LIMING OF QOZ SOILS

 Land Use Planning Note AAH/1/88

 

CONTENTS

1 INTRODUCTION

2 SOIL MATERIAL / PREVIOUS LAND USE

3 LIMING MATERIALS

3.1 General

3.2 Gypsum

3.3 Limestone

3.4 Burnt or Quick Lime

3.5 Hydrated or Slaked Lime

4 PLANT POTS

5 LIMING RATES

6 COMPARATIVE INPUTS OF CALCIUM

7 APPLICATION OF MATERIALS

8 WATERING

9 SAMPLING AND pH DETERMINATION

10 FINDINGS

11 GROWTH OF REFERENCE CROP

12 CONCLUSIONS

13 RECOMMENDATIONS

 

Appendix

__________________________________________________________________________________________ 

1 INTRODUCTION

As proposed in the LUP Inception Report (1986) a simple pot experiment to study the effects of liming materials on Qoz was set up. The aim being to apply various rates of different liming (sources of calcium) materials to an exhausted Qoz sand and note:

 

2 SOIL MATERIAL / PREVIOUS LAND USE

Two samples of Qoz topsoil were collected from Uru Jumai some 5 km south of Kilo. The farmer stated that the area had been farmed for 40 - 50 years using a millet, groundnut, sesame rotation without any fertiliser input or planned fallow. Yields had steadily fallen and were currently 2 - 3 sacks (millet) per makhomas; compared to 10 - 15 sacks about ten years ago. The farmer blamed Striga for the yield decline and claimed that there was no Striga ten years ago.

Soil was collected in bulk from the upper 20 cm of two sites;

  1. a level, lower lying area (Low Qoz)and
  2. (b) an elevated area (High Qoz) or crest site.

Yields were stated to be marginally better from the High Qoz, though still very poor.

 

  1. LIMING MATERIALS
    1. General

All materials used have been called liming materials though sources of calcium might be a more accurate description. The materials used were Gypsum, Ground Limestone, Burnt or Quick Lime and Hydrated or Slaked Lime. The materials are described in the following sections and analyses are presented in Section 5.

3.2 Gypsum

The gypsum was drawn from the WSDC stores and was in powder form which all passed through a 60-mesh sieve. Gypsum, calcium sulphate, is relatively soluble and safe to handle.

3.3 Limestone

Rock fragments, gravel and dust were collected from the lime-yard at about km 5 on the Zalingei road. The rock is trucked-in from Berdan, about 2 hours away. The limestone was hand ground and passed through a 60-mesh sieve before use. It was assumed that this material was mainly calcium carbonate, and safe to handle.

3.4 Burnt or Quick-lime

The above lime-yard prepares this material by burning the limestone in pits. Before use, the burnt limestone was hand ground and passed through a 60-mesh sieve. Burnt lime is calcium oxide which readily absorbs water, to form calcium hydroxide, and is a caustic material and requires careful handling.

3.5 Hydrated or Slaked Lime

Hydrated lime, calcium hydroxide, was made at the lime-yard by placing the burnt lime in ponds of water. The resulting slurry was air-dried, ground and passed through a 60-mesh sieve. This material is non-caustic and is safe to handle.

4 PLANT POTS

Clay plant pots of a nominal 18-cm diameter and 20 cm height were obtained from the Nyala Nursery. The pots were filled to 18 cm depth with the Qoz sand described in Section 2.Prior to use the individual samples of sand were thoroughly mixed to try and obtain uniformity.

5 LIMING RATES

LUP Note AAH/01/86 showed that between 0.1 and 0.7 tonnes of calcium carbonate per hectare would be required to reduce aluminium saturation percentages (ASP), and increase soil pH, to acceptable levels to a depth of 20 cm on acidic (exhausted) Qoz. Based on this, rates of 0.1, 0.2, 0.3, 0.4, 0.5 and - with gypsum and hydrated lime - 1.0 tonnes per hectare of the liming materials were applied to the soil in the pots. Due to non-availability of materials no replicates were set up.

Samples of the materials were analysed by Phosyn Chemicals LTD, U.K., and the analyses are shown in Table 1.

Table 1 Calcium and Magnesium Contents of Liming Materials

Material

% Calcium

% Magnesium

Gypsum

27

0.08

Limestone

25

1.48

Burnt Lime

37

2.41

Hydrated Lime

44

2.17

 

For both the High and Low Qoz two control pots were set up - one control receiving no input at all whilst the other was watered, as described in Section 8 below.

6 COMPARATIVE INPUTS OF CALCIUM

Table 2 shows the amount of calcium (Kg/Ha) applied by each rate of input of the various materials.

