AN EVALUATION OF LIME EFFECTS ON TEMPORAL CHANGES IN SOIL ACIDITY PROPERTIES AND MAIZE GRAIN YIELDS

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Soil chemical and nutrient uptake dynamics of maize (Zea mays L.) as affected by neutralization and re-acidification after liming

Geology and soils The geology of the area is homogeneous, mostly underlain by quartz monzonite of the Mpuluzi Granite formation (Myburgh & Breytenbach, 2001). The study area is characterized by highly acidic soils and soils with humic characteristics are common. A soil survey done by Booyens et al. (2000), using Soil Classification – A Taxonomic System for South Africa (Soil Classification Working Group, 1991) found that the soil forms in the intensively cultivated areas are dominated by distrofic yellow apedal soils belonging to the Clovelly (Xantic Ferralsols) and Magwa (Humic Ferralsols; FAO-ISS-ISRIC, 1998) soil forms (Map 1.2). The Clovelly soil form is characterized by an A-horizon yellowish in colour, weak in structure without water stagnation, underlain by yellow-brown, structureless, sandy clay subsoil. Magwa soil form is characterized by a humic Ahorizon underlain by yellow-brown, structureless subsoil. The subdominant soil forms in the district consist of dystrophic red apedal soils, Hutton (Rhodic Ferralsols) and Inanda (Humic Umbrisols; FAO-ISS-ISRIC, 1998) as indicated in Map 1.2. The Hutton soil form is characterized by a reddish coloured, weak structure in which water stagnation does not take place. The rest of the district is dominated by Mispah (Dystric Leptosols; FAOISS-ISRIC, 1998) soils, shallow soils underlain by a hard rock layer, and rock outcrops (Booyens et al., 2000).

Demographic information

The study area forms part of the Albert Luthuli (MP301) municipality area with approximately 80 000 people of which more than 99% are African. Of these, around, 36 000 are male and 44 000 are female. The age group 16 to 35 represents 33% of the population and 4% of the population is 65 years and older. Twenty-one percent of the people 15 years and older is illiterate. Amongst those aged 15 to 65 years, 61% are unemployed. IsiZulu is spoken by 47% of the people followed by SiSwati (34%). Out of the 13 012 households in the area only 42% live in a formal dwelling. Only 19% of the households use electricity for cooking, whilst only 7.4% of households have sanitation facilities. Water is available to only 7% of the district’s population in the form of water piped to their dwellings. The area is characterized by subsistence-based farming and rangelands are generally community-owned and managed (Stats SA, 1996).

Planting and yield estimates

Maize seed of cultivar CRN 3631 was hand-planted annually under a dryland farming system at the end of October, using a row spacing of 0.91 m. The plant population density at planting was 55 000 plants ha-1, which was thinned out to approximately 35 000 plants ha-1. The trials were harvested annually in May. The seed mass and moisture content were determined and final seed yields were adjusted to 12.5% moisture content. Trial management was done in a collaborative research-farmer initiative. Maize yields could not be determined for the years 2001 and 2003 in the Oakleaf soil form because the trials were harvested by the farmer before yields could be determined in 2001 and livestock entered the trial area and grazed on the maize grain in 2003. All trials were farmer managed with assistance from ARC personnel. The evaluation of critical threshold values for soil acidity indices was based on relative grain yield values. The advantages and shortcomings of the relative yield concept were discussed by Bray (1944) and Van Biljon et al. (2008), but the conclusion was that applying the relative yield concept to field data makes it possible to include results from different climatic zones, soil types, maize cultivars, plant spacing and seasons. Relative grain yield per plot was obtained by expressing absolute yield as a percentage of the mean of the highest yielding treatment. Averages were calculated from the replicate values to represent the relative grain yield per treatment.

