Nutritional status of soil and herbs from annual ryegrass and permanent kikuyu pastures from 40 dairy farms in the Tsitsikamma region was evaluated. The low Ca : P ratio measured in annual ryegrass pastures, and more specifically in kikuyu grass, highlighted the low Ca content of the herb and also the kikuyu grass's tendency to accumulate large concentrations of P. The large K concentrations and high K : Ca+Mg ratios identified in pasture herbs suggest the potential for nutritional problems in animals such as hypomagnesemia. It was concluded that although kikuyu is an excellent pasture in terms of dry matter production, it tends to be deficient in Ca (and sometimes Na) and may contain prohibitively high K levels which are likely to induce Mg deficiency in grazers animals.
LIST OF TABLES
Mean soil nutrient content, standard error and range of values for soils under kikuyu and ryegrass grass in the three regions of Tsitsikarnma. Mean plant nutrient content, standard error and range of values for kikuyu and ryegrass pastures in the three regions of Tsisikarnma.
Results from an adjacent annual ryegrass field (see Figure 4.1), which had not been subsoiled, are shown for comparison.
CHAPTERl
Introduction
The earth can actually be considered a non-renewable resource in terms of a human time frame. The development of the soil quality concept and soil quality indicators has been a breakthrough in relation to the maintenance of the soil resource base (Hortensius and Nortcliff, 1991).
SOIL QUALITY AND SOIL QUALITY INDICATORS
- Defining soil quality
- Soil quality indicators and their use
- The importance of soil quality
The concept of soil quality provides a basis on which the effects of different management practices can be compared. Soil quality monitoring is already carried out by environmental protection agencies in many parts of the world.
CENTRAL ROLE OF ORGANIC MATTER IN SOIL QUALITY
- The central importance of soil organic matter
- How organic matter effects the soil physical, chemical and biological properties
- Soil structure and it's importance
TIlls relationship to each other depends largely on a common factor; it is the content of organic matter in the soil. They represent an important pool of organic matter in the soil (5 - 20% of the total organic C in the soil), (Gregorichet et al., 1994).
PERMANENT VERSUS ANNUAL I ARABLE PASTORAL SYSTEMS
- Permanent pastoral systems
- Physical characteristics
- Biological characteristics
- Chemical characteristics
- Physical characteristics
- Biological characteristics
When arable land is converted to permanent pasture there is usually a significant increase in soil organic matter content (Haynes and Francis, 1993). Soil bulk density is also generally reduced under permanent pastoral systems (Haynes, 1995), due to increases in soil organic matter content and increased porosity.
INR TR
THE EFFECTS OF OTHER MANAGEMENT PRACTICES
- The effects of fertilizer, lime and manure applications
A higher yield caused by fertilizer application generally means a higher return of organic matter to the soil in the form of rotting roots, litter and crop residues (Praser, 1994). Urea hydrolysis occurs rapidly after urination and large amounts of NH4+ accumulate in the soil (Haynes and Williams, 1993).
DISCUSSION AND CONCLUSIONS
Aggregation is extremely important for the maintenance of soil structure and can be used both as an indicator of soil structural stability and soil quality (Haynes and Beare, 1996). The concepts of soil quality and soil resilience and the use of chemical, physical and biological indicators of soil quality to investigate the comparative. Concerns have arisen in recent years about the possible soil degradation occurring under annually cultivated ryegrass dairy pastures in the Tsitsikamma. underground compaction, significant losses of soil through wind erosion and suggestions that there was a significant loss of soil organic matter.
Materials and Methods
The results were expressed as the weight mean diameter (mm), which is the sum of the fraction of soil remaining in each sieve after sieving for the standard time multiplied by the mean diameter of the inner opening. The maximum value for the average weight diameter is 4 and the minimum is 0.25 mm. The pH(water) values for the experimental sites are shown in Figure 3.1 and ranged from 4.1 under native vegetation at Kenmore to 6.9 under annual ryegrass at Kenmore. The acidic soil at Kenmore is podzolic in nature with an E horizon of 25-30 cm. At Brandkop, Heidehofand Kenmore, values under annual rye tended to be lower than those under native vegetation.
