Beans are becoming an important source of protein in more crop rotations and getting the agronomy right is key to consistent performance. Todd Jex from Agrii gives his insights for success.

Why grow beans?
The old adage that ‘you’ll never get rich growing beans’ is now out of date, as farmers look for alternative sources of nitrogen in the rotation and supply chains move away from imported soya as a source of protein in animal nutrition.

Higher prices for manufactured fertiliser nitrogen and the growing pressure on imported soya mean the market and use of beans in the rotation are likely to grow. The crop also allows the opportunity to control grass weeds and improve soil health, and in my experience, the agronomic challenges that have followed on from the ‘legume fallow’ option in the Sustainable Farming Incentive have meant that, at a rotational gross margin level, a productive bean crop is a profitable option.

The positives for beans
Legumes work well in arable and grassland rotations as they are not reliant on nitrogen fertiliser to achieve good yields. The key agronomic advantages include:

Other merits of beans include:

Controlling grass weeds
For many arable farmers the challenges with grass weeds are increasing. Black grass has been a problem for many decades with most farm populations showing resistance and insensitivity to a wide range of active ingredients and modes of action.

Last autumn, details of the first glyphosate-resistant weed population were published which, to some people’s surprise, was identified in Italian ryegrass rather black grass. Although generally not grabbing the headlines as often as black grass, IRG is a far larger problem globally, and in the UK is a much more difficult weed to control.

Propyzamide is one of very few active ingredients still available, in combinable crops, to which IRG and BG show no signs of resistance. Five or so years ago the prevalence of winter oilseed rape helped keep populations in check but the sharp decline in acreage, due to Cabbage Stem Flea Beetle and other issues, has meant many have lost this valuable tool. This can be replaced by growing beans.

Achieving consistency
Consistency and yield performance are often levelled against beans, but there is plenty we can do to maximise chances of success.

Like all crops, the start matters, and the rotation and state of the soil are key. To avoid building up soil-borne diseases and nematodes, a rotation gap of at least four years should be maintained.

Establishment
The next step in achieving success is establishment which can be split into four key areas:

Crop protection
Broad leaved weeds can be very competitive, especially those of the Brassicaceae family like runch and charlock. Options are limited and the best results will always come from a well applied pre-emergence herbicide.

Chocolate spot is the key disease, but bean rust and downy mildew can also feature and shouldn’t be ignored. Mildew is linked to manganese levels in the plant, so I’d encourage regular tissue testing.

Nutrition
Beans should be managed in the same way as any crop – tailoring all inputs to match crop requirement. Testing is a helpful tool whether that’s grain analysis post-harvest, soil testing predrilling or sequenced tissue testing in season.

Beans are capable of fixing up to 400kg/ha of N but it’s generally much lower at 150-200kg/ha. The level of fixation is driven by a whole range of factors including soil temperature, nutrient availability, sunlight and most importantly nodulation. Maximising nodulation will always be a fundamental factor in the success of the crop. Again, this is driven by a range of factors, some of which we can influence, others less so:

The target GAI (green area index) for beans is 3-4 which is equivalent to 90-120kg/ha of N being fixed by the crop.

Late season, when the crop starts to fill the seeds, beans will remobilise stem soluble carbohydrates from leaves to fill seeds. This process often brings on senescence faster meaning yield potential is lost. We’ve been using tramline and plot trials, over the last five years, to see if we can prolong photosynthetic area with foliar nitrogen and endophytes.

The data on foliar nitrogen seems to present a very clear message with an average yield improvement of 0.4t/ha over the five years on the three sites. Yield improvement from the endophyte is even more impressive but that’s from only one year’s worth of data on what was a challenging year for beans.

And we mustn’t forget sulphur. This nutrient is important in protein formation in the crop and optimising yield, and our data clearly shows that applying sulphur improves root nodulation.