Experts at ADAS say checking and adjusting nutrition strategies throughout the season is vital for good crop performance and efficient input use

With spring in full swing, crop walks across the country should be focusing not just on spotting pests and diseases, but increasingly on evaluating crop nutrition. This is according to Dr Sarah Kendall, crop physiologist at ADAS, who says visual checks provide a vital opportunity to refine nutrient strategies in real-time.

“The first fertiliser plan often comes together before the season starts,” she says. “But if you stick rigidly to that, you miss the opportunity to respond to how well crops have actually established or any seasonal quirks. In-season observations help to tailor nutrient applications more precisely.”

Dr Kate Storer, ADAS crop physiologist, is urging growers to pay close attention to signs such as crop growth stage, leaf colour, shoot number, and rooting. These can indicate emerging nutrient deficiencies sometimes before physical symptoms are obvious, she warns.

“It’s not about scouring every square metre,” she says. “Use guides like AHDB’s RB209 to know what symptoms to look for. Focus on field areas where issues are likely such as corners or low-lying ground. Then assess whether any action is worthwhile — some deficiencies can be too advanced to correct or low product efficiencies can minimise potential to rectify.”

If a deficiency is identified and treatment is viable, adjusting fertiliser strategy should be targeted and measured. “One of the simplest methods is to leave an untreated tramline,” says Kate. “But be careful to not choose a tramline with unrelated issues like compaction or different soil types.”

If an issue can’t be corrected this season, Kate recommends grain analysis after harvest to inform decisions for next year. “It’s still incredibly valuable data. You may not solve the problem this time, but you’re setting yourself up to avoid it in future seasons.”

When it comes to assessing crop nutrient status mid-season, several tools are available — each with their own strengths and limitations.

Kate recommends firstly looking at soil mineral nitrogen levels which can vary widely across fields, especially following wet winters. ADAS recommends either using the field assessment method (based on soil type and previous cropping) or the measurement method, which involves laboratory testing. “Where soil nitrogen supply is uncertain, particularly after heavy rainfall, lab tests offer a clearer picture,” she says. “That gives more confidence in adjusting N rates appropriately.”

NDVI tools often integrated into drone or satellite imagery platforms can also be used to estimate canopy size and greenness. While potentially useful for identifying spatial variability, Kate warns to not rely on NDVI alone. “It’s best used to compare relative differences such as treatment trials. But other factors like pest pressure or soil differences can also affect readings; NDVI doesn’t always correlate well with final yield.”

Broad-spectrum leaf analysis is another approach which offers a snapshot of nutrient status – although interpretation still lacks consistency across laboratories, adds Kate. “The most useful way to use leaf tests is comparatively—take samples from a problem area and a healthy area. That gives you a better handle on what’s going on, just be sure to stick with the same lab year on year.”

In terms of areas to watch, she warns that sulphur deficiency is becoming more common particularly in cereals due to reduced atmospheric deposition and leaching during wet winters. “By the time you see symptoms, it’s often too late. If in doubt, test leaf tissue using a malate sulphate test. We’ve had very good responses to sulphate application in trials where deficiency was confirmed.”

This article was taken from the latest issue of CPM. For more articles like this, subscribe here.

Sign up for Crop Production Magazine’s FREE e-newsletter here.