimate an average saving of 30-40 kg P/ha from a 4-litre/ha application of Agrii-Start Release,” Tom said.
“The savings in fertiliser costs, estimated at as much as £123.60/ha for DAP purchased at May 2025 prices of £618/t, alone justify its use while any improvement in the marketable yield fraction arising from increased soil availability will further support the gross margin,” he added.
To avoid having to make a standalone spray application Agrii has investigated the tank-mix compatibility of Agrii-Start Release with a range of other products typically applied at this timing. “It can be applied in-furrow with Rhizoctonia solani treatments such as azoxystrobin or fluxapyroxad or across the ridges with either pre- or post-emergence herbicides or liquid fertilisers. A single application will be active for about 60 days,” Tom said.