Table 2 Kg/Ha of Calcium Applied by Each Treatment

Rate (t/Ha)

0.1

0.2

0.3

0.4

0.5

1.0

Liming Material

Kg Calcium applied per Hectare

Gypsum

27

54

81

108

135

270

Limestone

25

50

75

100

125

N/A

Burnt Lime

37

74

111

148

185

N/A

Hydrated Lime

44

88

132

176

220

440

Note: N/A; Not applicable, rate not applied

7 APPLICATION OF MATERIALS

The liming materials (0.25 - 2.5g) were weighed out using a torsion balance then sprinkled on to the surface of the dried soil, which was then mixed to a depth of about 2cm,by stirring, to achieve evenness of application.

8 WATERING

To simulate the effects of a wet season each pot, apart from the dry controls, received 300ml of water daily for a period of one month. The figure of 300ml being arrived at by utilising the current average rainfall, as quoted in WAP-2, of 366mm

On average Wadi Nyala water contains about 60mg and 9mg of calcium and magnesium respectively (WAPS-2, December 1985). Hence the watering process could have added about 500mg and 80mg of calcium and magnesium respectively. If the WAPS-2 data are correct then the watering process added the equivalent of about 200Kg of calcium per hectare.

9 SAMPLING AND pH DETERMINATION

After the 30 days watering, samples were taken from 0 - 5cm and 7 - 12cm depths in each pot. The samples were air dried and stored for subsequent pH determination (1:5 soil water).

To measure the pH 50ml of distilled water were added to 10g of soil and the suspension stirred then allowed to stand for 60 minutes. The pH of the supernatant was read after the glass electrode of an electronic pH meter had been immersed in the supernatant for 2 minutes. Results are presented in Annex 1 and summarised in Table 3 below.

Table 3 Mean Soil pH Values

Soil

Input

0

0.1

0.2

0.3

0.4

0.5

1.0

High

Gypsum

6.74d

7.78

7.55

7.46

7.38

7.29

7.79

 

L/Stone

6.90w

7.30

7.34

7.53

7.44

7.36

/

 

Burnt Lime

/

7.21

7.39

7.39

7.34

7.44

/

 

Hydrated Lime

/

7.76

7.88

7.98

8.37

8.34

8.36

 

 

 

 

 

 

 

 

 

Low

Gypsum

7.25d

7.83

7.78

7.74

7.86

7.71

7.91

 

L/Stone

7.42w

7.70

7.73

7.75

7.56

7.52

/

 

Burnt Lime

/

7.65

7.58

7.56

7.54

7.53

/

 

Hydrated Lime

/

8.01

8.11

8.12

8.23

8.42

8.50

Notes d:dry control

w:wet control

10 FINDINGS

  1. Low Qoz topsoil appears to be less acidic than High Qoz topsoil with mean pH values of 6.7 and 7.3 respectively.
  2. Addition of Wadi Nyala water alone caused an increase in pH of just over 0.15 pH units.
  3. Addition of the lowest rates of liming materials caused increases in pH of between 0.3 and 0.9 pH units and 0.2 and 0.6 pH units in High and Low Qoz respectively - these figures make allowance for the changes due to the addition of the water.
  4. In most cases burnt lime caused least change in pH and hydrated lime the greatest change.
  5. Increasing rate of hydrated lime caused corresponding increases in pH, but increased rates of the other materials did not follow this pattern.

11 GROWTH of REFERENCE CROP

The plant pots were sunk into prepared holes in an area of sand so that the surface of the soil inside and outside the pots was the same, the treatment pots being randomly distributed. Approximately 10 undressed millet seeds were sown in each pot and also at two sites in the surrounding sand.

There was germination in a few pots but there was no subsequent growth and no recordable results ensued.

 

12 CONCLUSIONS

All treatments produced substantial changes in soil pH but only with the hydrated lime (calcium hydroxide) was there a correlation between rate of application and change in soil pH. No attempt is made here to explain the apparent vagaries in the results produced by the other liming materials.

All the materials were surface applied and there were changes in the pH throughout the depth of the soil in the pots; suggesting that downward leaching effects would bring about pH changes in the sub-soils of Qoz using any of these liming materials.

The Low Qoz had an initial pH greater than the High Qoz and this could be due to run-off effects and lateral drainage, from the High Qoz, bringing-in and depositing small amounts of dissolved calcium. If this were the case then the quoted better yields on the High Qoz would appear inconsistent with pH and calcium levels in the soil. Only full scale soil sampling and analyses would shed light on this.

With pH levels of 6.74 and 7.25 (refer Table 3) the samples of Qoz used for this trial was significantly less acidic than the topsoils found at Dimsu DC where values are in the range 5.4 to 6.1, with a mean value of 6.0 (1987 Detailed Survey). The results from this trial hence do not enable recommendations to be made on the rate of liming material which needs to be applied, but they do indicate that of the materials used the hydrated lime has the greatest effect, though over-liming would be very easy.

 

13 RECOMMENDATION

For the coming wet season a field liming trial should be set up at Dimsu DC, preferably on a site with known acidity problems as determined by the 1987 survey and analyses. Various rates of the local hydrated lime, and possibly the limestone, should be applied and subsequent changes in soil pH within the full depth of the profile should be measured after the wet season.

