Osmar Henrique de Castro Pias

Eficiência de malhas amostrais utilizadas na caracterização da variabilidade espacial de fósforo e potássio

The objective of the research was to evaluate the efficiency of the sampling grids, used in areas managed with precision agriculture, for the characterization of spatial variability levels of phosphorus (P) and potassium (K). The study was conducted in 30 agricultural areas, located in Rio Grande do Sul state, presenting soils classified as Oxisols. The sizes of the sampling grids studied were: 100x100m (10 areas), 142x142m (10 areas) and 173x173m (10 areas).Were analyzed the levels of P and K, in depth of sampling from 0.00-0.10m. The data were subjected to descriptive statistical analysis and geostatistical analysis. In, general, the areas showed average levels of P and K suitable for crops development. However, were observed subareas with low levels of P, justifying fertilization on site-specific. Based on geostatistical parameters, sizes of the sampling grids used are efficient to capture the different scales of spatial variability of P and K, however, it is indicated smaller sampling grids to consider the spatial variability over short distances.

Controle de Helicoverpa armigera (Lepidoptera: Noctuidae) em soja com inseticidas químicos e biológicos

The objective of this work was to evaluate the performance of insecticides authorized on an emergency basis to control of Helicoverpa armigera (Lepidoptera: Noctuidae) in soybean. Seven insecticides were sprayed on the field and, 24 hours after that, soybean pointer leaves were collected and offered to 2nd instar larvae in the laboratory. Fourth instar larvae received the last trifoliate leaf that was fully expanded at the time of spraying. Another larvae group was exposed to leaves collected from 72 hours onwards after spraying. In the field, six insecticides were sprayed, and then the plants were infested with 2nd and 3rd instar larvae. In the first study, flubendiamide, chlorantraniliprole, chlorfenapyr, indoxacarb, and methoxyfenozide caused 100% mortality of the 4th instar, eight days after the beginning of exposure, while baculovirus and Bacillus thuringiensis (Bt) caused 60–75% mortality, which reached 88–90% at the end of the pupal stage. For 2nd instar larvae, only flubendiamide and chlorantraniliprole caused 100% mortality. Flubendiamide, chlorantraniliprole, and chlorfenapyr showed the lowest lethal time for the 4th instar, and flubendiamide and chlorantraniliprole for the 2nd instar. Seventy-two hours after spraying, the performance of insecticides was not satisfactory. In the field, there was satisfactory efficiency of flubendiamide, spinosad, baculovirus, and Bt on 2nd and 3rd instar larvae.

Componentes de rendimento e produtividade de híbridos de milho em função de doses de NPK e de deficit hídrico em estádios fenológicos críticos

Water stress and nutritional deficiency are the main factors that affecting grain yield of maize crops. In this sense, the aim of this study was to evaluate the yield components and productivity of maize hybrids through the use of fertilizer levels and drought stress at different periods of the reproductive stage. The study was carried out in a greenhouse using plastic vases with 15 liter capacity. A randomized block design in a factorial scheme (3 x 4 x 3) with three repetitions was used. The factors were constituted by maize hybrids (P30F53, AS1551 and AG5011), fertilization levels (0, 0.5, 1 and 1.5 times the recommended dose) and drought stress (without deficit, deficit in tasseling (VT) and grain filling (R2). The plant height, stem diameter, number of spikes, spike length, dry matter and grain yield were evaluated. Regardless of hybrid, maize crop is more tolerant to water stress at the tasseling period when compared to grain filling stage. The AS1551 hybrid showed the most grain yield as well as being more tolerant to drought water and malnutrition. The non-application of NPK fertilizer restricted severely grain yield, and with increasing doses there was a significant increase in productivity. The proper soil fertilization in AS1551 and AG5011 hybrids mitigate the effects of drought stress when applied at grain filling stage.

Caracterização da variabilidade espacial do índice relativo de clorofila na cultura do trigo

Site-specific nitrogen application, based on relative chlorophyll index from leaves, may provide many economic and environmental benefits, however, the knowledge on sampling methodologies is still incipient. Thus, this study aimed to evaluate the use of different sampling grids to characterize the spatial variability of relative chlorophyll index of leaves from wheat crop and elaborate thematic maps for site-specific nitrogen application. For determining the relative chlorophyll index, a CFL 1030 chlorophyll meter was used on a regular sampling grid of 10 m x 10 m with 472 sampling points. Based on the initial sampling grid, by using the point elimination method, the simulation was performed in the following sampling grids: 10 m x 20 m; 20 m x 20 m; 20 m x 30 m; 30 m x 30 m; 30 m x 40 m; and 40 m x 40 m. The increase of the sampling grid reduced the diagnostic accuracy of relative chlorophyll index in wheat leaves. As the sampling grid increased, the maps became more general and information on the spatial variability of the relative chlorophyll index were lost. Sampling grids smaller or equal to 20 m x 20 m were effective to detect the spatial variability of the relative chlorophyll index in wheat leaves and enable the elaboration of thematic maps for site-specific nitrogen application.