INFLUENCE OF RANGELAND MANAGEMENT PRACTICES ON ORGANIC MATTER CONTENTS AND AGGREGATION DYNAMICS OF CLAYEY SOILS IN THE SEMI-ARID GRASSLAND BIOME, SOUTH AFRICA by Elmarie Kotzé, Alexandra Sandhage-Hofmann, Chris du Preez, Wulf Amelung University of the Free State, Bloemfontein, South Africa
BACKGROUND Rangelands cover half of world s land surface. In arid to semi-arid environments of South Africa, more than 75% of land is used for livestock production. Rangelands are often subjected to degradation, mainly driven by poor land management.
OBJECTIVES To evaluate the impact of different rangeland management systems on soil degradation. To measure the decline in SOM content and aggregate stability along grazing gradients. To determine which soil property is the most sensitive/resilient to soil degradation.
STUDY-AREA
STUDY-AREA Grassland biome (sweet grasses dominating) Altitude : 1400 1600 m Semi-arid climate Annual summer rainfall : 550 mm per year Evapotranspiration level : 1800 mm per year Soil type : Lixisols Clay content : 34%
RESEARCH PROJECT LAYOUT 3 x Rangeland management systems Commercial farming Communal farming Land-reform farming Nature Reserve as reference (ungrazed by domestic animals) 3 x Grazing gradients Poor rangeland condition Moderate rangeland condition Good rangeland condition
COMMERCIAL FARMING
COMMUNAL FARMING
LAND-REFORM FARMING
3 x Rangeland management systems Commercial farming Communal farming Land-reform farming Nature Reserve as reference (ungrazed by domestic animals) 3 x Grazing gradients within each system Poor rangeland condition Moderate rangeland condition Good rangeland condition
GRAZING GRADIENT
Good rangeland condition Thermeda Triandra (Red grass) Moderate rangeland condition Eragrostis curvula (Weeping Love Grass) Poor rangeland condition Grazing gradient e.g. Cynodon dactylon (Couch Grass) Aristida congesta (Tassel Three-awn) or none
SAMPLING AND ANALYSES 0-5, 5-10, 10-20 cm depth intervals ph Bulk density Particle size analyses Aggregate-size (6 fractions) C and N Plant nutrients (P, K, Ca, Mg, Na) Micronutrients (Cu, Mn, Fe, Zn) Amino-acids, enzymes
SOIL SAMPLING
RESULTS Aggregate-size C as index of soil organic matter
TYPICAL BARE PATCHES In Poor rangeland condition CO : 60-78% CF : 20-40%
Aggregates (%) Poor field 100 95 90 85 Small Micro-aggregates Large Micro-aggregates Small Macro-aggreagtes Large Macro-aggregates 80 CF CO LF NR
Aggregates (%) Moderate field 100 95 90 85 Small Micro-aggregates Large Micro-aggregates Small Macro-aggreagtes Large Macro-aggregates 80 CF CO LF NR
Aggregates (%) Good field 100 95 90 85 Small Micro-aggregates Large Micro-aggregates Small Macro-aggreagtes Large Macro-aggregates 80 CF CO LF NR
C (kg/ha) 0-5 cm 30 25 20 15 10 CF CO LF NR 5 0 Poor Moderate Good
C (kg/ha) Macro-aggregates 30 25 20 15 10 CF CO LF NR 5 0 Poor Moderate Good
RESULTS Aggregation is integrative indicator for the soil s overall quality.
RESULTS Aggregation is integrative indicator for the soil s overall quality. Aggregation affects physical and hydrological functioning of soil, and is associated with capability in sequestrating organic C, and production. impacts primary
CONCLUSION Rangeland management in this biome is affected by different property rights, which then effects grazing systems, and furthermore soil properties nearby water points.
CONCLUSION Rangeland management in this biome is affected by different property rights, which then effects grazing systems, and furthermore soil properties nearby water points. Rotational grazing systems in fenced camps gives soil and vegetation resting times for recovering, accompanied by adapted stocking rates.
CONCLUSION Continuous grazing & overstocking is common in communal areas, and leads to soil degradation which is driven by two processes:
CONCLUSION Continuous grazing & overstocking is common in communal areas, and leads to soil degradation which is driven by two processes: deterioration of aggregates and associated SOM losses in poor and moderate rangeland condition,
CONCLUSION Continuous grazing & overstocking is common in communal areas, and leads to soil degradation which is driven by two processes: deterioration of aggregates and associated SOM losses in poor and moderate rangeland condition, and nutrient losses are caused by lower plant cover and litter input in sacrifice area of piosphere.
CONCLUSION Although rotational grazed camps showed little evidence of soil degradation, they exhibited early deterioration of aggregate structures close to water points.
CONCLUSION Although rotational grazed camps showed little evidence of soil degradation, they exhibited early deterioration of aggregate structures close to water points. Losses in macro-aggregate C may serve as early warning indicator for future ecosystem development.
CONCLUSION Climate-adapted stocking rate and duration of the resting time will remain necessary in future for all management systems.
Questions?? KOTZE, E et al., 2013 Journal of Arid Environments 97, 220-229