Michael P. Bange

Radiation use efficiency increases when the diffuse component of incident radiation is enhanced under shade

Theoretical analyses have shown the radiation use efficiency of maize, soybean, and peanut to increase with a decrease in the level of incident radiation and an increase in the proportion of diffuse radiation. This study compared the growth and radiation use efficiency of Panicum maximum cv. Petrie (green panic) and Bothriochloa insculpta cv. Bisset (creeping bluegrass) beneath shading treatments (birdguard and solarweave shadecloths) with that in full sunlight. A level of incident radiation reduced by 25% under birdguard shadecloth decreased final yield and final leaf area index, but increased canopy leaf nitrogen concentration and radiation use efficiency (19-14%) (compared with the full sun treatment). A similar level of reduced incident radiation under solarweave shadecloth (which provided an increased proportion of diffuse radiation), increased final yield and radiation use efficiency (46-50%). An understanding of the effects of composition of incident radiation on radiation use efficiency of tropical grasses enables more accurate estimation of potential pasture growth in shaded environments. It also has impact upon crop production in glasshouses and greenhouses.

The Potential Value of Seasonal Climate Forecasting in Managing Cropping Systems

There is considerable interest in exploring the value of seasonal climate forecasts in assisting farmers to manage cropping systems, not only for short-term decisions on crop management but also for longer-term strategic decisions on crop rotations. This paper reviews a range of applications for climate forecasts, but focuses on cropping systems issues that would benefit from long lead-time forecasts. A specific case study is used to demonstrate the potential for using the Southern Oscillation Index in assisting the incorporation of opportunity cropping into dryland cotton production systems.

SIRATAC and CottonLOGIC: persevering with DSSs in the Australian cotton industry

Abstract We have reviewed three generations of Decision Supports Systems (DSSs) developed over two decades in the Australian cotton growing industry. The purpose of the DSSs was to deliver results of scientific research to crop managers in the industry in order to assist their decision making. Pest management was the dominant domain of the DSSs, but fertiliser and irrigation management were also addressed. The content, delivery and use of the systems are described briefly. Anecdotal evidence and objective studies were reviewed in order to evaluate the DSSs. There was demand for DSS in the industry which the systems met in part, and there was consensus that the systems delivered science and influenced management practice. Current and future developments include roles in Best Management practice, in Area Wide Management of pests and in education. Issues arising in the course of the development are discussed. We have tried to document, not only the achievements, but also the failures, the problems, the conflicts and the recurring issues in order to elicit lessons for the future.

Timing of crop maturity in cotton. Impact of dry matter production and partitioning.

Cotton is an indeterminate species; the timing of crop maturity is determined by the capacity of the plant to continue the production of new fruiting sites. According to the nutritional hypothesis, the cessation of fruit production (‘cutout’) occurs when the demand on the resource supply by growing fruit leaves none for the initiation of new fruiting sites. The aim of this work was to determine whether differences between cultivars in dry matter production or partitioning contributed to the timing of crop maturity. Growth analysis was conducted on a short- and a long-season cultivar grown in four fully irrigated field experiments. The production of dry matter, as a function of radiation-use efficiency (RUE) and light interception, and its partitioning to various plant parts were calculated as indirect measures of resource supply. The cultivars rarely differed in total dry matter production. When differences were measured, the earlier cultivar produced more dry matter due to greater RUE and light interception. Its light interception was greater due to an earlier production of a larger canopy and not differences in light extinction coefficient. Early in reproductive growth, the shorter-season cultivar consistently partitioned a greater proportion of dry matter into reproductive structures than the long-season cultivar in a pattern consistent with its higher growth rate at that time. There was therefore no indication that fruiting in the long-season cultivar was maintained due to greater dry matter production. While differences in partitioning were found, it is not clear whether this contributed to differences in timing of maturity or was a consequence of an earlier development of fruit demand in the early cultivar due to its higher rate of square production.

