The development of sensors to measure fruit internal quality variables is one of the challenges of post-harvest technology. Several variables can currently be measured, including sugar content, acid content, firmness and internal disorders. This article reviews the state of the art of non-destructive fruit firmness sensors. These include static and on-line sensors that use different technologies for determining force-deformation relationships, impact forces, the acoustic response to vibrations or impacts, and optical properties. The rebound technique and nuclear magnetic resonance is also used. Although many techniques are under development, some companies already market instruments that determine the internal quality of fruit.
A non-destructive impact sensor to measure on-line fruit firmness was evaluated. This sensor is an adaptation of a static model used in the laboratory to measure fruit quality and was installed in an experimental fruit packing line with a commercial sizer chain. The firmness index is related to the acceleration-time curve supplied by an accelerometer attached to an impacting arm. The main objective of this study was to evaluate sensor performance and sources of variation. We made classification trials on three fruits: peaches (Prunus persica (L.) Batsch), apples (Malus domestica Borkh.), and pears (Pyrus communis L.), as well as working trials, such as placing the fruit, orientation, and others. The sensor works correctly at a speed of 7 fruits s -1 (0.63 m s -1 ) and allows fruit classification at three levels of firmness using specific software. Good discrimination was obtained only for soft peaches. There were variations in results between different fruits and different parts of the same fruit mainly due to the non-uniformity of fruit shape and lack of ripeness homogeneity of each one.
Renewable energies have attracted considerable attention in the past few years, not only at a national level, but also on a global one. This work investigates the use of cactus pear (Opuntia ficus-indica) plantations, as the main source for the production of biogas, and their energy potential for northern Chile. Biogas is an alternative energy for the agricultural sector and is obtained by fermentation processes of different wastes produced daily. Besides the generation of biogas, it is also possible to obtain a stabilized waste, called digestate, which can be incorporated into the soil. The soil in dry and semi-dry zones of northern Chile is poor in organic matter content, which makes it difficult to grow crops. Cactus pear is easily adapted to poor soils and deficient environmental conditions. This species presents the Crassulacean acid metabolism (CAM), and is characterized by a superficial fleshy root system that facilitates the absorption of water, allowing it to adapt well to arid conditions. Another important feature of this species is its biomass production, which can reach around 30 Mg ha-1 with the application of good management practices. For this reason, and for its high potential to produce biogas, it is considered a good energy alternative for northern Chile. The selection of the right biodigester will depend on the use and associated costs. The estimated potential for biogas production from Opuntia plantations in northern Chile is 13,406 m 3 kg-1 d-1 , and can be further improved by adding other wastes produced in the area.
In order to assess the mechanical behaviour of a soil depending on its structural quality, a Mollisol (Maipo Serie) managed with conventional tillage (LC) and meadow (P) was ploughed with a disc harrow, followed by three tractor passes over the same path. Soil samples were taken at two depths (0-20 cm and 30-50 cm) in the initial condition, after ploughing, and after the first and third tractor passes. Penetration resistance was also measured at these moments. We measured bulk density (Db), pore size distribution and consolidation test, the last one performed at two water contents (air-dry and water tension of 60 hPa) determining the deformation, recovery and bearing capacity. After ploughing, Db in P site decreased from 1.44 to 1.06 Mg m-3 , and subsequent transits unchanged this value, while in the LC site, tillage caused a decrease of Db from 1.44 to 1.23 Mg m-3. However, subsequent transits caused consolidation, increasing the Db to 1.42 Mg m-3 in the third pass. In both soils, the coarse porosity initially increased by tillage, however, this fraction decreased with the subsequent transits in the LC site, including the 30-50 cm depth. The mechanical strength was high in both sites; the highest value was reached in LC post tillage and traffic (7 MPa). The predominance of coarse porosity in P site, determined greater sensitivity to loads and lower bearing capacity, however, the recovery was higher than in the LC site. In conclusion, the LC site showed a higher mechanical strength, but its physical properties determine a low quality for crop production.
In order to reclaim a disturbed Inceptisol (1 m depth, sandy loam) after subsurface sand extraction, pre-compaction labours with different water contents were made, to assess the impact of this management on some soil physical properties. Randomized field plots (20 m 2 ) were used to achieve three increasing pre-compaction levels (T1, T2 and T3) and a control without compaction (T0), considering four replicates. A pea crop (Pisum sativum L.) was established as biological indicator. Bulk density, water content, pre-compaction by Proctor test (laboratory and field), infiltration rate and resistance to penetration were measured in the soil, while dry matter was measured in the crop. Soil bulk density values ranged between 1.25 Mg m -3 for T0 and 1.49 Mg m -3 for T3, the higher precompaction treatment. Field Proctor test showed results similar to those found in the laboratory assessment, with a parabolic adjustment pattern. Soil resistance to penetration reached maximum values fluctuating between 180 and 280 kPa, concentrating in the surface and dissipating below 30 cm depth. Increased water storage was generated by pre-compaction treatments, although T3 promoted a significantly lower infiltration rate. The best crop yield was observed in T2, with a bulk density of 1.41 Mg m -3 , showing the best water/air/ resistance relation which resulted in a higher crop yield.
The area planted with grapes in Chile has grown nearly 50 % in the last 12 years, causing a drastic increase in use of agrichemicals. In particular, herbicides need to be applied more precisely to reach the desired targets. Weeds are a limiting factor in nurseries, mostly because of the reduced distance between rows. The spray nozzles are of vital importance because they distribute the mixture over the target. A comparative study between conventional extended rage flat spray (XR) and drift reducing nozzles (TT, DG and AI) was conducted in Vitis vinifera L. cv. Thompson Seedless plants self-rooted in the nursery, studying the drift detection and quantification, of a 5.8 km.h-1 wind breeze, using the food tracer Brilliant Blue FD & C-1. Under this breeze condition, at the plants level, the drops produced with the XR nozzle suffered a trajectory deviation. A strong decrease in the spray deposits occurred while the spray area distance increased. At ground level, it was appreciated that with wind conditions, there is an increase in all the nozzles of the tanks before the plant, next to it, and after cultivation, but these did not become statistically significant at this wind level
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