RESUMO Objetivou-se, neste estudo, avaliar a produtividade da água em biomassa e açúcar de 23 variedades de cana-de-açúcar (segunda soqueira) irrigada por gotejamento sob dois níveis de irrigação. Dois experimentos foram instalados e conduzidos em casa de vegetação. Experimento 1: nove variedades em um solo argiloso e Experimento 2: 14 variedades em um solo franco-arenoso. Dois tratamentos de irrigação foram adotados: T100 - plenamente irrigado com reposição de 100% da evapotranspiração de cada variedade, mantendo a umidade do solo próximo à capacidade de campo; e T70 - irrigação com 70% da lâmina aplicada no tratamento T100. Avaliaram-se a produtividade da água em biomassa fresca de colmo (PABFC) e a produtividade da água em açúcar (PARBA). Houve variação na PABFC de 11,45 a 18,45 kg m-3. Observaram-se os maiores valores nas variedades CTC14, CTC6, RB867515 e SP81-3250 (T100) e nas variedades CTC6 e CTC14 (T70). A PARBA variou de 1,68 a 2,22 kg m-3, destaque para as variedades CTC6, RB967515, SP81-3250 e RB925211 em T100 e CTC6, CTC14 e SP81-3250 em T70.

ABSTRACT The aim of this study was to evaluate the water productivity into biomass and into sugar for 23 sugarcane varieties (second ratoon crop) under two levels of drip irrigation. Two experiments were conducted in a greenhouse. Experiment 1 comprised nine sugarcane varieties grown in a clay soil and Experiment 2 was composed of 14 varieties in a sandy-loam soil. Moreover, two irrigation treatments were adopted: T100 - full irrigation with 100% crop evapotranspiration replacement, maintaining soil moisture near field capacity for each variety; and T70 - irrigation with 70% T100 water depth. Water productivity was evaluated in terms of stem fresh biomass (WPFB) and sugar (WPGSY). The results showed that WPFB ranged from 11.45 to 18.45 kg m-3. The highest values were observed for varieties CTC14, CTC6, RB867515, and SP81-3250 (in T100) and for the varieties CTC6 and CTC14 (in T70). The WPGSY values ranged from 1.68 to 2.22 kg m-3, with emphasis placed on CTC6, RB9675-15, SP81-3250, and RB925211 (in T100) and on CTC6, CTC14, and SP81-3250 (in T70).

ABSTRACT This study aimed to quantify water deficit levels that compromise sugarcane initial growth exposed to different availability soil depths. The experiment was conducted in a greenhouse by using 100-liter capacity asbestos-cement boxes filled with different soil layers simulating depths of 10, 20, 30, and 40 cm. Water deficit levels were represented by accumulated reference evapotranspiration of 0, 40, 80, 120, 160, 200, 240, and 280 mm, which was considered from planting to irrigation return. Soil moisture at field capacity at planting time was sufficient to promote sprouting and emergence regardless the water deficit level that was subsequently exposed. For soil depths of 10 and 20 cm, a 160-mm water deficit level caused total plant death. On the other hand, for soil depths of 30 and 40 cm, a 200-mm water deficit level promoted plant death. A water deficit level from 40 mm significantly reduced plant growth regardless soil depth.

A disponibilidade hídrica é a principal causa da redução da produtividade, sendo o início do desenvolvimento o período mais sensível ao déficit hídrico. O presente trabalho teve como objetivo avaliar a resistência à seca das variedades de cana-de-açúcar RB867515 e SP81-3250 durante o início do desenvolvimento, utilizando diferentes níveis de déficit hídrico, em quatro profundidades de solo. O experimento foi realizado no Departamento de Engenharia de Biossistemas da Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ/USP), em estufa, em solo classificado como Latossolo Vermelho-Amarelo, textura francoarenosa (Série "Sertãozinho"). Uma vez esgotado o nível de água disponível do solo, a resistência à seca das variedades estudadas é relativamente baixa. Balanços hídricos com valores menores que -13 mm causam queda significativa na população final de plantas, independentemente da variedade, e valores abaixo de -35 mm, levam à morte o total de plantas.

Soil water availability is the main cause of reduced productivity, and the early development period most sensitive to water deficit. This study aimed to evaluate the drought resistance of the varieties of sugar-cane RB867515 and SP81-3250 during the early development using different levels of water deficit on four soil depths. The experiment was conducted at the Department of Biosystems at Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ/USP) in a greenhouse in soil classified as Oxisol, sandy loam texture (Series "Sertãozinho"). Once exhausted the level of available water in the soil, the dry strength of the studied strains are relatively low. Water balance with values less than -13 mm cause a significant decrease in the final population of plants, regardless of the variety, and values below -35 mm, leads to the death of all plants.