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Lettuce is one of the leading vegetables in Brazil. However, studies concerning its fertilization for the Northeastern region of the country are still scarce. This work was carried out to evaluate the effects of mineral Nitrogen supply and organic fertilization on the production and nitrate accumulation in lettuce, cultivar Elba, in the semi-arid zone of Paraíba, Brazil. A randomized block design, with four replications, was used to test five doses of cattle manure (30; 60; 90; 120, and 150 t ha-1), five doses of N supplied as urea (30; 60; 90; 120, and 150 kg ha-1), and a control without fertilization. Along with mineral N, the other nutrients were also supplied using mineral sources. No additional nutrients were supplied where organic fertilization was used. Lettuce yield was significantly higher when organic fertilization was used, compared to the mineral nutrient supply. Taking into account most of the fertilization doses recommended for growing lettuce in the Brazilian Northeastern States, N mineral fertilization in sandy soils with low organic matter contents can be fully replaced by organic fertilization with cattle manure. Plant total (PTY) and commercial yield (PCY) as affected by the mineral N supply fitted into a quadratic model, in which the doses 94.5 and 95.7 kg ha-1 corresponded to respectively the highest PTY (381.9 g plant-1) and PCY (321.6 g plant-1). Where organic fertilization was used, PTY and PCY fitted into a linear model. Therefore, the highest PTY (523.9 g plant-1) and PCY (449.48 g plant-1) were observed at the highest manure doses. Nitrate content on roots, stems, and leaves increased linearly with Nitrogen and manure application. In roots, the nitrate content (mg kg-1 of fresh matter) reached 93.96 (N mineral (Nm)) and 65.09 (organic fertilization (OF)); in stems, 183.45 (Nm) and 98.22 (OF); and in leaves, 121.98 (Nm) and 75.62 (OF). The maximum nitrate content observed in leaves was far below the risk level for human health. A alface é uma das hortaliças mais populares no Brasil. Porém, estudos referentes à sua adubação na região Nordeste são escassos. O objetivo deste trabalho foi avaliar a produção e o acúmulo de nitrato em alface, cultivar Elba, em função do fornecimento de nitrogênio a partir de uma fonte mineral (uréia) e da adubação orgânica. O delineamento experimental foi de blocos ao acaso, com quatro repetições e onze tratamentos: cinco doses de esterco bovino (30; 60; 90; 120 e 150 t ha-1), cinco doses de nitrogênio (30; 60; 90; 120 e 150 kg ha-1) e uma testemunha sem adubação. Nos tratamentos com fornecimento mineral do nitrogênio, os demais nutrientes também foram fornecidos através de fontes minerais. Nos tratamentos em que se utilizou esterco, não houve adubação adicional. A adubação orgânica resultou em produtividade significativamente mais alta do que o fornecimento de N mineral. Considerando a recomendação de adubação para o cultivo de alface no Nordeste, a adubação mineral com N, em solo arenoso com baixo teor de matéria orgânica, poderia ser integralmente substituída pela adubação com esterco bovino. Para o fornecimento de N mineral, as produtividades total (PT) e comercial (PC) se ajustaram a um modelo quadrático. As doses 94,5 e 95,7 kg ha-1 corresponderam respectivamente aos valores mais altos de PT (381,9 g planta-1) e PC (321,6 g planta-1). Para a adubação orgânica, a resposta foi linear. Portanto, os maiores valores de PT (523,9 g planta-1) e PC (449,48 g plant-1) foram observados quando as doses mais altas de esterco foram utilizadas. O teor de nitrado nas raízes, caule e folhas aumentou linearmente com o fornecimento de N mineral e com a adubação orgânica. Nas raízes, o teor de nitrato (mg kg-1 de peso fresco) alcançou 93,96 (N mineral (Nm)) e 65,09 (adubação orgânica (Org)); no caule, 183,45 (Nm) e 98,22 (Org) e, em folhas, 121,98 (Mn) e 75,62 (Org) mg kg-1 de peso fresco. Os teores mais altos de nitrato observados nas folhas ficaram muito abaixo do limite de risco para saúde humana

Nitrate production and accumulation in lettuce as affected by mineral Nitrogen supply and organic fertilization