A trial run by South East Water in Hampshire has used soil data to better understand timing and drivers of nitrate risk in order to inform targeted, evidence-led crop management. This could help reduce the amount of fertiliser wasted and leaching into waterways and groundwater benefitting both farmers and water companies.

Results showed that:

• Cover crops consistently showed the lowest nitrate losses
• Bare soils and stubbles were higher-risk, particularly during wet periods
• Winter wheat showed higher losses in winter, underlining the importance of autumn and early-season management
• Rainfall and recharge events are the main drivers of nitrate movement, not single actions in isolation

Continuous soil monitoring stations provided by Paul-Tech, which joined the project as a monitoring and analysis partner, tracked nitrate movement alongside soil moisture, temperature and weather conditions which helped to identify when soils shift from holding nutrients to transporting them downwards into the ground water.

Soil monitoring data in real time can inform management decisions

Mark Slater, Operational Catchment Lead at South East Water, said:

“Soil monitoring tells an important story of how fertiliser can be lost, meaning unnecessary time, effort and money spent on application. However, the decisions that led to that application are in the past as by the time nitrate appears at depth or in groundwater the conditions that caused it may have been weeks, months or even years ago.

“By bringing Paul-Tech in to provide continuous soil monitoring, we have strengthened our interpretation of results by using insight into what is happening below the surface in real time which can inform management decisions.”

Rob Vanhoucke, Business Development Manager at Paul-Tech, explained:

“By monitoring what is going on in the soil we can understand risk as it develops, rather than after the fact. Understanding when soils begin to transport nutrients and how crops are taking them up, enables us to identify high-risk periods such as wet recharge events following nitrate release, or periods of drought after applications, and understand why losses occur under some conditions but not others.

“Fertiliser and timing rates matter, but there are other factors to consider. Nitrogen must first become plant-available nitrate, whether from applied fertiliser (bagged or organic) or the breakdown of organic matter and crop residues. This conversion is driven by biological activity and can take weeks or months, depending on soil temperature and moisture. By viewing nitrate availability alongside crop growth stage and demand, the data enables us to distinguish between nutrients likely to be absorbed and those that become available too early or too late. These insights help us understand the risk of leaching around the timing and quantities of our applications during the season.

“This perspective helps shift the conversation from what was applied to when nutrients actually become available and needed.”

The soil data has been analysed alongside porous pot measurements at depth and wider analysis by South East Water of nitrate trends. Together, they show a consistent pattern: that changes in the soil are often reflected later in porous pots and water indicators, providing confidence in the interpretation of risk periods and mitigation effects.

Mark Slater added:

“Maximising nitrate uptake and reducing the amount lost to the environment is a win-win for farmers and water companies alike. Our end goal is the same, to have better crops with less wastage. When nutrients are used more efficiently on farm, less is lost beyond the root zone supporting resilient farming businesses while reducing the risk of nitrate reaching waterways and groundwater.”