S Lisson

What is limiting canola yield in southern New South Wales? A diagnosis of causal factors

During the 1990s there was considerable evidence from grower surveys and other regional statistics to suggest that canola (Brassica napus) yields were declining in the medium and high rainfall areas of southern New South Wales (NSW). A paddock survey was conducted across three regions of southern NSW over three consecutive seasons (2003–05) to explore the importance of disease and other possible causes of low productivity. Under-performing paddocks were identified by comparing measured paddock yields with simulated potential yields. The causes of the resultant yield gaps were identified by analysis of the survey results with growers and consultants and from insights provided by the simulation analysis. Seasonal water supply and emergence date accounted for around 70% of the variation in yield across the survey, although no dependence on these variables was evident in 2005 as a result of high spring rainfall. A majority (95) of the 132 paddocks surveyed yielded to within 20% of the simulated potential yield. Disease, while significant in some paddocks, was limited by the dry seasons, there was no evidence for widespread micronutrient deficiencies and most crops were adequately supplied with nitrogen. There was no single cause of under-performance and the impact of those causes varied across regions and seasons. Subsoil constraints (seven paddocks) and late season water stress (six paddocks) were the most common factors associated with under-performance, while five paddocks had inexplicable yield gaps. Restrictions to taproot growth were widespread, especially in the southern region where around 60% of paddocks had significantly restricted taproots in all seasons (>3 on a 0–5 scale). Survey paddocks in which significant root restriction was found were between 10 and 50% below potential yield. Subsequent soil profile analysis identified a range of possible subsoil constraints including high soil strength, sodic or saline subsoils or subsurface acidity and further research is warranted to determine their impact on canola productivity in the region.

Determining the frequency, depth and velocity of preferential flow by high frequency soil moisture monitoring

Preferential flow in agricultural soils has been demonstrated to result in agrochemical mobilisation to shallow ground water. Land managers and environmental regulators need simple cost effective techniques for identifying soil - land use combinations in which preferential flow occurs. Existing techniques for identifying preferential flow have a range of limitations including; often being destructive, non in situ, small sampling volumes, or are subject to artificial boundary conditions. This study demonstrated that high frequency soil moisture monitoring using a multi-sensory capacitance probe mounted within a vertically rammed access tube, was able to determine the occurrence, depth, and wetting front velocity of preferential flow events following rainfall. Occurrence of preferential flow was not related to either rainfall intensity or rainfall amount, rather preferential flow occurred when antecedent soil moisture content was below 226 mm soil moisture storage (0-70 cm). Results indicate that high temporal frequency soil moisture monitoring may be used to identify soil type - land use combinations in which the presence of preferential flow increases the risk of shallow groundwater contamination by rapid transport of agrochemicals through the soil profile. However use of high frequency based soil moisture monitoring to determine agrochemical mobilisation risk may be limited by, inability to determine the volume of preferential flow, difficulty observing macropore flow at high antecedent soil moisture content, and creation of artificial voids during installation of access tubes in stony soils.

Host location and oviposition of lepidopteran herbivores in diversified broccoli cropping systems

1 Host location and oviposition are crucial steps in the life cycles of insect herbivores. A diversified cropping system may interfere with these processes, ultimately reducing pest colonization of crops and the need for chemical interventions.

Development of a hemp (Cannabis sativa L.) simulation model. 2. The flowering response of two hemp cultivars to photoperiod

The duration from sowing to flowering is an important determinant of fibre yield potential in hemp, since maximum stem yield occurs shortly after flowering. As a short-day plant, daylength has a key influence on the timing of flowering in hemp. This paper reports on studies into the effect of photoperiod on the thermal time duration from sowing to flowering for 2 hemp cultivars, and develops parameters to enable simulation of post-emergent phenology in the hemp model described in the final paper of this series. The hemp model divides the post-emergent period into a vegetative phase that ends at floral initiation, aflower development phase (FDP) between flower initiation and appearance, and a short phase between first flower appearance and harvest maturity (male anthesis). The vegetative phase is further divided into a temperature-dependent basic vegetative phase (BVP) and a daylength-dependent photoperiod induced phase (PIP). For a short-day plant, the duration of PIP is assumed to be zero degree days at daylengths below a base or maximum optimum photoperiod (MOP). Daylengths in excess of the MOP lead to an increase in thermal time within PIP, the duration of which is determined by a genotype’s photoperiod sensitivity (PS). Two hemp genotypes, Kompolti and Futura 77, were exposed to 6 different photoperiod regimes ranging from 8 to 16 h in a growth chamber. Thermal time durations from emergence to flower initiation and first flower formation (harvest) were calculated from thermograph plots. The flowering responses for the 2 cultivars were typical for a short-day plant, with flowering occurring rapidly in daylengths less than about 14 h and with increasing delay at longer photoperiods. With the exception of a longer thermal time duration from flower formation to harvest maturity in the case of Kompolti, the 2 cultivars had similar values for the key phenology parameters. Respectively, for Futura and Kompolti: BVP was 383˚Cd and 390˚Cd, MOP was 14 h and 13.8 h, PS was 266˚Cd/h and 252˚Cd/h, and FDP was 76.8˚Cd and 80.2˚Cd.

