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Campinas, Brazil

The aim of the work was to evaluate the probability of occurrence of daily extreme rainfall totals during each year (Preabs), considering the time series of 1890 to 2009 in the weather station of Campinas, State of São Paulo, Brazil. The probability calculations were based on the General Extreme Value distribution (GEV) from two methods of parameter estimations: the maximum likelihood and the L-moments. After evaluating the presence of no significant serial correlation, no trends, and no periodical components within the analyzed time series, it was verified that the GEV can be used to assess the probability of occurrence of the Preabs totals in the location of Campinas. The Lilliefors test and the Quantil-Quantil plots have indicated that the maximum likelihood method can be seen as a better model as compared to the L-moments in calculating the GEV parameters. It was also observed an increasing level of the wavelet energy after the 1990s. As the period between 1920 and 1935 has shown a similar feature on the wavelet sign, it can be inferred that the higher Preabs values are concentrated during these both periods (1920-1935 and after the 1990s).

The monitoring, on probabilistic standardized basis, of the rainfall temporal variability by the Standardized Precipitation Index (SPI) model has been used by governmental programs in order to detect regions under severe rainfall deficit conditions. However, some conceptual issues, inherent to an index that uses only precipitation amounts as independent variable, tend to distance the SPI application of the agricultural interests. The aim of the work was to investigate the possibility of applying the drought monitoring concept, proposed by the SPI model, on ten-day period series of the difference between precipitation and potential evapotranspiration (P-EP). Based on meteorological data colleted in a weather station of Campinas, São Paulo State, Brazil, between 1948 and 2008, it was observed that the P-EP series fits well to the General Extreme Value Distribution (GEV). This fit has allowed the incorporation of the SPI concept on ten-day P-EP series and, therefore, the development of the standardized difference between precipitation and evapotranspiration index (IPP-ETP).

The Mann-Kendall test has been widely used to detect trends in agro-meteorological as well as hydrological time series. Trend-free pre-whitening (TFPW-MK) is an approach that improves the performance of this test in the presence of serial correlation. The main goal of this study was to evaluate the ability of TFPW-MK to detect nonlinear trends. As a case study, this approach was also applied to 10-day values of precipitation (P), potential evapotranspiration (PE) and the difference between P and PE (P- PE) obtained from the weather station of Ribeirão Preto, State of São Paulo, Brazil. The results obtained from Monte Carlo simulations indicate that upward convex trends increase the power of this test, while upward concave trends decrease its power. The results obtained from the location of Ribeirão Preto reveal an increasing pressure on agricultural water management due to growing PE values. Thus, we conclude that the power of the TFPW-MK is affected by the shape of the trend and that the hypothesis of the absence of climate change in the abovementioned location cannot be accepted. © 2015, Acta Scientiarum. Agronomy. All rights received.

There are still doubts with regard to the efficiency of P fertilization in the sugarcane ratoon and the interaction between P and other nutrients that could affect the responses to P reapplication. An experiment was set up to evaluate the effects of P rates (45 and 90 kg ha-1 of P2O5) applied either in the absence or presence of Mg fertilizer (50 kg ha-1 of Mg) on the stalk yield, of sugarcane ratoon. P fertilization increased stalk yield in 17% compared to the control treatment (no P fertilizer). However, such response did not depend on Mg fertilization, suggesting that Mg was not critical to the occurrence of P response. The P nutritional status of sugarcane was not also affected by Mg application, being altered exclusively by P fertilization. P content in the leaves varied significantly (p<0.05) from 1.4 g kg-1 in the control to 1.7 g kg-1 and 1.9 g kg-1 in the treatments with application of 45 and 90 kg ha-1 of P2O5, respectively. P fertilization increased in 21% and 16%, the efficiency in the use of N and K fertilizers, respectively, compared to the control. The results suggest that increases in the yield of sugarcane ratoon cultivated in a low-P soil can be obtained with P reapplication, what might be related to the improvements on the P nutritional status of the plants.

Drought is a slow-moving hazard that occurs in virtually all countries of the world. In the light of this, several indices have been developed to improve the detection of drought's onset, as well as quantifying other features of this phenomenon. The Standardized Precipitation Index (SPI) is often used in order to characterize meteorological droughts. In addition, this index is largely used by Brazilian's agricultural institutions. In order to add important information to the drought literature, this review article described a general definition of drought, evaluated it from a statistical point of view, and also described the SPI strengths and limitations. An adaptation of the SPI that aims to develop a probability-based agricultural drought index was also presented. The results obtained herein, associated with several studies carried out throughout the world, demonstrated that the SPI is not an agricultural index. It is just a mathematical approach developed to transforming skewed distributions into the Gaussian form. If this standardization cannot be achieved, the use of this index becomes meaningless. Therefore, a normality test should be used in establishing a temporal lower limit for the SPI computations. It was also verified that for periods in which the probability associated with the zero precipitation value is close to 0.5, the SPI may erroneously indicate the end of an existing drought (or a decrease in its severity) in the presence of a decrease in the actual evapotranspiration values.

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