PHOSPHORUS is vital for potato growth, essential for root and shoot development, tuber formation, and overall yield. Because potatoes have a shallow root system, adequate phosphorus is needed, especially at planting, to ensure sufficient supply for early growth.
Without phosphorus, roots cannot develop, leaves cannot form, and yields collapse, but at the same time, too much phosphorus means increased risk of losses to the environment, Sajjad said.
“Phosphorus imbalances are widespread across the UK. From NRM’s extensive database of 170,000 fields analysed over the last five years, we found that nearly 30% of soils were deficient, while over 40% contained more than multiple crops over a rotation realistically need. This is a big problem,” said Sajjad.
“What we must remember is that phosphorus rarely acts alone. Crops require a balanced diet, and phosphorus interacts closely with nitrogen, potassium, sulphur, and other key nutrients. P imbalances reduce efficiency and hold back yield potential so it’s incredibly important to analyse throughout the year and make full use of your data to make the best decisions for your farm and the environment.”
Northeastern arable regions have tended to show deficiencies, he said.
“When pH drifts above or below the optimal range, phosphorus can bind with iron, aluminium, or calcium, reducing availability and preventing crops from achieving optimal yield,” Sajjad said.
Many growers may not realise that different tillage methods and required sampling depths may have an effect on P levels. If fields are ploughed, sampling to the traditional 15cm is advised.
“If they are min-tilled, we advise sampling to 23cm to avoid overestimating soil P content, which tends to accumulate nearer the soil service. Sampling to the correct depth prevents inaccuracies in the assumed content of P in the soil, giving farmers a clearer indication if they need to supplement with fertiliser or not.”
Nigel Simpson, Catchment Sensitive Farming (CSF) Agricultural Lead at Natural England, said only around 0.2% of soil phosphorus is immediately available to crops.
“This availability relates to soil pH, but as phosphorus losses to water in soil particles are also a major environmental issue, we can’t just apply more fertiliser,” he said. “Excess phosphate fuels algal blooms, which strip oxygen from lakes and rivers, threatening biodiversity, fish stocks, and rural livelihoods. In England and Wales, an estimated two million tonnes of soil and organic matter are lost to water each year, much of it carrying phosphorus with it. Losses can be especially severe on sloping clay soils, where runoff and sheetwash erosion risk can be high.”
To avoid these issues, Nigel suggested adopting more careful management practices.
Avoiding applications on high-index soils and applying fertiliser when the crop is going to use the nutrients can help limit losses and balance crop productivity with environmental stewardship, he said.
