Antônio Carlos da Silva

Agricultura de precisão no estudo de atributos químicos do solo e da produtividade de lavoura cafeeira

Precision agriculture appears as an important tool in the management of coffee farms where the knowledge of some soil fertility characteristics associated with the coffee production could help in specific application of fertilizers with positive environmental and economic results. So the aim of this article was to use precision agriculture and geoestatistics to evaluate the availability of phosphorus, potassium and yield of the coffee plant by evaluating the semivariogram and kriging maps and show that these tools are important for coffee management. This study was conducted on the Brejão farm in Três Pontas, Minas Gerais state, Brazil. As a data base we used soil chemical property data obtained by sampling in a georreferenced location using a quadricycle with a sampler and a GPS, and the yield data was obtained from manual harvest on the georreferenced location. The analysis of these data by using statistics and geostatistics tools allowed to characterize the spatial variability of the phosphorus, potassium, and the coffee yield, and allowed to analyze the relation among these variables. It was possible to observe that spatial dependence exists so it is possible to create maps of spatial distribution of the variables.

Desempenho operacional da colheita mecanizada e seletiva do café em função da força de desprendimento dos frutos

In mechanized harvesting, one of the difficulties encountered by farmers is to determine the appropriate time to start harvesting, as well as vibration and determine the most appropriate operating speed for each cultivar during the harvest period. In general, the regulation of vibration and operating speed of the harvester has been made by producers in an empirical way, by trial, seeking greater operational performance. This study aimed to evaluate the efficiency of mechanical harvesting of eight progenies according to the traction force required for detachment of the fruit. The tests were conducted with three replications using a completely randomized design (CRD) within the same plot in random plots containing five plants. We tried to raise the strength of detachment from coffee fruits on the plant, according to the ripening of fruits, and graded to determine the strength, the green fruits and cherries. We also evaluated the efficiency of the harvest in the progenies analyzed over two years of harvest. It was concluded that there are significant differences between progenies in both the force of detachment as to the efficiency of picking and that picking efficiency is directly related to the force of detachment of mature fruits on the plant.

Potencial de água no solo em diferentes estádios fenológicos do cafeeiro irrigado por pivô central

Irrigation management can be established, considering the soil water potential, as the limiting factor for plant growth, assuming the soil water content between the field capacity and the permanent wilting point as available water for crops. Thus, the aim of this study was to establish the soil water potential interval during four different phenological phases of coffee irrigated by center pivot. The experiment was set at the experimental area of the Engineering Department at the Federal University of Lavras, in Brazil. The coffee variety planted is designated as Rubi, planted 0.8 meters apart, with rows spaced 3.5 meters apart. The treatments corresponded to the water depths applied based on different percentages of Kc and reference evapotranspiration (ET0) values. Sensors were used to measure the soil water potential interval, installed 25 centimeters depth. In order to compare the results, it was considered as the best matric potential the one that was balanced with the soil water content that resulted in the largest coffee productivity. Based on the obtained results, we verified that in the phases of fruit expansion and ripening, the best results were obtained, before the irrigations, when the soil water potential values reached -35 and -38 kPa, respectively. And in the flowering, small green and fruit expansion phases, when the values reached -31 and -32 kPa, respectively.

Ni-GDC Nanocomposite Material Prepared by Aqueous Based Tape Casting

In this work aqueous-based tape casting was used to produce Ni-GDC substrates. Rheological properties of the slurries were measured at room temperature. The acrylic-based suspensions showed a pseudoplastic behavior and remained stable and homogeneous. Tapes with thickness between 100 and 220 um were produced and showed smooth and homogeneous surfaces and good flexibility. Sintered tapes showed good density and porosity values.

DINÂMICA DAS CARACTERÍSTICAS QUÍMICAS DE UM SUBSTRATO FLORESTAL EXPOSTO À IRRIGAÇÃO

The quality of seedlings produced at forest nurseries is related to several factors, including irrigation and the used substrate. Both have as their purposes the production of quality seedlings in a short time period, but over-irrigation can negatively affect the substrate nutrient content. This work aimed to evaluate the chemical characteristics dynamics of a forest substrate subjected to successive irrigation at sub-irrigation tanks in two plastic tubes sizes. To this end, plastic tubes of 110 and 300 cm³ were placed, containing forest substrate without the presence of new seedlings at two sub-irrigation tanks with recirculation, one for each tube size, built at Universidade Federal de Lavras. It was set up completely randomized design with two replications, being the treatment levels 0,6, 12, 18, 24 and 30 irrigations, five per day. The substrate chemical characteristics were evaluated: pH, phosphorus, potassium, iron, zinc, manganese, copper, calcium, magnesium, aluminum, boron, sulfur, effective CEC, organic matter and electrical conductivity. Additionally, before the irrigations counted as treatment, water samples were taken to check for possible changes in the quality of irrigation recycled water after successive irrigations. The sub-irrigations provided only changes in the potassium concentration in the substrate in both tubes, and most of the chemical characteristics assessed on the substrate were unchanged as a sub-irrigation function.