Preliminary modelling of sediment production and delivery in the Xihanshui River basin, Gansu, China

This paper outlines an analysis of the spatial distribution of sediment production, delivery and yield in the Xihanshui River basin, South Gansu, China, using the modelling tools of SedNet (Prosser et al., 2001). This model can assess the delivery efficiency to downstream locations, as well as identifying locations with high rates of sediment production. Preliminary model experiments assist understanding of the spatial dynamics of these sediment processes and evaluation of the effectiveness of soil conservation practices since the mid-1980s. Three scenario years (dry, average and wet) from the 1983–2005 record are identified and modelled, and land use and management are represented in the model to reflect known changes since the 1980s. Results show hillslope erosion to be a dominant source of sediment supply, causing the latter to decrease ten-fold between 1984 and 1997/2000. Estimated bank erosion and floodplain deposition rates are sensitive to parameter values, but bank erosion appears less sensitive than hillslope supply to rainfall. The model can be used to assess net changes in floodplain storage; for default parameters, floodplain deposition rates are 25–200 times the rates of bank erosion depending on the climate scenario. Comparing simulation results with measured sediment yields at the three gauging stations indicates encouraging agreement in 2000. In 1984 (the wet year), the model under-predicts, suggesting that additional unmodelled sediment production processes, especially mass movement and gully erosion, may be important in wet years. Mass movement inventory data could close the gap between the high yields measured in the wet scenario year and the estimated yield due to hillslope erosion alone. In 1997 (the dry year), the model over-predicts; this suggests that the land use change parameters required to reflect the effects of conservation may not have been sufficient, implying that conservation has been generally effective, and that evidence of declining sediment yield is not simply a reflection of drier conditions.     

米勒时间

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Effect of pH on Structural Changes in Perch Hemoglobin that Can Alter Redox Stability and Heme Affinity

pH can be manipulated to alter the oxidative stability of fish-based foods during storage. X-ray diffraction was used to investigate the ability of reduced pH to cause structural changes in fish hemoglobins that lead to enhanced oxidative degradation. Decreasing pH from 8.0 to 6.3 and 5.7 created a large channel for solvent entry into the heme crevice of perch hemoglobin beta chains. The proton-induced opening of this channel occurred between site CD3 and the heme-6-propionate. Solvent entry into the heme crevice can enhance metHb formation and hemin loss, processes that accelerate lipid oxidation. Reduced pH also decreased the distance between Ile at E11 in one of the alpha chains and the ligand above the heme iron atom. This sterically displaces O₂ and protonated O₂ which increases metHb formation. These studies demonstrate that pH reduction causes structural changes in perch hemoglobin which increase oxidative degradation of the heme pigment.     

Strengthening understanding and perceptions of mineral fertilizer use among smallholder farmers: evidence from collective trials in western Kenya

It is widely recognized that mineral fertilizers must play an important part in improving agricultural productivity in western Kenyan farming systems. This paper suggests that for this goal to be realized, farmers’ knowledge must be strengthened to improve their understanding of fertilizers and their use. We analyzed smallholder knowledge of fertilizers and nutrient management, and draw practical lessons from empirical collective fertilizer-response experiments. Data were gathered from the collective fertilizer-response trials, through focus group discussions, by participant observation, and via in-depth interviews representing 40 households. The collective trials showed that the application of nitrogen (N) or phosphorous (P) alone was insufficient to enhance yields in the study area. The response to P on the trial plots was mainly influenced by incidences of the parasitic Striga weed, by spatial variability or gradients in soil fertility of the experimental plots, and by interactions with N levels. These results inspired farmer to design and conduct experiments to compare crop performance with and without fertilizer, and between types of fertilizers, or responses on different soils. Participating farmers were able to differentiate types of fertilizer, and understood rates of application and the roles of respective fertilizers in nutrient supply. However, notions were broadly generated by unsteady yield responses when fertilizers were used across different fertility gradients, association with high cost (especially if recommended rates were to be applied), association of fertilizer use with hybrids and certain crops, historical factors, among other main aspects. We identified that strengthening fertilizer knowledge must be tailored within existing, albeit imperfect, systems of crop and animal husbandry. Farmers’ perceptions cannot be changed by promoting more fertilizer use alone, but may require a more basic approach that, for example, encourages farmer experimentation and practices to enhance soil properties such as carbon build-up in impoverished local soils.     