Row configuration as a tool for managing rain-fed cotton systems: review and simulation analysis

Rain-fed cotton production can be a significant proportion (average 17%) of the Australian Cotton Industry. One of the management techniques that rain-fed cotton growers have is to modify row configuration. Configurations that have entire rows missing from the sowing configuration are often referred to as ‘skip row’. Skip configurations are used to: increase the amount of soil water available for the crop, which can influence the potential lint yield; reduce the level of variability or risk associated with production; enhance fibre quality; and reduce input costs. Choosing the correct row configuration for a particular environment involves many, often complex, considerations. This paper presents an examination of how rain-fed cotton production in Australia is influenced by row configuration with different management and environmental factors. Data collated from field experiments and the cotton crop simulation model OZCOT, were used to explore the impact of agronomic decisions on potential lint yield and fibre quality and consequent economic benefit. Some key findings were: (i) soil water available at sowing did not increase the advantage of skip row relative to solid configurations; (ii) reduced row spacing (75 cm) did not alter lint yield significantly in skip row crops; (iii) skip row, rain-fed crops show reasonable plasticity in terms of optimum plant spacing within the row (simular to irrigated cotton); (iv) sowing time of rain-fed crops would appear to differ between solid and skip row arrangements; (v) skip row configurations markedly reduce the risk of price discounts due to short fibre or low micronaire and this should be carefully considered in the choice of row configuration; and (vi) skip configurations can also provide some savings in variable costs. In situations where rain-fed cotton sown in solid row configurations is subject to water stress that may affect lint yield or fibre quality, skip row configurations would be a preferential alternative to reduce risk of financial loss.

Impact of short-term exposure to cold night temperatures on early development of cotton (Gossypium hirsutum L.)

Regression analysis of field data has indicated that minimum daily temperatures below 11°C delay the development of cotton (Gossypium hirsutum L.) seedlings beyond what would be expected based on the accumulated degree-day sum. In Australian cotton production systems, events where the minimum daily temperature falls below this value are referred to as ‘cold shocks’. The number of cold shocks is used by growers and advisors in assessing retardation of crops in their areas. However, this effect has not been tested explicitly. The aim of this work was to empirically assess effects of cold shock on pre-flower development of cotton plants. Cotton seedlings were grown in controlled-temperature glasshouses. Plants were transferred to cold chambers ranging from 5 to 22°C during the night period for durations from 3 to 10 days. Negative effects were not seen until plants had been exposed to at least 10 nights at 10°C, or for at least 5 nights at 5°C. When differences were generated it did not delay development to first square any more than 4 days, nor was the effect consistent. These differences translated into delays to first flower, but had little effect on plant morphology, or on dry weight measured soon after flowering. In one experiment, a significant reduction in leaf photosynthesis was measured at two times of day on the day after cold shock at 5°C. Improving understanding of the effects of temperature extremes on cotton growth and development will help in developing more functional decision-support tools and field management strategies.

Environmental control of potential yield of sunflower in the subtropics

A simple framework was used to analyse the determinants of potential yield of sunflower (Helianthus annuus L.) in a subtropical environment. The aim was to investigate the stability of the determinants crop duration, canopy light interception, radiation use efficiency (RUE), and harvest index (HI) at 2 sowing times and with 3 genotypes differing in crop maturity and stature. Crop growth, phenology, light interception, yield, prevailing temperature, and radiation were recorded and measured throughout the crop cycle. Significant differences in grain yield were found between the 2 sowings, but not among genotypes within each sowing. Mean yields (0% moisture) were 6 . 02 and 2 . 17 t/ha for the first sowing, on 13 September (S1), and the second sowing, on 5 March (S2), respectively. Exceptionally high yields in S1 were due to high biomass assimilation associated with the high radiation environment, high light interception owing to a greater leaf area index, and high RUE (1 . 47-1 . 62 g/MJ) across genotypes. It is proposed that the high RUE was caused by high levels of available nitrogen maintained during crop growth by frequent applications of fertiliser and sewage effluent as irrigation. In addition to differences in the radiation environment, the assimilate partitioned to grain was reduced in S2 associated with a reduction in the duration of grain-filling. Harvest index was 0 . 40 in S1 and 0 . 25 in S2. It is hypothesised that low minimum temperatures experienced in S2 reduced assimilate production and partitioning, causing premature maturation.

