Cj Birch

Temperature and photoperiod sensitivity of development in five cultivars of maize (Zea mays L.) from emergence to tassel initiation

The ability to predict phenological development is crucial to the successful use of crop simulation in crop adaptation studies. Previous studies have shown existing predictive algorithms to be inadequate when applied to a broad range of cultivars and environments. The primary objective of the study was to quantify the temperature and photoperiod responses of the rates of development during emergence to tassel initiation (ETI) for a diverse set of maize cultivars. Five cultivars of maize, differing in maturity and adaptation, were sown on seven dates from 1 October 1993 to 29 March 1994 and grown under natural and extended (16.5 h) photoperiods at Gatton, South East Queensland, under non - limiting conditions of water and plant nutrient supplies. Timing of emergence and tassel initiation were observed for all treatments. The base, optimum, and maximum temperatures, and photoperiod sensitivity of each cultivar were determined using an iterative optimisation procedure. The critical photoperiod (12.5 h) was adopted from literature sources, as there was inadequate range in short photoperiods in the present study to determine it with confidence. Photoperiod extension increased the duration of ETI and increased the number of leaves on all cultivars, the largest increases occurring in a tropically adapted cultivar (Barker), in five of the seven sowings. No response to photoperiod extension occurred in the crops sown on 24 th February and 29 th March 1994. The temperature response was the same in all cultivars, and was best described by a three-stage broken-stick linear function. Photoperiod sensitivity was linear at photoperiods in excess of 12.5 h. The optimised base, optimum and maximum temperatures were 8, 34 and 40 degrees C respectively. Photoperiod sensitivity, expressed as the increase in number of leaves produced per hour of photoperiod in excess of 12.5 h, ranged from 0.3 to 1.5 leaves h-1. When expressed as the increase in thermal duration of the photoperiod sensitive interval prior to tassel initiation, it was 5.0 to 27.3 oCd h-1, (using the optimised base, optimum and maximum temperatures). The fitted values for the real time duration of ETI were in close agreement (RMSD = 2.1 days) with the 60 observed values, which spanned a range of 13 - 34 days. The optimised values for temperature and photoperiod responses should be used for improved prediction of tassel initiation in maize crop simulation models that include detailed prediction of crop ontogeny.

Modelling kinetics of plant canopy architecture¿concepts and applications

Most crop models simulate the crop canopy as an homogeneous medium. This approach enables modelling of mass and energy transfer through relatively simple equations, and is useful for understanding crop production. However, schematisation of an homogeneous medium cannot address the heterogeneous nature of canopies and interactions between plants or plant organs, and errors in calculation of light interception may occur. Moreover, conventional crop models do not describe plant organs before they are visible externally e.g young leaves of grasses. The conditions during early growth of individual organs are important determinants of final organ size, causing difficulties in incorporating effects of environmental stresses in such models. Limited accuracy in describing temporal source-sink relationships also contributes to difficulty in modelling dry matter distribution and paramaterisation of harvest indices. Functional-architectural modelling overcomes these limitations by (i) representing crops as populations of individual plants specified in three dimensions and (ii) by modelling whole plant growth and development from the behaviour of individual organs, based on sound models of organs such as leaves and internodes. Since individual plants consist of numerous organs, generic models of organ growth applicable across species are desirable. Consequently, we are studying the development of individual organs, and parameterising it in terms of environmental variables and plant characteristics. Models incorporating plant architecture are currently applied in education, using dynamic visual representation for teaching growth and development. In research, the 3D representation of plants addresses issues presented above and new applications including modelling of pesticide distribution, fungal spore dispersal through splashing and plant to plant heterogeneity.

Phyllochron responds to acclimation to temperature and irradiance in maize

Crop models need accurate simulation of leaf canopy development. The thermal interval for leaf tip appearance (phyllochron) is critical for predicting the duration of vegetative development. The phyllochron in maize is shorter in temperate than in tropical and subtropical environments. As existing data has been evaluated in a narrow range of environments, the underlying mechanisms that affect phyllochron have not been adequately examined. The objectives of this study were to quantify the response of phyllochron to environmental variables and determine its stability across maize cultivars, to aid modelers in developing tools which accurately predict phenology. Maize was grown in field experiments at Wageningen, The Netherlands, Temple, Texas, USA, and three sites in Mexico, and in controlled environments at Wageningen. The experiment at Temple included grain sorghum and shading treatments to alter irradiance of the crop. Detailed data on leaf production and environmental conditions were collected. These data were combined with published data from field studies. Maize phyllochron acclimated to temperature and increased as mean daily temperature before tassel initiation increased from 12.5 to 25.5 degrees C, and increased in maize and sorghum in response to low irradiance. Temperature was the dominant influence, with phyllochron increasing by 1.7 degrees Cd per degrees C increase in daily mean temperature, as daily mean temperature before tassel initiation increased from 12.5 to 25.5 degrees C, and declined or remained constant when mean daily temperature before tassel initiation exceeded 25.5 degrees C. Only small differences in phyllochron occurred among cultivars. Phyllochron increased by 2 to 4 degrees Cd per MJ photosynthetically active radiation (PAR) as irradiance decreased from 9.6 to 1.1 MJ PAR m-2 day-1.

