How improving soil health can reduce weed burdens on Welsh farmland

Balancing soil nutrient levels by applying calcium to farmland could help farmers reduce weed populations, alongside synthetic fertiliser and chemical use.

Similar to many Welsh farmers, lamb and egg producers Ben Anthony and Diana Fairclough face a perpetual battle to control thistles, docks, nettles and other common weeds on their 73-hectare farm in Carmarthenshire.

When they recently hosted a Farming Connect event led by agronomist Daniel Lievesley, he suggested that an incorrect balance of soil nutrients could be a reason for those annual weed burdens at Frowen Farm, Login, where lamb is produced from 370 breeding ewes, and eggs from free range hens.

Analysis

Weeds are not only problems to be dealt with but indicators of issues in soil balance. Getting soil analysed should be a first step to addressing weed issues, advised Daniel from DJL Agriculture.

Daniel said: “Weeds establish where there’s a nutrient deficiency. For example, docks mine for calcium, so if you address the calcium deficiency, you take away the very reason for the docks to be there.

“You will often find that the forage that grows around a weed is high in nutrients because the weed tap roots draw up minerals from deep in the soil to feed it.”

Daniel warned farmers against focusing solely on chemicals to control weeds, recommending that they address the nutritional function in their soils.

At Frowen, for example, soil sampling shows that the clay soils have a high iron content, locking up phosphorous and zinc.

Introducing air into the soil with aeration is a means of addressing this, but so too is rectifying the mineral imbalances.

Common farmland weeds like nettles, chickweed and fat hen are indicators of high nitrates, for example, while low calcium levels encourage docks and thistles.

When calcium levels are low, Daniel advocates applying gypsum as a means of changing cations in the soil, supplying calcium to replace some of the magnesium bound by soil particles, particularly in clay soils.

Calcium is closely linked with mycorrhizal fungi soil interactions too, which keeps weeds at bay. The calcium:magnesium ratio on a soil analysis report should ideally sit at around 8:1; any less and the calcium deficiency needs to be addressed to prevent weeds taking hold.

“Mined gypsum is a wonderful way to apply calcium sulphate to release the magnesium into the soil,” said Daniel.

Gypsum is best applied when there is rain in the weather forecast. Daniel specifies use of naturally-mined gypsum, not reclaimed plasterboard which contains resins, glues, and heavy metals which present issues for livestock.

At current prices, gypsum comes at a cost of £20–£32/tonne, depending on a farm’s proximity to a quarry, and a further £5–£10/acre spreading charge.

Burdens

Integrating trees into agricultural systems can also reduce weed burdens. With shade from trees, weeds are deprived of light, forced to compete for resources in the soil, and suppressed through the mulching effect of leaf litter.

Tree and hedgerow root systems draw nutrients from deeper soil layers and these are circulated within the ecosystem, contributing to overall soil health and significantly adding to the soil’s carbon content through storing carbon in roots and the decomposition of root biomass and leaf litter.

Farming Connect’s Forestry Specialist, Geraint Jones, a speaker at the event, explained that trees improved soil health and establish physical barriers against the spreading of weed seeds.

Geraint explained: “Many tree species form symbiotic relationships with mycorrhizal fungi in the soil.

“These fungi extend the reach of the tree’s root system, significantly increasing the surface area for nutrient and water absorption that they mine from deeper layers.”

In exchange, the tree provides the fungi with carbohydrates. These fungal networks also connect different plants, potentially facilitating nutrient transfer between them.