Agricultural drought analyses for temperate Australia using a biophysical pasture model. 1. Identifying and characterising drought periods

2008 ◽  
Vol 59 (11) ◽  
pp. 1049 ◽  
Author(s):  
G. M. Lodge ◽  
I. R. Johnson
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
New South ◽  
New South Wales ◽  
Agricultural Drought ◽  
Wagga Wagga ◽  
Winter Rainfall ◽  
Seasonal Drought ◽  
South Wales

The SGS Pasture Model was used to estimate daily total soil water content (mm) for the period 1998–2001 (using experimental data) and from July 1905 to June 2005 (using a 100-year daily climate file). For both model simulations, the correlation coefficient for actual and predicted data was >0.86. Four sites were examined, three in the winter-rainfall zone (Albany, Western Australia; Hamilton, Victoria; and Wagga Wagga, New South Wales) and one in the predominantly summer-rainfall zone (Barraba, New South Wales) of temperate Australia. Trends were detected in long-term rainfall data for lower mean annual rainfall at the Albany site since the mid 1950s and at the Hamilton site since the mid 1970s. Analyses of days in which herbage accumulation was likely to be limited only by water allowed a minimum soil water content to be defined; below this value, soil water was in deficit. A drought period was defined as occurring after >50 consecutive days of predicted soil water deficit. For the four sites, six categories of drought duration were described, ranging from >50–120 days (seasonal drought) to >364 days (exceptional drought). Numbers of predicted droughts were 90, 90, 65, and 60, respectively, at Albany, Hamilton, Wagga Wagga, and Barraba sites. At the three winter-rainfall sites, most predicted droughts occurred in a regular pattern and were an extension of a seasonal drought, but at the Barraba site they were of a longer duration and irregular in occurrence.

Effects of continuous and seasonal grazing strategies on the herbage mass, persistence, animal productivity and soil water content of a Sirosa phalaris - subterranean clover pasture, North-West Slopes, New South Wales

2003 ◽  
Vol 43 (6) ◽  
pp. 539 ◽  
Author(s):  
G. M. Lodge ◽  
S. R. Murphy ◽  
S. Harden
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
New South ◽  
New South Wales ◽  
Subterranean Clover ◽  
Animal Production ◽  
North West ◽  
South Wales ◽  
Continuous Grazing

An experimental site was established in 1997 on the North-West Slopes of New South Wales to further investigate the use of strategic grazing management to improve the persistence of phalaris (Phalaris aquatica cv.�Sirosa) and subsequent effects on animal production and soil water content. The pasture was sown in 1992 to Sirosa phalaris, subterranean clover (Trifolium subterraneum var. subterraneum cv. Seaton Park) and lucerne (Medicago sativa cv. Aurora). Four grazing treatments were applied in a randomised 3-replicate design. Treatments consisted of continuous grazing at 12.3 sheep/ha (C12 or control); continuous grazing at 6 sheep/ha (C6), and 2� spring and autumn strategies of either resting from grazing for 6 weeks in each season (SAR0), or reducing stocking rate from 12.3 to 4.0 sheep/ha (SAR4). Despite annual applications of fertiliser and high clover content, Sirosa phalaris herbage mass in plots continuously grazed at 12.3 sheep/ha declined from a mean of 3300 kg DM/ha in spring 1997 to < 700 kg DM/ha by May 1998. At the end of the study (February 2001), Sirosa mean herbage mass in these plots was 670 kg DM/ha and lower (P < 0.05) than for the other treatments (mean value 5400 kg DM/ha). These marked changes in herbage mass, and the degradation of the Sirosa-based pasture to an annual pasture by continuous grazing at 12.3 sheep/ha, were not generally reflected in either short-term animal production or substantial differences in soil water content. Wool production (kg/head) was not significantly different among treatments each year. Compared with continuous grazing at 12.3 sheep/ha, sheep liveweights were higher (P < 0.05) in plots continuously grazed at 6.1 sheep/ha from November 1997 to February 1999. However, from February 1999 to 2001, sheep liveweights in the 2 treatments with the highest Sirosa phalaris content were lower (P < 0.05) than those continuously grazed at 12.3 sheep/ha. Only the soil water content for the C6 and SAR4 treatments at 0–30�cm was significantly different to the control treatment, but the differences were predicted to be < 2.5 mm/year. In the root zone (0–90 cm), mean soil water content ranged from 159 to 309 mm (mean 220 mm), while plant available water (soil water content – soil water content at –1500 kPa) was a mean of 79 mm, ranging from 11 to 168 mm.

