Content and Composition of Dry Matter in Onion (Allium cepa L.) as Influenced by Developmental Stage at Time of Harvest and Long-term Storage

Some of the chemical changes inside the bulb of onions (Allium cepa L.) and the influence of various harvesting criteria on dry matter content and composition were studied during long-term storage. Onion weight, dry matter content, total N and the non-structural carbohydrates, glucose, fructose, sucrose and total fructans were examined. Significant (P<0.05) interseasonal differences were observed in the weight of the onions, dry matter content, glucose and total non-structural carbohydrates. Furthermore, the dry matter content and composition differed inside the onion bulbs depending on the length of the storage period. The stage of maturation at the time of harvest also significantly influenced the weight of the onions, the dry matter content in individual onions and the fructose content.     

Particle arrangement and internal porosity of coarse fragments affect water retention in stony soils

Information about water retention in stony soils lags behind due to methodological difficulties. We applied a new strategy to measure the water retention in soils with coarse fragments (CFs) and to get insights into the effect of CFs porosity on water retention. Water retention at zero, 10, and 150 m suction, bulk density, and the mass fraction of six particle size classes were measured in undisturbed blocks from soils with variable CFs contents, originating from three parent materials. The results showed that some soils contain porous CFs (2–250 mm) with a water holding capacity as high as the fine fraction (<2 mm). The water held in the suction range of 1–150 m in a soil with porous CFs was twice as high as in soils with non-porous CFs. Multilinear regressions revealed that both the water retention capacity at 1 m suction and in the range 1–150 m were more dependent on bulk density than on the fraction of CFs and fine particles. In the soil with porous CFs, there was no correlation between their fraction and soil water retention. These results show that the bulk water retention capacity of soils with CFs is underestimated when not considering the internal porosity of the CFs. A better understanding of the effect of the porosity of CFs on bulk soil porosity and water retention is important to propose suitable pedotransfer functions and refine physically-based hydraulic functions for stony soils.     

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

Canopy‐forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life‐history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta‐analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal‐associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life‐history stage. Major overlap (40%–43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal‐associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal‐associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal‐associated fish and fisheries.     

Scales in single root water uptake models: a review,analysis and synthesis

Scales in transport of water to roots are compared with the length and volume scales by using the concepts associated with the representative elementary volume (REV). The possibility of a mismatch between model scale and system scale when using a Darcy‐Buckingham‐based model to describe soil water transport to a single root is evaluated. In the absence of a mismatch, the replication requirements for evaluating the Darcy‐Buckingham‐based model near a single root are discussed by using a synthesis of the elementary scales involved, including those for soil, plant and roots, and of the measurement device. By using REV scales from lattice‐Boltzmann simulations, the effective half‐root mean distance and the available measurement techniques, the evaluation of Darcy‐based single root uptake models is possible in roughly 50% of the combinations of soil‐ and root‐system properties. On the basis of an assessment of the scale characterizing natural soil variability, the number of replicates required to assess the average root water uptake profile near a single root is large, and either requires miniaturization of the measurement methods for the hydraulic transport characteristics, or very homogeneous (artificial) growing media with little variability. Variability of water uptake per unit root length will increase the number of samples required.     

From unplanned to planned agricultural use: making an asset out of wastewater

Urban wastewater is increasingly used for agricultural production, particularly in those areas where access to fresh water resources is limiting. Depending on the prevailing institutional arrangements, this agricultural use is planned or unplanned. If planned, a general policy is to minimise health risks and environmental pollution, leading to an often centralised collection of the city’s sewage, followed by primary, secondary and further treatment until the prevalent discharge effluent use standards are met. If society can afford them, advanced treatment technologies are installed, backed by a well functioning institutional infrastructure. In contrast, in less prosperous countries the agricultural use of wastewater is driven by the high needs for water and the absence of affordable fresh water resources along with insufficient financial means to construct treatment systems and distribution networks that comply with the official regulations. Combined with a poor institutional framework, this results in unplanned and unguided direct or indirect use of raw, partially treated or diluted wastewater. In an effort to mitigate health and environmental problems, we propose using a reverse water chain design approach, in which the ultimate fate of the water is the basis for the design of conveyance and treatment facilities.     

Content of Free Amino Acids in Onion ( Allium cepa L.) as Influenced by the Stage of Development at Harvest and Long-term Storage

The changes in free amino acid (FAA) composition during long-term storage of onions ( Allium cepa L.) were investigated over a 3 year period. The influence of development at the time of harvest on the FAA composition of onions was investigated over a 2 year period. In addition, the composition of FAA in different morphological parts was analysed over a 1 year period. The most abundant amino acids were arginine and glutamine. The results indicated that the later the onions were harvested the lower the content of almost all the FAA in the dry matter. These differences in content were maintained throughout long-term storage. The percentage of FAA in the dry matter increased in relation to the centrality of leaves in the bulb but was independent of storage time.     

Management of insecticide resistance in Oriental fruit moth (Grapholita molesta; Lepidoptera: Tortricidae) populations from Ontario

The development of resistance in the Oriental fruit moth, Grapholita molesta (Busck) to organophosphorus (OP) insecticides (azinphos-methyl and phosmet) is a serious threat to the tender fruit industry in Ontario (50% crop losses in 1994). Resistance to carbamate insecticides and increased survival of field-collected moths at diagnostic concentrations of pyrethroids were widespread. As a result, four different treatment regimes were tested to manage resistance in G molesta, and the changes in resistance frequencies under each treatment regime were monitored from 1996 to 1999. The data indicated that the levels of resistance were significantly influenced by the various treatment regimes. The seasonal pattern of resistance was similar for all treatment regimes, in that resistance peaked in mid-season and declined in the late season. Levels of resistance in G molesta to OPs decreased from 55% to 14% and that to pyrethroids declined from 30% to 10% from 1996 to 1999 under a treatment regime consisting of endosulfan-organophosphate-pyrethroid rotation. Similarly, under a treatment regime implemented in commercial orchards (organophosphate-pyrethroid rotation), resistance to OP insecticides declined from 50% to 12% and resistance to pyrethroids evolved to around 16%. The overall data indicated that resistance was unstable; a strategy based on rotation of insecticides by class for each generation of G molesta was successful in managing resistance to both OP and pyrethroid insecticides. The rotational strategy has been widely adopted by growers and is applied to ca 85% of the acreage.