Fabiana Luiza Matielo de Paula

Soma térmica de algumas fases do ciclo de desenvolvimento da batata (Solanum tuberosum L.)

Thermal time has been used to represent the effect of the air temperature on plants growth and development. Thermal time is a simple method and a better time descriptor than calendar days in plants. The objective of this study was to calculate the thermal time by different calculation methods for different developmental phases (emergency to tuber initiation, from tuber initiation to beginning of senescence and from beginning of senescence to harvest time) in field grown potato cultivar Asterix. Field experiments were carried out at Santa Maria RS, Brazil, with eleven planting dates during 2003 and 2004. The experimental design was a complete randomized block design with four replications. Thermal time for different developmental phases varied according to planting date, calculation method, and cardinal temperatures. These results indicate that the thermal time should be used with caution to tell time in potato.

Improving predictions of leaf appearance in field grown potato

The calculation of leaf appearance rate (LAR) and number of accumulated or emerged leaves (NL) on the main stem are part of many crop simulation models. The purpose of this study was to adapt and evaluate a model (WE model) for simulating the main stem LAR and NL in potato (Solanum tuberosum L.). The WE model is a non-linear multiplicative model that takes into account the effect of genotype and environmental factors on LAR. A linear model (Phyllochron model) was also used as a comparison with the WE model. A series of field experiments with 14 planting dates over two years (2003 and 2004) was carried out in Santa Maria, RS, Brazil, using the cultivar Asterix. Coefficients of the WE model and the phyllochron model were estimated with data from four planting dates in 2003, and the models were validated with data from the other ten plantings, which are independent data. The statistics used to quantify model performance was the root mean square error (RMSE). The WE model was a better predictor of NL (RMSE=2.0 leaves) than the phyllochron model (RMSE=3.7 leaves). The WE model has coefficients with biological meaning and a non-linear temperature response function, which renders generality and robustness to this LAR model.

Filocrono em batateira afetado pelo tamanho do tubérculo-semente e pela época de cultivo

The objective of this study was to estimate the phyllochron of the potato cultivar Asterix in plants derived from different tuber seed sizes in two field growing seasons using the concept of degrees-days for calculating the phyllochron. The experiment was conducted in Santa Maria, RS, during Spring 2003 and Fall 2004. Four classes of tuber-seed diameter of the potato cultivar Asterix were used: 2-4 cm, 4-6 cm, 6-8 cm and 8-10 cm. The phyllochron was estimated as the inverse of the slope of the linear regression of main stem leaves number against the thermal time calculated with three methods: method 1 - considering only the base temperature, method 2 - considering the base temperature and the optimum temperature, and method 3 - considering the base temperature, the optimum temperature and the maximum temperature. Tuber-seed size did not affect the phyllochron of the potato cultivar Asterix, but the method of calculating thermal time and the planting date affected the phyllochron. For the method of calculating thermal time in the phyllochron of the potato cultivar Asterix, it is recommended to use the base temperature and the optimum temperature, because it produced similar phyllochron values in the two growing seasons.

Production and quality of Tifton 85 pastures overseeded with black oat: effects of irrigation and nitrogen fertilization

The objective of this work was to evaluate the effects of irrigation and nitrogen fertilization on the bromatological quality, forage production, and botanical and structural composition of Tifton 85 (Cynodon sp.) pastures overseeded with black oat (Avena strigosa). Four treatments were evaluated in a 2 × 2 factorial scheme (irrigated and non-irrigated × fertilized and non-fertilized), with three replicates, in a completely randomized design. In irrigated paddocks, the irrigation system was activated when the soil matric potential reached a value equal to, or higher than, 10 kPa and 135 kg N ha-1 was applied to fertilized paddocks, divided into four applications. The forage mass pre- and post-grazing, total forage production, and the botanical, structural, and bromatological composition of the pastures were evaluated. No interaction was observed between the irrigation and nitrogen fertilization factors for any of the variables and no significant differences were observed in forage mass between pre- and post-grazing or in Tifton leaf and stem percentages. Nitrogen fertilization had a significant effect on forage production, which was 2626.41 kg dry matter (DM) ha-1 higher in fertilized pastures than in unfertilized pastures. In addition, fertilization resulted in a lower percentage of dead material (6.66%), higher percentage of oat leaves (30.84%), higher leaf:stem ratio (1:45), higher crude protein content (24.13%), lower levels of neutral detergent fiber (NDF) (64.57%) and acid detergent fiber (ADF) (32.86%), and higher in vitro dry matter digestibility (73.01%) than in unfertilized pastures. The use of irrigation did not influence total forage production, however, it resulted in pastures with lower NDF (65.97%) and ADF (33.54%), and higher in vitro dry matter digestibility (73.48%) than unirrigated pastures. Nitrogen fertilization produced improvements in pasture structure, associated with higher dry matter yield and bromatological quality, while irrigation only produced pastures with lower fiber content and greater digestibility.