Interest in crop nutrition is greater than ever, with 40% of respondents to a Farmers Weekly survey reporting that deficiency symptoms were more common in crops now than they were 10 years ago.

However, the survey, carried out in association with Headland, also highlighted concerns about soil testing and an insufficient understanding of hidden deficiencies.

Two-thirds of the 600 respondents felt fairly or very knowledgeable about the role of each of the main nutrients in crop health, although only 42% felt fairly or very confident in differentiating between macronutrients – namely nitrogen (N), phosphorus (P), potassium (K), magnesium, sulphur and calcium/lime – and micronutrients.

As many as 15% admitted they couldn’t distinguish between a macro- and a micronutrient, such as manganese, boron, copper, zinc and molybdenum.

That lack of understanding doesn’t surprise Brian Chambers, head of soils and nutrients at ADAS.

“It can be difficult to remember what constitutes a macro- and a micronutrient. The important thing is to recognise which elements are needed routinely and which only on certain crops when soil or tissue analysis points to a problem,” said Prof Chambers.

Most farmers considered applications of sulphur essential to crop yield, alongside the three mainstays, N, P and K. Between a third and two-thirds recognised that magnesium, calcium, manganese and boron are also critical, and fewer than 30% thought copper, zinc and molybdenum essential to yield.

That’s not far off the mark, said Prof Chambers, warning cereal growers in particular of the increasing problem of sulphur deficiency. Boron is less likely to be limiting yield in cereals, he added.

Monitoring

The survey highlighted the importance farmers place on measuring pH and assessing N, P, K and magnesium. Almost 90% of respondents recognised that comprehensive soil analysis, for those and other elements, is fairly or very important to their business.

However, while most recognised the need for correcting nutrient deficiencies, there was some discrepancy between the number considering certain nutrients very important to crop production and the number actually monitoring them. This was notable for sulphur and manganese in cereals, and boron across most crops.

For example, only 36% monitored for manganese when 56% considered it essential to maximise yield. The figures were 42% and 72%, respectively, for sulphur.

Headland’s Charlie Bannister found this worrying, and urges growers to always go for a comprehensive nutrient analysis, plus pH and soil organic matter status. This information is needed to understand interactions and balance all elements in the system.

Prof Chambers supported the view that soil nutrient testing is crucial, and a relatively low-cost way to establish the need for treatment. He expected sulphur and manganese to be at low levels in the majority of oilseed rape fields and some cereal crops this spring, due to heavy leaching over winter and cold soil conditions.

“There’s likely to be a need for sulphur application on many arable crops, and manganese at least on light land farms, but there is no harm in testing to make sure. Soil tests are adequate for most elements, though a leaf tissue test is better for pinpointing manganese deficiency because availability depends on the soil and root interaction,” said Prof Chambers.

Symptoms

Sixty percent of survey respondents understood the term “hidden deficiencies”, which left 40% unsure of the term meaning that symptoms may not be obvious when the element is limiting crop performance.

As a researcher of plant mineral deficiencies, Philip White of the James Hutton Institute understands the term better than most. “It’s natural that if you can’t see a problem, you believe everything is alright. The only way to tell that you have a deficiency is to have soil or tissue tested,” he stressed.

Asked whether or not symptoms were more common now than 10 years ago, 40% of those surveyed said yes and a similar number felt they had stayed the same, while 18% thought they were less.

Mr Bannister feared there is insufficient understanding of hidden deficiencies, and explained that trials show evidence of plant damage well before any symptoms show. He was interested to see that of those who understood the term, 80% believed they had had a very or fairly negative impact on their yields over the past 10 years.

“We can see that the nutrients considered more limiting today than 10 years ago in cereals are primarily, though not exclusively sulphur, manganese and copper. In oilseed rape they are primarily sulphur, boron and molybdenum.”

Yield

While the main benefit of correcting deficiencies was improved yield across all crops – noted by 87% of respondents – greater consistency of yield was cited by almost as many.

More than half had seen better vigour and quality. Between 30-40% cited improved disease resistance, standing power, and reduced need for N fertiliser. Only 5% hadn’t seen any response to correcting deficiencies.

Vigour and quality improvements are well-documented, said Prof Chambers.

Foliar applications?

When it came to foliar nutrients, just over half of farmers applied a programmed approach, and more than half of those treated in the autumn and spring rather than just in the spring. Larger farms more often tended to adopt a programmed approach.

Of those who took a programmed approach, 64% tailored their inputs to specific crops. Many factors determined policy, notably past history, the market, and soil and tissue analysis results.

Only 19% of those surveyed adopted a single approach to all crops on the farm. A fifth of farmers said their nutrient policy varies over time and place, one respondent noting “much depends on weather and growing conditions.” Many left the decision to an agronomist.

Of the total, about a fifth of farmers – mostly from the small farm category – don’t use foliar treatments, and a fifth apply foliar nutrients to crops only if they know of a particular problem.

Prof White was not surprised by that. “Foliar fertilisers are often used during the season to correct specific nutrient deficiencies and to optimise the timing of nutrient applications. They are especially useful for delivering elements locked up in soil.”

Knowledge

Many farmers highlighted areas where they felt more research could be useful. A common concern was the lack of information on how nutrients are locked up and released by soil, and how they interact with each other in the system.

This issue is being addressed at the James Hutton Institute.

Prof White suggested that in future, the principles of precision agriculture might be adopted for all nutrients, to improve yields and reduce costs.

More on this topic

Cereals 2009: Yara launches Active Crop Nutrition Programme for Arable Crops