Irrigation scheduling of cotton in a climate with uncertain rainfall

Summary An investigation was made of the irrigation requirements of cotton grown in a sub-humid environment with significant but highly variable rainfall. In the first year of the study, no additional yield benefits accrued to subsequent irrigations following a pre-emergent irrigation due to above average rainfall (550 mm) throughout the growing season. In the second year a similar rainfall amount (502 mm) fell but significant yield increases to irrigation resulted due to the uneven distribution of the rainfall. The main effect was associated with later rains which influenced the number of bolls set. The maximum amount of water extracted by cotton from a deep grey cracking clay was 178 mm. It was found that 70% of this amount could be depleted before irrigation without loss of yield. Crop evapotranspiration varied from 607 mm with no irrigation after emergence to 775 mm following three irrigations. Irrigation was associated with significant losses from rainfall runoff. Too frequent irrigation creates a risk that soil will be too wet to permit utilisation of natural rainfall. Therefore, the use of soil water information to maximise the interval between irrigation is proposed as a necessary basis for efficient irrigation management.     

Real-time adaptive irrigation scheduling under a limited water supply

The problem of real-time irrigation scheduling under limited water supply is considered. The goal is to develop an irrigation operation policy which maximizes crop yields and is responsive to current season changes in weather and other variables. Because irrigation decisions are sequential and dependent on crop and soil water status, and also because crop yields can only be known at the end of the season, the decisions are arrived at by a two-stage process. In the first or the design stage, irrigations are planned for the entire season at weekly intervals using historical data and an optimal irrigation scheduling model. In the second stage, the decisions for the subsequent weeks are revised each week after updating the status of the system with real time data up to that week and solving the irrigation optimization model once again for the new conditions. Thus, each week an irrigation decision is made, the entire planning horizon is kept in view. The procedure is illustrated by application to a case study.     

Assessing impact of climate change on forest cover type shifts in Western Himalayan Eco-region

Climate is a critical factor affecting forest ecosystems and their capacity to produce goods and services. Effects of climate change on forests depend on ecosystem-specific factors including dimensions of climate (temperature, precipitation, drought, wind etc.). Available information is not sufficient to support a quantitative assessment of the ecological, social and economic consequences. The present study assessed shifts in forest cover types of Western Himalayan Eco-region (700?4500 m). 100 randomly selected samples (75 for training and 25 for testing the model), genetic algorithm of rule set parameters and climatic envelopes were used to assess the distribution of five prominent forest cover types (Temperate evergreen, Tropical semi-evergreen, Temperate conifer, Subtropical conifer, and Tropical moist deciduous forests). Modelling was conducted for four different scenarios, current scenario, changed precipitation (8% increase), changed temperature (1.07°C increase), and both changed temperature and precipitation. On increasing precipitation a downward shift in the temperate evergreen and tropical semi-evergreen was observed, while sub-tropical conifer and tropical moist-deciduous forests showed a slight upward shift and temperate conifer showed no shift. On increasing temperature, an upward shift in all forest types was observed except sub-tropical conifer forests without significant changes. When both temperature and precipitation were changed, the actual distribution was maintained and slight upward shift was observed in all the forest types except sub-tropical conifer. It is important to understand the likely impacts of the projected climate change on the forest ecosystems, so that better management and conservation strategies can be adopted for the biodiversity and forest dependent community. Knowledge of impact mechanisms also enables identification and mitigation of some of the conditions that increase vulnerability to climate change in the forest sector.     

Augmented growth of long pepper in response to arbuscular mycorrhizal inoculation

Arbuscular mycorrhizal (AM) technology is a soil-based fertilization practice for sustainable crop productivity. We evaluated six indigenous Arbuscular mycorrhizal fungi (AMF) strains for their symbiotic response with Piper longum (long pepper), a non-timber forest product holding promise as a commercial crop for its medicinal fruits and roots. Piper saplings were raised in a 10 cm thick sand and soil mix inoculated with various AMF. Under field conditions, plants inoculated with AMF demonstrated better survival (≥80%) than non mycorrhizal plants (58%). Almost all the studied AMF strains increased the plant growth, biomass and nutrient content (N and P) over the uninoculated control. Mycorrhizal inoculation with four AMF species, viz: Glomus fasciculatum, G. clarum, G. etunicatum and G. versiforme greatly enhanced long pepper growth both in the nursery and field conditions.     

