School of Agriculture, Food and Ecosystem Sciences - Theses

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Start date: 1980 × End date: 1999 × Type: Masters Research thesis × Author: O'Connell, M. G. (Mark Glenn) ×

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    Fallow-crop water balance and recharge relationships in the Victorian Mallee
    O'Connell, M. G. (Mark Glenn) (University of Melbourne, 1998)
    Background: The Victorian Mallee has a semi-arid climate and cereal production is the major agricultural landuse. Alkaline calcareous soils dominate the region. Cropping in the Mallee is subject to variation in growing season rainfall. Long (winter) fallows are a robust and common practice prior to wheat. Fallows may be viewed as a drought prevention strategy in the rainfed Mallee. Water conserved by fallows supplements growing-season rainfall and thereby reduces annual yield variability. The risk is wind erosion and deep drainage beyond the rootzone of crops. Deep drainage represents incomplete utilisation of water for crop production and contributes to dryland salinity when it enters saline groundwater (potential groundwater recharge) (Chapter 1). This thesis presents work conducted in the field by experimentation and by simulation modelling. A field study at Walpeup (35� 07' S., 141� 58' E.) was conducted over 5 years (1993-1997) to investigate substituting mustard (Brassica juncea) for 18-month long-fallows. Two crop sequences (fallow-wheat-pea [FWP] v. mustard-wheat-pea [MWP]) were examined. The field experiments were designed to appraise FWP v. MWP sequences by investigating soil-water balance, productivity, potential recharge to groundwater and episodic drainage (Chapters 2 & 3). Determination of crop interception and utilisation of photosynthetically active radiation (PAR) were investigated in the field (Chapter 4). Simulation modelling was used to identify cropping practices conducive to longterm productivity and minimal drainage in the region. The O'Leary-Connor model (O'Leary and Connor 1996a,b) was appraised against observed measures (1993- 1998) of growth and yield of wheat, and rootzone soil-water balance under wheat and fallow (Chapter 5: Experiment I). Effects of crop rotation, stubble and tillage management on deep drainage of light (sandy loam) and heavy (clay) textured soils were then investigated by running the O'Leary-Connor model using 58 y of historical climatic data (Chapter 5: Experiment II). Field experimentation: The field experiment demonstrated effects of substituting mustard for fallowing. Aspects of water balance, growth and yield of FWP and MWP sequences were investigated in Chapter 2. Water limited crop production in each growing-season throughout the study. Rootzone soil-water conservation from fallowing in sequence FWP increased wheat growth, yield and water use under severe drought. By contrast, the data reveal that pea water relations and productivity was not influenced by crop sequence. Mustard growth was variable with low yields. Deep drainage was investigated (1993-1998) under FWP and MWP sequences by measuring changes in subsoil-water and by drainage lysimetry (Chapter 3). The former showed greater drainage of FWP (12 mm/y) compared to MWP (5 mm/y). Two major drainage events were confined to a specific phase of the FWP sequence (5.0 mm & 4.3 mm), illustrating the difficulty of reconciling drainage estimates by alternative approaches in a semi-arid environment over a relatively short period 5 y). Radiation interception by wheat, pea and mustard was investigated in Chapter 4. The fraction of intercepted PAR (f), canopy extinction coefficient and radiation-use efficiency were determined for each crop. Aridity resulted in incomplete canopy cover. Fallowing increased f of wheat under favourable (1996) and drought (1994) growing seasons. Estimates of extinction coefficient for wheat, pea and mustard were 0.82, 0.76 and 0.68, respectively. Estimated pre-anthesis radiation-use efficiency for wheat, pea and mustard were 1.75, 1.47 and 1.85 (g aboveground biomass/MJ intercepted PAR), respectively. Simulation modelling: The O'Leary-Connor model provided a good representation of wheat growth, and rootzone soil water (Chapter' 5: Experiment I), justifying use of the unadjusted model, as a tool for examination of water balance under agronomic scenarios in this study (Chapter 5: Experiment II). The investigation suggested greater soil-water conservation under fallowing compared to continuous cropping. Simulated grain yield responded to trends in soil water in accordance with water limitations imposed by the rainfed environment. Simulated drainage was episodic. Soil hydraulic properties and agronomic management influenced total drainage. Least drainage occurred on the heavy textured clay, reflecting soil-water holding capacity and water use associated with crop production. No direct relationships between drainage and rainfall were evident. Continuously cropped (WW) sequences drained less than fallow-wheat (FW). Fallow management influenced water storage and drainage. Stubble-retained zerotilled fallows conserved more soil water and subsequently had greatest drainage. Conventional tillage and stubble burning decreased drainage, but increased runoff and soil surface evaporation. On the lighter soil type, WW and FW drained ~6 % of years without stubble retention, but 10-70 % of years when stubble was retained, with a increase in drainage from 0.5 mm/y to 10-20 mm/y, respectively. By contrast, the heavier clay failed to drain without stubble, and drained in the range, 5-24 % of years when stubble was retained (range, 2-17 mm/y). Overall, fallowing reduced yield failure, but, in conjunction with stubble retention, increased episodic and total drainage on both soil types under the climatic conditions experienced in the Mallee. Conclusion: Outcomes of both field and simulation studies confirms that fallowing increases drainage (potential groundwater recharge). Although, non-fallow annual cropping sequences failed to provide a dry soil profile at sowing for prevention of drainage, especially in wet years. Strategies that use agronomic perennials to dewater subsoils prior to sowing require further investigation.