DISCUSSION
- Soil pH
- Soil organic carbon content
- Aggregate stability
This reflects the degrading effect that annual cultivation has on soil organic matter content. Microbial C biomass is generally positively related to soil organic matter content as the higher the organic matter content the more substrate is available for microbial growth (Sparling, 1997; Dalal, 1998). Since soil organic matter is essential for the formation and stabilization of soil aggregates (Tisdall and Oades, 1982) and there is normally a close relationship between soil organic matter content and stable soil water accumulation (Chaney and Swift, 1984 ; Haynes and Naidu, 1997).
Conclusions
The negative effect of cultivation on aggregate stability is mainly mediated by the loss of organic matter and associated microbial activity in the soil (Karlenet al., 1994). Aggregate stability was increased in accordance with organic C values and microbial biomass size and activity. lower than annual kikuyu pasture at every site (except Lanark), (Figure 3.1). It was suggested that soil moisture stress under annual dry pastures limited soil microbial activity and resulted in very high metabolic quotient values recorded in the eastern end of the region. The lower organic matter under annual ryegrass than permanent kikuyu pastures resulted in an associated lower aggregate stability under annual pastures.
Introduction
However, it is significantly affected by factors such as crusting and/or compaction and therefore land use is extremely important due to its direct effect on the soil physical properties. In this study, the effects of annual and permanent pastures on the soil physical properties (water retention, bulk density, saturated hydraulic conductivity, porosity, penetrometer resistance and air permeability) and root density are compared with those under the native vegetation. In addition, the effects of the subsoil of an annual pasture, where a subsoil compacted layer was identified, on the soil physical properties and root density were also investigated.
Materials and Methods
For each replicate, three cores were taken and pooled at each depth. Samples were taken in increments of (0-15 cm, 15-30 cm, 30-45 cm and 45-60 cm) depending on the rooting depth of the field being sampled. Then the soil was washed off, the roots collected and dried. The relationship between some of the measured properties was examined and significance was determined using simple linear regression. The statistical program Genstat 5, version 4.1 was used. However, at Brandkop and Kenmore, values under both kikuyu and ryegrass meadows were higher than those under native vegetation. Bulk density values in the 0-15 cm layer ranged from an exceptionally low value of 0.86 Mg m" under native vegetation at Kenmore to 1.68 Mg m" under ryegrass meadow at Heidehof.
Mean Total Porosity
Mean r otal Porosity
Wate r Retention
Bulk Density
Hydraulic conductivity
Air Permeability
Water Retention
The effects of undermelting greatly increased air permeability in the 0–15 cm layer below and between the teeth (Figure 4.5), which was also true at –100 kPa in the 15–30 cm layer. Beneath the cradle at Lanark and Heidehof, the peak resistance was in the 10–20 cm layer, indicating the presence of a compacted subsoil layer. The resistance of the penetrometer was significantly lower under the tines of the collapsed field than in the adjacent non-subsoil (Figure 4.2). Between the teeth, the subsoil greatly reduced the resistance in the 10 - 20 cm layer, where a compacted layer was evident in the unsubsoiled profile.
Hydraulic Conductivity
Discussion
- Root density
- Bulk density and total porosity
- Air permeability and saturated hydraulic conductivity
- Effect of subsoiling
Although bulk density was lowest under kikuyu pasture in the 0–15 cm layer at Lanark and Heidehof, it was actually highest at Brandkop and Kenmore. The amount of water that remains in the soil depends on the volume of pores filled with water. The highest penetrometer resistance (>4000 kPa) was recorded in the layer 10 - 20 cm below the annual pastures at Lanark and Heidehof.