Subsurface Lateral Flow in Texture-Contrast (Duplex) Soils and Catchments with Shallow Bedrock

Development-perched watertables and subsurface lateral flows in texture-contrast soils (duplex) are commonly believed to occur as a consequence of the hydraulic discontinuity between the A and B soil horizons. However, in catchments containing shallow bedrock, subsurface lateral flows result from a combination of preferential flow from the soil surface to the soil—bedrock interface, undulations in the bedrock topography, lateral flow through macropore networks at the soil—bedrock interface, and the influence of antecedent soil moisture on macropore connectivity. Review of literature indicates that some of these processes may also be involved in the development of subsurface lateral flow in texture contrast soils. However, the extent to which these mechanisms can be applied to texture contrast soils requires further field studies. Improved process understanding is required for modelling subsurface lateral flows in order to improve the management of waterlogging, drainage, salinity, and offsite agrochemicals movement.

Host location and parasitism of Brevicoryne brassicae in diversified broccoli cropping systems

Host location is a crucial step in the life cycle of the cabbage aphid, Brevicoryne brassicae (L.) (Homoptera: Aphididae). Diversified cropping systems have the potential to inhibit or interfere with host location processes to reduce the severity of aphid outbreaks. We altered the vegetation mix of a broccoli [Brassica oleracea var. italica (Plenck) (Brassicaceae)] cropping system by substituting broccoli with strips of potatoes [Solanum tuberosum (L.) (Solanaceae)], planting broccoli into a cereal rye [Secale cereale (L.) (Poaceae)] cover crop, or both. The probability of aphid infestation was significantly reduced by the presence of the cover crop, whereas strips of potatoes slightly increased initial numbers. The effectiveness of the cover crop treatments was primarily due to fewer alate aphids initially colonizing broccoli plants. Aphid parasitism by Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) did not explain the observed differences in the number of aphid colonies present in each treatment.

Development of a hemp (Cannabis sativa L.) simulation model 1. General introduction and the effect of temperature on the pre-emergent development of hemp

In recent times, there has been a revival of interest in hemp (Cannabis sativa L.), principally as a source of fibre in paper and pulp manufacture. Studies assessing the production potential and optimum crop management of hemp could benefit from the use of a simulation model that captures crop growth and development processes in response to management, genotypic, soil and climate factors. Such a model would complement the more traditional agronomic field trial programs by helping to identify the need, extent and nature of such trials, and by extrapolating limited field results across both temporal and spatial dimensions. The hemp model described in the final paper in this series, divides crop phenology into 5 phases, the first of which includes the pre-emergent processes of germination and the subsequent elongation of hypocotyl and radicle. This first paper reports on a study into the response of these pre-emergent processes to temperature. The primary objectives were to establish a simple model for predicting the duration from sowing to emergence and to obtain estimates for the cardinal temperatures of hemp growth and development. Cardinal temperatures are required for the estimation of thermal time, which drives phenological development and canopy expansion in the hemp model. The germination response of the hemp cultivar Kompolti was measured at 13 different temperatures in incubators set between 1 and 55°C. Similarly, the response of radicle and hypocotyl elongation to temperature was measured at 8 different temperatures in incubators set between 10 and 40°C. Development rates for each phase of pre-emergent development were then calculated from time response plots of germinant number, hypocotyl and radicle length. Finally, piecewise linear models were fitted to plots of development rate versus temperature in order to calculate thermal time durations for each phase and cardinal temperatures for hemp growth and development. Estimates of the optimum and maximum temperatures from the elongation study were relatively consistent, with average values of 28.6 and 40.7°C, respectively. Base temperature estimates were less consistent, ranging from 1.4°C for the hypocotyl linear phase, to 6.2°C for the radicle lag phase. This variability made it difficult to identify a common base temperature for use in the hemp model. However, there was some evidence to support previously reported base temperature estimates ranging from 0 to 2.5°C. Assuming a common base temperature of 1°C, the average thermal time requirements for germination and the lag and linear phases of hypocotyl elongation were 24.1°Cd, 44.5°Cd and 1.34°Cd/mm, respectively.

