Using practical science to optimise soil mechanics for GB potato production JENNY BASHFORD, AHDB BLAIR M C KENZIE, JAMES HUTTON INSTITUTE MARK STALHAM, NIAB CUF
Outline Who we are - introduction Functions and strength of soil Managing compaction risk Operating depths Consistency Stability Conclusions
Structure = arrangement Structure is the arrangement of particles (and hence pores) that allows: Roots to anchor the plant Water to drain through pores and cracks Water retention Air to roots for favourable gas exchange Nutrients release to roots Stability of the structure more later
Functions depend on depth & time: we ask a great deal of our soils Surface: allow water entry, remain stable and not crack Mid-ridge: allow for tuber expansion, water storage, root growth and prevent light penetration for greening Base and Subsoil: allow for root proliferation, water storage and drainage Furrow: support traffic but not become an erosion flow path
Functions depend on time What happens to functions after harvest? Source: Abi Croshaw, SGS UK Ltd
Soil strength and connection to function Delivery on all these things depends on lots of interactions. Soil strength is a key determinant but is not just one thing! Richard Cope Silsoe Research Inst photo courtesy of Richard Whalley
Penetrometer to quantify soil strength Do penetrometers of different sizes reveal different information? Demonstration of penetrometer working in soils of different wetness and packing density
Compaction is making our soils shallower 100% Proportion of potential rooting depth 80% 60% 40% 20% 50 43 46 36 Unfulfilled 2-3 MPa 1-2 MPa 0-1 MPa 0% 2010-2014 1992-2004
A model to establish risk from loading Terranimo (www.soilcompaction.eu) Scenario: 330 HP tractor, 10.5 t, 650/85R38 rear tyres at 0.6 bar, sandy clay loam at field capacity, no recent cultivation Conclusion: high compaction risk down to 40 cm, intermediate risk down to 70 cm. Recommendations: change tyre, reduce pressure (primarily affecting stresses in upper soil layers), reduce wheel load (primarily affecting stresses in the deeper soil layers), wait until soil has dried (will increase soil strength).
Soil water content and plastic limit 2012 22 % clay 14 % clay 2013 15 % clay 22 % clay 2014 10 % clay 24 % clay
Depth of plastic limit, GVAP-H (SCL) 2012-2014 Year Depth below top of bed (cm) Depth to flat soil surface (cm) 2012 32 24 2013 30 22 2014 28 19 5 cm variation in critical depth of cultivation
Critical cultivation depths, zoned by EC
We can use visual markers for critical depth
Tillerstar 25 cm Tillerstar 33 cm Clod production is more closely related to depth of cultivation than to machine type or pitch
Poorly-timed cultivation reduces resource use efficiency Cultivated Dry Unirrigated Cultivated Wet Unirrigated
We can deliver more but the soil can t supply it to the plant Cultivated Wet 0 mm irrigation 200 N 0 N Cultivated Wet 65 mm irrigation 300 N
Yield is higher the shallower we destone (GVAP Norton Road 2012) Area Destoner depth (cm) Total yield (t/ha) Light 1 Shallow 67.6 (SL) 2 67.9 3 Commercial 65.7 4 65.7 5 64.6 6 Deep 65.0 S.E. (15 D.F.) 2.81 Heavy 1 Shallow 79.3 (SCL) 2 76.6 3 Commercial 71.7 4 69.1 5 66.9 6 Deep 61.8 S.E. (15 D.F.) 3.19
Yield from 16 experiments Reducing depth from commercial to optimum = +1.8 t/ha
Strength and cultivation Mark has talked about strength by penetrometer and as load bearing capacity. He has introduced the plastic limit. Now want to think about strength and cultivation Same bed looking in opposite directions across soil types
Soil consistency limits Typical Plastic limits Sandy loam 16% Sandy clay loam 25% Clay 36%
Why are consistency limits important? Demonstration of drop shatter test
Is the soil structure stable? How do we measure? Why is it important? Can it be managed?
Is the soil structure stable? Demonstration of wet soil sieving
Impact of management on stability More data needed but response to organic matter addition.
How stable are ridges to slumping? Remember spring 2012?
SPot Farm 2015 Bedtilling (Fendt 936 Vario + Grimme RT6000) Bedforming depth Bed depth posttilling GPS speed (km/h) Spot rate (ha/h) Spot fuel (l/ha) Spot fuel ( /ha) Fuel + labour ( /t) Shallow (37 cm) Shallow (39 cm) 2.2 1.23 (+48 %) 29.2 15.34 0.44 (-47 %) Standard (45 cm) Deep (56 cm) 1.5 0.83 64.1 33.65 0.83
Economics Calculated costs for destoning at a) 34 cm; b) 28 cm and c) difference 34 cm vs 28 cm for a single Grimme CS150 destoning 120 ha of stony sandy loam soil. Yields used: 34 cm, 53.2 t/ha; 28 cm, 55 t/ha. 56 ha grower = 13,100 extra revenue and 1,900 savings in costs. a) c) b) But, ability to travel 20 % faster will be worth more than 1.8 t/ha in wet planting seasons.
Conclusions Preserving functions Less is more in the pocket