This paper presents the foundations and applications in agriculture of the main systems used for the geometrical characterization of tree plantations, including systems based on ultrasound, digital photographic techniques, light sensors, high-resolution radar images, high-resolution X-ray computed tomography, stereo vision and LIDAR sensors. Amongst these, LIDAR laser scanners and stereo vision systems are probably the most promising and complementary techniques for achieving 3D pictures and maps of plants and canopies. The information about the geometric properties of plants provided by these techniques has innumerable applications in agriculture. Some important agricultural tasks that can benefit from these plant-geometry characterization techniques are the application of pesticides, irrigation, fertilization and crop training. In the field of pesticide application, knowledge of the geometrical characteristics of plantations will permit a better adjustment of the dose of the product applied, improving the environmental and economic impact. However, it is still necessary to resolve several technological and commercial questions. The former include improving detection systems, especially with regard to developing software for the post-processing steps and improving the speed of calculation and decision making. Amongst the latter, it is essential to produce low cost sensors and control systems in order to facilitate large-scale deployment. Obtaining a precise geometrical characterization of a crop at any point during its production cycle by means of a new generation of affordable and easy-to-use detection systems, such as LIDAR and stereo vision systems, will help to establish precise estimations of crop water needs as well as valuable information that can be used to quantify its nutritional requirements. If accurate, this can provide valuable information on which to base more sustainable irrigation and fertilizer dosages. These would be able to meet crop needs and could also be used as part of specific management systems, based on prescription maps, for the application of variable quantities of water and fertilizers. The availability of measurement tools that allow a precise geometric characterization of plantations will also facilitate and enhance research aimed at developing better crop training systems that ensure an optimal distribution of light within the treetops and higher fruit quality. It is therefore of vital importance to continue devoting major efforts to the development of increasingly accurate, robust and affordable systems capable of measuring the geometric characteristics of plantations, which support the development of the different areas of a sustainable and precision agriculture.This work has been funded by the Spanish Ministry of Science and Innovation and by the European Union through the FEDER funds and is part of research projects Pulvexact (AGL2002-04260-C04-02) and Optidosa (AGL2007-66093-C04-03)

The changes in the shape and size of vines during the growing season require a continuous adjustment of the applied dose to optimize spray application efficiency. Target detection with ultrasonic sensors can be used to adapt the applied dose following the principles of the variable rate technology. A multi-nozzle air-blast sprayer was fitted with three ultrasonic sensors and three electro-valves, to modify the flow rate from the nozzles in real time, in relation to the variability of crop width. A constant application rate of 300 l ha−1 was compared with a variable rate application using the tree row volume principle at a 0.095 l m−3 canopy. The total flow rate sprayed by the nozzles was modified according to the variations of crop width measured by the ultrasonic sensors. On average 58% less liquid was applied compared to the constant rate application, with similar deposition on leaves with both treatments. A detailed analysis of savings indicates differences between the lower, middle and top part of the crop, in accordance with the leaf area distribution with crop height. No significant differences between treatments were detected in uniformity of liquid distribution and capability to reach the inner parts of the crop. This important reduction in spray volume could be followed by an equivalent reduction of plant protection products but further research work is needed to guarantee biological efficacy of a reduced dose.This work was funded by the Spanish Ministry of Education and Science, and it is part of the funded research project AGL2002-04260-C04-0