Plant development and leaf area production in contrasting cultivars of maize grown in a cool temperate environment in the field

Crop models need accurate simulation of the interdependent processes of crop development and leaf area production. Crop development proceeds according to genotype characteristics and environmental influences, specifically temperature and photoperiod. It can be partly described by thermal requirements for development intervals and coefficients that describe genotype adaptation. The objectives of this study were to (a) quantify (i) time of tassel initiation, tasselling and silking; (ii) thermal intervals for initiation, appearance and expansion of successive leaves (iii) thermal duration from initiation to tip appearance and from tip appearance to collar appearance, and (iv) leaf area and canopy cover as measured by leaf area index (LAI) in contrasting cultivars of maize grown in the field in a cool environment; and (b) relate these to plant characteristics and environmental variables, particularly temperature. For these purposes, three cultivars of maize were grown in three and four cultivars in two serial plantings from 18 April to 24 June in field experiments at Wageningen, The Netherlands, in 1997, and detailed data on crop development, leaf production and environmental variables were collected. The base temperature (Tb) for maize was confirmed as 8 degrees C, but thermal time calculation needs to be re-examined to explore a recovery period after chilling injury. Equations that relate foliar properties to total leaf number and ordinal leaf position were derived. Individual leaf area can be described by the modified bell curve, and differences in temporal increase in LAI were related to parameters of leaf initiation, appearance and expansion.

The Many Turnings of Agricultural Extension in Australia

Abstract Purpose: This article outlines the development of extension as a discipline in Australia, its organization, and the ideological changes that have occurred from the second half of the nineteenth century through to the present. Design/Methodology/Approach: It considers the evolution of extension across the different states of Australia from a national perspective and describes how the research development and extension (RD&E) complex has rotated through cycles of crises, highs, awakenings in thought and practice, and periods where achievements and institutions unravel. Findings: Discussed is the tension between public and private sector extension, as well as the successes and failures of various paradigms. It considers the impacts of different agricultural policy on Australian agricultural RD&E across the decades. In particular it deals with the current ‘unravelling’ of the agricultural RD&E system in Australia, and tries to anticipate future demands on agricultural extension and how these services might be delivered into the future. Practical Implications: The article challenges the reader to consider the discipline of extension as a subset of the greater society in which it exists. It provides an insight into how the agricultural research, development and extension capacity of a nation can be observed to ebb and flow over generations in accord with the rhythm of society. Originality/Value: The article presents a perspective that has not been fully captured or understood until now.

Development and evaluation of a sorghum model based on CERES-Maize in a semi-arid tropical environment.

Birch, C.J., Carberry, P.S., Muchow, R.C., McCown, R.L. and Hargreaves, J.N.G., 1990. Development and evaluation of a sorghum model based on CERES-Maize in a semi-arid tropical environment. Field Crops Res., 24: 87-104. This paper reports on the development and evaluation of a grain sorghum model (CERESSorghum ( SAT ) ) for use in the semi-arid tropics. The model was developed from a version of CERESMaize, previously adapted for use in this climatic zone. Functions for phenology, leaf growth, leaf senescence, assimilate accumulation and grain growth were modified using a small subset of sorghum data and validated against a much larger field-data set. When tested with cultivar De Kalb DK55 at Katherine, Northern Territory, the model successfully predicted grain-yield with a root mean square deviation of 0.972 to ha- ~ over a range of sowing dates and water regimes resulting in observed yields ranging from 1.56 to 6.28 t ha -~. Deviations of predicted from observed yields were no greater than those of maize predictions by the parent model. Prediction of components of yield and biomass were also satisfactory. Calibration required 28 changes to the CERES-Maize(SAT) model, of which 15 were changes to coefficients in equations rather than substantial changes to the model. Because of the ease of conversion and the time-use efficiency found in these analyses, the techniques used in this paper could have application where locally calibrated models are required.

