TILLAGE TRIAL - JUMEIZA 1987

Land Use Planning Note AAH/3/88

 

CONTENTS

1 INTRODUCTION

2 MONITORING

3 SOIL SAMPLING

4 SOIL MOISTURE (POST HARVEST)

4.1 DEPTH OF MOISTURE PENETRATION

4.1.1 Methodology

4.1.2 Findings

4.1.3 Conclusions

4.2 MOISTURE CONTENTS

4.2.1 Methodology

4.2.2 Findings

4.2.3 Conclusions

5 SOIL pH and STRUCTURAL STABILITY

5.1 INTRODUCTION

5.2 SOIL pH

5.2.1 Methodology for Soil pH

5.2.2 Results

5.2.3 Observations

5.3 STRUCTURAL STABILITY

5.3.1 Estimation of Soil Dispersion

5.3.2 Results

5.3.3 Observations

5.4 CONCLUSIONS

6 CROP DATA

6.1 INTRODUCTION

6.2 STAND COUNT

6.2.1 Results

6.2.2 Findings

6.3 HEAD COUNT

6.3.1 Results

6.3.2 Findings

6.4 FRESH GRAIN YIELD

6.4.1 Results

6.4.2 Findings

6.5 DRY GRAIN YIELD

6.5.1 Results

6.5.2 Findings

6.6 STOVER WEIGHT

6.6.1 Results

6.6.2 Findings

6.7 CONCLUSIONS

7 RAINFALL DATA and EFFECTS

7.1 GENERAL

7.2 OBSERVATIONS

8 CONCLUSIONS, RECOMMENDATIONS and FUTURE STUDIES

8.1 CONCLUSIONS

8.2 RECOMMENDATIONS

8.3 FUTURE STUDIES

NB Figures mentioned in this note not yet located or rebuilt

APPENDIX

 Table Number Contents

A1 Soil Moisture Contents

A2 Soil pH

A3 Estimates of Soil Dispersion

A4 Crop Data

__________________________________________________________________________________________ 

1 Introduction

The background data leading to the design and installation of this trial is to be found in the LUP Annual report 1986/87, the Appendices accompanying that report, and in the report of the visiting Agricultural Engineer - Berry 1987.

In brief the Nagaa soils are non-saline sodic and structurally unstable. In their natural state they allow only very low infiltration of surface water and can prevent seedling emergence, because the surface seals.

The trial was designed to asses the effects of tillage, with water- harvesting and gypsum application, on the soil pH, structural stability, moisture penetration, moisture contents and crop yields. The trial was a randomised 4 treatments with 4 replicates. The treatments were;

run-off:run-on ratio

0 : 1.0

0.5 : 1.0

1.0 : 1.0

2.0 : 1.0

Each run-on plot (cropping area) had 2 sub-plots with either nil input or 10 t/ha input of gypsum. Tillage consisted of a pass across the slope with a chisel plough operating at 15cm depth.

A crop of sorghum was sown by the Agronomy Section staff once the wet season had properly started.

 2 Monitoring

The trial was monitored regularly during the growing season by staff of the Jumeiza DC. The following items were noted:

- Rainfall

- Flooding

- Farm operations (weeding etc)

- Crop growth

- Pest and disease attack

- Surface soil condition and stability

- Evidence of erosion etc

All recorded data can be found on file LUP/8/1 in the WSDC office, Nyala.

 3 Soil Sampling

At the end of the growing season, after harvest of the sorghum, soil samples were collected from all sub-plots and from some run-off areas. Samples were taken from 10, 25, 50 and 75 cm depths. The depth of moisture penetration was measured by continuing to auger until either dry soil was found or the auger would not penetrate further. The moist soil samples were placed in sealed polythene bags, immediately on recovery, and transported to the laboratory.

In total some 132 samples were collected, with 10% being from the uncultivated, run-off areas to act as controls.

 4 Soil Moisture (Post Harvest)

4.1 Depth of Moisture Penetration

4.1.1 Methodology

As stated in Section 3, depth of moisture penetration was measured by augering until dry soil was found or until the auger would not enter any deeper - the latter being a good indicator of dry Nagaa soil.

4.1.2 Findings

The depths of moisture penetration found are as shown in Table 1 below.

Table 1 Depth of Moisture Penetration (cm)

Run-off:Run-on ratio

0:1

0:1

0.5:1

0.5:1

1:1

1:1

2:1

2:1

Control

Input

Gyp

Nil

Gyp

Nil

Gyp

Nil

Gyp

Nil

Nil

Replicate 1

98

105

118

98

116

98

121

98

98

Replicate 2

98

105

98

98

98

110

107

98

98

Replicate 3

65

92

92

92

98

115

80

50

24

Replicate 4

95

98

22

22

40

42

98

94

82

Mean

89

100

78

78

88

91

102

85

76

Notes; - Gyp = 10 t/ha gypsum

- Nil = nil input

4.1.3 Conclusions

There were no obvious differences, or even trends, between the depths of moisture penetration and the various run-off:run-on ratios. But, all treatments increased depth of moisture penetration compared with the control (untilled) areas. Addition of gypsum would appear to cause an increase in depth of moisture penetration. Mean depths of moisture penetration, ignoring water-harvesting ratio, were:

 4.2 Moisture Contents

The moisture contents presented are the approximate percentage of water in the soil at the sampled depths of 10, 25, 50 and 75 cm, as measured at the end of the growing season - which more or less corresponds with the end of the rainy season.