APPENDIX

 

Table A1 Soil pH (1:5 water) of Upper* Sample - Qoz

Soil

 

 

 

 

 

 

 

 

High Qoz

Input Rate

0

0.1

0.2

0.3

0.4

0.5

1.0

 

Lime Type

pH

pH

pH

pH

pH

pH

pH

 

Nil (d)

/

/

/

/

/

/

/

 

Nil (w)

6.96

/

/

/

/

/

/

 

Gypsum

/

7.93

7.59

7.50

7.42

7.39

7.90

 

Limestone

/

7.37

7.32

7.54

7.46

7.36

/

 

Burnt Lime

/

7.23

7.31

7.46

7.39

7.49

/

 

Hydrated Lime

/

7.88

7.99

8.12

8.55

8.54

8.68

Low Qoz

Input Rate

0

0.1

0.2

0.3

0.4

0.5

1.0

 

Lime Type

pH

pH

pH

pH

pH

pH

pH

 

Nil (d)

/

/

/

/

/

/

/

 

Nil (w)

7.33

/

/

/

/

/

/

 

Gypsum

/

7.91

7.77

7.74

7.67

7.74

7.98

 

Limestone

/

7.68

7.71

7.71

7.54

7.63

/

 

Burnt Lime

/

7.73

7.62

7.58

7.59

7.55

/

 

Hydrated Lime

/

8.05

8.09

8.28

8.24

8.52

8.60

Notes * - upper sample from 0 - 5 cm depth

Rate** - rate of application of liming material, in t/ha

Type*** - type of liming material or source of calcium

(d) - dry control

(w) - watered control

  

Table A2 Soil pH (1:5 water) of Lower* Sample - Qoz

Soil

 

 

 

 

 

 

 

 

High Qoz

Input Rate

0

0.1

0.2

0.3

0.4

0.5

1.0

 

Lime Type

pH

pH

pH

pH

pH

pH

pH

 

Nil (d)

/

/

/

/

/

/

/

 

Nil (w)

6.84

/

/

/

/

/

/

 

Gypsum

/

7.63

7.51

7.41

7.33

7.19

7.67

 

Limestone

/

7.22

7.36

7.52

7.41

7.36

/

 

Burnt Lime

/

7.18

7.47

7.32

7.29

7.39

/

 

Hydrated Lime

/

7.63

7.76

7.83

8.19

8.13

8.03

Low Qoz

Input Rate

0

0.1

0.2

0.3

0.4

0.5

1.0

 

Lime Type

pH

pH

pH

pH

pH

pH

pH

 

Nil (d)

/

/

/

/

/

/

/

 

Nil (w)

7.51

/

/

/

/

/

/

 

Gypsum

/

7.75

7.79

7.74

8.04

7.68

7.84

 

Limestone

/

7.71

7.74

7.79

7.58

7.41

/

 

Burnt Lime

/

7.57

7.53

7.54

7.49

7.51

/

 

Hydrated Lime

/

7.97

8.12

8.21

8.21

8.32

8.39

Notes * - lower sample from 0 - 5 cm depth

Rate** - rate of application of liming material, in t/ha

Type*** - type of liming material or source of calcium

(d) - dry control

(w) - watered control

 

Table A3 Mean Soil pH ( 1:5 water) of Samples* - Qoz

Soil

 

 

 

 

 

 

 

 

High Qoz

Input Rate

0

0.1

0.2

0.3

0.4

0.5

1.0

 

Lime Type

pH

pH

pH

pH

pH

pH

pH

 

Nil (d)

6.74

/

/

/

/

/

/

 

Nil (w)

6.90

/

/

/

/

/

/

 

Gypsum

/

7.78

7.55

7.46

7.38

7.29

7.79

 

Limestone

/

7.30

7.34

7.53

7.44

7.36

/

 

Burnt Lime

/

7.21

7.39

7.39

7.34

7.44

/

 

Hydrated Lime

/

7.76

7.88

7.98

8.37

8.34

8.36

Low Qoz

Input Rate

0

0.1

0.2

0.3

0.4

0.5

1.0

 

Lime Type

pH

pH

pH

pH

pH

pH

pH

 

Nil (d)

7.25

/

/

/

/

/

/

 

Nil (w)

7.42

/

/

/

/

/

/

 

Gypsum

/

7.83

7.78

7.74

7.86

7.71

7.91

 

Limestone

/

7.70

7.73

7.75

7.56

7.52

/

 

Burnt Lime

/

7.65

7.58

7.56

7.54

7.53

/

 

Hydrated Lime

/

8.01

8.11

8.12

8.23

8.42

8.50

Notes * - simple mean of upper and lower samples

Rate** - rate of application of liming material, in t/ha

Type*** - type of liming material or source of calcium

(d) - dry control

(w) - watered control