aridiano lima de deus (6) sUmmarY nitrogen is the most important nutrient for rice (Oryza sativa l) yields. this study aimed to evaluate the response of upland rice cultivars to n rate and application times in a randomized block design, in subdivided plots with four replications. the studied factors were five rice cultivars (Brs mg curinga, Brs monarca, Brs Pepita, Brs Primavera, and Brs sertaneja), three application times (100 % at planting, 50 % at planting -50 % at tillering and 100 % at tillering) and four n rates (0, 50, 100, and 150 kg ha -1 ). all cultivars responded to increased rates and different times of n application, especially Brs Primavera and Brs sertaneja, which were the most productive when 50 % n rates were applied at sowing and 50 % at tillering. the response of cultivar Brs monarca to n fertilization was best when 100 % of the fertilizer was applied at tillering. index terms: Oryza sativa l, nitrogen fertilization, production components.(1) Part of monograph the first author, presented the course in agronomy, federal University of ceará -Ufc. received for publication in may 4, 2011 and approved in January 24, 2012. (2) agronomist, federal University of ceará -Ufc. Post office Box 12168, ceP 60356-000 fortaleza (ce). e-mail: jhbbarreto@ yahoo.com.br (3) associate Professor of soil science department, Ufc. e-mail: ismail@ufc.br (4) researcher of emBraPa -agricultural center of the mid-north. Post office Box 01, ceP 64006-220 teresina (Pi). e-mail: almeida@cpamn.embrapa.br (5)

R E S U M OO objetivo do trabalho foi verificar possíveis efeitos alelopáticos exercidos por extratos aquosos de folhas de cumaru (Amburana cearensis) e malva-santa (Plectranthus barbatus) sobre a germinação de sementes de caruru (Amaranthus deflexus). As sementes de caruru foram colocadas para germinar em placas de petri em contato com extratos vegetais aquosos obtidos a partir de folhas de cumaru e malva-santa sob dois métodos de preparação -extrato aquoso das folhas frescas e extrato aquoso por infusão das folhas secas -e duas dosagens -50 e 100 g L -1 . Foi utilizado o delineamento inteiramente casualizado com 4 repetições e uma testemunha isolada compondo um fatorial 2 x 2 x 2 + 1. Foi determinada a porcentagem final e o índice de velocidade de germinação. A análise dos dados revelou diferença entre os tratamentos e a testemunha, condicionando graus diferentes de alelopatia para os extratos usados afetando drasticamente a germinação do caruru. O extrato a base de folhas frescas de cumaru apresenta alto nível de alelopatia de modo a impedir quase que completamente a germinação do caruru. A dose, com efeito, mais prejudicial para a germinação do caruru foi a de 100 g L -1 . Palavras-chave: Alelopatia; caruru; folhas frescas; infusão A B S T R A C TThe objective was to verify possible allelopathic effects exerted by aqueous extracts of leaves of Amburana cearensis and Plectranthus barbatus on the seed germination of the weed Amaranthus deflexus. A. deflexus seeds were put to germinate in Petri plates containing aqueous plant extracts obtained from A. cearensis and P. barbatus leaves under two tillage methods -aqueous extract from fresh leaves and aqueous extract by infusion of dried leaves -and two dosages -50 and 100 g L -1 . We used a completely randomized design with 4 replications and a detached witness composing a factorial 2 x 2 x 2 + 1. It was determined the final percentage and germination speed index. Data analysis revealed differences between treatments and the witness, conditioning different allelopathy levels for the extracts used, dramatically affecting the germination of A. deflexus. The A. cearensis fresh leaves extracts has a high level of allelopathy since they prevent almost completely the germination of the weed A. deflexus. The most damaging dosage for germination of A. deflexus was 100 g L -1 .