A mathematical programming model of a crop-livestock farm system

A whole-farm mathematical programming model has been built for dryland crop-livestock farms in Western Australia. The multidisciplinary approach used for model building is presented and the resulting model structure is described. It is a mixed integer programming model which represents, in some detail, the biological, technological and financial relationships of the farming system and stresses the interdependencies of enterprises. The model is used to investigate the extent to which positive interactions between different enterprises influence the optimal farm plan. The management issue considered is the division of land between crop and pasture production. It is concluded that, for the farming system considered, interactions do have an influence on profit and the optimal farm plan.     

Effect of protein source and level on growth and performance of the captive freshwater prawn,Macrobrachium rosenbergii

Growth, feed conversion and survival were determined for juvenile Macrobrachium rosenbergii held in tanks under semi-controlled environmental conditions. Feeding trials incorporated water-stable diets at three levels of protein (15, 25 and 35%). The principal protein source combinations consisted either of soybean and tuna meal, or of soybean, tuna and shrimp meal. In a 244-day comparison of these diets, higher protein content produced larger prawns (P < 0.01), but differences between sources were not significant. No significant differences existed between feed conversion ratios (range 1.36–1.72) or percentage survival (range 90.3–93.6%). Trials of several other diets were also conducted, including soybean and Tilapia meal, and copra and Tilapia meal (25% protein level) as principal protein source combinations. After 167 days on these diets, growth was inferior to that obtained with soybean and tuna meal or soybean, tuna and shrimp meal combinations. No significant differences existed between feed conversion ratios or percentages of survival.For the 244 days, a control group of prawns received no formulated diet. Growth and survival in this group during the first 110 days suggested that naturally occurring algae contributed substantially to the prawns' nutrition.Mean prawn length after 244 days on the best diet (35% protein from soybean and tuna meal) was 73 mm, and growth rate was equivalent to that achieved under pilot pond conditions.     

Cell-mediated and humoral immune response to Mycoplasma hyopneumoniae in pigs enhanced by dextran sulfate

The effect of dextran sulfate (DS), known to be cytotoxic to macrophages, on the cell-mediated and humoral immune response to nonviable Mycoplasma hyopneumoniae in pigs was investigated. The cell-mediated immune response was determined by means of lymphocyte transformation a test, using uptake of [3H]thymidine in a microculture system and the humoral immune response by means of a microplate complement-fixation test. Peripheral blood lymphocytes from pigs vaccinated with nonviable M hyopneumoniae and DS incorporated substantially more [3H]thymidine than did those from pigs given Mycoplasma or DS alone. The transformation of lymphocytes from M hyopneumoniae-DS vaccinated pigs was enhanced when M hyopneumoniae cells used in the assay system were heated at 60 C for 30 minutes. Similarly prepared M flocculare and M hyorhinis cells also stimulated lymphocytes from M hyopneumoniae-DS vaccinated pigs, but not nearly as great as when M hyopneumoniae cells were used. The humoral antibody response and the cell-mediated immune response to nonviable M hyopneumoniae was markedly enhanced by DS. Pigs were vaccinated with nonviable M hyopneumoniae and/or DS 4 times and challenge exposed intratracheally with viable M hyopneumoniae. Pigs vaccinated with M hyopneumoniae and DS had less severe pneumonia than did nonvaccinated pigs.     

Stress wave sorting of red maple logs for structural quality

Existing log grading procedures in the United States make only visual assessments of log quality. These procedures do not incorporate estimates of the modulus of elasticity (MOE) of logs. It is questionable whether the visual grading procedures currently used for logs adequately assess the potential quality of structural products manufactured from them, especially those for which MOE is of primary concern. The purpose of this study was to investigate the use of stress wave nondestructive evaluation techniques to sort red maple logs for the potential quality of lumber obtained from them. Ninety-five red maple logs were nondestructively evaluated using longitudinal stress wave techniques and sorted into four stress wave grades. The logs were then sawn into cants and lumber. The same procedure was used to obtain stress wave times in the cants and lumber. The lumber specimens were then dried and graded using a transverse vibration technique. The results of this study showed that good relationships existed between stress wave times measured in logs, cants, and the lumber produced from the logs. It was found that log stress wave grades have positive relationships with the lumber grades. Logs with high stress wave grades produced high-grade lumber. These findings indicate that the longitudinal stress wave technique has potential in sorting logs and cants for the production of high MOE products.The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright.     

Leaf-trait variation explained by the hypothesis that plants maximize their canopy carbon export over the lifespan of leaves

Measured values of four key leaf traits (leaf area per unit mass, nitrogen concentration, photosynthetic capacity, leaf lifespan) co-vary consistently within and among diverse biomes, suggesting convergent evolution across species. The same leaf traits co-vary consistently with the environmental conditions (light intensity, carbon-dioxide concentration, nitrogen supply) prevailing during leaf development. No existing theory satisfactorily explains all of these trends. Here, using a simple model of the carbon-nitrogen economy of trees, we show that global leaf-trait relationships and leaf responses to environmental conditions can be explained by the optimization hypothesis (MAXX) that plants maximize the total amount of carbon exported from their canopies over the lifespan of leaves. Incorporating MAXX into larger-scale vegetation models may improve their consistency with global leaf-trait relationships, and enhance their ability to predict how global terrestrial productivity and carbon sequestration respond to environmental change.     