4.2.1 Methodology

The moist soil samples (Section 3) were transported to the laboratory and were weighed, using a torsion balance. After weighing, the sealed bags were opened and the soils allowed to dry. Weights were checked at intervals until such time as there was no further weight loss and the soils were assumed to be air-dry.

Moisture content was calculated as the weight of moisture in the moist soil and expressed as a percentage. The full, recorded data are to be found in Table A.1 in the Appendix.

4.2.2 Findings

Moisture contents, as measured by weight loss on air-drying, of the soils within the trial all increased with depth to show a maximum at about 50 cm. Below this depth there was then a reduction in moisture content. Generally, plots treated with gypsum had slightly higher contents than plots not receiving gypsum. Moisture contents of the control areas (run-off zones) were usually much higher than in the cropped, tilled areas - the reason for this probably being that with no crop there would have been no transpiration losses. These trends can be seen in Figure 1 and in Table 2.

Table 2 Mean Soil Moisture Contents (%)

Depth

Input

Gypsum

Nil

Mean

Control

 

Ratio

 

 

 

 

10cm

0.0:1.0

2.31

2.17

2.24

3.61

 

0.5:1.0

2.49

1.82

2.16

 

 

1.0:1.0

3.01

2.22

2.62

 

 

2.0:1.0

1.86

3.05

2.46

 

 

Means

2.42

2.32

2.37

 

 

 

 

 

 

 

25cm

0.0:1.0

5.07

6.16

5.62

10.37

 

0.5:1.0

5.82

5.98

5.90

 

 

1.0:1.0

6.39

5.85

6.12

 

 

2.0:1.0

5.65

7.11

6.38

 

 

Means

5.73

6.28

6.01

 

 

 

 

 

 

 

50cm

0.0:1.0

6.55

5.92

6.24

11.46

 

0.5:1.0

7.92

6.47

7.20

 

 

1.0:1.0

8.17

7.94

8.06

 

 

2.0:1.0

8.30

7.26

7.78

 

 

Means

7.74

6.90

7.32

 

 

 

 

 

 

 

75cm

0.0:1.0

6.09

5.78

5.94

8.47

 

0.5:1.0

6.52

5.78

5.94

 

 

1.0:1.0

7.11

7.25

7.18

 

 

2.0:1.0

6.21

7.02

6.62

 

 

Means

6.48

6.46

6.47

 

Note; Soil Moisture as:

Weight of Moisture

---------------------x100

Weight of Moist Soil

The relationships between soil moisture content and run-off:run-on ratio, at the various depths, are shown in Figure 2. As can be seen from this figure, the moisture contents on gypsum treated plots all increase from the 0:1 ratio to the 1:1 ratio and then usually decline at the 2:1 ratio. The exception to this trend being at 50 cm depth where there is a slight increase with the 2:1 ratio.

The sub-soils (50 and 75 cm) of the non-gypsum treated plots show the same trends as the gypsum treated plots. But, the topsoils without gypsum input show a decrease in moisture content then an increase and usually the level of moisture, with 2:1 ratio, exceeds the level in the gypsum treated plots.

Monitoring of the plots on 30/9/87, near the end of a 16 day dry spell, showed that the crop on the 0:1 and 0.5:1 run-off:run-on ratio plots were generally showing signs of moisture stress (drought), as were some of the plants on the 2:1 ratio plots, whereas on the 1:1 ratio plots there were no obvious signs of moisture stress. Also, more plants on plots without gypsum showed drought effects than on plots which received gypsum. This would suggest that a 1:1 ratio, with addition of gypsum, is more likely to ensure crop survival during drought periods.

The lower moisture levels found on the 2:1 ratio plots could be associated with poorer infiltration caused by greater soil slaking and dispersion brought about by excessive moisture - monitoring of the trial did suggest that the 2:1 ratio plots looked more dispersed and sealed than the other plots.

Plotting yield of dry grain (Section 6.5) against soil moisture showed no obvious correlations and points appeared to fall in a random manner.

 4.2.3 Conclusions

Moisture contents increased with depth, to reach a maximum at about 50 cm, and with increasing run-off:run-on ratio, to a maximum on plots with a 1:1 ratio. Observations made during monitoring suggest that plots with maximum moisture in-put (2:1 ratio) looked more sealed, due to excess slaking and dispersion, and this is confirmed by the lower soil moisture contents in these plots.

Subsoils (50 - 75 cm depth) on plots with and without gypsum had almost identical maximum soil moisture contents (7-8 %) with the 1:1 run-off:run-on ratio.

No clear relationships could be found between post harvest moisture contents and yield of dry grain. Moisture contents in the soils of the control areas were all higher than in the cropped plots. This would be explained by the moisture reserves not having been used up through transpiration; and evaporation losses at that time of season would have been minimal. But, moisture contents in these controls would have been much higher than in normal bare Nagaa since water was ponded on these run-off zones. The ponding being caused by the cut-off and protection bunds and the fact that the tilled areas were raised above the normal soil surface.

