Greenwood small agricultural catchment study - soil management (Queensland) 1978-1984
Description
This study was established to examine the influence of soil surface conditions on runoff and soil erosion, on a site representative of one of the major soil types of the eastern Darling Downs. This dataset containa 7 years of daily record of rainfall, runoff, suspended sediment and soil movement, along with periodic soil sampling for soil water, soil surface cover and roughness. This project examined the influence of rainfall intensity, runoff rate and ground cover on suspended sediment moving through a flume at the exit from a contour bay and the effects of contour banks on sediment delivery to streams were evaluated. Several methods of sampling and calculating suspended soil loss were evaluated. Key findings: Surface cover was effective in reducing soil movement and runoff from contour bay catchments. Runoff and sediment concentration were both inversely related to surface cover and total soil movement was greatly reduced by surface cover. Greater than 75% of the variance in soil movement from single events was explained by surface cover and peak runoff rate. This dataset provides a sound basis for developing and testing water balance/water quality models for cropping and pastures in southern Queensland.
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Four catchments were devoted to winter crop (wheat) with intervening summer fallow and a fifth to summer crop. Throughout the summer fallows, a variety of stubble management and fallowing practices provides a range of soil conditions (cover, tillage). Treatments were described as: • winter crop, stubble burnt, bare soil summer fallow • winter crop, disc tillage, stubble incorporated summer fallow • winter crop, blade or chisel tillage, stubble mulched summer fallow • winter crop, no tillage (herbicide weed control), zero tillage summer fallow • summer crop, chisel tillage, winter fallow Measured data Rainfall was measured using a network of three tipping bucket recording rain gauges, a manual rain gauge at each side of the catchment, and a gauge at the farm residence approximately 1 km south. Runoff was measured through recorded gauge height using Cipoletti (trapezoidal) weirs at 5 minute time intervals and summed to daily (9am to 9am) values in this data collection. Runoff water was sampled using rising stage and in some cased timed samplers at the weir outlet to determine suspended sediment concentrations. Total soil movement, as described by Freebairn and Wockner (1986a) was measured in this study by estimating the volume of rills and sediment deposits after each major runoff event. Surface cover (green and dead) was measured after each runoff event, after cultivation operations, at time of soil sampling and periodic site visits. Expressed as percentage (%) of total soil cover Surface roughness was described using a semi-quantitative scale (1-5) based on a visual assessment made at the same time as soil cover. Soil moisture was determined at nine locations in each bay to a depth of 1.5 m in 6 depth increments. A mean of the nine-samples per depth was used in further analyses. Soil moisture was determined three times per year; post harvest, mid fallow and pre-planting, typically November, February and May. Bulk density was measured on several occasions using 10 cm diameter cores, and used to convert gravimetric values to a volumetric basis. To estimate a PAWC for the site, the mean of the five driest and wettest samplings were used. Expressed as mm available to plants. Grain yield was determined by harvesting 400 m long strips in each bay using a commercial harvester (6m wide). Evaporation (E) in fallows was determined by difference as E = Rainfall-Runoff -change in soil water over the fallow. Fallow efficiency was defined as the change in plant available soil water over a fallow period as a percentage of rainfall. Expressed as percentage (%)
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Funding
Queensland Government