Variability of trace metal concentrations in Jeffrey pine (Pinus jeffreyi) tree rings from the Tahoe Basin, California, USA

Trace metal accumulation in tree rings of Jeffrey pines (Pinus jeffreyi) from the Lake Tahoe basin (Sierra Nevada, CA, USA) was determined using high resolution inductively coupled plasma mass spectrometry (HR-ICP–MS). The objectives of this study were (1) to establish baseline values for aluminium (Al), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), strontium (Sr), cadmium (Cd), barium (Ba), and lead (Pb); (2) to investigate the intra-tree and inter-tree variability of these trace metals, and (3) to assess differences in metal concentrations related to automobile traffic. Two field collection sites were selected with similar ecologic attributes, one proximal to a heavily traveled highway, and the other isolated from any local source of auto emissions. At each site two trees with similar features were selected, and two increment cores collected from each tree. Cores were cross-dated, cleaned of contamination, dissected into 5-year increments, ashed, and acid digested, before analysis by HR-ICP–MS. Time series spanning 191–326 years were developed for the 12 trace metals. Variability was high within and between trees, most likely because of physiologic mechanisms for element sequestration and allocation. The best intra-tree correlation was found for Ba, Sr, Mn, and Co; of these elements, Co showed an overall increase over time, whereas Sr and Ba displayed an opposite trend, and Mn fluctuated over time. Mean Co concentration at the near-highway site was higher, whereas mean Sr, Ba, and Mn concentrations were lower, than at the control site.     

A thermogravimetric study of the pyrolysis of the bark and chemically-modified bark of jack pine,pinus banksiana lamb

The pyrolysis of native jack pine bark has been studied from 200 to 340°C by thermogravimetric (TG), and isothermal weight-loss methods. The effects of particle size, solvent extraction and additions of zinc (II) and iron (III) chlorides on the pyrolysis behaviour have also been examined. The bark was characterized by infrared spectroscopy and low-temperature gas adsorption. Residues were analysed for CHN contents and structural changes which occurred on heating were examined by optical and scanning electron microscopy. The TG characteristics were not affected by solvent extraction or particle size variation while the metal chloride additions inhibited the loss of volatile materials from the bark probably by stabilizing chemical bonding in the bark components. Isothermal decomposition data were found to fit established kinetic expressions associated with inorganic decompositions. The physical mechanics of pyrolysis have been interpreted on the assumption that pyrolysis is initiated through the formation of planes of lateral strain which are sites for decomposition and which decrease in number inversely with time. It is suggested that these sites are produced by an oxidation mechanism which may be rate-controlling in the pyrolysis. This hypothesis is supported by the observation that the data fit a reaction rate compensation curve, often associated with oxidation processes but more generally with heterogeneous catalytic reactions. The compensation curve also relates the kinetic parameters found by other workers for a large variety of wood-derived materials.     

Modelling the influence of site and weed competition on juvenile modulus of elasticity in Pinus radiata across broad environmental gradients

Data from a nationwide set of Pinus radiata D. Don plots established at a range of conventional stand densities were analysed at age 6 to (i) determine how environment and competition from weeds influence dynamic modulus of elasticity (E) of the lower stem base, (ii) develop a predictive multiple regression model of E for basal stemwood and (iii) identify significant direct and indirect environmental influences (through stem slenderness) on E using path analysis.Site had a highly significant (P < 0.001) influence on E, which exhibited a 3-fold range from 1.6 to 5.3 GPa, across 30 sites. When compared to the weed-free controls, weed competition had a significant (P < 0.0001) and substantial effect on E, increasing values by on average 16% (2.76 GPa vs. 2.38 GPa).The positive linear relationship between stem slenderness (determined as tree height/ground-line tree diameter) and E was by far the strongest relationship (R² = 0.71; P < 0.001) among the 20 variables that were significantly related to E. A multiple regression model that included stem slenderness, mean minimum air temperature in mid-autumn, T_min, as positive linear relationships and net nitrogen (N) mineralisation in a negative linear form accounted for 86% of the variance in E. A cross-validation indicated that this model was stable and unbiased, with the validation accounting for 82% of the variance in E. The final path analysis model included T_min, net N mineralisation, below canopy solar radiation and stem slenderness as significant (P < 0.05) direct influences on E. Below canopy radiation, maximum air temperature during mid-summer, soil total phosphorus and carbon:nitrogen ratio were indirectly associated with E through their significant (P < 0.05) direct relationship with stem slenderness.These results provide considerable insight into how environment regulates E of juvenile P. radiata. Low fertility sites that have warm air temperatures and either a high canopy leaf area index, or high levels of woody weed competition, are most likely to produce trees with high stem slenderness and high E. Conversely, sites that are cool over summer and autumn and high in fertility, with low levels of intra- or inter-specific competition for light are likely to produce trees with low stem slenderness and low E.