Deep-rooting grass cultivars could contribute to flood risk management

Introducing grass leys into arable rotations has the potential to improve soil structure and organic matter. This has benefits to the arable rotation, but can also increase water infiltration rates during storms, with resulting benefits in terms of flood risk management at the catchment scale. Reduced runoff from agricultural catchments can also result in improved water quality and aquatic ecology.

In one of our replicated plot experiments in the EU funded SoilCare project, we selected five modern deep-rooting agricultural grass cultivars as being the most likely to create pathways for water to reach deep into the soil profile, rather than running off the surface. Each cultivar was represented as a 50% component of an otherwise standard ryegrass and clover mix, with control plots comprising this standard mixture alone. The whole area was grazed by sheep and cut for silage following standard practice, but in years three and four of the experiment, we fenced off a three metre wide strip which was ungrazed and uncut.

We found that water infiltration rates were highest for the Festulolium cultivar, 'Fojtan' and the cocksfoot cultivar, 'Donata' in Year 1 of the experiment, but this was not repeated in subsequent years. A detailed assessment of root volume through the soil profile in Year 3 revealed that Fojtan root biomass was nearly four times higher than the standard ryegrass mixture at 70cm, but this was the case only where there was no grazing or cutting. In the adjacent cut and grazed areas, the standard ryegrass mixture had higher biomass at 70cm, but this was only half that of the ungrazed Fojtan. In Year 4, when root volume for all five cultivars was measured, four of them had higher values in ungrazed areas than grazed areas, but this difference was not statistically significant.

Soil compaction at 10cm was significantly higher in the grazed and cut areas than the fenced off portions of the strips, and within the fenced off area there was a 40% difference in sward volume between the areas with highest and lowest compaction. As root volume reflects above ground biomass, compaction is likely to be limiting water infiltration both directly, and by limiting root growth.

The results suggest that while some deep-rooting grass cultivars have the potential to contribute to landscape scale flood risk management, their capacity to do so may be limited by soil compaction associated with grazing livestock and harvesting of silage. As autumns become increasingly wet, grazing during this period can be particularly damaging to soil structure. For objectives such as flood risk management and water quality improvement to be met, a balance may need to be struck between the management adopted to meet the objectives of farm businesses and those of wider society. Economic incentives within the new Sustainable Farming Initiative to increase sward height and manage stocking densities to minimise poaching and soil compaction may enable farmers to meet both objectives if the right balance can be struck between payments and practice on different soil types.

There are more details of our research in: Stoate, C., Bussell, J. and Fox, G. 2021. Potential of deep-rooting agricultural grass cultivars for increasing water infiltration and soil organic carbon. In: Intercropping for Sustainability: Research developments and their application. Aspects of Applied Biology 146.

Soil moisture and management

Understanding soil moisture is important to improve the effectiveness of cultivations. Wet soil is prone to compaction, but soil moisture is important to soil cohesion, maintaining channel shape at depth when mole ploughing. To reduce damage to soil structure during feld operations, soil should be dry on the surface. Dry soil is also more friable, breaking down easily to produce cracking at the required depth during subsoiling. With help from Agrii, we have been using soil moisture sensors to help understand how the data generated might inform decisions about timing of field operations at different depths in the soil profle.

You can download a pdf summarising our results here.

 

Feeding willow to ruminants could reduce greenhouse gas emissions

Trees provide shelter and shade for livestock, and some offer additional forage.  In 2019, we were one of three research sites which contributed to a study of the potential of goat willow, oak and alder leaves as a source of supplementary minerals.  Willow was consistently higher in zinc and cobalt which is often deficient in grass and is important for the synthesis of vitamin B12. If you have not seen it, you can find the summary here.

In 2019, we also carried out an experiment with Nottingham University School of Veterinary Science in which willow leaves were fed to weaned lambs to determine whether the higher cobalt in leaves was reflected in higher concentrations in the animals.  Blood samples taken before and after feeding willow for a two-week period confirmed that blood cobalt concentrations and vitamin B12 were significantly higher in willow-fed lambs.

Lambs feeding on willow leaves at Loddington

Condensed tannins in willow leaves have the potential to supress microbial activity in the rumen, reducing uptake of nitrogen into the blood, and ultimately into urine.  This has the potential to reduce emissions of nitrogenous gases, primarily nitrous oxide and ammonia from urine patches.  Inhibition of microbial activity in the soil could have the same effect.  As nitrous oxide is a major greenhouse gas, and ammonia has negative air quality implications, the use of willow to reduce these gaseous emissions from urine could potentially contribute to climate change and human health targets.

In August 2020, we fed 200g of goat willow leaves per day to two groups of six weaned lambs over a two-week period.  Another two groups of six lambs were not fed willow.   At the end of the experiment, we identified fresh urine patches by direct observation of the lambs (six willow-fed, and six not willow-fed) and used our Gasmet gas analyser to measure emissions of carbon dioxide, as well as nitrous oxide and ammonia.  We did this within 20 minutes of urination, and again one and two weeks later.

There was a consistent trend for urine patches in pens with lambs that were fed willow to have lower emissions than those that were not fed willow for each of the three gases, although this was only statistically significant for nitrous oxide in Week 2, probably because of the small number of urine patches sampled.  Ammonia emissions declined rapidly, nitrous oxide emissions were mainly in Week 2, and carbon dioxide emissions declined gradually over the two-week period.  Lower carbon dioxide emission suggests that microbial activity was supressed in the soil, rather than in the rumen, but we cannot discount a contribution from the latter.  Willow is well suited to mechanical harvesting, or to direct browsing of coppiced trees if livestock access is managed to ensure sustainability, and our results suggest that feeding willow to ruminants could contribute to climate change and air quality targets.

 

Stoate, C., Fox, G., Bussell., J. & Kendall, N.R. 2021. A role for agroforestry in reducing ammonia and greenhouse gas emissions from ruminant livestock systems. Aspects of Applied Biology 146.