Conspecific negative density dependence in a long-lived conifer,yew <Emphasis Type="Italic">Taxus baccata</Emphasis> L.

Conspecific negative density dependence in tree species can have major consequences for structuring of communities, yet in temperate forests this phenomenon remains largely unexplored. We investigated density-dependent recruitment in the long-lived conifer yew (Taxus baccata L.), for which low levels of regeneration have been linked with reduced light availability beneath conspecific canopies and speculative autotoxic effects. We combined in situ assessment of yew regeneration in a temperate forest in southwest Ireland with ex situ pot experiments to assess whether light and/or beneath conspecific canopy conditions inhibit the germination and early growth of yew. In field experiments, recruitment was related to distance from adult conspecifics, with higher levels of regeneration found in areas not beneath yew canopies. However, reduced light availability beneath the dense yew canopy was not responsible for this pattern, with abundant seedlings found in areas of equivalent or even lower light availability. Pot experiments showed that seedling survival was highest in deep shade treatments. Experiments also demonstrated that the addition of yew needles negatively affected seedling growth, but not seed germination. Together, our results suggest that under natural forest conditions, the absence of regeneration beneath mature yew canopies, often attributed to low light availability, may at least be partly related to substances in yew canopy or leaf leachates.     

Soil impact and radiation dose to native plants in forest ecosystem

A radiation dose assessment model was applied to determine naturally occurring radionuclides ²³⁸U, ²¹⁰Po and ²³²Th in trees like Elaeocarpus oblongus, Evodia roxburghiana (Juice of the leaves that are used to treat fever), Vaccinium neilgherrense, Viburnum hebanthum and Michelia nilagirica and shrubs like Lasianthus coffeoiaes and Hedyotis stylosa in the agroforests of the Western Ghats, India and these areas were used for different agroforestry models of land development systems. The concentration of radionuclides in the biota and corresponding soil was measured using a gamma ray spectrometer and an alpha counter. The concentration ratios of these radionuclides varied substantially between the species, and E. oblongus showed a preferential uptake of all the radionuclides and hence useful for bio-indication of radionuclides in such soils. ERICA assessment tool was employed to provide an assessment of the potential doses to biota’s growing in agro forest E. oblongus appears to be much prone to radiation absorption from the dose risk point of view. The annual effective dose (AED) due to ingestion of these radionuclides in E. roxburghiana was also estimated, and was found to be lower than the world average.     

Individual tree aboveground biomass for <Emphasis Type="Italic">Castanopsis indica</Emphasis> in the mid-hills of Nepal

Quantitative information of tree biomass is useful for management planning and monitoring of the changes in carbon stock in both forest and agroforestry systems. An estimate of carbon stored in these systems can be useful for developing climate change mitigation strategies. A precise estimate of forest biomass is also important for other issues ranging from industrial forestry practices to scientific purposes. The individual tree-based biomass models serve as fundamental tools for precise estimates of carbon stock of species of interest in forest and agroforestry systems. We developed individual tree aboveground biomass models for Castanopsis indica using thirty-six destructively sampled tree data covering a wide range of tree size, site quality, growth stage, stand density, and topographic characteristics. We used diameter at breast height (DBH) as a main predictor and height-to-DBH ratio (a measure of tree slenderness) and wood density (a measure of stiffness and cohesiveness of wood fibres) as covariate predictors in modelling. We, hereafter, termed the biomass models with former two predictors as first category models (density independent models) and the models with all three predictors as second category models (density dependent models). Among various functions evaluated, a simple power function of the form \(y_{i} = b_{1} x_{i}^{{b_{2} }}\), in each category, showed the best fits to our data. This formulation, in each category, described most of the biomass variations (\(R_{adj}^{2}\) > 0.98 and RMSE < 72.2) with no significant trend in the residuals. Since both density dependent and density independent models exhibit almost similar fit statistics and graphical features, one of them can be applied for desired accuracy, depending on the access of the input information required by the model. Our biomass models are site-specific, and their applications should therefore be limited to the growth stage, stand density, site quality, stand condition, and species distribution similar to those that formed the basis of this study. Further research is recommended to validate and verify our model using a larger dataset with a wider range of values for site quality, climatic and topographic characteristics, stand density, growth stage, and species distribution across Nepal.     