Effect of gypsum on vertisols of the Gwydir Valley, New South Wales. 2. Ease of tillage

1989 ◽  
Vol 29 (1) ◽  
pp. 63 ◽  
Author(s):  
DC McKenzie ◽  
HB So
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Fuel Consumption ◽  
New South ◽  
New South Wales ◽  
Soil Strength ◽  
South Wales

An experiment was carried out to deter- mine the effect of applied gypsum on the ease of tillage in 3 vertisols of the Gwydir Valley, New South Wales. The soils were classified as 'poor' and 'good' on the basis of past dryland wheat yields and structural of their surface aggregates.Where gypsum had been applied 22 months earlier at a rate of 7.5 t ha-1, tractor fuel consumption per centimetre of soil tilled was reduced by as much as 37% (0.85 v. 0.54 L ha-1 cm-1). The effect was most marked on the more sodic clays. The reduction in fuel consumption due to gypsum was associated with instability creased soil water content (0.127 v. 0.224 kg kg-1) and lower soil strength (330 v. 140 kPa).

Forecasting wheat yields using a water budgeting model

1989 ◽  
Vol 40 (4) ◽  
pp. 715 ◽  
Author(s):  
I Cordery ◽  
AG Graham
Keyword(s):  
Water Balance ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
New South ◽  
Meteorological Data ◽  
New South Wales ◽  
Balance Model ◽  
Soil Layers ◽  
South Wales

A model has been developed to forecast soil water variations and wheat crop growth in dry land situations. The forecast of the yield to be expected if sowing occurred today is obtained by running the calibrated model for all years for which meteorological data are available. The soil water content on today's date in each year is fixed at today's observed soil water value. From each year of observed meteorological data, an estimate is made of the yield. These yield data allow construction of a frequency distribution of yield which can be used to make a probabilistic forecast. The model involves two sub-models, a water balance model and acrop development model. The two sub-models interact to provide 5-day estimates of soil water content, actual evaporation and transpiration, runoff and increments to biomass and grain yield. The water balance model takes inputs of daily rainfall and estimated potential evapotranspiration. Available energy is partitioned between evaporation and transpiration depending on leaf area index. There are two soil layers plus a surface interception and depression store. Water removal from the soil layers is dependent on root development and the location of available water. Biomass production is driven by actual transpiration and transpiration efficiency and so biomass and grain development are dependent on the timing and amount of water and energy utilization by the crop. The model was first calibrated in northern New South Wales with 13 years of research station data. With minor recalibration, it provided good estimates of observed district wheat harvests for a continuous period of 75 years. Further recalibration with 30 years of shire data from Queensland, 29 years of single farm data in southern New South Wales and with 31 years of county data from northwestern USA., indicated the model is able to accurately reproduce observed yields and has the potential to provide reliable forecasts of yield, in a range of different climates.

