Lecture 6a Soil Weight and Tillage

1. Lecture 6aSoil Weight and Tillage

2. Soil Weight & Bulk DensityNote: Since gravity will not change we will use mass and weight interchangeable. • BD = mass / volume or grams/cc • Soil mass = BD x Volume • BD always measured on oven dry soil (water is not considered in BD calculations) • BD changes as the pore space changes ie. compaction = > BD • BD of common surface soils = 1.1 - 1.4 g/cc • BD of common subsoils = 1.3 - 1.7 g/cc Using a penetrometer to measure soil bulk density indirectly

3. Acre Furrow Slice Tilled Soil D W AFS = D x W = 2,000,000 pounds

4. What is an Acre? • An acre was initially defined as the area that a man and ox could cultivate in one day. In France the equivalent area was called a journal (in French jour means day). (about size of a football field) • Medieval period acres varied from locale to locale as can be imagined. • Eventually uniformity came about, at least in Britain. There a 10-acre square was defined as a furlong on each side. • Football field is about 1.3 acres

5. Furlong is Old English and originated as furh (furrow) + long, i.e. a long furrow. A furlong measures 1/8 mile, 220 yards, 660 feet, or 60 poles. • The furlong, the "long furrow", came into use only after the adoption of the horse (and horse collar) and the heavy wheeled plow. Until then, with oxen and a light plow, which could be easily turned, the fields were more or less square. DG Baker

6. Calculation of soil loss or tons of soil loss per acre • 1 g water = 1cc • & 1 ft3 water = 62.4 lbs • example soil BD = 1.2g/cc or • the soil is 1.2 times heavier than water or • ratio of soil and water = 1/1.2 = 62.4/X • or X = 1.2 x 62.4 = 74.9 lbs. per cubic foot

7. BD problem • For soil with BD of 1.2g/cc that lost 3 inches of soil per acre how many tons of soil were lost? • Solution: BD= (mass(x) ÷ vol.) or (1.2x62.4) = (X lbs) ÷ (43560 ft2/acre x3/12 ft) • X = (74.9 lbs/ft3 x 43560 ft2 x 3/12 ft.) = 815,661 lbs or • 815661bs ÷ 2000lbs/ton = 407 tons/acre Volume = L×W×H or Area × H & 1 acre = 43,560ft2

8. Particle density • Particle density is the mass of the soil particles divided by the volume of the soil particles • Particle density normally is 2.65 g/cm3 Example: Soil Core = 300 cc = volume of soil (soil particles + pore space) pore space = 165 cc, (only volume of soil pores) solids = 135cc , (volume of soil particles) Soil weight = 358g PD = soil mass ÷ vol. of solids = 358g ÷ 135 = 2.65 g/cc BD = soil mass ÷ soil volume = 358 ÷ 300 = 1.19 g/cc Porosity =pore space ÷ soil volume = 165 ÷ 300 x 100 = 55%

9. = Between soil particles and organic matter are open spaces called pores Water which fills all or parts of the pores is soil water Soil porosity directly influences soil water movement Particle Density & Porosity Soil Water pore Air pore

10. Porosity (P) • Porosity (P) = the volume of the pores divided by the bulk soil volume. • P = pore vol ÷ soil volume Data from previous slide: Porosity = 165cc ÷ 300cc x 100 = 55% • P = {1 –{ BD ÷ PD} }x100 or • P={1-(1.19 ÷ 2.65)}x100 = 1- .45 =.55 x 100 = 55% porosity }

11. Bearing Capacity-determined by Soil Texture • Ability of the soil to withstand a load • Or the average load per unit area that will cause failure by rupture of a supporting soil mass. • Soil stabilization - any method that prevents a soil system from moving under a load. • Compaction - increase the density - thereby increasing stability - apply large pressure to soil at optimum moisture

12. Shrink / Swell Potential- • soils with more than 30% clay have a high Shrink Swell > clay more S.S. Potential (if clay is 2:1) • to avoid this problem soil must be compacted and water must be kept out. • without the above - Shrink/swell will crack foundations and pavements or move telephone poles.

13. Settling of foundation due to unstable soil due to high shrink swell potential

16. Bearing capacity of Materials Load bearing Pressure (psf) • Crystalline Bedrock 12,000 • Sedimentary rock 6,000 • Sandy gravel or gravel 5,000 • Sand, silty sand, clayey sand, silty gravel and clayey gravel 3,000 • Clay, sandy clay, silty clay, and clayey silt 2,000 • Psf ( pounds per square foot) • BOCA National Building Code, 1996

17. Chemical Soil Stabilization • Lime, cement, and pozzolan (high silica volcanic ash) can be used as chemical additives. • Lime is most effective on clay soils, and can be used in combination with cement and pozzolan.

