Alternatives to bagged nitrogen put to the test

Alternatives to bagged nitrogen put to the test22 August 2023

With volatile fertiliser prices and an increased focus on carbon footprints prompting a desire to use nitrogen more efficiently, ProCam is putting a number of solutions to the test in a network of UK trials.

The surge in granular nitrogen (N) fertiliser prices in 2021/22 kickstarted a catalyst for change, believes ProCam technical development manager, Rob Adamson.

Although prices have since eased, he says the concept of improving N use efficiency remains high on growers’ agenda – for both financial and environmental sustainability.

Mr Adamson says: “We’ve certainly experienced farmers asking how they can reduce N dose – and for a range of reasons. There are ways to achieve this – for example by enhancing the efficiency with which the crop utilises N and by applying alternative N sources – and these have the potential to challenge the norm of synthetic N inputs.”

Initial winter wheat findings from the work at ProCam’s flagship research hub at the Stockbridge Technology Centre (STC), in Yorkshire, identified a range of potential solutions when used singly.

This year, the trial work was extended across the country to investigate how these products might contribute to a complete N programme in winter wheat and barley. In a replicated on-farm wheat trial in County Durham, the performance of a wide range of alternative N strategies is being evaluated when used with the farm’s standard 180 kg N/ha programme, but also with the programme inputs reduced by 25% and 50%.

Mr Adamson explains: “As well as examining whether these alternative N products can add additional yield on top of a full-rate N programme, we’re also investigating whether they can bridge the gap to maintain yield if the standard N dose is reduced.

“Early N is critical for tiller retention. So our trials maintain the normal first N dose and make the percentage N cutbacks in the second and subsequent doses only. The work in Durham is complemented by similar work in winter wheat in Cambridgeshire and in winter barley at STC.

“Overall the work is evaluating three types of solutions: products to improve plant uptake of N from the soil; products to help plants utilise the N they have absorbed more efficiently; and products to provide N to plants in alternative ways. By using programmes which include a range of these, we want to see how far we can push reductions in synthetic fertiliser,” he adds.

Looking at the first strategy – improving plant access to soil N – Mr Adamson says this is chiefly based around enhanced rooting.

He says: “The theory is simple; if we build better roots it helps plants to scavenge better for nutrients in the soil. There are many ways this can be achieved. Phosphites and brown seaweed extracts are particularly effective. However, it’s important to build roots while the crop is in its vegetive growth phase, so these solutions sit early in the programme – applied at T0.”

Turning to the second technique, Mr Adamson says the efficiency with which N is utilised once absorbed by the plant can be limited by a range of factors, so ProCam is looking at how to mitigate this, for example by applying pidolic acid, a compound involved in N metabolism. By providing this and or other metabolic stimulants directly to the plant, he says it helps to ensure N is utilised into yield-forming components.

“While the first two aspects of our work are concerned with evaluating how we can make plants make better use of the N available, the third part is looking at N from other sources.

“These include a range of different N-fixing bacteria, which take atmospheric N and make it directly available to the plant. For example, SR3 is a soil-based rhizobacteria which fixes N around the root zone, and we’ve seen about a 5% yield uplift from using this. But we’re also evaluating other bacteria, which work slightly differently. One that is exciting is an endophyte bacteria – called Encera.

“Discovered in sugar cane and developed at Nottingham University, the Encera bacteria have a tail, or flagellum, which allows them to move along the leaf surface and colonise the whole plant, fixing N inside the plant’s own cells in a symbiotic relationship. The plant gives the bacteria sugar in return for readily available N.

“Once Encera is in the plant, it also moves from leaf to leaf as the plant grows. Having N available directly where needed mitigates the risk of slow N uptake due to dry conditions. This was put to the test in the heat of 2022 when we saw a 7.5% yield improvement in winter wheat at the STC.”

Mr Adamson says the diverse range of N-fixing bacteria available means it is not necessarily an either/or decision when choosing them. He anticipates a stacked benefit from products such as SR3 and Encera.

“Historically, N fixation is associated with legumes, so at our site in Cambridgeshire we’re also evaluating companion cropping as an additional means for delivering N. This is timely as growers look to access the £55/ha SFI payment for companion cropping.

“This aspect is in its infancy, and there’s a lot to consider – including weed control and timely, effective control of the companion species. But there is a range of potential benefits and, if the issues can be addressed, the SFI payment gives further reason to consider companion species as another tool.

“Ultimately, these programmes have to stack up financially for farmers compared with granular N, but there are other important reasons for evaluating them.

“The first is an insurance policy for field situations where granular N uptake is compromised – for example in dry soils. But the other reason is sustainability. We have to think of the carbon footprint of traditional N fertiliser. There’s an increasing awareness of this, and it is diligent to not only make sure the traditional N that is applied works efficiently, but also to use alternatives to support traditional fertiliser where feasible. If end markets want lower carbon footprint produce, these types of solutions may help growers towards that goal.”

Article first published in Agronomist and Arable Farmer magazine