Agricultural drought analyses for temperate Australia using a biophysical pasture model. 2. Relationship between rainfall and the start and end of predicted droughts

2008 ◽  
Vol 59 (11) ◽  
pp. 1061 ◽  
Author(s):  
G. M. Lodge ◽  
I. R. Johnson
Keyword(s):  
New South ◽  
Summer Rainfall ◽  
Growing Season ◽  
Agricultural Drought ◽  
Wagga Wagga ◽  
Climate Data ◽  
Winter Rainfall ◽  
Rainfall Occurrence ◽  
South Wales ◽  
The Relationship

This paper reports relationships between predicted soil water content (SWC) on the first day of the month (SWCFOM, mm of water) and previous monthly rainfall for 100 years of daily climate data (1905–2005) at four sites (Albany, Western Australia; Hamilton, Victoria; and Wagga Wagga and Barraba, New South Wales). Overall, predicted SWCFOM was correlated (P < 0.05) with rainfall in the previous one, two, or three months. However, the proportion of variation in SWCFOM that could be attributed to its regression on previous rainfall was variable and the relationship tended to improve when individual months were examined. At the three winter-rainfall sites (Albany, Hamilton, and Wagga Wagga), there was a reasonably good relationship between the start of a predicted drought and the end of the growing season and also between the end of a predicted drought and the occurrence of break-of-season. However, for the summer-rainfall dominant site at Barraba, rainfall occurrence was less seasonally defined and there was no clear relationship. While analysis of historical rainfall data for the months in which predicted agricultural droughts started or ended provided some useful insights, it was concluded that it would probably be more instructive to model SWC outcomes for a range of future rainfall scenarios and then examine their likelihood of occurrence using rainfall percentiles.

Effects of grazing and management on herbage mass, persistence, animal production and soil water content of native pastures. 1. A redgrass - wallaby grass pasture, Barraba, North West Slopes, New South Wales

2003 ◽  
Vol 43 (8) ◽  
pp. 875 ◽  
Author(s):  
G. M. Lodge ◽  
S. R. Murphy ◽  
S. Harden
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
New South ◽  
Linear Trend ◽  
Subterranean Clover ◽  
Ground Cover ◽  
Basal Cover ◽  
South Wales ◽  
Continuous Grazing

A study was conducted on a native pasture (dominated by redgrass, Bothriochloa macra) in the Barraba district of northern New South Wales to examine the effects of 5 grazing treatments on total herbage mass, litter mass, basal cover, ground cover, sheep liveweight, wool production and soil water content (SWC, mm) at different depths. Plots were grazed with Merino wethers and data were collected from spring 1997 to spring 2001 and analysed to determine the effects of treatments on both production and sustainability. Five grazing treatments were applied in a randomised 3 replicate design. Grazing treatments were: continuous grazing at 4 and 6 sheep/ha (C4 and C6), continuous grazing at 8 sheep/ha, with subterranean clover (Trifolium subterraneum) oversown and fertiliser applied (C8+sub), and, rotational grazing at an annual stocking rate of 4 sheep/ha with pasture grazed for 4 weeks and rested for 4 weeks (R4/4), or rested for 12 weeks (R4/12).Total herbage mass declined in the C4 (control) treatment throughout the experiment and, compared with this treatment, the C6 treatment had less (P<0.007) linear trend over time, while the R4/12 treatment had a greater (P<0.001) linear trend. Stocking rates could not be maintained in the C4 and C6 treatments and sheep were supplementary fed or removed from these treatments for a total of 133 and 263 days, respectively. For ground cover, the linear trend was greater (P<0.05) in the C8+sub, R4/4, and R4/12 treatments compared with the continuously grazed C4 and C6 treatments and for litter mass this trend was also greater (P<0.05) for the R4/12 treatment than the C4 treatment. Basal cover of wiregrass (Aristida ramosa), wallaby grass (Austrodanthonia spp.) and windmill grass (Chloris truncata) was not affected by grazing treatment but for redgrass the linear trend was greater (P<0.05) in the C8+sub, R4/4, and R4/12 treatments compared with the C4 and C6 treatments. Sheep liveweight (kg/head) was greater (P<0.001) in the C8+sub treatment compared with the C4 treatment. Annual wool production (kg/head) was also higher (P<0.05) in the C8+sub treatment compared with all other treatments. Compared with the C4�treatment, significant differences in soil water content occurred in the R4/12 and C8+sub treatments, but these were predicted to be only 2.9 mm per year for the R4/12 treatment (0–30 cm depth) and 5.7 mm per year for the C8+sub treatment (30–170 cm). Use of a biophysical model indicated that evapotranspiration was the largest output term in the soil water balance and that both drainage and surface runoff of water were episodic events. A sustainability index derived from economic (equivalent annual net return ($/ha) for a 10-year period), animal production, pasture, soil health and soil water data indicated that the C4 and C6 treatments had the lowest scores for each of these parameters and the lowest overall indices. These scores were highly correlated with subjective assessments of the impact of the treatments (r�=�0.93). Overall, these data indicated substantial benefits of either rotationally grazing or the addition of fertiliser and subterranean clover to the production and sustainability of the native pasture studied.