 5 Soil pH and Structural Stability

5.1 Introduction

LUP Note AAH/13/86 pointed out that, in general, Nagaa soils were non-saline alkali and that this alkalinity would be associated with the known structural instability. The question of structural instability being discussed in Note AAH/9/87, where it was shown that Nagaa usually fell into Emmerson Stability Classes 2 or 3.

Soil pH was measured on the samples, collected as described in Section 3, and estimates were made of soil dispersion / stability on these same samples.

 5.2 Soil pH

5.2.1 Methodology for Soil pH (1:5 soil water)

Ten grams of air dried soil, previously ground by mortar and pestle, were weighed into a beaker and 50 ml of distilled water added and the suspension stirred. After 60 minutes the supernatant was poured into another beaker. The pH was measured by immersing a combined glass electrode of an electronic pH meter in the supernatant and taking the meter reading after exactly 2 minutes.

 5.2.2 Results

All data collected are presented in Table A.1 in Appendix A. The following table (Table 3) presents the mean values of the 4 replicates of each sub-treatment, at the various depths, and for the control samples.

 Table 3 Soil pH (1:5 soil water)

 

Water Harvesting Ratio

 

 

0:1

0:1

0.5:1

0.5:1

1:1

1:1

2:1

2:1

Control

Input

Nil

Gypsum

Nil

Gypsum

Nil

Gypsum

Nil

Gypsum

 

Depth

 

 

 

 

 

 

 

 

 

10cm

8.1

7.10

7.95

7.13

8.02

7.07

7.97

6.96

7.60

25cm

8.50

7.46

8.47

8.09

8.15

7.17

8.12

7.36

8.26

50cm

8.86

8.41

8.71

8.53

8.69

8.24

8.42

8.47

9.18

75cm

8.94

8.72

8.61

8.28

8.71

8.80

8.43

8.28

8.88

 

5.2.3 Observations

With gypsum the mean pH at 10cm depth was reduced by 1 pH unit and water harvesting had no obvious effect. The pH of the control samples was less (7.60) than that of the nil-input plots (8.03) and this is assumed to be due to the action of gypsum that dissolved, and spread, when the site flooded.

At 25cm depth addition of gypsum caused a pH reduction of 0.8 units and no obvious effects of water-harvesting ratio were found, but the plot with the 1:1 ratio showed the biggest pH change.

At 50cm depth the addition of gypsum gave a mean reduction of 0.3 pH units with the 1:1 water harvesting ratio showing the largest change. Compared to the controls, both gypsum and nil-input plots show a reduction in soil pH (control 9.18, nil-input 8.67 and gypsum 8.41). This would have been caused by the gypsum, dissolved in the water percolating through the gypsum plots, mixing with the rest of the groundwater and diffusing into the local sub-soil.

At 75cm depth the effect of the added gypsum tailed-off though a slight reduction in soil pH occurred with all but the 1:1 water harvesting ratio.

5.3 Structural Stability

With 130 odd samples no attempt was made to determine the Emmerson Class number for each sample. What was done was to take note of the clarity of the supernatant used for pH determination and use this as a measure of soil dispersion / stability.

5.3.1 Estimation of Soil Dispersion

The clarity, or cloudiness, of the supernatant used for the pH determination was noted and allocated a number as shown below:

Supernatant

Estimated Dispersion

Code

Clear

Nil

0

Slightly Cloudy

Slight

1

Cloudy

 

3

 

Table 4 Estimation of Dispersion

 

Water Harvesting Ratio

 

 

0:1

0:1

0.5:1

0.5:1

1:1

1:1

2:1

2:1

Control

Input

Nil

Gypsum

Nil

Gypsum

Nil

Gypsum

Nil

Gypsum

 

Depth

 

 

 

 

 

 

 

 

 

10cm

2.0

0.0

1.8

0.0

1.5

0.5

1.8

0.0

1.0

25cm

2.0

0.0

2.0

1.3

1.8

1.3

2.0

1.0

1.7

50cm

2.0

1.3

2.0

1.8

2.0

1.7

2.0

1.8

2.0

75cm

2.0

2.0

2.0

2.0

2.0

2.0

2.0

1.5

2.0

Note: Refer to Section 5.3.1 for definition of code

      1. Observations

The structural stability of the surface soil (0 - 10cm) changed from moderate to stable by addition of 10 t/ha of gypsum. This change has been confirmed by a plant pot trial and has been reported separately (AAH/2/88).

Gypsum effects have penetrated to 50cm depth with reduced dispersion, indicating better flocculation and, presumably, enhanced structural stability.

Water harvesting, with or without addition of gypsum, does not appear to influence the situation in any beneficial manner. In fact Table 4 above suggests that with no extra water (0:1 ratio) the changes are as great, if not greater, (to 50 cm depth) than with extra water.

