Assessing and Repairing Structural Damage

Transcription

1 Assessing and Repairing Structural Damage Dick Godwin Visiting Professor - Harper Adams University

2 Outline Effects of structural damage Yield Tillage Runoff/Erosion/Flooding Assessing structural damage Repairing structural damage Moling and Subsoiling Drainage Concluding comments

3 Cost of soil degradation in England and Wales The assessment explored the total costs of soil degradation: The total quantified costs of soil degradation are estimated at between 0.9 bn and 1.2 bn per year. Compaction and loss of soil organic content account for 39% and 45% respectively of annual costs. Silts and sands account 67% of total estimated erosion costs, and clays and sands for 91% of compaction costs. Almost 80% of total quantified costs occur offsite. In terms of soilscapes, arable farming accounts for over 70% of erosion and compaction related costs. Defra Report CTE0946 by Cranfield University, 2011 Spatial distribution of predicted probability of compaction

4 Dry matter yield, t/ha Relationship between maize silage yield and soil bulk density (Quebec) 12 Sandy loam soil % Soil dry density, t/m 3 After: Negi et al, % at c. 700/ha* = 100/ha 1.7 t/ha (dm) at 79/t** = 134/ha * Nix, 39 th Edition **IGER Date???

5 Draught force, tonnes Relationship between draught force and soil bulk density Blade Sandy loam soil Tine 250% increase or 60% reduction Soil Dry Density, t/m 3 After: Godwin, 1974

6 Traffic control effects on energy/costs requirements (kwh/ha) ( /ha*) *After: Nix 43 rd Edition (2013) c.25p/kwh at 65% Tractive efficiency (Innes and Kilgour, 1980) No traffic Trafficked Shallow plough 13 ( 5) Shallow plough 32.5 ( 13) A 60% reduction After: Chamen, 1992 Harrow 7.0 Spring tine 16.0 Drill 7.5 Power Harrow 30.0 Roll 7.5 Harrow 8.0 Drill 8.6 Roll 8.4 TOTAL 22 ( 9) 71( 30) A 70% reduction

7 A serious problem Runoff Erosion Poor Drainage Flood Management Soil condition can radically affect rate of overland flow and can exacerbate surface water flooding, Richard Smith, EA Poor soil condition is widespread in South West, Richard Smith, EA Soil loss no protection 3-5 t/ha/year - Soil regeneration 1 t/ha/year Drainage installation 1980 ~ 150,000 ha/year - Now 5,000 ha/year 40,000 homes and 7,000 businesses in Severn region were affected by flooding in June-July 2007

8 Relationship between compaction and infiltration rate After: Chyba, Soil Density g/cc

9 Infiltration rate (mm/hour) Infiltration ~ soil type Main factors affecting infiltration Soil type Vegetation/surface cover Sandy loam Loam Clay loam Time (hours)

10 Infiltration rate mm/hr Infiltration ~ surface cover Old permanent pasture or heavy mulch 4 to 8-year old permanent pasture 3 to 4-year old permanent pasture lightly grazed Permanent pasture moderately grazed Hays Permanent pasture heavily grazed Strip-cropped or mixed cover Weeds or grain Clean tilled Time (min) Bare ground 10

11 Rainfall and runoff rates (mm h Effect of infiltration rate on runoff Parrett and Tone Catchment, Haselbury Plucknet/Chiselborough 6-1 ) 5 Rainfall ^ q poor = Peak runoff (mm h ^ - 1 ), 1-4 mm/hr q good = Peak runoff (mm h - 1 ), 4-8 mm/hr 4 3 Rainfall % Reduction in peak flow 25% 23% 21% 19% ^ q poor =3.3 Rainfall q ^ good = ^ q poor =1.6 ^ q good =1.23 ^ q poor =1.7 ^ q good =1.35 Rainfall ^ q poor =0.89 q ^ good = rd December 24 th December 25 th December After: Godwin and Dresser, 2003 From: Schwab et al., 1993

12 Soil structure Structureless sand Massive (structureless clay) Prismatic Blocky Granular Platy

13 Assessing soil structure After: Vaderstad, TARGET on establishment

14 After: Shepherd (2000), Visual Soil Assessment, Volume 1, Landcare Research, New Zealand Visual Soil Assessment

15 Root development

16 Evaluation of structural damage Profile pit Penetrometer Electromagnetic Induction Conductometer 0.3m and 0.9m ranges

17 Assessing soil structure Source: Chamen, 2011

18 EMI survey data. (After: Smith, 2001) Before sub-soiling After sub-soiling Gateways Compaction

19 Wheel traffic Chamen, 2015

20 Comparison of forage chopper harvester and round baler traffic 63.8% and 63.4% respectively

21 Subsoiling Plain tine Wide point, high lift wing Narrow point, low lift wing After: Spoor and Godwin, 1978

22 Soil looseners Chisel tine (Shakerator) Conventional Subsoiler High lift Winged Subsoiler Low lift wings + leading disc Paraplow Moleplough

