The effect of field margin management on crop yield and weed biomass in the crop edge (headland) was investigated. Treatment did not have any significant effect on cereal yields, and taking a one metre strip out of crop production to establish a sterile, natural regeneration or sown strip, did not significantly reduce yields compared to cropping to the field edge. Conservation headlands generally contained greater amounts of weed biomass than fully sprayed headlands, but grain yields were not significantly reduced. Soil compaction affected yield in one of the field experiments, but not the other, where soil density values were fairly uniform. No relationship was found between fertiliser application and yield. In a survey of cereal headlands, distance from the field boundary was the most important factor affecting yield. Where yield increased with distance from the field boundary, there was a strong linear relationship with log distance (P < 0.001). Weed dry matter was related to distance, and there was a significant relationship between weed dry matter and grain yield in the first year of the survey (p < 0.001), but not in the second. Communities of herbaceous field margin species were established, and the effects of nitrogen fertiliser and sublethal glyphosate application were examined over two years. Cover abundance of grasses was greater than that of dicotyledonous species throughout. Bromus sterilis was the most abundant species in 1995, but by 1996 it had been replaced by Arrhenatherum elatius. Increasing fertiliser rate had a negative effect on total vegetation cover in 1995, due to individual plants lodging. During 1996, fertiliser application increased the cover abundance of the dominant perennial species A. e/atius (p < 0.001), and also the annuals B. sterilis and Galium aparine (p < 0.05). Sublethal doses of glyphosate significantly reduced total cover abundance (P < 0.001), and had a greater effect on grasses compared to dicotyledonous species. Measurement of spray drift into a hedgerow showed that positioning the end of the tractormounted spray boom 2m or 6m away from the crop edge reduced drift into the hedgebottom compared with spraying up to the crop edge (P < 0.001).

Although projected terrestrial CO2 levels will not reach 1000 μmol moI-1 (0.1%) for many decades, CO2 levels in growth chambers and greenhouses routinely exceed that concentration. CO2 levels in life support systems in space can exceed 10,000 μmol moI-1 (1%) CO2. Numerous studies have examined CO2 effects up to 1000 μmol mol-1, but theoretical and some experimental evidence indicates that the beneficial effects of CO2 continue past 1000 μmol mol-1 and are near-optimal for wheat at about 1200 μmol mol-1. We studied the effects of near-optimal and superoptimal CO2 levels (>1200 μmol mol-1) on yield of two cultivars of hydroponically grown wheat in 12 trials. Increasing CO2 from suboptimal to near-optimal (350 to 1200 μmol mol-1) increased vegetative growth by 25% and seed yield by 15% in both cultivars. Yield increases were primarily the result of an increased number of heads m-2. Further elevation of CO2 to 2500 μmol mol-1reduced seed yield by 22% in cv. 'Veery-10' and by 15% in cv. 'USU-Apogee'. Superoptimal CO2 did not decrease the number of heads m-2, but reduced seeds per head by 10% and mass per seed by 11%. CO2 toxicity occurred over a wide range of light levels. Subsequent trials revealed that superoptimal CO2 in the 2 weeks before and after anthesis mimicked the effect of constant superoptimal CO2. Furthermore, near-optimal CO2 in the 2 weeks before and after anthesis mimicked the effect of constant near-optimal CO2. Nutrient concentration of leaves and heads was not affected by CO2. The yield decreases may be a response mediated by ethylene.

The effects of petroleum mulches on the emergence and yield of tomatoes were studied at the Farmington Field Station, Greenville Field Station, North Logan, and the greenhouse. The mulches were applied as surface overlays above the seed or incorporating before plantin. Seedling emergence and yields were measured. Data recorded from trials conducted under cool weather conditions indicated that petroleum mulch overlays can be effective in increasing seedling emergence. The increased seedling emergence with petroleum mulch is due to increased soil temperature , less moisture loss from the surface, and a minimum of soil crust formation.

"Pasture is the natural food of all domesticated herbivore, especially the ruminant, and the only single feed upon which it can be maintained in health indefinitely."

No description available.

No description available.