Soil pH, extractable acidity, Al and acid saturation

Temporal changes in soil acidity parameters at different lime application rates for the experimental soils are shown in Table 2.5. Hutton soil form: Liming had a highly significant (P<0.001) effect on all soil acidity parameters (Table 2.4). A significant interaction between lime and seasons after lime application was recorded for all soil acidity parameters (Table 2.4). In the first season, lime significantly (P<0.05) increased soil pH (H2O) by 0.60 and 0.75 pH units in the 5 and 10 tonnes lime ha-1 treatments, respectively (Table 2.5). The reported optimal pH (H2O) for maize production, namely 5.5 to 6.5 (Buys, 1986), was attained for both the 5 and 10 tonnes lime ha-1 applications within the first season of lime application. A continued significant (P<0.05) increase in soil pH (H2O) was recorded until the highest values of 6.21 and 6.57 were reached within three seasons after liming in the 5 and 10 tonnes lime ha-1 rates, respectively. This time lag of three years found between the lime application and the attainment of maximum soil pH (H2O) can be attributed to the relatively slow reactivity of the dolomitic lime that was used. A similar lack in equilibrium between free limestone and the soil mass was found by Walker (1953) and Bolton (1972, 1977).
The pH (H2O) data in the highest lime treatment showed a significant (P<0.05) increase over the 5 tonnes lime ha-1 treatment for the last four years of the trial. The Hutton soil continued to show significantly (P<0.05) higher soil pH (H2O) values due to lime after 6 years, where the 5 and 10 tonnes lime ha-1 rates resulted in 1.01 and 1.47 pH unit increases, respectively, over the unlimed treatment. This indicates that the beneficial effect of lime persisted for at least 6 years after application under the specific production practice that was used. Extractable acidity and Al, and acid saturation decreased (P<0.001) with lime application (Table 2.4). In the first season after liming, the initial extractable acidity, Al and acid saturation levels of 0.34, 0.21 cmolc kg-1 and 21.5%, respectively, were significantly decreased (P<0.001) to near zero levels, with 5 and 10 tonnes lime ha-1 application (Table 2.5). The residual effect of lime in reducing the values of the various soil acidity properties to near zero levels was observed for at least 6 years after the onceoff lime application in 1997.

Soil BC vs soil acidification rate

Hutton soil form: The soil BC is needed as a measure of soil acidification rates as calculated from Equation 3.4. Although the soil BC for a given soil is not constant over the whole pH range (Bache, 1988), numerous studies used a constant value for soil BC in estimating acidification rates (Singh et al., 2003; Noble et al., 2002; Hill, 2003; Helyar et al., 1990). Non-linear regression analysis was used to identify critical pH values where a change in soil BC could be expected. Figure 3.1 (a, c & e) shows that minimum buffering (maximum slope of pH versus added OH- ) occurs between 5.51 to 7.44, 5.54 to 7.47 and 5.51 to 7.54 in the 0, 5 and 10 tonnes lime ha-1 treatments, respectively. In order to evaluate the potential of soil BC in estimating soil acidification rates, the rate of predicted soil acidification (Equation 3.4), using soil BC at different pH ranges (<5.55, 5.55- 7.50,>7.50 and 4.20-8.50), was correlated with measured soil acidification rate as indicated in Figure 3.2 (a). The measured acidification rate (pH units year-1) was calculated from the measured annual change in basic cations, and the relationship between pH and extractable basic cations as described in Equation 3.6.
All four calculated acidification rates correlated highly significantly (P<0.001) with measured soil acidification rates (Figure 3.2 (a)). The ability of the four soil BCs to predict soil acidification rates is arranged as follows according to correlation with measured acidification rates: BC(<5.55)>BC(4.2- 8.5)=BC(>7.50)>BC(5.55-7.50). The soil acidification rate determined with the soil BC(4.2-8.5) crossed the 1:1 line at 0.03 pH units year-1. Below this value the soil BC(4.2-8.5) slightly overestimated acidification rates and above 0.03 acidification rates were slightly underestimated. The soil BC(4.2-8.5) gave a regression line nearly parallel to the 1:1 line, and is therefore the most appropriate of all the soil BCs for direct prediction of soil acidification rates.