5.4 Conclusions

Addition of gypsum at the rate of 10 t/ha appears to have ameliorated the soil to a depth of 50 cm in that the soil pH and soil dispersion have been altered, compared to untreated soil.

The soil pH at 10 and 25 cm has been lowered to a level where any adverse effects of exchangeable sodium would have been removed (Refer to LUP Note AAH/13/86) with pHs of 7.1 and 7.5 respectively. At 50 cm depth there has been a reduction in pH not only under the treated area but also in the adjacent subsoil, pHs are still relatively high at 8.4 (treated plot) and 8.8 (untreated plot) but these compare with 9.2 from the control area.

Gypsum has also reduced the degree of dispersion that occurs and this reduction correlates with the changes in pH. Decrease in pH equates with less dispersion, which indicates more structural stability.

Water harvesting has had no measurable influence on either soil pH or structural stability (dispersion). But the increased supply of water may well have influenced the solution of the gypsum and its diffusion at depth, especially if a transient water table was formed after heavy rains (no investigations were made to establish if a water table did form).

6 Crop Data

6.1 Introduction

As stated in Section 1 a crop of sorghum was sown on the run-on plots. The crop was monitored throughout the growing season and several criteria were measured when the crop was harvested. The parameters measured included:

The main point that emerged from the monitoring during the growing season was that the plants growing on plots with gypsum input were a greener colour. Monitoring records are to be found on file LUP/8/1.

6.2 Stand Count

6.2.1 Results

Full data are presented in Table A.5 in Appendix A and mean values are shown in Table 5 below.

Table 5 Sorghum Crop Stand count

Input

Ratio

Gypsum

Nil

Mean

No. of Samples

0.0:1.0

15.25

18.25

16.75

8

0.5:1.0

16.75

14.00

15.38

8

1.0:1.0

10.25

9.25

9.75

8

2.0:1.0

14.25

12.25

13.50

8

Mean

14.25

13.44

13.84

 

No of Samples

16

16

32

 

 

6.2.2 Findings

No clear pattern was found relating number of plants surviving to harvest with run-off:run-on ratios, though there could be a trend to fewer plants on plots with greater moisture inputs (1:1 and 2:1 ratios).

Overall means show that gypsum treatments gave 14 plants per plot and nil input plots had 13 plants per plot.

6.3 Head Count

6.3.1 Results

Full data are presented in Appendix A and mean values are shown in Table 6 below.

Table 6 Sorghum Crop Head Count

Input

Gypsum

Nil

Mean

No. of Samples

Ratio

 

 

 

 

0.0:1.0

22.75

24.00

23.38

8

0.5:1.0

25.00

18.00

21.50

8

1.0:1.0

30.25

25.75

28.00

8

2.0:1.0

41.75

19.75

30.75

8

Mean

29.94

21.88

25.91

 

No of Samples

16

16

32

 

 

6.3.2 Findings

Increasing moisture (run-off:run-on ratio) alone shows no clear trend in head count, but with addition of gypsum head count increases from about 23 per plot to almost 42 per plot as the run-off:run-on ratio increases.

The number of heads per plant shows wide variation in plots with 0:1 and 0.5:1 ratios and less variation in the 1:1 and 2:1 ratio plots.

With gypsum addition the number of heads per plant increases from 1.5 to over 3 in relationship to the amount of moisture that plots should have accumulated ( i.e. from 0:1 to 2:1 run-off:run-on ratios). This can be see from Table 7 below.

Table 7 Head Count : Stand Count Ratio

Input

Gypsum

Nil

Mean

Ratio

 

 

 

0.0:1.0

1.54

1.52

1.53

0.5:1.0

1.57

1.35

1.46

1.0:1.0

3.12

3.51

3.32

2.0:1.0

3.25

2.03

2.64

Mean

2.37

2.10

2.24

 

6.4 Fresh Grain Yield

6.4.1 Results

Full data are presented in Appendix A and summarised in Table 8 below.

Table 8 Mean Yields of Fresh Sorghum Grain (Kg/Plot)

Input

Gypsum

Nil

Mean

No. of Samples

Ratio

 

 

 

 

0.0:1.0

1.323

1.477

1.400

8

0.5:1.0

1.648

0.984

1.316

8

1.0:1.0

2.283

2.218

2.205

8

2.0:1.0

2.702

1.377

2.040

8

Mean

1.989

1.492

1.740

 

No of Samples

16

16

32

 

 

6.4.2 Findings

No clear relationship was found between weight of fresh grain and the water-harvesting ratios unless gypsum had been added. With gypsum, grain yield increased with run-off:run-on ratio from 1.3 Kg/plot to 2.7 Kg/plot, as can be seen in Table 8 above.

Ignoring water-harvesting ratio, overall means show that addition of gypsum gave a plot yield of almost 2 Kg (1.3 t/ha) compared to 1.5 Kg/ha (almost 1 t/ha) when no gypsum was applied.

6.5 Dry Grain Yield

6.5.1 Results

Full data are presented in Appendix A and summarised in Table 9 below.