18. Loss of bearing capacity - a wet soil allowed this heavy tractor to sink in to the axels. It required a pull to become un-stuck.

19. SOIL STRENGTH PENETROMETER • This penetrometer is a easy and reliable method for determining in‑place soil strength. • Great for checking building pads, excavations, or potential building sites. • Simply measure the penetration and look up soil strength on the strength chart included with the unit.

20. Tillage • Soil tillage - oldest procedure of agriculture to manipulate the soil to improve crop production. • Farmers of Burkino Fasso (West Africa) preparing their land for planting.

21. Tillage - old

22. Tillage - Modern

23. Tillage uses more energy than any other cropping procedure. • Tillage requires time, since lifting the soil and moving it can not be done rapidly.

24. Tillage - Objectives • Preparation of seedbed • Control of weeds • Fluff soil - reduce bulk density of root zone • Soil and Water conservation

25. Compaction

26. The Plow • A plow is a wedge that is dragged through the soil by a draft animal or a tractor. • It cuts away the top layer of soil. • The plow lifts and turns over the soil layer. • The plow is one of mankind’s oldest machines. • Wooden plows have been in use for about 5000 years. Metal plows date back less than 200 years. • http://www.historyforkids.org/learn/economy/plow.htm • http://video.google.com/videoplay?docid=6505199120210531414&q=CHISEL%20PLOW&hl=en

29. Tillage - Conventional & Cons. • Conventional - Moldboard plowing, disking, planting and cultivating. • http://video.google.com/videoplay?docid=7901297547942235489&q=plowing&total=1839&start=0&num=10&so=0&type=search&plindex=6 • http://video.google.com/videoplay?docid=3413143716172356867&q=plowing&total=1833&start=10&num=10&so=0&type=search&plindex=4 • Conservation - leaves crop residue on soil surface, leaves clods or ridges, increases infiltration and reduces runoff. • http://video.google.com/videoplay?docid=639653600966425831 • http://video.google.com/videoplay?docid=1368127058493687056&q=DISK+TILLAGE&total=6&start=0&num=10&so=0&type=search&plindex=4

30. energy saving time savings erosion control cold spring soils disease and insect problems lower yields compaction relief < OM incorporation < weed control harder Conservation TillageAdvantages Disadvantages

31. Chisel Plowing http://video.google.com/videoplay?docid=758554037778096590&q=CHISEL+PLOW&total=4&start=0&num=10&so=0&type=search&plindex=2

32. Chisel Plowing This system does not turn the soil over, but rather leaves it rough with clods of soil, with plenty of crop residue remaining. The soil density and amount of covering depends on the depth, size, shape, spacing, of the chisel blades. The residue and rough, cloddy surface of the soil reduces raindrops impact and reduces runoff velocities, thus reducingerosion.

33. Disk Plowing • Similar to Chisel plowing, some residues are turned under by the disk lifting and inverting the soil.

34. Ridge Tillage The annual ridges are formed by using a rolling disk bedder, and planting is done after only minor spring seedbed preparation.

35. Ridge tillage The extent of soil conservation depends on the amount of residue left and the row direction. Planting on the contour plus increased surface residues greatly reduce soil loss.

37. Strip Tillage –No Ridge • Strip tillage aims to retain crop residues, and establish crops with the least amount of soil disturbance while still maintaining crop yield. • Strip till techniques often involve fully cultivating a strip that is about one third of the row spacing wide. • The rest of the soil is left undisturbed, and provides a good carriage way for vehicles passing through the crop. http://video.google.com/videoplay?docid=6518049770349075983&q=STRIP+TILLAGE&total=83&start=0&num=10&so=0&type=search&plindex=0 • http://www1.umn.edu/umnnews/video/carbon.html

38. All planting requires: placing seed at accurate depth pressing and covering seed so each has an equal chance for germination & emergence, This provides uniformity and predictability of crop establishment. NO - Till Planting

39. No till This planting system prepares a seedbed 2 inches wide or less, leaving most of the surface undisturbed and still covered with crop residues. The result is a wetter, colder environment that protects the seed and soil with its insulating effect of the surface residue.

40. Turf Tillage • Objectives Improve Aeration Increase Infiltration Ease root movement • Procedures Coring Slicing

41. Coring and top-dressing golf greens

42. Dyad • Describe conservation tillage that you have seen or done, or describe some turf tillage that you have observed or participated in.

43. Soil Erosion in a field - 3% slope & conventional tillage. The End