-The objective of this work was to evaluate water storage in a Plinthaqualf under different straw levels during the fourth ratoon season of a sugarcane (Saccharum officinarum) crop. The study was conducted in the 2013/2014 crop season, with the cultivar SP-813250, at two soil depths (0.0-0.3 and 0.3-0.6 m), in a randomized complete block design, with five straw levels (0.0, 4.2, 9.5, 13.0, and 18.4 Mg ha ) of sugarcane straw on soil surface promotes better water retention in the soil per Mg of straw added and delays the reach of critical water storage in the soil by up to 11 days, when compared with soil without straw cover.Index terms: Saccharum officinarum, no-tillage, soil mulch, water balance. Armazenamento de água em Plintossolo Argilúvico cultivado com cana-de-açúcar sob níveis de palhadaResumo -O objetivo deste trabalho foi avaliar o armazenamento de água em um Plintossolo Argilúvico sob diferentes níveis de palhada durante o ciclo de quarta soca da cana-de-açúcar (Saccharum officinarum). O estudo foi conduzido na safra 2013/2014, com a cultivar SP-813250, em duas profundidades (0,0-0,3 e 0,3-0,6 m), em delineamento de blocos ao acaso, com cinco níveis de palhada (0,0, 4,2, 9,5, 13,0, e 18,4 Mg ha -1 ) e quatro repetições. A umidade do solo foi monitorada com reflectômetro de domínio de tempo. A palhada proporcionou ganho de até 20 Mg ha -1 de colmos e manteve o solo com maior armazenamento de água do que o sem palhada, em todos os períodos avaliados. A manutenção de até 50% (9,5 Mg ha -1 ) de palhada de canade-açúcar sobre a superfície do solo promove melhor conservação de água no solo por Mg de palha adicionada e retarda em até 11 dias o alcance do armazenamento crítico de água no solo, em comparação ao solo sem cobertura de palha.Termos para indexação: Saccharum officinarum, plantio direto, cobertura do solo, balanço hídrico.

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O objetivo deste estudo foi quantificar a demanda hídrica da cana-de-açúcar, por meio do método de balanço de energia (razão de Bowen), na microrregião de Teresina, Piauí. O experimento foi conduzido na Usina COMVAP, na microrregião de Teresina, Piauí. A cultivar utilizada foi a RB867515, irrigada por pivô central. Para a estimativa de evapotranspiração da cultura (ETc) usou-se uma torre equipada com sensores microeletrônicos instalada no centro de um talhão de 10 ha. A evapotranspiração de referência (ETo) foi estimada pelo método Penman-Monteith. A análise de consistência física dos dados de ETc mostrou que 33,9% dos 406 dias monitorados foram consistentes. A ETc média diária foi de 5,3 mm, totalizando uma demanda de 2.650 mm, para os 498 dias do ciclo. O coeficiente de cultivo (Kc) médio por fase foi de 0,9 (crescimento rápido), 1,32 (máximo desenvolvimento) e 1,07 (maturação).

The ability of rainfall to promote soil disaggregation and transport depends on its intensity and distribution over time, allowing proper soil and water management practices in order to minimize their effects in and outside food production fields. The objective of this study was to verify the intensity of the spatial and temporal distribution of rainfall erosivity in Goias and Federal District states using historical series of rainfall data available at the National Institute of Meteorology (Inmet) from 1986 to 2017. Rainfall erosivity (EI) for Goias and Federal District were estimated using the modified Fournier index. Annual average for factor R were obtained by the sum of the EI in the 12 months of the year. Data were placed to descriptive analysis and classification according to their erosive capacity. The annual mean of the factor R for the study region was 8,834±5.2 MJ mm ha-1 h-1 ano-1, being classified as a strong erosive potential. However, considering the territory, its intensity in Goiás and DF varied from very strong to moderate throughout the year, indicating the need to adopt a conservationist practice that protects the soil from the kinetic energy of rainfall. It is concluded, therefore, that the intensity and distribution of the rainfall erosivity fluctuate both between the municipalities of Goiás (from 4.514±2.5 to 11.215±1.8 MJ mm ha-1 h-1 year-1), and throughout the year (from 180±1.5 to 1.519±4.4 MJ mm ha-1 h-1 month-1).