A farm-scale, bio-economic model for assessing investments in recycled water for irrigation

Demand for water in Australia is increasing along with growing pressure to maximise the efficiency of irrigation water use and seek additional and alternative irrigation supplies. The scarcity of water supplies coupled with the need for urban communities to dispose of large quantities of treated recycled water from sewage treatment plants has led to increasing interest from urban and rural communities in the reticulation of this water for irrigating adjacent crop-production areas. Proposals to use recycled water inevitably lead to a complex range of issues that need to be addressed, including: • costs and benefits of supplying an additional source of water to current or new cropping systems; • optimum irrigation design and management, particularly where there are multiple sources of irrigation water; • management of overflow from on-farm water storages; and • environmental implications with regard to salinity, runoff, drainage, nitrate leaching, and environmental flows. Simulation models can capture many of the key factors and processes influencing irrigated crop production systems, and can play a useful role in exploring these issues. In this paper, we have described an approach that couples agricultural production system and economic models in a way that enables analysis of the likely benefits and risks of investing in recycled water, although the analysis is equally relevant to any assessment of the value of an additional source of irrigation water, particularly saline water. The approach has been illustrated with a case study of a mixed-crop farm in the Darling Downs region of Queensland, Australia, in which the farm-scale crop production, economic, and environmental implications of investing in recycled water were considered.

Development of a hemp (Cannabis sativa L.) simulation model. 4. Model description and validation

In studies assessing the prospects for a hemp industry, as well as in longer term research activities, the use of a hemp simulation model to complement the more traditional agronomic field trials would offer a number of potential advantages. In addition to being cost and labour intensive, field trials with hemp have political, social and security implications. With these implications in mind, a simulation model that captures the growth and development processes of hemp in response to management, genotypic, soil and climate factors, has the potential to increase research efficiency. The model could be used to assess the need, extent and nature of field trials, to help interpret field trial results, and to investigate temporal and spatial variability in selected crop responses. This paper describes a hemp crop growth and development model (APSIM-Hemp) and its validation against an independent dataset. The model was developed as a crop module within the framework of the larger systems model, Agricultural Production Systems sIMulator (APSIM), to extend the capability to encompass the agricultural system in which hemp is grown. APSIM-Hemp incorporates relationships developed in the previous papers in this series relating to pre- and post-emergent phenology and leaf area production. Other parameters relating to biomass partitioning, biomass production, water uptake and nitrogen uptake were derived from separate field studies and selected references. APSIM-Hemp adequately predicted phenology, leaf area and biomass production for the cultivar Kompolti at Forthside in north-western Tasmania, for a dataset comprised of results from trials conducted over 3 seasons and including treatments of sowing date, irrigation regime and plant density. Although performing well against this independent dataset, the performance of the model needs to be further validated over a range of other soil, climate and management conditions in order to assess its broader predictive capability. Notwithstanding these limitations, the sound basis of a model for simulating the growth and development of hemp has been developed.

Plant growth and soil responses to soil applied organic materials in Tasmania, Australia

Biosolids, poppy mulch (PM), and poppy seed waste (PSW) were applied to soils in barley and wheat field trials in two areas of Tasmania to determine crop and soil responses and the potential for these materials to substitute for inorganic fertiliser. Lime-amended biosolids (LAB) was applied at one, two, and five times the nitrogen-limiting biosolids application rate (NLBAR). Anaerobically digested biosolids (ADB) was applied at the NLBAR, and PM and PSW were applied at industry-recommended rates. The results indicated that ADB, LAB, PM, and PSW can substitute for inorganic fertiliser in meeting plant nutrient requirements but may be releasing more plant-available N than guideline assumptions. However, organic amendments are less easily managed and applied than inorganic fertiliser, and release of plant-available N from organic amendments may be too rapid for plant uptake to prevent leaching losses. LAB can also leave elevated residual extractable phosphorus in soil after two cereal crops, and PM and LAB can increase soil pH. Microbial biomass showed an inconsistent, and in some cases unexpected, response to organic amendments after 1 year and no significant relationship to changes in soil carbon.