The use of measured water flows in furrow irrigation management — a case study in Swaziland

The use of measured water in controlling flows for the irrigation of sugarcane was found to be vital for the rehabilitation and management of surface irrigation on a 5000 ha sugarcane project. Methods of water delivery, measurement and control at Inyoni Yami Swaziland Irrigation Scheme (IYSIS) are described. Improvements to the irrigation, using existing methods of water measurement, were carried out over a period of four years. The lessons gained in this programme of improvements confirmed the benefits of using modulus gates which allow a constant, measured, discharge of water.     

Characterization of alfalfa (Medicago sativa L.) following in vitro selection for salt tolerance

Summary Alfalfa (Medicago sativa L.) is a valuable forage crop which is grown in areas of limited rainfall, high temperature and where the land is often salt affected. Seedlings of the commercial variety CUF 101 and the more salt tolerant breeding line CUF101-1S were used as explant material to produce tissue cultures for an in vitro screen for salt tolerance. Callus cultures were placed on a regeneration medium containing 0–350 mol m^-3 NaCl to establish the highest possible salt concentration that would allow buds to regenerate and survive as plantlets. Buds were regenerated in 250 mol m^-3 NaCl then isolated, grown to maturity and set seed. The response to salt tolerance in the short term was investigated by exposing 14-day-old seedlings to 200 mol m^-3 NaCl. Measurement of growth, survival, proline concentration and the activity of antioxidant enzymes were made after 14 days exposure to NaCl. One somaclone in particular (6R2IV) compared with the parent line showed increased salt tolerance, greater accumulation of proline and a greater increase in the antioxidant enzyme, glutathione reductase. A potentially important gene is pA9 which is known to be responsible for the production of a proline rich cell wall protein. Polymerase Chain Reaction (PCR) amplification of a region of the pA9 gene indicated that it was present in both tolerant and sensitive lines. Southern blotting has shown that the copy number of the pA9 was present as multiple copies in the tolerant clone compared with a single copy in the parents.Abbreviations GR glutathione reductase     

Domestic Sewage and Oil Spills in Streams: Effects on Edaphic Invertebrates in Flooded Forest, Manaus, Amazonas, Brazil

The influence of the aquatic environment on the terrestrial environment in areas subject to natural seasonal flooding has been little studied; especially lacking are studies that include anthropogenic impacts on these areas. Soil samples (including a superficial layer of litter) were collected between September 2000 and May 2001 on the banks of three streams in Manaus, Amazonas, Brazil in four seasons of the year, as determined by the flood pulse of the Rio Negro. The objectives of this study were to verify how an oil spill and urban sewage affect the abundance and richness of edaphic invertebrates on the stream banks and if these forms of pollution also influence the effect of the flood pulse on the natural community. Our results suggest reductions in the abundance and richness of edaphic invertebrates in the impacted areas and changes in the composition of edaphic invertebrate communities show a disturbance gradient from the banks of the unimpacted stream (Cristalino) to the banks of the stream that was impacted by the oil spill (Cururu), with more similar patterns occurring in impacted streams. The streams also showed effects of the flood pulse. Acarina, Entomobryidae, Formicidae, Staphylinidae and Carabidae were the only taxa that occurred in all three of the areas studied and in all of the sampling periods.     

Wheat basal crop coefficients determined by normalized difference vegetation index

Crop coefficient methodologies are widely used to estimate actual crop evapotranspiration (ET_c) for determining irrigation scheduling. Generalized crop coefficient curves presented in the literature are limited to providing estimates of ET_c for “optimum” crop condition within a field, which often need to be modified for local conditions and cultural practices, as well as adjusted for the variations from normal crop and weather conditions that might occur during a given growing season. Consequently, the uncertainties associated with generalized crop coefficients can result in ET_c estimates that are significantly different from actual ET_c, which could ultimately contribute to poor irrigation water management. Some important crop properties such as percent cover and leaf area index have been modeled with various vegetation indices (VIs), providing a means to quantify real-time crop variations from remotely-sensed VI observations. Limited research has also shown that VIs can be used to estimate the basal crop coefficient (K _cb) for several crops, including corn and cotton. The objective of this research was to develop a model for estimating K _cb values from observations of the normalized difference vegetation index (NDVI) for spring wheat. The K _cb data were derived from back-calculations of the FAO-56 dual crop coefficient procedures using field data obtained during two wheat experiments conducted during 1993–1994 and 1995–1996 in Maricopa, Arizona. The performance of the K _cb model for estimating ET_c was evaluated using data from a third wheat experiment in 1996–1997, also in Maricopa, Arizona. The K _cb was modeled as a function of a normalized quantity for NDVI, using a third-order polynomial regression relationship (r ²=0.90, n=232). The estimated seasonal ET_c for the 1996–1997 season agreed to within −33 mm (−5%) to 18 mm (3%) of measured ET_c. However, the mean absolute percent difference between the estimated and measured daily ET_c varied from 9% to 10%, which was similar to the 10% variation for K _cb that was unexplained by NDVI. The preliminary evaluation suggests that remotely-sensed NDVI observations could provide real-time K _cb estimates for determining the actual wheat ET_c during the growing season.     