[Abstract]: Sugarcane farmers in Bundaberg have had limited access to irrigation water over the last ten years. The district has the potential of growing 3.8 million tonnes of sugarcane. However, a series of dry seasons saw this reduce to 2.1 million tonnes in 2002. Compounding the effects of both dry seasons and limited water supplies has been a 30% reduction in the sugar price over this period. The irrigation requirement of sugarcane in the Bundaberg area is 8 ML/ha. The original allocated volume for sugarcane production in this area was 4.5 ML/ha (based on 1970 production areas). However, as the area under production has increased and announced allocations in each year has reduced, this allocation is now equivalent to an application volume of about 2 ML/ha A change from the traditional practice of full irrigation is required as water supplies become depleted. As there were no clear guidelines on how growers could respond to diminishing water supplies, this research investigated opportunities to fine tune irrigation practices and the performance of irrigation systems (ie. low cost solutions) that would assist growers to maximise sugarcane yield. A grower survey was initially conducted to identify current practice and opportunities for change. Field investigations focused on the performance of water winch and furrow irrigation systems, which make up 91% of the irrigated area in the district. As most of these application systems have insufficient capacity to meet crop demands opportunities to schedule irrigations were limited to start up after rain. Improvements in irrigation system performance were found to provide the greatest potential to increase sugarcane yield under conditions of limited water. Investigations identified that irrigation performance could be significantly improved through relatively minor adjustment. Field trials found that wind speed and direction significantly influenced the performance of travelling gun irrigators. Although growers were generally aware of the effects of wind, meteorological data suggested that the opportunity to operate water winches in low wind conditions is limited. Changing to a taper nozzle under moderate to high wind conditions will reduce the effect of wind on performance. This practice was found to improve the uniformity (measured by Christiansen’s Uniformity Coefficient, CU) by 16%. The grower survey indicated that there was no preference towards the use of taper nozzles in windy conditions. Additional trial work developed a relationship between the variation in water applied to the field through non uniformity and sugarcane yield. An 8% reduction in yield was determined for a 10% reduction in CU. This indicated that changing to a taper nozzle could potentially increase sugarcane yield by 15% in high wind conditions. Other settings, which also influenced uniformity, included lane spacing and gun arc angle Simple changes to the operation of furrow irrigation systems were also found to dramatically improve irrigation performance. Field measurements in combination with simulation modelling of irrigation events using SIRMOD II identified that current irrigation performance ranged in application efficiency from 45 to 99% (mean of 79%) and a distribution uniformity from 71 to 93% (mean of 82%). Both application efficiency and distribution uniformity were increased to greater than 90% and 84% respectively, except on a cracking clay soil. Improvements in application efficiency and distribution uniformity were achieved by adjusting furrow flow rate (cup size), turning the irrigation off at the right time (ie. just as it reached the end of the field) and banking the end of the field. Growers had a good understanding of the correct cut off time and were attentive to reducing run off through either banking ends or tail water return. However, growers had a poor understanding of the significance of furrow flow rate. Other opportunities to improve irrigation performance on high infiltration soils included alternate furrow irrigation and shallow cultivation practices which maintained compaction in the interspace and reduced infiltration. Soil moisture and crop growth measurements indicated that sugarcane yield could be maximised by starting the irrigation rotation earlier after rainfall (ie. at a deficit equal to the irrigation amount). These observations were modelled using the crop simulation model APSIM sugar to assess the strategy over a longer time interval and the influence of seasonal variation. Simulation modelling showed that final sugarcane yields were not sensitive to irrigation start-up strategies. Yields for the start-up strategies modelled varied by less than 5 tc/ha. This minor difference occurred as the crop yield was driven by the total amount of water available to the plant. The limited amount of irrigation water available to the plant (2 to 3 ML/ha) had only a minor effect on the water balance and no significant change to effective rainfall between strategies. The greatest difference in yield occurred between irrigation treatments when water was left over at the end of the season (9.2 tc/ha). Starting irrigation earlier after rainfall events (on a 14 day rotation) provided the greatest opportunity to use all of the available irrigation supply. By comparison, delaying the application of the first irrigation after rainfall resulted in some of the irrigation water not being applied in 30% of years.

Includes bibliographical references (leaves 11-1-11-26). / xv, 222 leaves : ill. (some col.) : 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Adelaide University, Dept. of Agronomy and Farming Systems, 2001

A common challenge during deposition of slurries is segregation as large particles settle through the matrix of fines and water. Whether segregation occurs or not depends on the grain size distribution of the solids, the void ratio or solids content and the rheological properties of the fines-water matrix. The rheological characterization of slurry composed of different grain sizes and varying water chemistry was investigated. The vane yield stress was used to characterize different slurries composed of clay, silt and sand materials. Semi-empirical fractal theory showed good agreement with experimental data for fine slurry. Comparison of yield stress at same concentration but different composition showed a decreasing trend as the composition of either silt or sand material increases. The pore-water effect was studied for representative kaolinite slurry. The yield stress was insensitive for pH values in the acidic and neutral range, while in the basic range it showed significant response depending upon the type of the chemical used to achieve the pH: Ca(OH)2 and NaOH. A modified segmented standpipe was designed and used in a series of experiments to determine concentration profiles during the sedimentation processes. Analyses of the solid content profiles and sand content profiles in the standpipes indicated a capture of sand particles which could be correlated to the yield stress of the fines matrix. Theoretical calculations, however, showed over-prediction of the captured sand size. A correction factor of about 0.2 was applied. Flume test on a high solid content slurries showed that the dynamic segregation is governed by all the factors governing the static case. Beaching profile shapes were not a necessary indication of segregating and non-segregating type of slurries. Modified version plastic theory for flow slides was used to characterise profile shape. Computational fluid dynamics approaches based on kinetic theory and bi-viscous model analysis were implemented and showed a reasonable capability in modelling segregation when compared with experimental results. A statistical formulation for segregation index, SI, was proposed. The index accounts for variation in depth of samples. Finally recommendations for future research are proposed based on the observations and findings made from the study. / Geotechnical Engineering

With the expanding population of Texas and the resulting increase in demand for water, the scarcity of water is becoming an increasingly urgent issue and research is being conducted to find ways to improve water yield, the amount of water that is used for aquifer recharge and riparian areas (lakes, streams, etc). Rangelands provide a major catchment for both surface reservoirs and aquifers. The Edwards Aquifer Recharge Zone and the Twin Buttes Drainage Area were selected to determine the tradeoffs between brush management for increased water yield and wildlife habitat improvement. In April 2002, a mail survey of 300 randomly selected landowners was conducted in each of the two watersheds to gain information regarding their demographics, land cover, and willingness to enter into a cost-share brush removal program. A total of 131 usable questionnaires (43.7%) were returned by Edwards Aquifer area participants, and 141 usable questionnaires (47.0%) were returned by Twin Buttes area participants. Respondents were asked questions including attitudes towards brush amounts and management strategies, and certain constraints that may be included in a cost-share brush removal program. Most respondents indicated interest in enrolling at least part of their land in such a program. Reasoning behind interest varied in each study area. However, interest in various contractual agreements was neutral at best. Policy implications entail considering wildlife habitat mitigation, landowners' preferences, and potential for increasing water yield and determining if all can be managed, or if trade-offs must be considered.