Surface soil structure, the soil water balance and the effects of tillage

This study considers the effects of multiple-pass tillage on the surface soil structure of a Templeton silt-loam soil In Canterbury, New Zealand. The effects of pre-tillage soil water content (PTSW) and type of tillage operation are assessed for the freshly-tilled soil. A numerical simulation model (CONSERVB, van Bavel and Hillel, 1976) is evaluated as a method to assist in the identification of the soli properties which are most significant in determining evaporative loss of soil water. PTSW and Intensity of tillage operations interact to determine the aggregate size distribution resulting from multiple-pass tillage. Intensive tillage of a dry soil produces a high proportion of small wind-erodible soil aggregates and particles. The avoidance of intensive tillage reduces the likelihood of a PTSW effect occurring. Aggregates produced from tilling this soil at a water content near the lower plastic limit (LPL) are less mechanically stable (when dry) than those produced from tilling dry soil. Aggregate stability must be considered when assessing the most appropriate PTSW for the desired tillage objectives. Tillage-induced random roughness was quantified using a geostatistical method. Intensive tillage reduces aggregate size resulting in a smoother soil surface with a lower surface area. Intensive tillage decreases the macro-pore volume mainly through a decrease in the volume of aeration pores (pores >300µm diameter). PTSW does not have significant effects on macro-porosity or available water holding capacity. Near-saturation hydraulic conductivity is significantly reduced by intensive tillage as a result of decreased macro-pore volume. The Jackson (1972) model was evaluated by sensitivity analysis and found unsuitable for assessing the effects of tillage on unsaturated hydraulic conductivity. The output from the Jackson model showed extreme sensitivity to the 0 to -1.0 kPa matric potential section of the water characteristic input. Tillage-induced changes in soil porosity are reflected by changes in soil volumetric heat capacity and thermal conductivity. Tillage-induced soil structure changes affected shortwave albedo but to a smaller extent than previous studies indicated. The shortwave albedo on the tilled soil was low, due to the high organic matter content and rough surfaces. Predictions of evaporation, soil water content and soil temperature from the numerical simulation model CONSERVB were compared with field measurements from the tilled Templeton silt-loam soil. The CONSERVB model accurately simulated bare soil evaporation when the unsaturated hydraulic conductivity input function was determined by calibration. Simulated soil water and temperature profiles were generally good although water content near the soil surface was sometimes under-estimated and surface soil temperature was over-estimated in warm conditions. The CONSERVB model could be used In future to help in predicting benefits and risks from tillage operations. Identifying the tillage-sensitive soil properties which have the greatest influence on evaporative soil water loss is a research priority

Minimising costs of environmental service provision: water-yield, salt-load and biodiversity targets with new tree planting in Simmons Creek Catchment, NSW, a dryland farming/grazing area.

Although dryland farming and grazing have been practiced for over 130 years in the 17,000 ha Simmons Creek catchment without surface salinity problems, the area has been identified as a significant source of salt seepage to Billabong Creek in the NSW Murray catchment. Groundwater movement and salinity levels are spatially heterogenous at Simmons Creek. Groundwater of the upper catchment is relatively fresh and seemingly unconnected with the highly saline groundwater of the lower catchment. However, fresh surface water does flow from the upper to the lower catchment. This spatial diversity provokes the question of where high-water-use forest habitats might be placed to achieve different combinations of environmental services (greater water yield, lower stream salinity and greater biodiversity) at least cost. Agro-forestry and or carbon sequestration benefits are not considered here. This paper presents methods and preliminary calculations of land use changes for least-cost delivery of these environmental service targets.Optimisation, opportunity costs, forest-habitat, environmental services, Environmental Economics and Policy,

Evaluation of the Soil Water Infiltration and Movement model for Assessing the Effects of Grazing Intensity on the Soil Water Balance

There is an increasing concern that grazing animals cause soil structural damage. The pressures exerted by grazing animals are comparable to agricultural vehicles and, when soil conditions are conducive, can result in soil compaction. Compaction causes changes to soil physical properties which lead to changes in soil hydraulic properties affecting water entry, storage and movement within the soil. The aim of this study was to examine the effects of grazing on the soil water balance of a gleyed podzolic soil. The soil hydraulic properties, namely, the moisture characteristic and hydraulic conductivity function were measured, under a grazed and ungrazed pasture. The Soil Water Infiltration and Movement (SWIM) model was used to examine the consequences of changed hydraulic properties under grazing on the soil water balance. An evaluation was made of SWIM's ability to predict soil drainage. The study was carried out on a long term grazing trial near Armidale, NSW. The trial was set up in 1958. The two plots used in the experiments were an ungrazed plot and an adjacent plot that was stocked at 10 DSE per ha, situated on a gleyed podzolic soil type. The surface hydraulic properties were determined by both field and laboratory methods at three depths: above, within and below a compacted zone as indicated from soil strength measurements by Lemin (1992). The moisture characteristic was measured by the pressure plate method and unsaturated hydraulic conductivity was measured in the field using a negative head disc permeameter. Although there were no significant differences in the moisture characteristic between the two grazing treatments at 5-9 cm or 20-24 cm, surface infiltration was significantly higher in the ungrazed treatment compared to the grazed treatment. Differences in macroporosity and pore continuity at the soil surface could account for the higher infiltration rate. The treatment difference at the soil surface was for infiltration rates measured at tensions of 20 mm and 10 mm tension. The results suggest that the ungrazed plot has a greater number of pores that are greater than 1.5 mm in diameter and/or the pores are better connected

Minimising costs of environmental service provision: water-yield, salt-load and biodiversity targets with new tree planting in Simmons Creek Catchment, NSW, a dryland farming/grazing area.