Competition between invasive earthworms (Amynthas corticis, Megascolecidae) and native North American millipedes (Pseudopolydesmus erasus, Polydesmidae): Effects on carbon cycling and soil structure

Invasive earthworms can have significant impacts on C dynamics through their feeding, burrowing, and casting activities, including the protection of C in microaggregates and alteration of soil respiration. European earthworm invasion is known to affect soil micro- and mesofauna, but little is known about impacts of invasive earthworms on other soil macrofauna. Asian earthworms (Amynthas spp.) are increasingly being reported in the southern Appalachian Mountains in southeastern North America. This region is home to a diverse assemblage of native millipedes, many of which share niches with earthworm species. This situation indicates potential for earthworm-millipede competition in areas subject to Amynthas invasion.In a laboratory microcosm experiment, we used two ¹³C enriched food sources (red oak, Quercus rubra, and eastern hemlock, Tsuga canadensis) to assess food preferences of millipedes (Pseudopolydesmus erasus), to determine the effects of millipedes and earthworms (Amynthas corticis) on soil structure, and to ascertain the nature and extent of the interactions between earthworms and millipedes. Millipedes consumed both litter species and preferred red oak litter over eastern hemlock litter. Mortality and growth of millipedes were not affected by earthworm presence during the course of the experiment, but millipedes assimilated much less litter-derived C when earthworms were present.Fauna and litter treatments had significant effects on soil respiration. Millipedes alone reduced CO₂ efflux from microcosms relative to no fauna controls, whereas earthworms alone and together with millipedes increased respiration, relative to the no fauna treatment. CO₂ derived from fresh litter was repressed by the presence of macrofauna. The presence of red oak litter increased CO₂ efflux considerably, compared to hemlock litter treatments.Millipedes, earthworms, and both together reduced particulate organic matter. Additionally, earthworms created significant shifts in soil aggregates from the 2000-250 and 250-53 μm fractions to the >2000 μm size class. Earthworm-induced soil aggregation was lessened in the 0-2 cm layer in the presence of millipedes. Earthworms translocated litter-derived C to soil throughout the microcosm.Our results suggest that invasion of ecosystems by A. corticis in the southern Appalachian Mountains is unlikely to be limited by litter species and these earthworms are likely to compete directly for food resources with native millipedes. Widespread invasion could cause a net loss of C due to increased respiration rates, but this may be offset by C protected in water-stable soil aggregates.     

Phosphate fractionation and spatial patterning in ancient ruins: A case study from Yucatan

As time passes, phosphorus (P) in soils tends to become more tightly bound with minerals. Phosphate fractionation enables the measurement of loosely versus tightly bound P. Archaeologists have used P fractionation as a chronometric technique: older soils should have greater proportions of P tightly bound with minerals. Research at Chunchucmil, a large Maya ruin in Yucatan, Mexico, has used extractable P concentrations and other lines of evidence to investigate ancient uses of space. Because contemporary Maya villagers use the land among the Chunchucmil ruins in a number of ways, and because the ancient land surfaces are neither sealed nor deeply buried, we used P fractionation to determine whether geochemical signatures of activities such as gardening resulted from ancient or modern inhabitants. The fractionation results at Chunchucmil are unusual in comparison to studies from other sites. Furthermore, there are strong correlations between the sum of P fractions and carbonate. We discuss potential explanations for these patterns in P fractionation data. These explanations consider local pedology, differential length of ancient occupation, and localized dumping of the byproducts of maize processing. To examine the chemical signatures of maize processing, specifically soaking maize in lime water, contemporary samples of sediments and residues from this activity were analyzed. Our results suggest that dumping water from maize soaking provides a potential explanation for the ancient P patterns.     