Table 9 Mean Yields of Dry Sorghum Grain (Kg/Plot)

Input

Gypsum

Nil

Mean

No. of Samples

Ratio

 

 

 

 

0.0:1.0

0.631

0.528

0.580

8

0.5:1.0

0.635

0.326

0.481

8

1.0:1.0

0.946

0.791

0.868

8

2.0:1.0

1.134

0.496

0.815

8

Mean

0.837

0.535

0.686

 

No of Samples

16

16

32

 

 

6.5.2 Findings

No clear relationship was found between yields and moisture with water harvesting ratios unless gypsum was added. When gypsum was included the yield increased with run-off:run-on ratio from 631g (420 Kg/ha) at the 0:1 ratio to 1134g (756 Kg/ha) per plot at the 2:1 ratio.

Ignoring water-harvesting ratio, overall means show addition of gypsum gives 837 g/plot 558 Kg/ha) compared to 535 g/plot 357 Kg/ha). Refer to Table 9.

Overall, grain from plots without gypsum contained almost 65% moisture (fresh grain), whereas when gypsum was applied the percentage fell to just below 58. Refer to Table 10 below.

Table 10 Moisture Content of fresh Grain

 

(% weight loss on drying)

Input

Gypsum

Nil

Mean

Ratio

 

 

 

0.0:1.0

52.3

64.3

58.6

0.5:1.0

61.5

66.9

63.4

1.0:1.0

58.6

62.8

60.6

2.0:1.0

58.0

64.0

60.0

Mean

57.6

64.5

 

There is no clear relationship between the weight of dry grain per head with water-harvesting ratio or input; apart from the trend that, with gypsum, weights increase from the 0:1 ratio to the 1:1 ratio then decline. Overall, gypsum inputs gave a head weight of dry grain of almost 27g compared to almost 24g with nil input. This is an increase of 13.5% ,as can be calculated from Table 11 below.

Table 11 Weight of Dry Grain per Plant Head (g)

 

(% weight loss on drying)

Input

Gypsum

Nil

Mean

Ratio

 

 

 

0.0:1.0

26.1

22.5

24.3

0.5:1.0

26.5

20.9

23.7

1.0:1.0

28.2

27.1

27.7

2.0:1.0

26.8

24.2

25.5

Mean

26.9

23.7

25.3

6.6 Stover Weight

6.6.1 Results

The full, recorded data are presented in Appendix A and summarised in Table 12 below.

Table 12 Mean Stover Weights - Kg / Plot

Input

Gypsum

Nil

Mean

No. of Samples

Ratio

 

 

 

 

0.0:1.0

8.925

6.438

7.681

8

0.5:1.0

10.238

7.913

9.075

8

1.0:1.0

8.188

6.583

7.385

8

2.0:1.0

9.963

5.688

7.825

8

Mean

9.963

6.655

7.825

 

No of Samples

16

16

32

 

6.6.2 Findings

There was no clear relationship between stover weight and water harvesting ratio apart from the fact that maximum stover weights were produced on plots with the 0.5:1.0 run-off:run-on ratio. This was true for both with and without gypsum input (6.8 and 5.3 t/ha respectively).

Overall, gypsum does increase weight of stover to 6.6 t/ha compared to 4.4 t/ha. Refer to Table 12 above.

In general the stover weight per plant increases with increasing run-off:run-on ratio, as is shown in Table 13 below, apart from the 2:1 ratio without the addition of gypsum where the relationship breaks down.

Table 13 Stover Weight (Kg/plot):Stand Count Ratio

Input

Gypsum

Nil

Mean

Ratio

 

 

 

0.0:1.0

0.60

0.40

0.50

0.5:1.0

0.63

0.57

0.60

1.0:1.0

0.77

0.93

0.85

2.0:1.0

0.79

0.54

0.67

Mean

0.70

0.61

0.66

6.7 Conclusions

Though none of the yields are particularly good, compared to quoted possible / claimed yields (1.2 - 1.5 t/ha for farmers fields and over 10 t/ha in trials, WSDC 1976/77), it must be significant that this trial did yield a harvest whilst other, on-station, trials at Jumeiza gave no acceptable yields. This water-harvesting trial was planted very late, and after the last of several re-plantings of other on-station trials.

With tillage and water harvesting alone, only the weight of stover per plant showed a trend to increase with, assumed, increased moisture supplied by water harvesting. However, the increase reversed in the plots with the possible maximum extra water, on the plot with the 2:1 run-off:run-on ratio.

Where gypsum was also added the following measured responses increased with increasing moisture availability (run-off:run-on ratio);

The weight of dry grain per head increased from the 0:1 ratio to the 1:1 ratio but then declined with the 2:1 ratio.

Maximum values of most of the parameters measured were found on plots with the 1:1 run-off:run-on ratio where no gypsum was added and in the 2:1 ratio plots when gypsum was added, see Table 14 below.

Table 14 Water-harvesting Ratios Showing Maximum Responses

 

Ratio with Maximum Response

Parameter

Gypsum

Nil Input

Notes

Stand count

0.5:1.0

0.0:1.0

Nil > Gypsum

Head Count??