Effect of lime application on soil acidification rate

Hutton soil form: Soil acidification rates showed significant acceleration with lime application (Table 3.1). Lime addition significantly (P<0.01) increased the acidification rate from -0.046 to – 0.116 and -0.140 pH units year-1 starting at initial pH (H2O) values of 5.33, 6.31 and 6.47, respectively. Table 3.4 shows that liming resulted in a significant decrease in soil BC, consequently leading to accelerated acidification rates. Statistically significant differences in acidification rates were furthermore observed between the 5 and 10 tonnes lime ha-1 treatments. A significant (P<0.05) correlation existed between acidification rate and initial soil pH (H2O) (Figure 3.4 (a)). Figure 3.4 (a) shows that at an initial pH (H2O) of 4.40, an acidification rate of 0 is predicted, and at a pH (H2O) of between 5.5 and 6.0 an acidification rate of between -0.10 and -0.13 pH unit year-1 is predicted. Lime loss and maintenance lime rate Hutton soil form:
Liming highly significantly (P<0.001) increased the mean amount of extractable Ca and Mg (Tables 3.1 and 3.5). Mean extractable Ca increased from 0.71, to 1.56 and 2.10 cmolc kg-1, in the 0, 5 and 10 tonnes lime ha-1 treatments, respectively. Table 3.5 shows an increase in extractable Mg of 0.61 and 1.01 cmolc kg-1 compared to the unlimed treatment. Table 3.1 shows that no significant interaction was found between lime level and time. After lime application in 1997, maximum extractable Ca and Mg levels were obtained two to three years after lime application (Table 3.5). However, no significant decrease or increase in extractable Ca and Mg was recorded over 6 years, and significantly higher extractable Ca and Mg values were observed in the limed compared to the unlimed plots at the end of 2003. In 2003, no statistically significant differences in Mg values were found between the recommended 5 tonnes ha-1 application rate and 10 tonnes lime ha-1. A statistically significant (P<0.05) linear decrease in the sum of extractable Ca + Mg with time (Figure 3.5 (a)) was shown after maximum extractable Ca + Mg was reached.

TABLE OF CONTENT :

