Using an organic carbon-based fertiliser is helping Shropshire grower John Bubb become more sustainable and save on nitrogen fertiliser use.
The farm grows 184ha of potatoes for processing by McCain, alongside flowers for drying, wheat and oilseed rape. A whole raft of changes has been made to how these are grown. This includes multispecies cover crops before potatoes and flowers, growing catch crops between oilseed rape and wheat, and reducing cultivations, including before potatoes. One of the first changes was to include a carbon source to mitigate the effects of either cultivation or liquid fertiliser on soil biology. “The initial idea was to use it whenever we cultivated, as we couldn’t go completely zero till,” John explains. “Soil is oxygenated with every cultivation, waking up the soil microbes. They want to eat something, but we don’t want them to feed on our organic matter. The point of the molasses is to put some carbon in the soil – it’s a different form that they like.
“Using a carbon source is helping the soil biology, and helping us because they’re not consuming our organic matter.” In potatoes, the planter is equipped with an in-furrow applicator through which L-CBF Terra Fed is mixed with liquid fertiliser, along with humic acid. The farm uses a strip-till system to plant flowers and oilseed rape, where a small amount of fertiliser is placed, again with added L-CBF Terra Fed and humic acid, while in wheat it’s applied in combination with liquid fertiliser in the spring.
Softening fertiliser effects
Applying a carbon source with liquid fertiliser has the benefit of softening the effects of the nitrogen fertiliser on both the crop and soil, says John’s agronomist, Ed Brown of Hutchinsons. “There’s anecdotal evidence that it can potentially help reduce scorch. I would never rely on it fully because if it is the right weather to produce scorch, it won’t reduce scorch significantly. It’s also a good source of carbon for soil biology. I add humic acid to help cut ammonia losses. Ammonium is positively charged, while L-CBF Terra Fed and humic acid are negatively charged – obviously opposites attract. In this way, it’s essentially doing the same job as a urease inhibitor. In my opinion, this is a preferable method as it doesn’t interfere with soil biology as inhibitors do,” he says. Using the carbon source and humic acid isn’t the only adaptation to the nutrition programme. “The liquid fertiliser ratio has changed to 30% nitrogen plus sulphur, rather than a 9:5:11 blend, which has helped improve efficiency at planting by reducing the application rate from 1,200 litres /ha to 400 litres/ha,” says John.
Boron, calcium and PC25, a phosphate-solubilising bacteria, are added at planting and SAP analysis is used throughout the growing season to better understand the crop’s nutrient use and help tailor micronutrient for optimum crop health. All of those changes, plus the use of clover in cover crops, contributed to an 18% reduction in applied nitrogen in 2023 compared with the conventional potato growing year of 2019.