Soil PH - Lab Report Example

Introduction

Like all living organisms, plants require nutrients to complete their life cycle and to produce abundant yield. Plants require some nutrients in large amounts; these nutrients are nitrogen, phosphorus, potassium, and calcium. Microelements are equally important despite being required in very low amounts. Important microelements are iron, copper, molybdenum, manganese, and boron. Nutrients are taken up in their ionic forms; therefore, they have to be in solution when taken up. Due to this nutrient uptake is always coupled with the transpiration stream.

The most important factor affecting the availability of these nutrients is soil pH, a measure of the amount of hydronium ion (H+) that is present in solution. Pure water has a neutral pH of 7, lower values mean that the solution is acidic and soils with pH higher than 7 are alkaline. Different crops vary in their response to acid and alkaline soil conditions (Mathers, 2001). However, for most field crops, slightly acidic (pH = 5.6) to neutral soils are optimal for growth. Soil pH affects plant growth and productivity indirectly because, depending on the nutrient, availability is affected which can result in nutrient deficiency or nutrient toxicity. In higher pH or alkaline soils, result in deficiencies in the essential micronutrients iron, zinc, and manganese. Soil pH of less than 5.5 is already considered strongly acidic and will not support growth of economically important crops. Thus, the right soil pH is a requirement for maximum yield production.

The development of acid soils has been due to high weathering brought about by warm temperatures and rainfall, and manmade events like the continuous use of nitrogen fertilizers and acid rain effects. At pH below 6 or under acidic soils, increased availability of micronutrients like iron, manganese, zinc ,  copper and aluminium result in toxicity symptoms (CSIRO Plant Industry, 2004); while decreased availability of phosphorus results in deficiency of this element . This is very true in humid countries where soil acidity is often associated with low crop productivity (Schroth, Lehman, & Barrios, 2003). 

Hypothesis:

Null hypothesis:        The soil pHs from different sites are similar.

Alternate hypothesis: The soil pH of different sites are not similar.

Methodology

The class was divided into eight groups. Each group was asked to bring soil samples from the area near their residence. In the laboratory, the pH and temperature of pure water was determined. After adding water to the soil and mixing the slurry, the pH and temperature of each sample were measured. Mean values of the soil pH of each group were determined, and the hydronium ion concentration was calculated using the following formula:

[H+] = 10–pH

Where:  [H+] = hydronium ion concentration

pH = mean of three pH measurements

Results and discussion

Table 1 presents the raw and mean values of the soil pH and the hydronium ion concentration of the different soil samples. The average soil pH ranged from 5.7 (slightly acidic, sample of Group 2) to 8.32 (moderately alkaline, sample of Group 1). The hydronium ion concentration was also highest in Group 2 soil at 2.01 x 10 -06 Molar. Sample 2 also had the lowest amount of hydronium ions at 4.82 x 10 -09 moles H+ per liter of solution. However, water has a lower pH (7.62) than sample 1, which indicates that there are more H+ ions in the water compared to soil sample 1. The other slightly acidic soils are samples 3, 6, and 7. These soils, based on the literature, can support crop growth.

Table 2 presents the raw and mean data for soil temperature. However, it is observed that the temperature values varied widely and did not correlate with the soil pH values. Since the temperatures were not measured at the sampling site, changes in temperature could have occurred during the time when the samples were transported, or during handling.

Table 1. Soil pH values and H+ concentration of different soil samples.

Group/ Sample No.

Soil pH

Average soil pH

[H+]  

(moles per liter solution)

Rep I

Rep II

Rep III

1

8.1

8.4

8.45

8.32

4.82 x 10 -09

2

6.1

5.4

5.59

5.70

2.01 x 10 -06

3

6.12

6.64

7.03

6.60

2.53 x 10 -07

4

7.21

7.68

6.3

7.06

8.64 x 10 -08

5

7.54

7.22

7.3

7.35

4.43 x 10 -08

6

6.23

 -

 -

6.23

5.89 x 10 -07

7

6.94

6.73

6.98

6.88

1.31 x 10 -07

8

6.7

7.37

7.58

7.22

6.07 x 10 -08

water only

7.5

7.78

7.59

7.62

2.38 x 10 -08

Table 2. Soil temperature of different soil samples.

Group No.

Soil Temperature (degrees Centigrade)

Average

Rep I

Rep II

Rep III

1

23.8

23.8

23.6

23.73

2

23.5

22.9

22.3

22.90

3

22

21.8

22.6

22.13

4

22.3

23.2

21.2

22.23

5

30.9

31.1

30.8

30.93

6

22.6

22.60

7

24

21.9

21.6

22.50

8

23.6

22.8

27

24.47

water only

26.3

26.30

Conclusion

The different soil samples showed different pHs, ranging from slightly acidic to moderately alkaline. These values show that the soils are healthy and are suitable for growing most crop plants, like vegetables, ornamentals, and cereals.