Conclusions
This study has shown that subsoiling a ryegrass pasture is effective in reducing penetrometer resistance in the 10 - 20 cm layer (where a compacted layer in the subsoil was identified). Before applying the substrate, the existence of a compacted layer in the substrate must be confirmed. To be effective, factors such as soil water content, subsurface depth and tine spacing must be optimized. Longer term studies should be conducted to investigate the subsequent effects on grazing yields and therefore on the economic viability of such an operation.
CHAPTERS
Materials and Methods
Herb and soil samples were collected from fields of annual cultivated perennial ryegrass (Lolium perenne) and permanent kikuyu pastures (Pennisetum clandestinum) from dairy farms in the Tsitsikamma region. The grass samples were collected randomly (as close as possible to the fourth leaf stage) from three randomly selected replicate plots (100 m2 each). Twenty-five random soil samples were taken to a depth of 10 cm from each plot using a beater tube auger (inside diameter 25 mm). Samples from each plot were bulked, air dried, and sieved at 1 mm.
Results
- Soil properties
Extractable P values were generally very high and tended to be higher under kikuyu than ryegrass grazing. The frequency distribution of values for organic C, pH, exchangeable acidity and extractable P under kikuyu and ryegrass grazing is shown in Figure 5.1. Organic C (and thus the organic matter) content of the soil was generally high under kikou pastures and values were clearly skewed to the right (Figure 5.1).
Ryegrass
Kikuyu
K ikuyu
Phosphorus concentrations (Figure 5.5) were higher for kikuyu than ryegrass and this is illustrated by the fact that only 33% of the ryegrass samples were above 0.4%, while 53% of the kikuyu samples were above that concentration. Most of the herbage samples for both kikuyu (89 %) and ryegrass (82 %) were above 2.0 % (Figure 5.5) and K was generally not a limiting nutrient for pasture production. Seventy percent kikuyu and 73% ryegrass values were above 3.0% (Figure 5.6), reflecting the heavy amounts of fertilizer N used in the region.
Kikuyu Ryegrass
Nutritionally, the dietary requirement for Cu is approximately 10 mg kg" (Whitehead, 2000), and only 8 and 3 % of the kikuyu and ryegrass samples respectively were above 9 mg kg", indicating a need for Cu supplementation.
RyegrassKikuyu
Discussion
- Soil properties
- Herbage analysis
In turn, dietary P requirements are National Research Council, 1988; Mileset al., 1995), was also predominantly satisfied under both kikuyu and ryegrass. An adequate P supply is important because of the essential functions that P performs in the animal, such as its role as a structural component in the skeleton and teeth (National Research Council, Subcommittee, 1989; Whitehead, 2000), in the transfer of energy and its role in several other essential processes (Underwood and Suttle, 1999). A maximum allowable K concentration of 3.0% in the diet of dairy cows has been proposed by the National Research Council (National Research Council, 1988; Miles et al., [995). The N:S ratio (Figure 5.7) was higher in kikuyu grass, mainly due to higher N fertilizer applications under kikuyu than on ryegrass pastures.
Conclusions
Given such a complement, then kikuyu is definitely a very viable option as a pasture in the Tsitsikamma region. Along with the reduction in organic matter content in annual rye pastures, there was a decrease in soil pH and a loss of exchangeable cations, relative to permanent kikuyu pastures. A major problem in the dairy farming system currently used in Tsitsikamma is the loss of soil organic matter, soil microbial activity and aggregate stability that occurs in pastures cultivated annually with rye.
An investigation into the method of aggregate analysis by wet sieving in relation to the influence of various slates on arable soils.1.Soil Sci. In: Paul, E.A., Paustian, K., Elliot, E.T. Eds.), Soil organic matter in temperate agroecosystems: long term, CRC Press, Boca Raton, FI, USA, pp. In: Vaughan, D., and Malcolm, RE., (Eds.), Soil organic md biological activity Martinus Nijhoff, The Hague, p.
APPENDIX l