2.0:1.0

1.0:1.0

Gypsum > Nil

Fresh grain

2.0:1.0

1.0:1.0

Gypsum > Nil

Dry grain

2.0:1.0

1.0:1.0

Gypsum > Nil

Stover weight

0.5:1.0

0.5:1.0

Gypsum > Nil

Heads per plant

2.0:1.0

1.0:1.0

Gypsum > Nil

Stover per plant

2.0:1.0

1.0:1.0

Gypsum > Nil

Dry grain per head

1.0:1.0

1.0:1.0

Gypsum > Nil

Plant material in moist grain*

0.0:1.0

1.0:1.0

Gypsum > Nil

* Equates with least % of moisture in moist grain.

These findings would indicate that where nil input of gypsum was used a run-off:run-on ratio of 1:1 appears to give maximum benefit. This tillage input would be the easiest to install as little or no measurement or estimation would be required, the treatment being based on implement width.

With the addition of gypsum maximum responses were found on plots where the largest ratio was used (2:1). Reasons for this could be:

7 Rainfall Data and Effects

7.1 General

Rainfall data were collected by the staff of Jumeiza DC and are presented graphically in Figure 3 below. Monthly and accumulated precipitation was as follows:

 

May

June

July

August

September

October

Monthly (mm)

29.7

79.4

77.7

118.4

34.9

33.2

Accumulated (mm)

/

109.1

186.8

305.2

340.1

373.3

 

7.2 Observations

The total rainfall for the 1987 season was just over 373 mm, and 64% of that (240.5mm) occurred as massive events. Over 20mm per day is regarded as a massive event. With the low infiltration characteristics of the Nagaa soils much of this rainfall was probably lost as run-off and / or evaporation.

The sorghum was sown on 19 July, in the middle of a dry spell, but there was a significant rainfall on the 22 July when flooding occurred. The crop germinated on 23 July. Dry spells occurred throughout the growing season with one of the longer ones being 12 days from 27 August until 8 September. No drought effects were noted at this time.

Another longish dry spell occurred from 19 September until 3 October and this time drought effects were noted. Plants on 50 % of the nil input plots showed signs of moisture stress whilst only about 30 % of plots receiving gypsum showed any signs. The drought effects were more noticeable on the plots with the nil or very low run-off:run-on ratios.

Rainfall in early October overcame the drought effects and all plots contained relatively healthy crops which were harvested on 25 October.

 8 Conclusions, Recommendations and Future Studies

8.1 Conclusions

An input of 10 t/ha of gypsum altered soil pH from moderately or strongly alkaline to almost neutral over a depth of 25 cm, with a corresponding improvement in soil structural stability (as measured by dispersion). There were changes in soil pH to 50 and 75 cm depth with the magnitude of the change decreasing with depth. There were some improvements in structural stability to 50 cm but little change at 75cm depth.

Water harvesting did not appear to have any direct effect on either soil pH or stability. All treatments brought about an increase in the depth of moisture penetration but no correlation between run-off area and depth of penetration was found. Addition of gypsum appeared to increase depth of penetration.

Soil moisture contents increased with depth within the profile to reach a maximum at about 50 cm, with soils that received gypsum having slightly higher contents. With gypsum the moisture content correlated with the size of the run-off area but fell when the run-off:run-on ratio exceeded 1:1.

Although crop yields were not particularly good there was a yield whereas most other on-station trials gave little or no yield at all. This may have been due to the increased soil moisture reserves, brought about by water harvesting, or it may have been due to judicial planting time - just when there was rainfall.

With tillage and water-harvesting alone only the yield of stover appeared to increase in line with increased run-off area, up to a maximum with the 1:1 run-off : run-on ratio. When gypsum was also included in the treatment there were increases in:

These increases all correlated with increases in the run-off:run-on ratio. Whether the above increases in yield were due to chemical or physical factors has not been established but:

    1. better structure allowing better root development, and
    2. better structure giving increased moisture reserves through improved infiltration of surface water.

8.2 Recommendations

The Nagaa ploughing unit of the ADD could incorporate some of the findings from this trial in their operations. It has previously been suggested that for an individual village all the ploughing should be concentrated in one area, rather than done as isolated patches. This could lead to more cost-effective use of the equipment and would allow thought to be given to erosion control aspects. (It would also allow a communal application for registration of the land if it were considered that a secure land tenure lease was desirable)

The water-harvesting inputs which would appear to be beneficial from this small trial could be tried out on a larger scale as part of the village block ploughing idea.

What is indicated is that the village block could be ploughed, across the slope, incorporating a 1:1 run-off:run-on water-harvesting ratio. This would be relatively easy to install using implement width as the guide. It would, however, be worth installing some cut-off ditches and bunds to help combat mass surface flow of water and possible soil erosion. Monitoring did indicate that natural vegetation quickly establishes and flourishes in ditches and would help rehabilitate these bare areas.

If any farmer could afford to purchase gypsum, or if WSDC were to donate some to more progressive farmers, it could prove worthwhile attempting to ameliorate some of the ploughed area - but in this case the run-off:run-on ratio should be 2:1.

8.3 Future Studies

LUP Note AAH/2/88 indicated that lesser amounts of gypsum could bring about significant changes in soil pH and structural stability. If a Rotavator type cultivator could be located a field trial could be installed to verify the conclusion that better mixing of the soil and gypsum could allow lesser amounts of gypsum to be used.