• ABSTRACT
• CHAPTER 1: INTRODUCTION
  • 1.1 BACKGROUND
  • 1.2 JUSTIFICATION
  • 1.3 SOUTH AFRICAN LANDCARE PROGRAMME
    • 1.3.1 Goal of the national Landcare programme
    • 1.3.2 National Landcare principles
    • 1.3.3 Purpose of the South African Landcare programme
  • 1.4 THE MLONDOZI LANDCARE PROJECT
  • 1.5 PROJECT OBJECTIVES
  • 1.6 STUDY AREA
    • 1.6.1 Locality and physical features
    • 1.6.2 Climate
    • 1.6.3 Geology and soils
    • 1.6.4 Vegetation
    • 1.6.5 Land use
    • 1.6.6 Demographic information
  • 1.7 GENERAL STRUCTURE OF THE THESIS
• CHAPTER 2: AN EVALUATION OF LIME EFFECTS ON TEMPORAL CHANGES IN SOIL ACIDITY PROPERTIES AND MAIZE GRAIN YIELDS
  • 2.1 INTRODUCTION
  • 2.2 MATERIAL AND METHODS
    • 2.2.1 Soils and experimental design
    • 2.2.2 Soils sampling and analysis
    • 2.2.3 Planting and yield estimates
    • 2.2.4 Rainfall data
    • 2.2.5 Statistical analysis
  • 2.3 RESULTS AND DISCUSSIONS
    • 2.3.1 Soil pH, extractable acidity, Al and acid saturation
    • 2.3.2 Grain yield versus lime application
    • 2.3.3 Absolute grain yield versus soil acidity properties
    • 2.3.4 Relative grain yield versus soil acidity properties
  • 2.4 CONCLUSIONS
• CHAPTER 3: THE EFFECT OF LIMING ON SOIL BUFFER CAPACITY, ACIDIFICATION RATES AND MAINTENANCE LIMING
  • 3.1 INTRODUCTION
  • 3.2 MATERIALS AND METHODS
    • 3.2.1 Experimental soils
    • 3.2.2 Soil sampling and analysis
    • 3.2.3 Soil buffer capacity (soil BC)
    • 3.2.4 Acid production loads (APL) and acidification rates
    • 3.2.5 Maintenance liming
    • 3.2.6 Statistical analysis
  • 3.3 RESULTS AND DISCUSSION
    • 3.3.1 Effect of lime application on soil BC
    • 3.3.2 Acid production loads
    • 3.3.3 Soil BC vs soil acidification rate
    • 3.3.4 Effect of lime application on soil acidification rates
    • 3.3.5 Lime loss and maintenance lime rate
  • 3.4 CONCLUSIONS
• CHAPTER 4: LIMING EFFECTS OF SOIL PROPERTIES, NUTRIENT AVAILABILITY AND GROWTH OF MAIZE
  • 4.1 INTRODUCTION
  • 4.2 MATERIAL AND METHODS
    • 4.2.1 Experimental layout and procedure
    • 4.2.2 Soil and leaf sampling and analysis
    • 4.2.3 Statistical analysis and data interpretation
  • 4.3 RESULTS AND DISCUSSION
    • 4.3.1 Effect of liming on soil and leaf nutrient availability
    • 4.3.2 Critical soil nutrient concentrations and yield
  • 4.4 CONCLUSIONS
• CHAPTER 5: EFFECT OF SOIL ACIDITY AMELIORATION ON MAIZE YIELD AND NUTRIENT INTERRELATIONSHIPS IN SOIL AND PLANTS USING STEPWISE REGRESSION AND NUTRIENT VECTOR ANALYSIS
  • 5.1 INTRODUCTION
  • 5.2 MATERIAL AND METHODS
    • 5.2.1 Experimental procedure
    • 5.2.2 Soil and maize plant sampling and analysis
    • 5.2.3 Statistical analysis and data interpretation
  • 5.2 RESULTS AND DISCUSSIONS
    • 5.3.1 Interrelationship between maize grain yield, soil and leaf nutrients
    • 5.3.2 Nutrient uptake interactions
  • 5.3 CONCLUSIONS
• CHAPTER 6: RELATIONSHIPS BETWEEN SOIL BUFFER CAPACITY AND SELECTED SOIL PROPERTIES
  • 6.1 INTRODUCTION
  • 6.2 MATERIAL AND METHODS
  • 6.2.1 Soils
    • 6.2.2 Soil analysis
    • 6.2.3 Potentiometric titration curves
    • 6.2.4 X-ray diffraction analysis
    • 6.2.5 Statistical analysis
  • 6.3 RESULTS AND DISCUSSION
    • 6.3.1 Soil characteristics
    • 6.3.2 Potentiometric titration curves
    • 6.3.3 Soil buffer capacity over limited pH ranges vs soil properties
    • 6.3.4 Interrelationships between soil properties contributing to soil buffer capacity
    • 6.3.5 Relationship between dominant soil forms and selected soil properties
  • 6.4 CONCLUSIONS
• CHAPTER 7: ASSESSING THE POTENTIAL SOIL ACIDIFICATION RISK UNDER DRYLAND AGRICULTURE
  • 7.1 INTRODUCTION
  • 7.2 MATERIAL AND METHODS
    • 7.2.1 Study area
    • 7.2.2 Soil sampling and analysis
    • 7.2.3 Soil buffer capacity (BC)
    • 7.2.4 Acid production loads (APL), acidification rates and maintenance liming
    • 7.2.5 Spatial interpolation of soil properties and acidification risk
    • 7.2.6 Statistical analysis
  • 7.3 RESULTS AND DISCUSSION
    • 7.3.1 General and spatial soil characteristics
    • 7.3.2 Soil buffer capacity (BC)
    • 7.3.3 Critical soil acidity indices
    • 7.3.4 Actual soil acidity indices and lime requirement (LR)
    • 7.3.5 Acid production load (APL)
    • 7.3.6 Acidification risk assessment
    • 7.3.7 Relationship between acidification rate and selected soil properties
  • 7.4 CONCLUSIONS
• CHAPTER 8: GENERAL DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS
  • REFERENCES
  • ACKNOWLEDGEMENTS

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Soil chemical and nutrient uptake dynamics of maize (Zea mays L.) as affected by neutralization and re-acidification after liming