Use of simulation models to evaluate irrigation performance including water productivity, risk and system analyses

 Worsening water scarcity will increase pressure to use water more productively. In the classical view of irrigation research, some important aspects are often ignored: the total water balance approach, productivity of water, food security, and irrigation-system level analyses. These four approaches were evaluated using a detailed agro-hydrological model applied to an irrigation system in western Turkey. Emphasis was placed on the two dominant crops in the area: cotton and grapes. According to the classical point of view, the only result would be to irrigate the cotton with 1000 mm and the grapes with 800 mm. From the water productivity point of view, however, the water productivity of grapes appeared to be maximal without any irrigation; while for the cotton, irrigation at 600 mm maximizes water productivity. To minimize risks and increase yield stability, grapes perform better than cotton. Finally, from the irrigation system point of view, decisions can be made about the desirable cropping pattern and the distribution of water between crops. With limited amounts of water available for irrigation, a cropping pattern consisting mainly of grapes is desired; while with higher water availability, a mixture of cotton and grapes is preferable. The methods presented provide a clear methodology with which to achieve the most productive use of water. Received: 3 June 1999     

Influence of soil physicochemical properties, particle size fractions and mineralogy on the leaching potentials of arsenic and antimony in abandoned mine soils

At abandoned mine sites, arsenic (As)- and antimony (Sb)-enriched soils are often disposed of through onsite burial or capping. In highly weathered mine sites, the mobility of As and Sb is typically controlled by iron (Fe)(Ⅲ)/Fe(Ⅱ) phases; thus, the suitability of such disposal methods and appropriate testing techniques are questionable. In the present study, leaching potentials of As and Sb were examined using the toxicity characteristic leaching procedure (TCLP), waste extraction test (WET), and WET-extended procedure (WET-EXT) at three abandoned mine site soils in Australia. The leached concentration of As regularly exceeded USEPA criteria (5 mg L^-1). The highest leached concentrations of As and Sb were observed in the finest particle size fraction (< 0.053 mm) by WET-EXT (1 040 mg L^-1 for As and 21.10 mg L^-1 for Sb) followed by WET (800 mg L^-1 for As and 20.90 mg L^-1 for Sb). The TCLP method resulted in the lowest concentrations of leached As (0.000 9 mg L^-1) and Sb (0.000 3 mg L^-1). Crystalline and amorphous As-bearing Fe oxides were the main phases in the soils studied. However, the best correlations of leached As determined by TCLP (0.832), WET (0.944), and WET-EXT (0.961) were found with the non-specifically sorbed (NS1) As fraction. The mineralogical and sequential extraction data clearly indicate the dominant role of Fe geochemistry in controlling leachability of As and Sb. The TCLP method was unlikely to be suitable for assessing leachability, as it exhibited no relationship with leachable Fe and substantially lower leached As and Sb than the other two methods. Given the high to extremely high leachable As and Sb concentrations, most of the soil samples would not be recommended for placement in capping works, old shafts, or reduction systems (e.g., collection in drainage basins).     

Leaf physiology and morphology of Castanea dentata (Marsh.) Borkh., Castanea mollissima Blume,and three backcross breeding generations planted in the southern Appalachians,USA

Backcross breeding programs have been used to transfer disease resistance and other traits from one forest tree species to another in order to meet restoration objectives. Evaluating the field performance of such material is critical for determining the success of breeding programs. In eastern North America, The American Chestnut Foundation has a backcross breeding program that uses Chinese chestnut (Castanea mollissima Blume) to introduce resistance of the fungal pathogen chestnut blight [Cryphonectria parasitica (Murr.) Barr.] to the native American chestnut [Castanea dentata (Marsh.) Borkh.]. We compared physiological and morphological characteristics among seedlings of American chestnut, Chinese chestnut, and BC₁F₃, BC₂F₃, and BC₃F₃ hybrid chestnuts during their fourth growing season after field-planting. American chestnut and the BC₃F₃ breeding generation displayed photosynthetic light-response curves that were similar to each other but different from Chinese chestnut. Rates of photosynthesis were higher for American chestnut and the BC₃F₃ breeding generation when compared to Chinese chestnut for light levels ≥800 μmol m^?2 s^?1 photosynthetic photon flux density and for maximum photosynthetic capacity. Leaf morphology variables were not different between American chestnut and any of the breeding generations, but leaf area (on a per leaf basis) of Chinese chestnut was lower than that of any other chestnut type. Our results suggest that backcross breeding can be used to transfer desirable traits for restoration of native species threatened by non-native pathogens.     

Long-term realised and projected growth impacts caused by autumn gum moth defoliation of 2-year-old Eucalyptus nitens plantation trees in Tasmania,Australia

Insect damage to production forests has the potential to reduce financial returns by retarding tree growth and causing mortality, however, long-term realised quantification of these losses is rare. In order to help elucidate economic damage thresholds for making spray decisions we capitalised on a natural outbreak of autumn gum moth, Mnesampela privata, in a 2-year-old Eucalyptus nitens plantation. Following the partial chemical control of this insect outbreak we measured the tree growth variables diameter at breast height over bark and height of five differing tree defoliation classes for 75 months following tree damage. At the end of this period a threshold model was fitted to describe the relationship between tree defoliation and realised tree wood volumes. The model revealed that realised stand wood volume was not significantly affected up until defoliation exceeded 60% and then declined sharply after this defoliation level was reached. Further support for this defoliation threshold was evident from multiple comparisons among defoliation classes that showed 50% defoliated trees did not have significantly different wood volume compared to more lightly defoliated trees, but did have significantly greater wood volume compared to trees that were 72% or more defoliated. To determine if the realised differences in wood volume resulted in differences in yield over a plantation rotation the E. nitens growth model NITGRO was used to on-grow trees to age 15 years for a ‘best case’ (type 1 growth response, constant growth rates from last inventory until harvest) and ‘worst case’ (type 2 growth response, divergent growth rates from last inventory until harvest) scenario. The threshold model was then fitted to the outcomes of both scenarios and the economic consequences of defoliation were clearly dependent on the growth function assumed.     