Although dryland farming and grazing have been practiced for over 130 years in the 17,000 ha Simmons Creek catchment without surface salinity problems, the area has been identified as a significant source of salt seepage to Billabong Creek in the NSW Murray catchment. Groundwater movement and salinity levels are spatially heterogenous at Simmons Creek. Groundwater of the upper catchment is relatively fresh and seemingly unconnected with the highly saline groundwater of the lower catchment. However, fresh surface water does flow from the upper to the lower catchment. This spatial diversity provokes the question of where high-water-use forest habitats might be placed to achieve different combinations of environmental services (greater water yield, lower stream salinity and greater biodiversity) at least cost. Agro-forestry and or carbon sequestration benefits are not considered here. This paper presents methods and preliminary calculations of land use changes for least-cost delivery of these environmental service targets

Curvelet transform to study scale-dependent anisotropic soil spatial variation

Information on soil spatial variability is important for optimal management of agricultural and natural resources. Systematic studies to characterize and quantify soil spatial variability have identified various issues including sale dependence and anisotropy. In this research, we have introduced curvelet transform to characterize scale-dependent anisotropic soil spatial variation. The new curvelet transform is a multi-scale transform with strong directional sensitivity. It separates overall variations in soil properties in to a number of spatial scales and directions. It combines multiple methods including wavelet and ridgelet transforms. The curvelet transform is ideally suited for the presentation of soil variability information containing abrupt values or displaying discontinuity in its spatial distribution. Spatial variability in soil potassium (K) measured using airborne radiometric survey was characterized using the curvelet transform and is presented as a case study. Soil K data from radiometric survey is often used to characterize soil and its properties. Overall variation in soil K was separated and quantified at different scales and directions, which were indicative of the scales of different landscape modification processes and their directions. Percent contribution towards the total variance at different scales and directions indicated the importance of those processes that modified the landscape. The curvelet transform provided explicit information at different scales and directions to understand the variability in landscape processes in the study area. The spatial variability information at a wide range of scales, locations, and directions can also be used in multi-scale directional soil mapping, scale specific prediction of soil properties, and filtering, smoothing and denoising of satellite derived data

Objective selection of surrogate families to describe reef fish assemblages in a subtropical marine park

Effective representation of biodiversity in a marine park can be limited by lack of sampling at a suitable scale due to various methodological, logistical and taxonomic constraints. Surrogates that describe key components of biodiversity can benefit management planning and assist evaluation of zoning arrangements by improving efficiency and effectiveness of sampling. Reef fish are considered an important component of biodiversity in the Solitary Islands Marine Park (SIMP), New South Wales, Australia. Fish assemblages were surveyed using 30-min timed counts at 68 sites spread across the extent of shallow reef in the SIMP. The overall assemblage was compared with various subsets of taxa using the RELATE procedure in PRIMER to determine useful surrogates. Two families, Labridae and Pomacentridae, showed a high concordance with overall patterns and the highest correlation in estimating species richness by site. These families were the two most speciose (43, 32 species, respectively) comprising 30% of the species richness out of 66 families and 254 species. Surveying a subset of species that includes these two families has utility for marine park management in the SIMP, including evaluating the influence of ‘no take’ zones on assemblage patterns and systematic planning for biodiversity representation

Biogeographical and cross-shelf patterns of reef fish assemblages in a transition zone

Transition zones have complex patterns of biogeography and biodiversity which require consideration in conservation planning. Cross-shelf patterns of reef fish assemblage structure and biogeographic representation were determined for the Solitary Islands Marine Park (SIMP), positioned in a tropical-temperate overlap on the east coast of Australia. Sixty-eight sites were surveyed on shallow (\u3c25 m) reefs across an inshore–offshore gradient, using timed counts. Tropical taxa were most prevalent, comprising 50% of the 254 species recorded. Australian endemics accounted for 23% of species, with east coast endemics (14%) predominating. There was a strong cross-shelf gradient, with species richness increasing offshore. There was also a distinct biogeographical gradient with the proportion of temperate species decreasing and tropical species increasing with increasing distance from shore. This gradient was similar for endemic and cosmopolitan species as many of the endemics were temperate or subtropical, and many of the tropical species were widespread Indo-Pacific taxa. These patterns are consistent with sites further offshore being more frequently exposed to the tropical East Australian Current (EAC). Patterns on reefs further inshore are consistent with the high levels of endemism previously reported for temperate and subtropical Australian waters. The complex cross-shelf arrangement of tropical, subtropical and temperate species results in high regional biodiversity and needs to be recognised in marine-park planning