Root depth of native and sown perennial grass-based pastures, North-West Slopes, New South Wales. 2. Estimates from changes in soil water content

2006 ◽  
Vol 46 (3) ◽  
pp. 347 ◽  
Author(s):  
S. R. Murphy ◽  
G. M. Lodge
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
New South ◽  
Perennial Grass ◽  
Maximum Depth ◽  
Root Depth ◽  
North West ◽  
South Wales ◽  
Native Pasture

Root depth of pasture is an important hydrological parameter that has substantial implications for the use of rainfall by plants and in estimating deep drainage using biophysical modelling. Studies were undertaken for native and sown perennial grass-based pastures on the North-West Slopes of New South Wales to investigate 4 approaches that may identify the depth of plant roots based on objective assessments of change in soil water content (SWC). The 4 approaches were to examine traces of SWC measured with a neutron moisture meter (NMM) at about 4-week intervals (0–210 cm profile at 20-cm increments) for defined periods with root depth interpreted as, (i) the maximum depth at which there was a distinct decrease in SWC, (ii) the maximum depth at which there was a >0.01 m3/m3 decrease in SWC, (iii) the uppermost depth at which the change in SWC was significant using t0.05, and (iv) the uppermost depth at which the daily rate of change in SWC was significant using t0.05. For each of these approaches, 4 preliminary criteria were applied as filters to the SWC data before they were used in these analyses, (i) the depth of NMM tubes and maximum depth of measurement of SWC was greater than the anticipated pasture root depth, (ii) the depth of initial profile wetting was greater than the anticipated pasture root depth, (iii) there was a drying period of >3 months duration in the major pasture growth phase to allow pastures to extract soil water to the maximum extent, and (iv) the SWC was measured at a sufficient frequency to determine extraction of soil water by roots. SWC data were available from spring 1997 to spring 2001 for Barraba (45 access tubes, native pasture), Manilla (45 tubes, native pasture) and Nundle (36 tubes, sown pasture). Analyses of monthly rainfall compared with mean values identified 3 times where substantial rainfall was followed by an extended drying period. These periods occurred in 1998, 1999 and 2000. SWC data for the 1998 drying period best met all the preliminary filters, particularly criteria (ii) and (iii). Root depth values estimated from these data using the 4 approaches were not significantly different for Barraba (188 ± 4 to 190 ± 3 cm, n = 45), Nundle (142 ± 5 to 143 ± 7 cm, n = 13) and Manilla Red Chromosol (164 ± 7 to 176 ± 7 cm, n = 14), but were significantly different for Manilla Brown Vertosol (98 ± 7 to 121 ± 7 cm, n = 23). It was concluded that reliable estimates of root depth may be readily obtained for a range of soils and environments by firstly applying the 4 simple criteria used in these studies to the SWC data and by determining the depth of significant drying using t0.05. The depth of significant drying approach was the most objective, providing consistent results among sites and accounting for variance among NMM counts and tubes in these studies.

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