Evolution of agroforestry based farming systems: a study of Dhanusha District, Nepal

This paper examines how agroforestry-based farming systems evolved in the Dhanusha district of Nepal following the conversion of forest into agriculture during the early 1950s. Some data are from two focus group discussions with agroforestry farmers and one meeting with agroforestry experts. The farmers?? discussion traced the development of farming practices from 1950 to 2010 to identify the drivers of land use change. The experts?? discussion resulted in a scale to differentiate the prevailing farming systems in the study area considering five key components of agroforestry: agricultural crops, livestock, forest tree crops, fruit tree crops and vegetable crops. Data related to the system components were collected from the randomly selected households. The study reveals that land use had generally changed from very simple agriculture to agroforestry, triggered by infrastructure development, technological innovations, institutional support (subsidies and buy-back guarantees) and extension programs. A range of farming systems with varying degrees of integration was evident in the study area: simple agriculture; less integrated agroforestry; semi-integrated agroforestry and highly integrated agroforestry. The three types of agroforestry systems, which are the focus of this study, varied significantly in terms of farm size, cropping intensity, use of farm inputs, tree species diversity, tree density, home to forest distance and agricultural labour force.     

Investigation of the nutritional requirements of Australian snapper Pagrus auratus (Bloch & Schneider, 1801): effects of digestible energy content on utilization of digestible protein

This study used a curvilinear model to investigate the effects of different digestible energy (DE) levels on the digestible protein (DP) requirements of juvenile snapper Pagrus auratus. For each DE level (15, 18 or 21 MJ kg⁻¹), DP content was increased from about 210–560 g kg⁻¹ in seven evenly spaced increments by formulating a summit diet (highest DP content) and a diluent diet (lowest DP content) at the desired DE level and combining the summit and diluent diets in various ratios to achieve the desired DP content. This ensured the DE level remained relatively stable. Each of the 21 dietary treatments was fed to three replicate groups of snapper twice daily to apparent satiation for 57 days. At the completion of the trial, fish were weighed and killed for chemical analysis. Results indicated that the rapid growth of snapper weighing 30–90 g was highly dependent on the ratio of DP to DE and that optimum protein deposition did not occur until snapper were offered feeds with at least 350 g DPkg⁻¹, irrespective of DE level. According to the fitted models, diets formulated for snapper reared at temperatures from 20–25°C should contain approximately 23 g DP MJ DE⁻¹ to promote optimal weight gain and protein deposition. Based on the feeding regime used in this study, this could be achieved with practical diets containing a DP:DE ratio of 460:20, 420:18 or 350:15.     

Relating the survival and growth of planted longleaf pine seedlings to microsite conditions altered by site preparation treatments

Pine plantations in the southeastern United States are often created using site preparation treatments to alleviate site conditions that may limit survival or growth of planted seedlings. However, little is understood about how site preparations affect longleaf pine (Pinus palustris P. Miller) seedlings planted on wet sites. In a 2-year study (2004 and 2005) on poorly drained, sandy soils of Onslow County, North Carolina, we examined the effects of common site preparation treatments on microsite conditions and quantified relationships between microsite conditions and longleaf pine seedling survival and growth. Treatments used in the study included site preparations designed to control competing vegetation (chopping and herbicide) combined with those that alter soil conditions (mounding and bedding). During both years, mounding and bedding treatments reduced the amount of moisture within the top 6 cm of soil and increased soil temperatures when compared to flat planting (p < 0.001). Soil moisture was inversely related to seedling mortality in 2004 (r² = 0.405) and inversely related to root collar diameter in 2005 (r² = 0.334), while light was positively related to root collar diameter in 2005 (r² = 0.262). Light availability at the seedling level was highest on treatments that effectively reduced surrounding vegetation. Herbicides were more effective than chopping at controlling vegetation in 2004 (p < 0.001) and 2005 (p = 0.036). Controlling competing vegetation, especially shrubs, was critical for increasing early longleaf pine seedling growth.     

Summer habitat use and feeding of juvenile Arctic charr,Salvelinus alpinus,in the Canadian High Arctic

Abstract – Owing to limited knowledge of the habitat use and diet of juvenile Arctic charr from the High Arctic, particularly young‐of‐the‐year (YOY), we assembled data obtained from samples taken in and around Lake Hazen, Nunavut, Canada, to assess juvenile habitat use and feeding. Juvenile charr demonstrated a preference for stream environments, particularly those fed by warm upstream ponds. Charr occupying both stream and nearshore lake habitats were found to feed similarly, with chironomids occurring most frequently in diets. Some older stream‐dwelling charr preyed on smaller, younger Arctic charr. Preferred stream occupancy is likely mediated by physical barriers created mainly by water velocity, and by distance from the lake, lake‐ice dynamics, low water depth, and turbidity. Water velocities resulted in stream habitat segregation by size, with YOY mainly found in low‐velocity pools and back eddies adjacent to stream banks, but not in water velocities >0.1 m·s^?1. Greatest charr densities in streams were found in small, shallow, slow‐flowing side channels, which are highly susceptible to drought. Under predicted climate change scenarios, streams fed by small ponds will be susceptible to intermittent flow conditions, which could result in increased competition among juvenile charr for the remaining stream habitats. In addition, glacier‐fed streams are likely to experience increased flow conditions that will exacerbate physical barriers created by water velocity and further reduce the availability of preferred stream habitat.