During the coming season the trial at Jumeiza should again be planted to sorghum but it is suggested that land preparation should be attempted using animal draught. It might just be possible that the improvements in structure brought about by the 1987 input of gypsum would allow an animal drawn implement to work.

 

A.A.Hutcheon

March 1988

__________________________________________________________________________________________ 

APPENDIX

Table A1 Soil Moisture Contents (%)

Ratio

0 : 1

0.5 : 1

1 : 1

2 : 1

Control

 

Input

Gyp

Nil

Gyp

Nil

Gyp

Nil

Gyp

Nil

Nil

Depth

Replicate

 

 

 

 

 

 

 

 

 

10cm

1

1.96

1.60

2.55

1.95

2.17

3.98

2.32

4.00

6.49

 

2

2.62

1.27

2.22

1.94

5.51

1.74

2.66

3.42

3.82

 

3

3.35

2.85

3.48

2.03

3.07

1.31

0.87

2.38

1.58

 

4

1.32

2.94

1.69

1.37

1.28

1.85

2.60

2.38

2.56

 

Mean

2.31

2.17

2.49

1.82

3.01

2.22

1.86

3.05

3.61

 

 

 

 

 

 

 

 

 

 

 

25cm

1

4.89

4.01

5.72

4.90

4.76

7.28

4.74

8.30

13.93

 

2

5.15

6.80

5.86

6.20

8.57

5.82

6.20

7.55

11.95

 

3

6.61

7.47

6.63

6.84

7.13

5.39

4.41

5.47

/

 

4

3.62

6.35

5.08

/

5.10

4.92

7.23

7.12

5.22

 

Mean

5.07

5.82

5.82

5.98

6.39

5.85

5.65

7.11

10.37

 

 

 

 

 

 

 

 

 

 

 

50cm

1

5.01

5.71

6.83

5.79

8.45

8.75

7.80

8.35

19.74

 

2

7.13

5.22

7.32

6.64

7.84

8.79

7.85

7.66

7.98

 

3

6.56

6.73

8.91

6.97

8.14

6.29

7.75

4.10

/

 

4

7.49

6.03

8.60

/

/

/

9.79

8.93

6.65

 

Mean

6.55

5.92

7.92

6.47

8.17

7.94

8.30

7.26

11.46

 

 

 

 

 

 

 

 

 

 

 

75cm

1

5.67

5.74

5.23

5.95

6.72

6.06

5.51

7.18

14.34

 

2

6.28

6.58

6.38

5.79

6.00

6.17

6.85

5.23

3.95

 

3

/

4.54

7.00

5.60

8.62

9.52

4.60

/

/

 

4

6.32

6.27

7.47

/

/

/

7.89

8.65

7.13

 

Mean

6.09

5.78

6.52

5.78

7.11

7.25

6.21

7.02

8.47

Notes: Gyp - Input of 10 t/ha Gypsum

/ - No sample hence no data

Replicate - Replicate number

Ratio - Water-harvesting ratio; Run-off:Run-on

 

Table A2 Soil pH (1 : 5 / Soil : Water)

Ratio

0 : 1

0.5 : 1

1 : 1

2 : 1

Control

 

Input

Gyp

Nil

Gyp

Nil

Gyp

Nil

Gyp

Nil

Nil

Depth

Replicate

 

 

 

 

 

 

 

 

 

10cm

1

6.93

8.33

7.35

8.36

7.74

8.24

7.14

8.20

7.76

 

2

7.12

8.35

7.28

8.19

6.75

8.02

6.93

8.08

7.44

 

3

7.12

7.81

6.82

7.67

7.09

7.82

7.49

8.26

7.81

 

4

7.24

8.24

7.05

7.58

6.70

8.01

6.28

7.34

7.38

 

Mean

7.10

8.18

7.13

7.95

7.07

8.02

6.96

7.97

7.60

 

 

 

 

 

 

 

 

 

 

 

25cm

1

7.30

8.44

8.75

8.64

7.68

8.36

7.29

8.97

8.12

 

2

8.17

8.56

8.44

8.55

7.21

7.92

7.45

7.90

8.71

 

3

7.13

7.98

7.52

8.22

6.74

8.05

7.72

8.39

/

 

4

7.24

9.03

7.65

/

7.06

8.28

6.99

7.20

7.94

 

Mean

7.46

8.50

8.09

8.47

7.17

8.15

7.36

8.12

8.26

 

 

 

 

 

 

 

 

 

 

 

50cm

1

8.25

8.95

8.40

8.86

8.85

9.01

7.82

9.57

8.90

 

2

9.08

8.64

8.70

9.00

8.17

8.30

8.67

8.50

9.43

 

3

7.87

8.81

8.05

8.27

7.70

8.77

9.13

8.19

/

 

4

8.43

9.02

8.95

/

/

/

8.26

7.41

9.21

 

Mean

8.41

8.86

8.53

8.71

8.24

8.69

8.47

8.42

9.18

 

 

 

 

 

 

 

 

 

 

 