Measuring the Maturity of Developing Cotton Fibers using an Automated Polarized Light Microscopy Technique

Cotton fibers are trichome cells composed primarily of cellulose. Mature fibers have more cellulose and a greater degree of cell wall thickening, and perform better than less mature fibers during textile processing. An automated polarized light microscope instrument called Siro-Mat that measures cotton fiber cell wall thickening was employed to assess the maturity of developing fibers from single cotton fruit. Fruit were taken from the first fruiting branch and position on glasshouse grown Gossypium hirsutum L. (Upland) and G. barbadense L. (Pima) plants, sequentially harvested from 24 days postanthesis (dpa) at approximately four-day intervals up until approximately 50 dpa. The instrument assessed an average of 13,000 fiber snippets per fruit. Upland fibers matured at a slower rate than Pima fibers up to 35 dpa. However, after 45 dpa Upland fibers had achieved a higher average maturity (i.e. 0.99 birefringence maturity index (BMI), cf. 0.79 for Pima). For both species the uniformity of fiber maturity increased as fibers matured up until 35 dpa for Upland and 29 dpa for Pima (i.e. the BMI coefficient of variation decreased as BMI increased during fruit development). It is envisaged that SiroMat will be a useful tool in helping to understand and manage fiber maturity by characterizing the maturation dynamics of cultivars with different inherent fiber properties, and for cultivars subjected to different environmental and agronomic conditions.

Consequences of waterlogging in cotton and opportunities for mitigation of yield losses

Cotton is a major world crop that is notoriously susceptible to waterlogging damage, particularly when cultivated on fine-textured soils. However, damage is also exacerbated because of inadequate acclimation of roots to low oxygen levels, and secondary effects on shoots. Despite the commercial importance of cotton, very little has been published when compared with waterlogged cereals. This review provides a comprehensive view of the constraints on cotton in low-oxygen conditions, including absence of aerenchyma and the inadequacy of fermentation to overcome waterlogging damage. We emphasise the possibilities of improved tolerance through management practices, manipulation of hormone pathways and gene technologies to modify perception and response to low-oxygen environments.

Managing yields of high fruit retention in transgenic cotton (Gossypium hirsutum L.) using sowing date

Recently, genetically engineered (transgenic) cottons expressing genes from Bacillis thuringiensis (Bt) have been made available to cotton growers throughout the world. In Australia, cotton growers have access to Bt cotton that contains genes expressing the insecticidal proteins Cry1Ac and Cry2Ab (Bollgard II®). Bollgard II offers significant potential to reduce pesticide use for the control of major Lepidopteran pests (particularly Helicoverpa spp. in Australia). As a consequence of the improved insect control, retention of squares (flower buds) and young bolls is higher in Bollgard II varieties than in non-Bollgard varieties. A concern raised by Australian cotton growers is that in some regions, yield potential for Bollgard II may be limited because the demands of earlier high fruit retention reduce resources for continued growth and fruiting, thus leading to earlier maturity and reduced yield. Non-Bollgard crops with high early retention are known to mature earlier sometimes reducing yield. Three field experiments over three seasons, which varied sowing date and compared non-Bollgard II and Bollgard II cotton cultivars, were conducted to test the hypothesis that delaying sowing date in Bollgard II will increase canopy size (without delaying crop development) and alleviate the potential concerns for the effect of higher fruit retention reducing canopy size and the time to maturity, limiting the yield of Bollgard II. In non-Bollgard II crops, larger canopies resulting from early loss of fruit or apical meristem damage can support more fruit growth for longer, provided season length allows fruit to mature. Results showed that delayed sowing did not increase the yield of the Bollgard II cultivar through increased leaf area index at flowering compared with normal sowing dates. However, in comparison with the conventional cultivar, which had yields that became lower with later sowings, Bollgard II maintained its yield presumably through the shorter fruiting cycle (because of its consistently higher earlier fruit retention), allowing time to support growth of the same number of bolls as earlier sowings. Improvements in fibre quality were also recorded with later sowings for both cultivars. Varying sowing dates for Bollgard II in different production regions may offer opportunities for Australian growers to help optimise yield, fibre quality, and reduce risks associated with poor crop establishment when crops are sown too early.