People, values, and woodlands: A field report ofemergent themes in interdisciplinary research in Zimbabwe

The Value of Trees project, funded bythe International Development Research Council ofCanada (IDRC), supported the joint efforts of theUniversity of Alberta and the University of Zimbabweto investigate the economic costs and benefitsassociated with trees and forests in the small holderfarming sector in Zimbabwe. The Value of Trees project provided funding for graduate students andfaculty from the two participating universities tocarry out studies in the disciplines of forestry,agricultural economics, and sociology in order toprovide policy recommendations regarding the role ofwoodlands in sustainable small holder farming in acontext where agricultural production appears to putincreasing stress on woodlands. The numerous projectsincluded such topics as the following: the use offuelwood under conditions of scarcity, tree tenure andlocal institutions in woodland use and sustainability,gender and wealth as related to tree planting andconservation, time preferences in natural resourceconsumption, ownership and economic impact ofeucalyptus woodlots, cultural and economic valuesassociated with woodlands, and uses and conflictsrelating to woodlands across different land categoriessuch as resettlement land and state forests. Manyother studies were not funded by, but were associatedwith Value of Trees. The findings fall withintwo broad categories. The first set includes thosedirectly related to generating values for differentaspects of the woodlands, particularly from theperspectives of rural households. The main finding isthat despite being highly valued by local people forboth economic and social reasons, woodlands are rankedlower in importance by local farmers than agriculturalland. The second set of findings relates to thecomplexities of the social system of the woodlands.Local institutions, history, resource conflicts, andtenure issues emerge as key to understanding the waythat people interact with the woodlands. Finally,local people have valuable knowledge and strategies tooffer in the design of sustainable management. Thepolicy implications of these findings for Zimbabwe arethat economic incentives could be important in asustainable woodlands strategy, but that anysuccessful program must incorporate an understandingof the profoundly complex and at times contradictoryhuman dynamics of woodland use and values.     

Noble gas-actinide compounds: complexation of the CUO molecule by Ar, Kr, and Xe atoms in noble gas matrices

The CUO molecule, formed from the reaction of laser-ablated U atoms with CO in a noble gas, exhibits very different stretching frequencies in a solid argon matrix [804.3 and 852.5 wave numbers (cm(-1))] than in a solid neon matrix (872.2 and 1047.3 cm(-1)). Related experiments in a matrix consisting of 1% argon in neon suggest that the argon atoms are interacting directly with the CUO molecule. Relativistic density functional calculations predict that CUO can bind directly to one argon atom (U-Ar = 3.16 angstroms; binding energy = 3.2 kilocalories per mole), accompanied by a change in the ground state from a singlet to a triplet. Our experimental and theoretical results also suggest that multiple argon atoms can bind to a single CUO molecule.     

Comparison of Estimated Costs and Benefits of Site-Specific Versus Uniform Management for the Bean Leaf Beetle in Soybean

Six soybean, Glycine max (L.) Merrill, fields were examined to compare estimated costs and benefits for uniform and site-specific management (SSM) programs for the bean leaf beetle, Cerotoma trifurcata (Forster). Beetle counts and soybean yield were field-collected, insecticide and sampling costs were estimated. In five fields, site-specific management produced only slightly greater return. The inclusion of sampling costs in each scenario resulted in higher return for the uniform scenario. The uniform management scenario estimated pest pressure as well as the site-specific scenario when beetle populations were high or low. In one field with moderate pest pressure, the SSM scenario would have increased insecticide use. The estimations in this study are based on hypothetical scenarios and the application equipment to target insecticides based on map coordinates is not readily available. The economic estimations provide examples of current limitations of site-specific management that need to be addressed before this technology becomes valuable for soybean insect management.     

Conjunctive representation of position, direction, and velocity in entorhinal cortex

Grid cells in the medial entorhinal cortex (MEC) are part of an environment-independent spatial coordinate system. To determine how information about location, direction, and distance is integrated in the grid-cell network, we recorded from each principal cell layer of MEC in rats that explored two-dimensional environments. Whereas layer II was predominated by grid cells, grid cells colocalized with head-direction cells and conjunctive grid x head-direction cells in the deeper layers. All cell types were modulated by running speed. The conjunction of positional, directional, and translational information in a single MEC cell type may enable grid coordinates to be updated during self-motion-based navigation.