Maize ethanol feedstock production and net energy value as affected by climate variability and crop management practices

Ethanol from various plant resources, especially maize, is increasingly being used as a substitute for fossil fuels. The production potential of ethanol from maize varies with weather and climatic conditions and crop management practices. The merits and prospects of ethanol production have been evaluated based on its impact on greenhouse gas emissions, economic viability and national energy security. The net energy value (NEV), i.e. the output energy after all non-renewable energy inputs have been accounted for, is a measure of energy gain. At the same time, the NEV can be an indicator for the long-term sustainability of bio-ethanol production, regardless of other conditions e.g. climate change scenarios, global trade restrictions, or local variability in natural resources such as water availability. Crop management practices directly affect the NEV of ethanol. Moreover, both crop management practices and climate variability affect the NEV through the grain yield. The objective of this study was to assess the impact of crop management practices and climate variability on grain yield of maize for ethanol production and ethanol NEV for conditions that represent the southeastern USA. Maize grain yield was simulated with the dynamic crop growth model CSM–CERES–Maize and ethanol NEV was calculated using the simulated yield levels and crop management practices. The simulations were conducted for conditions representing Mitchell County, Georgia, USA, using weather data from 1939 to 2006 and local soil profile information. The impact of irrigation, nitrogen fertilizer, planting date and El Niño Southern Oscillation (ENSO) phases were determined for the maize cultivars DeKalb DKC 61-72 (RR2), Pioneer 31D58 and Pioneer 31G98. Crop management practices and ENSO phase had a significant impact on ethanol feedstock production and NEV. The NEV of ethanol produced from irrigated maize was more than two times higher and varied less than the NEV of ethanol from rainfed maize. NEV of ethanol produced from maize grown during La Niña years was significantly higher than maize grown during El Niño years, both under rainfed and irrigated conditions. This study showed the importance of crop management practices and climate variability on ethanol feedstock productivity and long-term energy sustainability as assessed by the NEV. We discuss methods of implementing the findings of this study in practical farming e.g. through market mechanisms and governmental initiatives.     

Psychological Factors Influencing Farmers’ Intention to Adopt Agroforestry: A Structural Equation Modeling Approach

ABSTRACT

The biophysical characteristics of the farm and farmers’ socioeconomic factors have been used to explain adoption of technologies in Africa. However, agricultural technology adoption requires that we also understand the psychological factors that can encourage or discourage farmer adoption of technologies. The aim of this article is to assess the psychological drivers of farmers’ intentions to adopt agroforestry technologies on their farms. We obtained data from 400 smallholder farmers in the Mt. Elgon region of Uganda. The Theory of Planned Behavior was used as the main framework. Quantitative data were analyzed using structural equation modeling to assess the impact of a set of psychological factors on farmers’ intention to integrate trees in coffee. The intention of farmers to integrate trees in coffee plantations was mainly driven by their evaluation of the benefits of shaded coffee (attitude) followed by beliefs about their own capability (perceived behavioral control). However, social pressure (subjective norm) was insignificant, implying that smallholder farmers tend to deny the influence of other people’s behavior on their actions. Therefore, farmers’ positive evaluation of shading coffee and the perceived capability to overcome tree planting barriers reinforced their intention to integrate trees in coffee. This renders attitude and perceived behavioral control as reliable predictors of farmer tree planting behavior, especially in the context of developing countries.     

Modeling seasonal dynamics of small fish cohorts in fluctuating freshwater marsh landscapes

Small-bodied fishes constitute an important assemblage in many wetlands. In wetlands that dry periodically except for small permanent waterbodies, these fishes are quick to respond to change and can undergo large fluctuations in numbers and biomasses. An important aspect of landscapes that are mixtures of marsh and permanent waterbodies is that high rates of biomass production occur in the marshes during flooding phases, while the permanent waterbodies serve as refuges for many biotic components during the dry phases. The temporal and spatial dynamics of the small fishes are ecologically important, as these fishes provide a crucial food base for higher trophic levels, such as wading birds. We develop a simple model that is analytically tractable, describing the main processes of the spatio-temporal dynamics of a population of small-bodied fish in a seasonal wetland environment, consisting of marsh and permanent waterbodies. The population expands into newly flooded areas during the wet season and contracts during declining water levels in the dry season. If the marsh dries completely during these times (a drydown), the fish need refuge in permanent waterbodies. At least three new and general conclusions arise from the model: (1) there is an optimal rate at which fish should expand into a newly flooding area to maximize population production; (2) there is also a fluctuation amplitude of water level that maximizes fish production, and (3) there is an upper limit on the number of fish that can reach a permanent waterbody during a drydown, no matter how large the marsh surface area is that drains into the waterbody. Because water levels can be manipulated in many wetlands, it is useful to have an understanding of the role of these fluctuations.     

Insecticidal activity and mode of action of 2,4‐diaminopyrimidines

Three 2,4‐diaminopyrimidines were tested against several insect species. They were active against lepidopteran pests with LC₅₀ values <3 mg liter⁻¹ for most species tested. They were also active against two‐spotted spider mite, Tetranychus urticae, (LC₅₀ 10–40 mg liter⁻¹). Folinate, but not hypoxanthine or thymidine was found to be an effective rescue agent, requiring a concentration of 100 mg liter⁻¹ diet to rescue half of the intoxicated larvae. The results confirm dihydrofolate reductase to be the site of action for these insecticides and are consistent with the mode of action of folinate rescue in mammals. © 2000 Society of Chemical Industry     

Development,evaluation and genetic analysis of sulfosulfuron herbicide resistance in sorghum

Herbicide tolerant varieties in combination with herbicide seed treatments can be used to manage Striga. However, there are no herbicide resistant sorghum varieties in Kenya. The objectives of this study, therefore, were to develop sulfosulfuron resistance in sorghum, to determine the level of resistance in resultant herbicide tolerant mutants, and to determine the genetic inheritance of herbicide tolerance in sorghum. Five ethyl methane sulphonate (EMS)-derived sulfosulfuron tolerant mutants (designated hb6, hb8, hb12, hb56, and hb462) were identified and selfed to M4 generation. Varying rates of sulfosulfuron, either as a spray or seed coat, were applied to determine the level of tolerance of the mutant lines. Mutant lines were also crossed with the wild-type Seredo and among themselves to determine mode of inheritance. Results showed that the susceptible wild-type Seredo was killed at the lowest herbicide rates of 0.5 g ha^-1 and 1 g ha^-1 sulfosulfuron. Dry matter from the spraying and seed coating experiments showed mutants to be up to 170 times more resistant to sulfosulfuron than the wild-type. The LD₅₀ values indicated a general trend of hb46 > hb12 > hb462 ~ hb56 > hb8 for level of tolerance under both spraying and seed coating experiments. The F₂ progeny of mutant X wild-type crosses segregated in a 1:2:1 fashion for resistant, intermediate, and susceptible, indicating semi-dominant inheritance. Intercrosses between mutant lines did not segregate for resistance in the F₂ generation indicating the same mutation could be responsible for the tolerance in all five mutants.