Effects of the nematode Phasmarhabditis hermaphrodita and of venom from the endoparasitic wasp Pimpla hypochondriaca on survival and food consumption of the pest slug Deroceras reticulatum; implications for novel biocontrol strategies

BACKGROUND: Controlling pests through disruption of biochemical pathways by physiologically active compounds/factors from animals and plants represents an expanding field of research. The authors investigated whether such factors in venom from the wasp Pimpla hypochondriaca (Retzius) can affect the viability and food consumption of the slug Deroceras reticulatum (Müller), and whether they can improve the efficacy of nematode-induced slug mortality. RESULTS: Exposure of slugs to 4 mL of water containing 500, 1000 and 5000 Phasmarhabditis hermaphrodita (Schneider) resulted in significant increases in mortality (with hazard ratios of 3.5, 3.9 and 5.8 respectively) and significant reductions in total food consumption and mean food consumption each day for 21 days. Injection of slugs with 4, 8 or 12 microL of P. hypochondriaca venom resulted in significant increases in mortality (with hazard ratios of 3.3, 4.5 and 9.0 respectively) and significant reductions in total food consumption compared with the controls. However, there was no significant effect of venom on the mean food consumption on individual days of the 21 day assay period, although significant reductions occurred for the 8 and 12 microL doses up to day 10. Injecting slugs with 4 microL of venom prior to exposure to 500 nematodes had no synergistic effect on either mortality or food consumption compared with either of the individual treatments. CONCLUSIONS: Pimpla hypochondriaca venom contains factors capable of killing and reducing food consumption by D. reticulatum. The utilization of these factors as components of integrated pest management strategies is discussed.     

Yield benefits of triticale traits for wheat under current and future climates

Triticale often out-yields wheat in both favourable and unfavourable growing conditions. Observed traits suggested for the higher yields in triticale include greater early vigour, a longer spike formation phase with same duration to flowering, reduced tillering, increased remobilization of carbohydrates to the grain, early vigorous root growth and higher transpiration use efficiency. To quantify the impact of these traits systematically across seasons and contrasting rainfall regions and soil types, these triticale traits were introduced into a wheat model (APSIM-Nwheat). The impact of each individual trait and their full combination was analysed in a simulation experiment for three Mediterranean growing environments, two contrasting soil types and long-term historical weather data. The simulated impact of these traits was compared with measured impacts from a range of field experiments across several environments. Simulated responses of various crop characteristics including yield, were in general similar to responses observed in wheat-triticale comparison field experiments across a large range of growing conditions. The simulation analysis indicated that the yield response to the incorporation of the triticale traits into wheat was positive, in both low and high yielding growing conditions, similar to measured differences, but the simulated benefit was on average lower than the range observed in data of triticale and wheat. This suggests that other traits might also be involved in higher-yielding triticale, or the magnitude of some of the traits may be underestimated in field experiments due to ‘trait by environment’ interactions. The simulation results suggest the highest yield benefit can be achieved from increasing transpiration use efficiency in wheat, but early vigour, remobilization of stem carbohydrates and early root growth also contribute positively to a yield increase in the different growing environments. The yield benefits from the triticale traits increased in the future climate change scenario in particular on soils with high water-holding capacity from contributions of increased early vigour, remobilization of stem carbohydrates and transpiration use efficiency, and remained stable on the lighter soils.     

Cover Image,Volume 73, Issue 11

The cover image, by Nicola K Richards et al., is based on the Research Article Genetic variation within species and haplotypes of the Wiseana (Lepidoptera: Hepialidae) complex and development of non‐sequenced based identification tools to aid field studies, DOI: 10.1002/ps.4620 . Photo Credit: Colin M. Ferguson, AgResearch‐ Invermay.

     

In vitro erythrocytic membrane effects of dibenzyl trisulfide, a secondary metabolite of Petiveria alliacea

We investigated the in vitro effect of dibenzyl trisulfide (DTS), a secondary metabolite of Petiveria alliacea, on erythrocyte elasticity, relaxation time and membrane morphology. Blood samples from 8 volunteers with hemoglobin AA were exposed to 100, 200, 400, 800 and 1000 ng/ml of DTS respectively and the elasticity and relaxation time measured. There were statistically significant, dose-dependent increases in elasticity and relaxation times. The changes in membrane morphology observed also increased with increased concentration of DTS. This suggests that DTS interaction with membrane protein resulted in increased elasticity, relaxation time and deformation of the erythrocyte membrane.     

Effects of Cultivation after Planting on Yields of Seed Cotton

Abstract

Experiments carried out over several seasons showed that, on a soil prone to crusting, cultivations after the establishment of a cotton crop only increased yields in a season of low rainfall. This yield increase appeared to have been due to enhanced entry into the soil of the limited effective rainfall. In one season of high rainfall, deep cultivation significantly reduced yields.