Soil 210: Soil Physics Question Paper
Soil 210: Soil Physics
Course:Bachelor Of Science In Agriculture
Institution: Chuka University question papers
Exam Year:2013
CHUKA
UNIVERSITY
UNIVERSITY EXAMINATIONS
EXAMINATIONS FOR THE AWARD OF DEGREE OF
BACHELOR OF SCIENCE AGRICULTURE
SOIL 210: SOIL PHYSICS
STREAMS: BSC AGRIC Y2S1 TIME: 2 HOURS
DAY/DATE: WEDNESDAY 24/4/2013 11.30 AM – 1.30 PM
INSTRUCTIONS:
ANSWER ALL QUESTIONS IN SECTION 1 AND ANY TWO IN SECTION II
SECTION I: (30 MARKS)
1. (a) What is soil consistency? [2 Marks]
(b) State and explain the three adverse effects of suboptimal aeration on plants and soils. [6 Marks]
2. (a) Explain the effect of soil temperature on:
(i) Soil water movement [3 Marks]
(ii) Seed germination [3 Marks]
3. (a) In relation to soil water retention what is hysteresis? [2 Marks]
(b) A sample of moist soil was weighed and placed in an oven and dried at 105? for 24 hrs after which the following data was recorded.
Mass of can + moist soil = 180g
Mass of can + dry soil = 153 g
Mass of empty can = 35g
Calculate the gravimetric water content (w) of the soil. [5 Marks]
4. A 100cm3 undisturbed soil sample has a mass of 165g. After oven drying a 100?, its mass is reduced to 134g. The particle density is 2.6g/cm3. Calculate its;
(i) Bulk density [3 Marks]
(ii) Porosity [3 Marks]
(iii) Volumetric water content. [3 Marks]
SECTION II: 40 MARKS
5. (a) Discuss how climate, soil properties and topography influence soil moisture
content. [15 Marks]
(b) Briefly explain the term osmotic potential. [5 Marks]
6. (a) A sorghum crop was planted on vertisol soil and soil moisture in the profile
measured at the beginning and end of a thirty day period. The following data was recorded.
Soil moisture in the profile on October( 01(Ml) = 300 mm
Precipitation or Rainfall (P) = 70 mm
Irrigation (I) = Nil
Contribution from ground water (C) = Nil
Run-off of 200 cubic m from 2 ha field (R) = 10 mm
Deep drainage (D) = Nil
Soil moisture in the profile on October 31 (M2) = 250 mm
Estimate evapotranspiration (ET) from the field during period 01 to 31 October. [10 Marks]
(b) Given that millet was planted on the adjacent field of sorghum above, and the data
below was recorded;
Soil moisture in the profile on November 10 (Ml) = 150 mm
Precipitation or Rainfall (P) = 600 mm
Irrigation (I) = Nil
Contribution from ground water (C) = Nil
Evapotranspiration (estimated) (ET) = 530 mm
Run-off of 200 cubic m from 1 ha field (RO) = 70 mm
Soil moisture in the profile on February 30 (M2) = 60 mm
Estimate the deep drainage (D) losses form the field during the crop period.
[10 Marks]
7. (a) Discuss the signs of compaction on soil and plant growth. [15 Marks]
(b) Briefly discuss means by which water is held in the soil. [5 Marks]
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