A perspective on the measurement of time in plant disease epidemiology

The growth and development of plant pathogens and their hosts generally respond strongly to the temperature of their environment. However, most studies of plant pathology record pathogen/host measurements against physical time (e.g. hours or days) rather than thermal time (e.g. degree-days or degree-hours). This confounds the comparison of epidemiological measurements across experiments and limits the value of the scientific literature

SE—Structures and Environment

Two optimal control strategies for carbon dioxide (CO2) enrichment in greenhouse tomato crops have been developed. One uses pure CO2 from a storage tank and the other uses CO2 contained in the exhaust gases of boilers burning natural gas. The optimal strategies maximize the financial margin between crop value and the combined costs of the CO2 used for enrichment and the natural gas used for heating. In this paper, the strategy for optimal control using pure CO2 is presented and compared with strategies used by growers. The optimal strategy for enrichment with exhaust gas derived CO2 is presented in an accompanying paper. Simulations show that at a cost of £0.09 kg-1 for pure CO2 and £0.10 m-3 for natural gas, the optimal enrichment strategy would increase the annual margin of crop value over CO2 and heating costs by £4.6 m-2 (27%) compared to a basic control strategy of enrichment to a concentration of 1000 v.p.m. (parts per million by volume) when ventilators are < 5% open, otherwise enrichment to 350 v.p.m. The optimal CO2 concentration was expressed as an algebraic function of solar radiation, wind speed and ventilator opening angle, and so enabled a quasi-optimal value to be obtained using variables measured by greenhouse environmental controllers. The quasi-optimal equation, with coefficients averaged from simulations over 4 years, gave an increased margin over the basic control strategy of £4.4 m-2 (26%). © 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved

SE—Structures and Environment

Two optimal control strategies for carbon dioxide (CO2) enrichment in greenhouse tomato crops have been developed. One uses pure CO2 from a storage tank and the other uses CO2 contained in the exhaust gases of boilers burning natural gas. The optimal strategies maximize the financial margin between crop value and the combined costs of the CO2 used for enrichment and the natural gas used for heating. In this paper, the strategy for optimal control using pure CO2 is presented and compared with strategies used by growers. The optimal strategy for enrichment with exhaust gas derived CO2 is presented in an accompanying paper. Simulations show that at a cost of £0.09 kg-1 for pure CO2 and £0.10 m-3 for natural gas, the optimal enrichment strategy would increase the annual margin of crop value over CO2 and heating costs by £4.6 m-2 (27%) compared to a basic control strategy of enrichment to a concentration of 1000 v.p.m. (parts per million by volume) when ventilators are < 5% open, otherwise enrichment to 350 v.p.m. The optimal CO2 concentration was expressed as an algebraic function of solar radiation, wind speed and ventilator opening angle, and so enabled a quasi-optimal value to be obtained using variables measured by greenhouse environmental controllers. The quasi-optimal equation, with coefficients averaged from simulations over 4 years, gave an increased margin over the basic control strategy of £4.4 m-2 (26%). © 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved

Study on Light Interception and Biomass Production of Different Cotton Cultivars

Identifying the characteristics of light interception and utilization is of great significance for improving the potential photosynthetic activity of plants. The present research investigates the differences in absorbing and converting photosynthetically active radiation (PAR) among various cotton cultivars. Field experiments were conducted in 2012, 2013 and 2014 in Anyang, Henan, China. Ten cultivars with different maturity and plant architectures were planted at a density of 60,000 plants ha-1 in randomized blocks, with three replicates. The spatial distribution of light in canopy was measured and quantified with a geo-statistical method, according to which the cumulative amount of intercepted radiation was calculated by Simpson 3/8 rules. Finally, light interception was analyzed in association with the biomass accumulation of different cultivars. The key results were: (1) late-maturing varieties with an incompact plant architecture captured more solar radiation throughout the whole growth period than middle varieties with columnar architecture and even more than early varieties with compact architecture, and they produced more biomass; (2) the highest PAR interception ratio and the maximum biomass accumulation rate occurred during the blossoming and boll-forming stage, when leaf area index (LAI) reached its peak; (3) the distribution within the canopy presented a significant spatial heterogeneity, and at late growing stage, the PAR was mainly intercepted by upper canopies in incompact-type plant communities, but was more homogeneous in columnar-type plants; however, the majority of radiation was transmitted through the canopy in compact-type colonies; (4) there was not a consistent variation relationship between the cumulative intercepted PAR (iPAR) and biomass among these cultivars over the three years of the study. Based on these results, we attempted to clarify the distinction in light spatial distribution within different canopies and the patterns of PAR interception in diverse cotton cultivars with different hereditary characters, thereby providing a significant basis for researchers to select cultivars with appropriate growth period and optimal plant architecture for improvement of light interception and utilization