23 Subsoiler Draught forces Subsoiling after tracks at 350mm 88hp Subsoiling after tyres at 450mm 240 hp 63% Reduction After: Ansorge and Godwin, 2007

24 Soil disturbance and critical depth Direction of travel a. Soil surface Soil failure planes Undisturbed soil b. Soil surface Critical depth = 6 x tip width under friable soil moisture conditions Compacted zone

25 Soil failure Herringbone cracks Horizontal cracks After: Spoor and Godwin, 1978

26 Mole plough & Herringbone cracks

27 Flow rate, ml/s Rainfall, mm Hydrograph of mole drain discharge with leg fissures Hydrograph of mole drain discharge without leg fissures Time, h After: Leeds Harrison, Spoor & Godwin, 1982

28 Addition of Wings <-Tension crack <-Horizontal crack Tension cracks Direction of travel Soil surface Wing Soil flow Godwin and Spoor, 2015 Lift height

29 Effects of winged tines Shear planes After: Spoor and Godwin, 1978

30 Total soil disturbance Tip Wing After: Spoor and Godwin, 1978

31 Effect of wings Draught kn kn Disturbed area m m 2 Specific resistance 208 kn/m kn/m 2 After: Spoor and Godwin, 1978

32 After: Spoor & Godwin, 1978 Leading shallow tines

33 Soil disturbance Draught Force (tonnes) Area of disturbance (m 2 ) Specific resistance (tonnes/m 2 ) Wings only Plus shallow leading tines Similar: Almost double: 45% reduction After: Spoor & Godwin 1978

34 Effects of tine spacing Too close Optimum Too wide Spacing After: Godwin, Spoor and Soomro, 1984

35 Multiple tine spacing Simple tines = 1.5 x depth of work Winged tines = 2.0 x depth of work Winged tines + shallow leading tines = 2. 5 x depth of work (of deeper tine) After: Spoor & Godwin, 1978

36 2 pass system 1 st Pass d 2nd Pass d 4d 2d Godwin and Spoor, 2015

37 Precautions in grassland Loosen as soil is moving into a wetting phase Ensure soil surface can support the tractor weight and thrust Machine set up Use leading discs or backward raked leg Low lift wings with narrow tip (Flatlift type) Consider slant leg device (Paraplow type) Do not operate too deep (minimise draft force and wheel slip) Consider a moling operation to create vertical cracks (could be smaller diameter foot if shallower operation) Do not re-compact either during or immediately after soil loosening Tread carefully in post loosening phase

38 In field evaluation of effective loosening Visual evaluation need not be conducted in every field if soil types and conditions are similar. The visual assessment of surface level provides a simple guide as to the appropriateness of tine spacing. If the surface elevation appears to show distinct heave then tine spacing is too wide. An even lifting of the soil surface usually indicates a uniformity of loosening and porosity increase. If not dig a hole and examine adjusting depth and spacing as required. Godwin and Spoor, 2015

39 c. 300/day to hire machine and man Clean ditches

40 Drainage Maintenance: Pipe Jetting for Blockages 40

41 Potential site for a short drain, ditch cleaning and grass waterway

42 Mole drain/furrow from the ditch + 2 nd tractor & chains or winch Herringbone cracks Fit duals and reduce inflation pressure Shallow, i.e deep, mini-mole with 2 diameter foot. No - Expander

43 Alternatively in arable conditions Dig a ditch Digger or spade Pull a furrow Starting from both ends Drill a hole or dig a soak-way Depends on the subsoil condition??

44 Concluding remarks Compaction Reduces yield by 10-15% Increases tillage energy, time and costs by % Reduces infiltration by and hence increases runoff and flooding Improved soil and water management is achieved by Reducing contact pressure, and Reducing traffic intensity These costs are small in comparison to the potential economic benefits Ensure adequate drainage Remember prevention is better than cure However, if all else fails equipment/techniques are available to alleviate compaction But take care on freshly loosened soil as it is vulnerable to recompaction.