ECONOMIC DEPTH OF DRIP IRRIGATION ON SUGARCANE SAMUEL SILVA 1 ; JOSE DANTAS NETO 2 ; IEDO TEODORO 3 ; SILVANETE SEVERINO DA SILVA 1 ; RONALDO DO NASCIMENTO 2 E GERALDO VERISSIMO DE SOUZA BARBOSA 4 1 Agronomy Engineer, Doctoral in Agricultural Engineering, Center for Technology and Natural Resources, Federal University of Campina Grande, Campina Grande PB Brazil, E-mails: {sam_capela, silvanete.h} @hotmail.com 2 Agronomy Engineer, Titular Professor, Center for Technology and Natural Resources, Federal University of Campina Grande, Campina Grande PB Brazil, E-mails: {zedantas1955, ronaldon453} @gmail.com 3 Agronomy Engineer, Adjunct Professor, Center of Agricultural Sciences, Federal University of Alagoas, Rio Largo AL Brazil, E-mail: iedoteodoro@ig.com.br 4 Agronomy Engineer, Coordinator of PMGCA/RIDESA/UFAL, Adjunct Professor, Center of Agricultural Sciences, Federal University of Alagoas, Rio Largo AL Brazil, E-mail: gvsbarbosa@gmail.com 1 ABSTRACT To optimize the use of irrigation along of the ratoons, was conducted a study was in Center of Agricultural Sciences of Federal University of Alagoas with seven irrigation depths (0, 25, 50, 75, 100, 125 and 150% of reference evapotranspiration-ET 0 ), in three cycles of production between January 2009 and February 2012. The adjustment of curve responses of the agricultural and agro-industrial yield of crop to irrigation depths has been performed. The irrigated sugarcane with 150% of ET 0 in the first, second and third production cycles has produced an average of 48.0 Mg ha -1 more than the sugarcane cultivated without irrigation. For an average value of 0.55 R$ kg -1 of commercially recoverable sucrose content (CRS), the depth of maximum economic efficiency was 666 (85% of ET 0 ), 290 (65% of ET 0 ) and 397 mm (70% of ET 0 ) with net revenue of US$ 3,272.07, US$ 2,456.90 and US$ 1,474.51 ha -1 in plant cane, 1 st and 2 nd ratoon, respectively. The final agro-industrial yield per acreage unit is more dependent of the stems yield and not of the amount of CRS per ton of cane. However, the economic irrigation depth in the range 0 to 150% of ET 0 is directly proportional to the increase in the price of CRS. Keywords: stems yield, CRS, cost of water for irrigation SILVA, S.; DANTAS NETO, J.; TEODORO, I.; SILVA, S. S.; NASCIMENTO, R.; BARBOSA, G. V. S. LÂMINA ECONOMICA DE IRRIGACAO POR GOTEJAMENTO NA CANA-DE-ACUCAR 2 RESUMO Para otimizar o uso da irrigacao ao longo das socarias de cana-de-acucar, foi conduzido um experimento no Centro de Ciencias Agrarias da Universidade Federal de Alagoas com sete lâminas de irrigacao por gotejamento (0, 25, 50, 75, 100, 125 e 150% da evapotranspiracao de referencia-ET 0 ), em tres ciclos de producao durante janeiro de 2009 a fevereiro de 2012. As curvas de respostas da produtividade agricola e industrial da cultura foram ajustadas as lâminas de irrigacao. A cana-de-acucar irrigada com 150% da ET 0 no 1o, 2o e 3o ciclos de cultivo, produziu em media 48,0 t ha -1 a mais do que a cana cultivada sem irrigacao. Para o valor medio de R$ 0,55 kg -1 de acucares totais recuperaveis (ATR), a lâmina de maxima eficiencia economica foi 666 (85% da ET 0 ), 290 (65% da ET 0 ) e 397 mm (70% da ET 0 ), com receita liquida de US$ 3.272,07, US$ 2.456,90 e US$ 1.474,51 ha -1 em cana-planta, 1a e 2a soca, respectivamente. O rendimento agroindustrial final por unidade de area cultivada e mais dependente da produtividade de colmos e nao da quantidade de ATR por tonelada de cana. No entanto, a lâmina economica de irrigacao no intervalo de 0 a 150% da ET 0 e diretamente proporcional ao aumento do preco do ATR. Palavras-chave: produtividade de colmos, ATR, custo da agua para irrigacao.