Yields of UK spring beans could be significantly improved by inoculating them with better strains of nitrogen-fixing bacteria, visitors to ProCam’s recent series of Trials Open Days were told. Whilst output is inherently variable in the crop, new work suggests increases of up to 1t/ha can be achieved by using better bacterial strains with even greater potential possible from adding mycorrhizal fungal treatments. The benefits of using mycorrhiza could even extend to cereal crops.

“There is increasing interest in beans as the result of the three crop rule but the bottom line is that there are not that many agronomic solutions that can really help growers get more from their crops. It is assumed that a crop producing proteins could benefit from a higher nitrogen supply but current NVZ regulations preclude the application of nitrogen fertiliser to legume crops. The bottom line is that if we’re going to get more out of this valuable crop, we’re going to have to look at more novel approaches to yield improvement.”

ProCam 4Cast  – the company’s database of grower inputs and yields – shows its spring bean growers achieved on average 4.7t/ha in 2015 with costs at around £75/tonne resulting in a final gross margin of around £300/ha. This is against a Defra average of 3.6t/ha yield for the crop.

“Beans can be a beneficial break crop providing good control of disease, pests and weeds and, being a spring sown crop, they may provide an opportunity to help reduce blackgrass, too. Furthermore, they can add around 50 kg/ha of residual nitrogen for following crops, but the low yields and margins put a lot of people off.”

But focusing on soil biology and the role of key bacteria and fungi in providing nutrition for the crop could produce significant benefits, Tudor Dawkins says.

“One of the biggest limiting factors in the yield of beans is the fact that the plant technically feeds itself through fixing atmospheric nitrogen in the root nodules so if this could be improved, yields should increase. Overlay a fungal system that improves phosphate delivery to the crop and there could be a real opportunity to turn crop yields around with a much better economic outcome.”

Strains of Rhizobia – nitrogen fixing bacteria  – are generally ubiquitous in UK soils and readily infect beans when they are sown, he points out.

“But through screening different populations we could identify those that are more efficient in supporting the plant and unlocking the existing yield constraint. In fact, researchers at the James Hutton Institute seem to have found a strain of Rhizobium bacteria from high yielding UK crops that can improve the efficiency of atmospheric nitrogen fixation so all bean crops could benefit.”

Yield improvments of 1t/ha have been identified by using the strain by itself but ProCam is now evaluating the potential for using fungal Mycorrhiza in the crop as well, Tudor Dawkins points out.

“Mycorrhiza deliver phosphate and zinc from the surrounding soil to the roots of the beans and they can also improve the plant’s ability to access water alleviating stress conditions later in the year. As with Rhizobia, by identifying the strains of Mycorrhiza that colonise the root most effectively, we may be able to drive better root and crop growth and hence yield. There could also well be synergistic benefits from using the two biological systems of Rhizobia and Mycorrhiza in combination to create a significant effect on yields.”

Early indications from using soil applied Mycorrhiza also show the approach could be used to improve yields in spring cereal crops, such as spring barley, Tudor Dawkins adds.

“Trials conducted by ProCam in conjunction with Nottingham University have shown that the use of Mycorrhiza can increase root growth in some cereal crops which can help to get the crop off to a good start. In our spring barley trials with Mycorrhiza at Fowlmere near Cambridge last year, we saw an definite improvement in yield with the control crop producing 7.96 t/ha and the Mycorrhiza treated plots delivering 8.65t/ha”.

For bean crops, both bacterial and fungal treatments are placed with the crop at drilling time but Dr Dawkins admits it could be a couple of years before some of the technology will be ready for use on a larger scale.

“This is very much the subject of ongoing work for the company and one which we hope to have some interesting and practical results on very soon. It’s early days, but the results are looking very promising. Application is relatively simple, the products are available in the UK and so far the results have been very consistent.”