With harvest 2025 underway, growers throughout the UK should be gearing up to test soil pH to ensure next season’s crops are given every opportunity to meet their full potential. That is the advice from ProCam’s Phil Burrell who explains that the post-harvest, pre-planting interval is the ideal time to test soils thanks to the ground being bare of crops. He also advocates testing nutrient availability to offset a potential rise in fertiliser costs which could result from rising political tensions in the Middle East.

“As one cropping cycle comes to an end, and growers start to get ready to drill next year’s crops, now is the ideal time to test soils, not just for pH, but also for residual reserves of N, P, K and S,” Phil Burrell, Plant Health Business Manager for ProCam explains.

“The fundamental factor to get right at this stage in proceedings is to ensure soil pH is as close to 6.5 as possible, as this is the optimal level for the availability of micro and macro nutrients,” Phil continues. “If soil pH falls below 6.5, meaning soils are too acidic, macronutrients such as phosphate, nitrogen and potassium will be locked up in the soil matrix and therefore be less available for uptake by the next crop in the rotation.”

Phil explains that at pH 6.0, the availability of phosphate falls to 52%, decreasing to 48% at pH 5.5. Similarly, N and K availability fall to approximately 77% at pH 5.5.

“According to the latest data, almost two-thirds (62%) of UK arable soils are below the optimum pH of 6.5,” Phil continues. “Likewise, one-in-three grassland soils are below their optimum pH of 6.0. Given the current political unrest in the Middle East, and the impact this could have on global fertiliser prices, it makes sense to test and adjust pH now, to ensure those nutrients already in the ground remain available for the next round of crops to utilise.”

There’s no silver bullet when it comes to unlocking crop yield Phil continues, but rectifying pH should be on every grower’s to do list, especially as low pH can easily and cost-effectively be resolved with the application of lime.

In addition to pH, N, P and K, Phil also urges growers to test for sulphur. “Sulphur and the efficiency of nitrogen are closely linked, with any deficiency in the former resulting in reduced nitrogen use efficiency,” he explains.

“Atmospheric sulphur deposition has fallen steadily since the 1970s when acid rain was at its peak, with 95% of soils now deficient. At the same time, only 55% of arable ground routinely receives a treatment of sulphur, while just 12% of grassland receives supplemental applications. Rightly or wrongly, many farmers assume the shortfall will be made up by applications of farmyard manure or slurry, but unless these inputs have been tested to assess their nutrient content, it’s impossible to predict with any accuracy if soils are receiving sufficient sulphur.”

Where sulphur is lacking, oilseed rape yields fall by an average of 0.5 t/h, while wheat output is reduced by an average of 0.35-0.4 t/ha. “Crop quality will also be affected, with OSR seed having reduced oil content and milling wheats less likely to hit their required protein target,” Phil adds. “Grass swards will also suffer, with lower dry matter yields and reduced protein production impacting milk and meat yields.”

To counter these effects, sulphur and nitrogen should be applied at a ratio of between 5:1 and 3:1 depending on the soil’s indices.

“Including sulphur also reduces the total amount of N required,” Phil continues. “For example, winter wheat requires an average of 240 kg/ha of straight N to achieve its optimal yield. This figure falls to 210 kg/ha when sulphur is added into the equation, and a further reduction to an average of 190 kg/ha is possible when nitrogen is applied in combination with S, P and K.”

In all scenarios, the three key steps to improving crop performance are:

1. Test soil pH and nutrient content on a field-by-field basis in the autumn and/or spring so that appropriate adjustments can be made ahead of cropping.
2. Carry out in-season leaf/plant tissue analysis to assess the crop’s ongoing nutritional needs.
3. Carry out post-harvest grain analysis to highlight any enduring nutrient deficiencies.

“Grain analysis from the 2024 harvest indicated that 60% of wheat crops were deficient in sulphur,” Phil adds. “This points to a significant shortfall in fertiliser programmes and is a clear indication that growers shouldn’t always assume that a ‘standard’ bag of fertiliser will be appropriate. Instead, soils should be tested, and the results scrutinised with the help of a FACTS approved agronomist who’ll be able to ground-truth the findings and devise a suitable nutrient programme for each field.

“Fertiliser spreaders should also be calibrated to ensure what could become an increasingly expensive commodity is applied accurately and in the right quantity. And where the relevant machinery is available, variable rate application maps, such as those produced by ProCam’s FieldSense platform, should be used to maximise the yield benefit and margin over input costs.”