Predicting soil water content at - 33 kPa by pedotransfer functions in stoniness 1 soils in northeast Venezuela.

Soil water content is a key property in the study of water available for plants, infiltration, drainage, hydraulic conductivity, irrigation, plant water stress and solute movement. However, its measurement consumes time and, in the case of stony soils, the presence of stones difficult to determinate the water content. An alternative is the use of pedotransfer functions (PTFs), as models to predict these properties from readily available data. The present work shows a comparison of different widely used PTFs to estimate water content at-33 kPa (WR-33kPa) in high stoniness soils. The work was carried out in the Caramacate River, an area of high interest because the frequent landslides worsen the quality of drinking water. The performance of all evaluated PTFs was compared with a PTF generated for the study area. Results showed that the Urach's PTF presented the best performance in relation to the others and could be used to estimate WR-33kPa in soils of Caramacate River basin. The calculated PTFs had a R2 of 0.65. This was slightly higher than the R2 of the Urach's PTF. The inclusion of the rock fragment volume could have the better results. The weak performance of the other PTFs could be related to the fact that the mountain soils of the basin are rich in 2:1 clay and high stoniness, which were not used as independent variables for PTFs to estimate the WR-33kPa.

Interception of spray drift by border structures. Part 1: wind tunnel experiments.

This research investigated the drift-intercepting potential of structures surrounding the field borders, like artificial screens and crops, which are not yet a part of the drift mitigation measures for field crop sprayers in Belgium. Drift-interception experiments were performed in the wind tunnel of the International Centre for Eremology (Ghent University, Belgium) with various interception structures: Artificial screens with heights of 0.5, 0.75 and 1 m and screen open areas of 16, 36 and 63%; a row of plastic Christmas trees with heights of 0.5 and 0.75 m; and a potato canopy. The interception structure was positioned at 1 m from the field border. From the results it was found that type of border structure has a pronounced effect on the drift interception, while the height of the border structure had no significant effect.

Classification of spray nozzles based on droplet size distributions and wind tunnel tests.

Droplet size distribution of a pesticide spray is recognised as a main factor affecting spray drift. As a first approximation, nozzles can be classified based on their droplet size spectrum. However, the risk of drift for a given droplet size distribution is also a function of spray structure, droplet velocities and entrained air conditions. Wind tunnel tests to determine actual drift potentials of the different nozzles have been proposed as a method of adding an indication of the risk of spray drift to the existing classification based on droplet size distributions (Miller et al, 1995). In this research wind tunnel tests were performed in the wind tunnel of the International Centre for Eremology (I.C.E.), Ghent University, to determine the drift potential of different types and sizes of nozzles at various spray pressures. Flat Fan (F) nozzles Hardi ISO 110 02, 110 03, 110 04, 110 06; Low-Drift (LD) nozzles Hardi ISO 110 02, 110 03, 110 04 and Injet Air Inclusion (AI) nozzles Hardi ISO 110 02, 110 03, 110 04 were tested at a spray pressures of 2, 3 and 4 bar. The droplet size spectra of the F and the LD nozzles were measured with a Malvern Mastersizer at spray pressures 2 bar, 3 bar and 4 bar. The Malvern spectra were used to calculate the Volume Median Diameters (VMD) of the sprays.

Wind tunnel evaluation of several tracer and collection techniques for the measurement of spray drift.

In the history of pesticide drift measuring techniques, different tracers and a lot of different collection techniques have been used. At the start of a new Flemish project 'Protecting the Flemish environment against drift - The importance of drift-reducing techniques', wind tunnel tests have been executed to select the most efficient tracer and collection technique. As tracer types a fluorescent tracer Renaissance W15, 2 different chelates, a NaCl-solution and a fungicide Tolylfluanide were used. 2 different collection techniques were tested: drains incorporated in the wind tunnel floor filled with filter paper and filled with cloths. The recovery of the different tracers combined with the 2 collection materials was calculated. The advantages and disadvantages of the tracers and collection materials are enumerated in this article.

An integrated approach for impact assessment of water harvesting techniques in dry areas: the case of oued Oum Zessar watershed (Tunisia).

In the arid regions of Tunisia, considerable investments are being made to maintain the old water harvesting techniques and introduce new ones to capture the scarce amount of rainwater (100 mm to 230 mm annually) for agricultural and domestic purposes. However, no detailed assessment of the multiple effects and the costs and benefits of these techniques have been made so far. This paper summarizes the results of an in depth investigation of the multiple impacts (runoff mobilization, ground water recharge, agro-socio-economic impacts) of the water harvesting works undertaken in the watershed of oued Oum Zessar (southeastern Tunisia). The importance of interdisciplinary and integrated approaches was revealed through this detailed impact assessment and economic evaluation. In fact, the profitability of the water harvesting works depends largely on the criteria chosen. However, further refinements are needed to better include all possible impacts (positive and negative) that occur as a result of the installation of the water harvesting structures.

Simulation of drift of pesticides: development and validation of a model.

Over the last decade drift of pesticides has been recognized as a major problem for the environment. High fractions of pesticides can be transported through the air and deposited in neighbouring ecosystems during and after application. A new computer-two steps-drift model is developed: FYDRIMO or F(ph)Ysical DRift MOdel. In the first step the droplet size spectrum of a nozzle is analysed. In this way the volume percentage of droplets with a certain size is known. In the second step the model results in a prediction of deposition of each droplet with a certain size. This second part of the model runs in MATLAB and is grounded on a combination of two physical factors: gravity force and friction forces. In this stage of development corrections are included for evaporation and wind force following a certain measured wind profile. For validation wind tunnel experiments were performed. Salt solutions were sprayed at two wind velocities and variable distance above the floor. Small gutters in the floor filled with filter paper were used to collect the sprayed droplets. After analysing and comparing the wind tunnel results with the model predictions, FYDRIMO seems to have good predicting capacities.