Project 4: Study of the influence of tillage on soil physical properties

Project 4: Study of the influence of tillage on soil physical properties

Fifty per cent of the soil’s compositions is void (occupied by air and water) which can be modified by anthropogenic activities like tillage, farm mechanization, etc. The void space is formed by both micro (small) and macro (large) pores. Water is easily drained out from the macro pores and is retained more in micro pores. Roots require water and air from soil for the growth which depends on how much water and air the soil can hold. When the soil gets compacted by traffic load, the total pore space is decreased which affects water retention as well as root penetration. Bulk density is the index that measures the compaction of soil. High bulk density value indicates high compaction and less pore space. It also implies the closer contact of the soil particles that increases the heat conduction within the soil. Tillage disintegrates soil particles, modifies soil pore spaces and slows down soil conduction in soil as compared to untilled or compacted soil. The modification depends on the intensity or frequency and types of tillage use. As for example, a tractor drawn ploughing differs in depth with country plough.
By looking comparison between tilled and untilled soil, the question of whether different intensity and type of tillage affect the physical properties of soil will be addressed. The question will be answered by comparing the bulk density, water holding capacity, presence of micro and macro pores and soil temperature.
Objectives:
3. To study the influence of tillage on water holding capacity of soil
4. To find out the influence of tillage on bulk density
5. To identify the influence of tillage on soil porosity
Materials required:
• Agricultural fields in which a) ploughing is done through power tiller/tractor, b) ploughing is done through country plough c) Pasture/barren land where (no ploughing done)
• 9 GI pipes of 6 cm height and 5 mm diameter to be used as soil core
• Knife, Hammer, Wooden plank, Spade, Small cloth, Rubber band, Weighing Balance, Drier, Beaker, Thermometer
• Funnel fitted with a polythene pipe of 100 cm length
• A clump attached at 100 cm height

Methodology:
Experiment -1 : Bulk density of soil (g/ cm3)
1. Scrap the soil surface with spade where the core is to be inserted
2. Insert a core with the use of a wooden plank and hammer
3. Pull the core from the soil with the help of a spade
4. Cut the extra soil present in the two open ends with knife and clean the soil from the outer of the core by hand
5. Weigh the empty can and put the excavated soil from the core and keep it in the drier at 105o C for 24 hrs
6. Measure the volume of the core as: πr2h (3.17 x 2.52 x 6)
7. After deducting the empty weight of the can from No 5, measure the dry weight of the soil in can.
8. Measure the bulk density of soil as-
Bulk density (g/ cm3) =
Experiment - 2: Water holding capacity (%)
1. Same as from Sl No. 1 to 4 of Study 1.
2. A small piece of cloth is covered in one end of the core with the help of a rubber band
3. Place the core in a Petri dish and water is poured 1/3rd in it
4. Keep this as such for 24 hrs, in that time the soil gets saturated
5. Take the core out of the Petri dish and keep it on the table for 10 min.
6. Collect 5 tea spoon moist soil from the core in an empty can
7. Weight the soil in can and keep it in the drier at 1050C for 24 hrs
8. After deducting the empty weight of the can, measure the moist and dry weight of the soil in can
9. Calculate the soil moisture content in the soil core as:

10. The calculated value indicates the water holding capacity of the soil. As all the pores here are occupied by water, the calculated water holding capacity also indicates the total porosity of the soil.

Experiment- 3: Soil porosity (%)
1. Calculate percent total pore space (Micro and macro pores) present in a soil core using the following formula –

2. The value of bulk density can be obtained from Sl. No. 8 of Study 1
3. The value of particle density (also known as True density) can be considered as 2.65 g/ cm3, which is the average value considered for all practical purposes.
4. One can find out separately both micro and macro pores of the soil by other way too as given below
(A) Micro porosity
1. Same as from Sl No. 1 to 4 of Expt. 2
2. Clamp the funnel at 100 cm height
3. Place a beaker at the end of the pipe fitted in the funnel.
4. Keep the core on to the funnel for 24 hrs
5. Collect 5 tea spoon moist soil from the core in an empty can
6. Same as from Sl No 7 to 9 of Expt. 2..
7. The moisture content thus calculated indicates the moisture present in the smaller/micro pores i.e., micro porosity.

(B) Macro porosity
Deduct the values obtained in Sl No. 10 of Exp. 2 and Sl. 7 of Exp 3.
Experiment-4: Soil temperature (0C)
• Insert thermometers in tilled and untilled soil up to a depth of 5 cm (2 inches) at the morning (8 hr) and record the soil temperature
• Compare the variations in soil temperatures
Relevance:
With the increase in intensity of tillage: (1) soil gets compacted i.e., bulk density is increased, (2) total pore space is reduced (3) micro pore space is decreased (4) water holding capacity is decreased (5) soil temperature is increased.