This experiment iis testing whether seed mixtures of different diversity can be direct-drilled into established pasture for carbon, biodiversity, dietary and economic benefits.
Background to this work. Pasture is often improved by ploughing and harrowing the degraded pasture, treating with herbicides, then sowing with improved grass species mixture dominated by perennial ryegrass. These species are highly productive with appropriate fertiliser inputs. However, this process can be very destructive of soil structure and costly in terms of carbon loss from the soil and field operations. Furthermore, it is optimised for nutrients supplied by continued fertiliser and manure applications.
This experiment investigates questions complementary to the ‘Sward diversification, biodiversity and forage quality’ project. Primarily we will assess productivity, but also determine what establishes and whether the forage quality is improved.
From crop mixtures and intercropping work both for combinable grain and for forage, we have demonstrated the value of species complexity and complementary functional types. In particular, incorporation of legumes at low added nitrogen inputs has proved beneficial to efficiency and productivity.
Here, we seek to benefit from the same synergies in a grazed pasture situation.
Direct drilling has the advantage of causing minimal disruption to mature soil structure, maintains good soil microbial and biotic populations including mycorrhizae and earthworms, and is far less costly than re-seeding through ploughing. It causes negligible carbon loss from the soil and can be carried out with smaller machinery. However, we have found that for optimum outcomes in arable crops the varieties, species mixtures, their proportions and densities when direct drilling differ from those for inversion tillage. Drilling into established pasture introduces yet more questions that need to be investigated.
For our first pasture enhancement experiment (spring 2021), we have sown seven species mixtures of different complexity and a control using a bespoke ‘plot drill’ based on the John Deere 750a disk direct drilling system. These contain up to 14 species including Late Diploid Perennial Ryegrass, LOFA (Fesculolium; Tall Fescue x Italian RG), Meadow Fescue, Smooth Leaf Cocksfoot, Tall Fescue, Timothy, Hybrid Ryegrass, Chicory, Plantain, Burnett, Sheeps Parsley, Crimson Clover, Birdsfoot Trefoil, and a White Clover Blend.
Each ‘plot’ is 3m wide by 24m long and there arere two ‘treatments’ (each with 4 replicates), one of which is a ‘biostimulant’. Across each 3m plot, seed were sown in May 2021 into 16 slots cut by the discs, with alternate slots set at different depths to accommodate different sowing depth preferences of the species chosen.
Grazing the trial would be ideal but impractical to obtain measurements of productivity and quality on this small plot scale. Therefore, we will cut the pasture to measure overall yield and analyse the composition for quality. We will also analyse sample quadrats to compare with overall measurements, but also to determine the actual plant species composition and identify what established (and how well) from the sowing mixtures.
The global context. We need to reduce our carbon losses from soils, enhance our soil structure and health, reduce our inputs especially artificial fertiliser, and enhance our biodiversity, all of which will contribute to slowing climate change. Also, we need to enhance posture resilience and adaptation to changing practices such as mob grazing that is also improving efficiency and productivity. This work will help establish approaches to achieve these transformations in an efficient and practical way.