The Effects of Clearfelling a Sitka Spruce Stand on the Water Balance of a Peaty Gley Soil at Kershope Forest, Cumbria

From 1981 to 1985 the water balance of four 2 ha plots of aploughed and drained Sitka spruce plantation was monitored.During 1983, three plots were clearfelled and a fourth was leftstanding as a control. A ground level raingauge over-collected during snow, but otherwisecollected 3 per cent more water than standard raingauges. Annualprecipitation (1259–1688 mm) averaged 1439 mm. The forest canopy intercepted 38 per cent and transpired 12per cent of gross precipitation. Fifty per cent of gross precipitationwas evaporated while the other 50 per cent left the site asrunoff. Throughfall and stemfiow fractions of net precipitationwere 0.87 and 0.13 respectively. After clearfelling, annual runoff increased to 68 per cent ofgross precipitation. After adjustment using the before and aftercomparison in the control plot, the decrease in annual evaporativeloss resulting from clearfelling was 290 mm.     

Mise en évidence d'une relation entre la teneur en fluor et la chute de production dans les forêts résineuses soumises à une pollution fluorée

The relationship between fluoride content of needles and decrease in yield in conifer forests subject to fluorine pollution . In conifer forests (Picca abies Lk.), subject to fluoride pollution, a logarithmic correlation exists between the F-content of unwashed needles and the decrease in wood production.     

Use of two fungal species to induce agarwood resin formation in Gyrinops walla

Gyrinops walla Gaertn. is the only species growing in Sri Lanka that belongs to the agarwood family,Thymelaeaceae. Although agarwood resin induction and extraction from Aquilaria species of the same family have been practised for many decades in Southeast Asian region,the ability of producing agarwood resins in G. walla was discovered recently. Since previous studies were on agarwood resins formed due to natural causes, the present study was conducted to identify the potential fungal species that are capable of artificially inducing agarwood resin formation in G. walla. Since this is the first ever study conducted on artificial inducement of agarwood resin formation in G.walla, Aspergillus niger and Fusarium solani were selected owing to their high abundance in the naturally formed agarwood resinous tissues collected from 25 G. walla trees.Both fungal species were separately grown in yeast extract glucose agar and used to inoculate healthy G. walla trees under aseptic conditions. Three holes were made for each tree and 2 g of fungal culture including the medium were placed in each hole. Tissue discoloration, characteristic aroma, resin content and resin constituents were checked at10 cm intervals above and below the inoculation points for a period of 1 year. Results revealed that tissue discoloration and resin content were higher in the trees inoculated with A. niger. Other than at 10 cm above and below the inoculation points, samples collected at all locations had significantly higher resin contents when inoculated with A. niger compared to F. solani. Sixteen agarwood resin constituents, which were also recorded in Aquilaria species, were identified from the discolored tissues using GC–MS analysis. Jinkohol, agarospirol and 2(2-phenyl)chromone derivatives were found in all discolored tissues collected at 10-cm intervals of the trees inoculated with both fungi. b-Seline, c-eudesmol and valerenal were found in nine of 10 sample points on the stem. c-Elemene was recorded only in one sample. The characteristic aroma during burning was stronger for dark-colored tissues than the light-colored ones. The present study confirmed the potential use of certain fungal species to induce agarwood resin in G. walla and that A. niger is more effective than F.solani.