  • Item
    No Preview Available
    Fallow-crop water balance and recharge relationships in the Victorian Mallee
    O'Connell, M. G. (Mark Glenn) (University of Melbourne, 1998)
    Background: The Victorian Mallee has a semi-arid climate and cereal production is the major agricultural landuse. Alkaline calcareous soils dominate the region. Cropping in the Mallee is subject to variation in growing season rainfall. Long (winter) fallows are a robust and common practice prior to wheat. Fallows may be viewed as a drought prevention strategy in the rainfed Mallee. Water conserved by fallows supplements growing-season rainfall and thereby reduces annual yield variability. The risk is wind erosion and deep drainage beyond the rootzone of crops. Deep drainage represents incomplete utilisation of water for crop production and contributes to dryland salinity when it enters saline groundwater (potential groundwater recharge) (Chapter 1). This thesis presents work conducted in the field by experimentation and by simulation modelling. A field study at Walpeup (35� 07' S., 141� 58' E.) was conducted over 5 years (1993-1997) to investigate substituting mustard (Brassica juncea) for 18-month long-fallows. Two crop sequences (fallow-wheat-pea [FWP] v. mustard-wheat-pea [MWP]) were examined. The field experiments were designed to appraise FWP v. MWP sequences by investigating soil-water balance, productivity, potential recharge to groundwater and episodic drainage (Chapters 2 & 3). Determination of crop interception and utilisation of photosynthetically active radiation (PAR) were investigated in the field (Chapter 4). Simulation modelling was used to identify cropping practices conducive to longterm productivity and minimal drainage in the region. The O'Leary-Connor model (O'Leary and Connor 1996a,b) was appraised against observed measures (1993- 1998) of growth and yield of wheat, and rootzone soil-water balance under wheat and fallow (Chapter 5: Experiment I). Effects of crop rotation, stubble and tillage management on deep drainage of light (sandy loam) and heavy (clay) textured soils were then investigated by running the O'Leary-Connor model using 58 y of historical climatic data (Chapter 5: Experiment II). Field experimentation: The field experiment demonstrated effects of substituting mustard for fallowing. Aspects of water balance, growth and yield of FWP and MWP sequences were investigated in Chapter 2. Water limited crop production in each growing-season throughout the study. Rootzone soil-water conservation from fallowing in sequence FWP increased wheat growth, yield and water use under severe drought. By contrast, the data reveal that pea water relations and productivity was not influenced by crop sequence. Mustard growth was variable with low yields. Deep drainage was investigated (1993-1998) under FWP and MWP sequences by measuring changes in subsoil-water and by drainage lysimetry (Chapter 3). The former showed greater drainage of FWP (12 mm/y) compared to MWP (5 mm/y). Two major drainage events were confined to a specific phase of the FWP sequence (5.0 mm & 4.3 mm), illustrating the difficulty of reconciling drainage estimates by alternative approaches in a semi-arid environment over a relatively short period 5 y). Radiation interception by wheat, pea and mustard was investigated in Chapter 4. The fraction of intercepted PAR (f), canopy extinction coefficient and radiation-use efficiency were determined for each crop. Aridity resulted in incomplete canopy cover. Fallowing increased f of wheat under favourable (1996) and drought (1994) growing seasons. Estimates of extinction coefficient for wheat, pea and mustard were 0.82, 0.76 and 0.68, respectively. Estimated pre-anthesis radiation-use efficiency for wheat, pea and mustard were 1.75, 1.47 and 1.85 (g aboveground biomass/MJ intercepted PAR), respectively. Simulation modelling: The O'Leary-Connor model provided a good representation of wheat growth, and rootzone soil water (Chapter' 5: Experiment I), justifying use of the unadjusted model, as a tool for examination of water balance under agronomic scenarios in this study (Chapter 5: Experiment II). The investigation suggested greater soil-water conservation under fallowing compared to continuous cropping. Simulated grain yield responded to trends in soil water in accordance with water limitations imposed by the rainfed environment. Simulated drainage was episodic. Soil hydraulic properties and agronomic management influenced total drainage. Least drainage occurred on the heavy textured clay, reflecting soil-water holding capacity and water use associated with crop production. No direct relationships between drainage and rainfall were evident. Continuously cropped (WW) sequences drained less than fallow-wheat (FW). Fallow management influenced water storage and drainage. Stubble-retained zerotilled fallows conserved more soil water and subsequently had greatest drainage. Conventional tillage and stubble burning decreased drainage, but increased runoff and soil surface evaporation. On the lighter soil type, WW and FW drained ~6 % of years without stubble retention, but 10-70 % of years when stubble was retained, with a increase in drainage from 0.5 mm/y to 10-20 mm/y, respectively. By contrast, the heavier clay failed to drain without stubble, and drained in the range, 5-24 % of years when stubble was retained (range, 2-17 mm/y). Overall, fallowing reduced yield failure, but, in conjunction with stubble retention, increased episodic and total drainage on both soil types under the climatic conditions experienced in the Mallee. Conclusion: Outcomes of both field and simulation studies confirms that fallowing increases drainage (potential groundwater recharge). Although, non-fallow annual cropping sequences failed to provide a dry soil profile at sowing for prevention of drainage, especially in wet years. Strategies that use agronomic perennials to dewater subsoils prior to sowing require further investigation.