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Cereal crops lacking in magnesium this spring – Agronomist & Arable Farmer – Simon Wilcox

Arable farmer and Hutchinsons agronomist Simon Wilcox tells how important the mineral is when soils are washed out by high rainfall ...

Following a relatively wet winter, tissue testing has highlighted that cereal crops are likely to be lacking in magnesium as we head into spring.

The Met Office recently reported that the provisional total rainfall for winter 2020/2021 was 401mm, which is 122% of the 1981-2010 average. Mr Wilcox explains that because of this, soils are likely to be washed out.

“I’ve been tissue testing more frequently over the past five years and there’s been a general trend towards a lack of magnesium early on in the season,” he says.

“This was especially a problem last year because of the previous wet winter followed by the dry spring, as dry, hot weather tends to highlight the problem more.”

Mr Wilcox explains that historic agronomy templates say manganese sulphate should be applied early in the programme as a matter of course. However, he says that things have moved on when it comes to crop nutrition, and magnesium should also be factored in.

Simon Wilcox, agronomist

“The way we farm has drastically changed over the last 10 years and this, in conjunction with a new era of cultivation techniques, means that mindsets need to change when it comes to crop nutrition applications.”

He attributes the majority of these changes to grass weed pressures and the resulting delays in drilling to help mitigate this. “Historically, most drilling would happen in early to mid-September, which meant crops and their root systems were much bigger and more robust coming out of winter because they could become well established when the weather was typically warmer.

“In the last five to 10 years, but especially in the last five years, the move has been to a mid-October to even early November drilling date. This means crops generally come through the winter a lot smaller than they would have done in the past. Add to this that they are often drilled in wetter and colder conditions, it means establishment isn’t as perfect as it once was.”

There are also implications on soils too. Mr Wilcox says: “Soils are also starting to be impacted because we are working them a lot more in harsher and wetter conditions. As a result, crops can have compromised rooting systems. This is why nutrition is even more important and magnesium plays a vital role in this.”

Magnesium in winter cereals

Mr Wilcox adds: “When coming out of a wet winter I find foliar nutrition applied early doors is where it can make a big difference to crops. It’s all about getting in front of a problem and making sure crops aren’t ever under stress.

“Magnesium is a really key element in crop production. You can’t get away from the fact that it’s a main macro element and plays a vital role in chlorophyll production for photosynthesis.”

He routinely tissue tests a week to 10 days before he wants to make an application to see what is lacking in the crop. “I use a foliar product called Root 66 from FMC that contains magnesium and manganese as my base for applications. I find it’s a great co-form with the right magnesium to manganese ratio (Mn 60g/l and MgO 100g/l) which provides all that my crops need. I’m also able to add anything else to it, depending on the situation,” he says.

“It’s also a nitrate formulation rather than sulphate based, which I prefer as nitrate-based products are more readily taken up by the plant. Hutchinsons assessments have shown a 19% improvement in uptake from nitrate vs sulphate formulations.”

Mr Wilcox explains the key to success is getting it on early. “I tend to get good results from feeding the crop early on – especially in the foundation stages which is everything up to GS30. It’s all about removing constraints at this time and enhancing root structure and tiller production,” he adds.

“The Yield Enhancement Network has also highlighted the importance of the foundation growth period and that magnesium should be utilised earlier in that period. My main aim is to create a robust crop canopy for harvest which ideally should be 600 ears/sqm. All crops will go through a period of tiller loss and will abort up to 40% of tillers up to GS30-31. So, to get 600 ears I ideally need to produce 1,000 tillers/sqm. This is why correct nutrition is so important to help reduce crop stress and maximise tiller and crown root production.”

He applies magnesium and manganese as a maintenance dose at every key timing, based on the soil type. “On heavy clay soils I use 1.5L/ha three times in the spring and then use a straight magnesium on the ear. Sandy or gravel- based soils tend to be more magnesium hungry so I would increase this,” Mr Wilcox adds.

Magnesium in spring crops

Magnesium is also important in spring crops and he suggests that it’s often a forgotten element in this area.

“Many people treat spring crops like half a crop, but I treat them the same as I would a winter wheat,” he says. “Spring barley, in particular, responds really well to magnesium and I’ve had really good results when applying early in the season.”

Mr Wilcox usually applies foliar magnesium at GS30-31, then GS39 and GS65. “This means you are in the crop quite a lot in a short space of time, but it allows me to use growth regulators at the same time to manipulate the crop,” he adds. “Barley growers can’t compensate on grains per ear, they just have to concentrate on ears/sqm. So, by going in as early as GS30, it helps maximise small tillers and give the crop a boost.”

The role of magnesium

According to Charlie Bannister, crop nutrition commercial technical manager at FMC, magnesium is the ‘forgotten element of crop nutrition’. “Magnesium often gets outshone by the high-profile macronutrients of nitrogen, phosphorus and potassium, and the ‘glamorous’ micronutrients like manganese and boron. But it’s a vital nutrient for crop success because of its role in the photosynthesis process,” he says.

While, traditionally, magnesium has been applied later in the spring, its importance in numerous reactions in the plant means this element should be readily available from start to finish. “Perhaps the most easily recognised role of magnesium is as a central ion in the chlorophyll molecule, linking in other compounds in the light capturing complex,” says Mr Bannister.

“But that’s only a small, although vitally important, part of its impressive CV. The real strength of magnesium lies in its ability to link compounds together or to act as a bridging element. “Magnesium catalyses over 300 reactions within the plant and it does this by acting as a link or sometimes attaching itself to a compound to maintain the structure of that compound, enabling a reaction to take place.”

He explains that the main reason why magnesium is often deficient, as Mr Wilcox has observed, is because of its behaviour in the soil. “In soil, magnesium has a ‘love-hate’ relationship with other essential elements like potassium and calcium, both of which can antagonise uptake,” Mr Bannister adds.

“Published research data points strongly to a domineering position taken by potassium over magnesium, in terms of plant uptake, especially where soil potassium is high,” says Mr Bannister.

“Ammonium ions are also said to antagonise the uptake of magnesium, so on high-calcium calcareous soils we should also expect a reduction in uptake.” Mr Bannister explains that magnesium is very prone to leaching and this is because its movement in soil is very much determined by its inherent characteristics as an ion (an atom in charged form).

“In dehydrated form and not surrounded by water, magnesium is far smaller than either potassium or calcium. However, in hydrated form in the soil and attached to water, it increases in size by about 400 times, meaning it is less tightly bound to soil colloids, causing leaching,” he adds.

Therefore, he says, applying magnesium routinely from the start to the end of the season could pay dividends with increased crop health and performance.

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