RESUMOEstudos da distribuição espacial e temporal das chuvas, com determinação das curvas de intensidade-duraçãofrequência, são de extrema importância para segurança no planejamento e dimensionamento de projetos hidráulicos e conservação do meio ambiente. . Atualmente, o estado do Maranhão disponibiliza de poucas informações relacionadas às curvas de intensidade-duração-frequência das chuvas, necessárias para caracterização dessa variável hidrológica para seus diversos municípios. Diante desse contexto, objetivou-se ajustar os parâmetros das curvas de intensidadeduração-frequência para 163 estações pluviométricas localizadas no estado do Maranhão. Os dados foram obtidos do banco de dados da Agencia Nacional de Águas. Para ajuste das curvas de intensidade-duração-frequênciautilizou-se o método de desagregação das chuvas, usando o modelo probabilístico de Gumbel para estimar os valores máximos em diferentes tempos de durações e período de retorno. De posse desses valores, os parâmetros K, a, b e c das curvas intensidade-duração-frequência foram ajustados pelo método dos mínimos quadrados. Os parâmetros K, a, b e c das curvas intensidade-duração-frequência apresentaram bons ajustes, com 99,7% das equações apresentando r 2 superior a 0,98. Palavras-chave: Chuvas extremas; modelos probabilísticos; período de retorno ABSTRACT RAINFALL INTENSITY EQUATIONS FOR THE STATE OF MARANHÃO, BRAZILStudies of spatial and temporal distribution of rainfall are of extreme importance for security in planning and execution of hydraulic projects and environmental conservation, so work to determine the intensity-duration-frequency curves of rainfall are indispensable for the planning and construction of hydraulic works. Currently the state of Maranhão provides little information related to the curves of intensity-duration-frequency of rainfall, so studies are necessary to develop the curves for its various municipalities. In this context the objective of this work was to determine the parameters of the intensity-duration-frequency equation for 163 rainfall stations located in the state of Maranhão. Data were obtained from the National Water Agency database. For adjustment of intensity-duration-frequency curves the rainfall breakdown method was used, considering the probabilistic model of Gumbel for estimating the maximum values in different time durations and return period. Upon acquisition of these values the parameters K, a, b and c of the intensity-duration-frequency curves were adjusted by the least squares method. The parameters K, a, b and c of the intensity-duration-frequency curves show good adjust, with 99.7% of curves presenting r 2 greater than 0.98.

The great extension of the cultivated area, associated with the low water availability to supply the sugarcane demand in the periods of drought and the high evapotranspiration demand, requires varieties adapted to these specific conditions. The aim of this study was to assess 16 sugarcane varieties regarding the efficiency in water use (EWU) and in photosynthetically active radiation (PAR), cultivated under a water restriction, in the production of stalks dry matter, sugar and alcohol. The experiment was carried out in the Brazilian savannah biome, Goiás State, during the 2011/2012 crop year, in a randomized blocks design, with four repetitions. The treatments consisted of 16 varieties of sugarcane cultivated on a supply of only 50% of the water demand demanded by the crop. The EWU and EUPAR of the varieties were evaluated for the production of stalk dry mass (SDM), sugar and alcohol. During the crop cycle there was sufficient precipitation to supply the water demand of sugarcane; however, the irregular distribution of rainfall resulted in a water deficit of -697 mm during its cycle. The varieties IAC 91-1099, CTC-15, CTC-11, SP 86-0042 and IAC 87-3396 showed higher EWU and better photosynthetically active radiation for the production of stalks dry matter, sugar and alcohol. IACSP 94-2094 and CTC 09 varieties presented the same efficiency in industrial yield and lower dry matter yield than the five following varieties IAC 91-1099, CTC-15, CTC-11, SP 86-0042 and IAC 87-3396. Therefore, these last varieties are the most efficient in water use and photosynthetically active radiation aiming the stalks dry matter, sugar and alcohol production under water restriction.

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