Modelling leaf production and crop development in maize (Zea mays L.) after tassel initiation under diverse conditions of temperature and photoperiod

Prediction of the initiation, appearance and emergence of leaves is critically important to the success of simulation models of crop canopy development and some aspects of crop ontogeny. Data on leaf number and crop ontogeny were collected on five cultivars of maize differing widely in maturity and genetic background grown under natural and extended photoperiods, and planted on seven sowing dates from October 1993 to March 1994 at Gatton, South-east Queensland. The same temperature coefficients were established for crop ontogeny before silking, and the rates of leaf initiation, leaf tip appearance and full leaf expansion, the base, optimum and maximum temperatures for each being 8, 34 and 40 degrees C. After silking, the base temperature for ontogeny was 0 degrees C, but the optimum and maximum temperatures remained unchanged. The rates of leaf initiation, appearance of leaf tips and full leaf expansion varied in a relatively narrow range across sowing times and photoperiod treatments, with average values of 0.040 leaves (degrees Cd)-1, 0.021 leaves (degrees Cd)-1, and 0.019 leaves (degrees Cd)-1, respectively. The relationships developed in this study provided satisfactory predictions of leaf number and crop ontogeny (tassel initiation to silking, emergence to silking and silking to physiological maturity) when assessed using independent data from Gatton (South eastern Queensland), Katherine and Douglas Daly (Northern Territory), Walkamin (North Queensland) and Kununurra (Western Australia).

Predicting broccoli development: II. Comparison and validation of thermal time models.

Models predicting broccoli ontogeny and maturity should ideally be precise and readily adopted by farmers and researchers. The objective of this study was to compare the predictive accuracy of thermal time models for three broccoli (Brassica oleracea L. var. italica Plenck) cultivars (‘Fiesta’, ‘Greenbelt’ and ‘Marathon’) from emergence to harvest maturity (Model 1), from emergence to floral initiation (Model 2), and from floral initiation to harvest maturity (Model 3). Comparisons were also made between Model 1 and Model 4 (Models 2 and 3 combined). Model 1 is useful when the timing of floral initiation is not known. When Model 1 was tested using independent data from 1983 to 1984 sowings of three cultivars (‘Premium Crop’, ‘Selection 160’ and ‘Selection 165A’), it predicted harvest maturity well. Prediction of floral initiation using Model 2 is useful for timing cultural practices, frost and heat avoidance. Where timing of floral initiation was recorded, predictions of harvest maturity were most precise using Model 3, since the variation which occurred from emergence to floral initiation was removed. The good predictions for Model 4 suggests that it would best predict the chronological duration from emergence to harvest maturity. # 2000 Published by Elsevier Science B.V.

Reliability of production of quick to medium maturity maize in areas of variable rainfall in north-east Australia

Maize may assume a more significant role in grain crop production systems in north-east Australia if the probability of producing low yields associated with given amounts of available water can be reduced. Growing hybrids with very early maturity provides a possible way to achieve this. Simulation studies of dryland maize production in areas of highly variable rainfall in north-east Australia were undertaken using long-term weather data input to the APSIM model configured for quick to medium maturity maize. The studies focussed on sowing time options, population density, cultivars, and water availability at sowing. Simulation outputs included predicted mean and median yield, measures of yield variability, and the probability of producing low to very low yield (< 2 t/ha). The study showed that optimum sowing date varied with location, and that low populations gave more reliable production, despite some potential yield losses in favourable years. The results of the simulation study provide estimates of yield and thus economic viability of maize production that are interpreted in terms of seasonal variability. They indicate that maize is a viable dryland cropping option provided that cultivar, sowing time and starting water conditions are optimised. Non-optimal conditions of water supply at sowing should be avoided, as greater variability in yield and reduced viability are predicted.

Sowing time and tillage practice affect chickpea yield and nitrogen fixation. 2. Nitrogen accumulation, nitrogen fixation and soil nitrogen balance

Following long-term studies at Warra, on the western Darling Downs, chckpea (Cicer anetinum) was selected as a useful grain legume cash crop with potential for improvement of its nitrogen (N) fixing ability through management. This 2-year study examined the effect of sowing time and tillage practice on dry matter yield, grain yield (Horn et al. 1996), N accumulation, N2 fixation, and the subsequent soil N balance. Generally, greater N accumulation resulted from sowing in late autumn-early winter (89-117 kg N/ha) than sowing in late winter (76-90 kg N/ha). The amount of N2 fixed was low in both years (15-32 kg N/ha), and was not significantly affected by sowing time or tillage. The potential for N2 fixation was reduced in both years due to high initial soil nitrate levels and low total biomass of chickpea because of low rainfall. Nitrogen accumulation by grain was higher under zero tillage (ZT) than conventional tillage (CT) for all sowing times, and this affected the level of grain N export. The consequence of low N2 fixation and high N export in chickpea grain was a net loss of total soil N, (2-48 kg N/ha under CT and 22-59 kg N/ha under ZT). Management practices to ensure larger biomass production and lower soil nitrate-N levels may result in increased N2 fixation by chickpea and thus a positive soil N balance.