75cm

1

8.53

9.06

7.93

9.26

9.39

8.99

7.47

9.52

8.69

 

2

8.94

8.98

8.44

8.68

8.05

7.83

9.10

8.09

9.22

 

3

/

8.64

7.85

7.89

8.97

9.30

8.27

/

/

 

4

8.70

9.09

8.91

/

/

/

8.27

7.67

8.72

 

Mean

8.72

8.94

8.28

8.61

8.80

8.71

8.28

8.43

8.88

Notes: Gyp - Input of 10 t/ha Gypsum

/ - No sample hence no data

Replicate - Replicate number

 

Table A3 Estimates of Soil Dispersion

Ratio

0 : 1

0.5 : 1

1 : 1

2 : 1

Control

 

Input

Gyp

Nil

Gyp

Nil

Gyp

Nil

Gyp

Nil

Nil

Depth

Replicate

 

 

 

 

 

 

 

 

 

10cm

1

0

2

0

2

0

1

1

1

1

 

2

0

2

0

2

1

2

0

2

1

 

3

0

2

0

2

1

2

0

2

1

 

4

0

2

0

1

0

1

0

2

1

 

Mean

0

2

0

1.8

0.5

1.5

>0

1.8

1

 

 

 

 

 

 

 

 

 

 

 

25cm

1

0

2

1

2

1

2

1

2

2

 

2

1

2

1

2

2

2

1

2

1

 

3

0

2

1

2

1

2

1

2

/

 

4

0

2

2

/

1

1

1

2

2

 

Mean

>0

2

1.3

2

1.3

1.8

1

2

1.7

 

 

 

 

 

 

 

 

 

 

 

50cm

1

1

2

1

2

1

2

1

2

2

 

2

2

2

2

2

2

2

2

2

2

 

3

1

2

2

2

2

2

2

2

/

 

4

1

2

2

/

/

/

2

2

2

 

Mean

1.3

2

1.8

2

1.7

2

1.8

2

2

 

 

 

 

 

 

 

 

 

 

 

75cm

1

2

2

1

2

1

2

1

2

2

 

2

2

2

2

2

2

2

2

2

2

 

3

/

2

2

2

2

2

2

/

/

 

4

2

2

2

/

/

/

1

2

2

 

Mean

2

2

1.8

2

1.7

2

1.5

2

2

Notes: Gyp - Input of 10 t/ha Gypsum

/ - No sample hence no data

Replicate - Replicate number

Ratio - Run-off : Run-on water harvesting ratio

 

Table A4 Crop Data

Ratio

0 : 1

0.5 : 1

1 : 1

2 : 1

 

Input

Gyp

Nil

Gyp

Nil

Gyp

Nil

Gyp

Nil

Stand Count

Replicate

 

 

 

 

 

 

 

 

(Number)

1

15

20

8

14

10

10

6

6

 

2

14

18

23

9

4

15

15

14

 

3

14

24

19

18

12

1

17

14

 

4

18

11

17

15

15

11

21

15

 

Mean

15.3

18.3

16.8

14.0

10.3

9.3

14.8

12.3

 

 

 

 

 

 

 

 

 

 

Head Count

1

0

36

17

32

34

38

30

27

(Number)

2

60

14

37

15

14

46

48

23

 

3

9

14

26

21

43

6

51

11

 

4

22

32

20

4

30

13

38

18

 

Mean

22.8

24.0

25.0

18.0

30.3

25.8

41.8

19.8

 

 

 

 

 

 

 

 

 

 

Fresh Grain

1

0

1.915

1.816

1.723

3.001

3.202

1.007

1.716

(Kg)

2

2.998

1.666

1.999

1.009

0.556

3.954

2.873

1.915

 

3

0.394

0.419

1.773

0.902

3.616

0.578

3.227

0.656

 

4

1.898

1.909

1.003

0.003

1.957

0.779

3.700

1.222

 

Mean

1.323

1.477

1.648

0.984

2.283

2.129

2.702

1.377

 

 

 

 

 

 

 

 

 

 

Dry Grain

1

0

0.705

0.530

0.521

1.405

1.118

0.701

0.684

(Kg)

2

1.666

0.465

0.697

0.308

0.174

1.602

1.233

0.675

 

3

0.174

0.196

0.837

0.355

1.440

0.113

1.526

0.218

 

4

0.685

0.747

0.476

0.120

0.766

0.329

1.077

0.405

 

Mean

0.631

0.528

0.635

0.326

0.946

0.791

1.134

0.496

 

 

 

 

 

 

 

 

 

 

Stover

1

8.60

7.55

5.95

11.35

13.15

10.00

7.95

5.65

(Kg)

2

11.60

6.00

14.50

4.60

1.55

10.13

10.50

7.10

 

3

8.95

4.40

8.35

8.70

10.50

1.60

10.95

4.50

 

4

6.55

7.80

12.15

7.00

7.55

4.60

10.45

5.50

 

Mean

8.93

6.44

10.24

7.91

8.18

6.58

9.96

5.69

Notes: Gyp - Input of 10 t/ha Gypsum

/ - No sample hence no data

Replicate - Replicate number