Aplicação de esterco bovino e uréia na couve e seus reflexos nos teores de nitrato e na qualidade

Abstract

RESUMOO excesso de nitrato nos alimentos é indesejável devido à sua conversão a nitrito, composto conhecido por participar de reações formadoras de compostos cancerígenos e modificadores da hemoglobina. A influência da aplicação de esterco bovino, uréia e a associação destes nos teores de N-NO 3 -presente nos tecidos foliares de couve (Brassica oleracea var. acephala) foi avaliada, com o objetivo de verificar o efeito de fontes e doses diferentes de nitrogênio no acúmulo deste composto. Para tanto, um experimento foi conduzido a campo, de março a agosto de 1995, na Embrapa Agrobiologia. O delineamento experimental adotado foi o de blocos ao acaso, com quatro repetições e seis tratamentos: adubação com esterco bovino (20 t/ha), aplicação de N-uréia (900 kg/ha), associação de esterco (20 t/ha) com doses crescentes de N-uréia (225; 450 e 900 kg/ha) e testemunha. O espaçamento foi de 0,6 m entre plantas, 0,6 m entre linhas e 0,8 m entre fileiras duplas, perfazendo um total de 24 parcelas com 9,6 m 2 cada. Verificou-se que as plantas adubadas exclusivamente com esterco apresentaram nos limbos foliares, menores conteúdos de nitrato que aquelas que receberam uréia complementar (17,6 mg/g M.F. e 303 a 579 mg/g M.F.), respectivamente. Enquanto os teores de N-NO 3 -nos pecíolos de todos os tratamentos foram pelo menos três vezes maiores que os observados nos limbos foliares (1.830 e 561 mg/g M.F.), respectivamente. A OMS recomenda uma dose diária aceitável (DDA) de 53,3 mg de N-NO 3 -, para um adulto de 65 kg, isto é, a quantidade máxima deste composto que pode ser ingerida diariamente, através dos alimentos e da água. Considerando-se os dados obtidos no experimento, seria necessário o consumo de 2,67 kg de couve (limbos foliares) quando produzida apenas com esterco (20 t/ha) e 0,18 kg quando adubadas com esterco (20 t/ha) + 111 kg/ha de uréia (próximo a dosagem recomendada pelo Manual de Adubação do Rio de Janeiro), para atingir a DDA. Devido aos menores teores de nitrato encontrados na couve adubada exclusivamente com esterco, conclui-se que este adubo proporcionou um produto de melhor qualidade para consumo. High levels of nitrate in food is undesirable, as it may be easily converted to nitrite, which is a well known carcinogenic compound that can also interfere with hemoglobin activity. The objective of this study was to evaluate the influence of different forms of N-fertilizer (cattle manure, urea and a mixture of both) on the N-NO 3 -concentration observed on leaf tissues of kale (Brassica oleracea var. acephala). A field experiment was conducted from March until August 1995, at the Embrapa-Agrobiology Research Center. The experiment was laid out in a randomized block design, with six treatments: cattle manure addition (20 t/ha), urea addition (900 kg/ha), mixtures of cattle manure (20 t/ha) with increasing urea levels (225, 450 and 900 kg/ha) and a control. A total of four replicates was used. The distance between plants in a row and between single rows was 0.6 m, and 0.8 m was the distance between double rows. A t...

Collard green yield and nutritional quality with mineral and organic fertilization

“…Research results show distinct responses to fertilizer sources on leafy vegetable yield. Zago et al (1999) evaluated the effect of urea, cattle manure and biofertilizer also found no significant differences between these sources in the collard yield, supporting the results presented here. Shingo and Ventura (2009) also verified that organic fertilization with different organic compounds and pyroligneous acid resulted in collard green yield similar to standard fertilization with mineral fertilizer.…”

“…Still, in this table, leaf N concentration ranged from 29.0 to 35.7 g kg -1 and, was significantly greater with the application of mineral fertilizer (urea), and lower with the application of fertilizer organic (pig slurry or poultry manure. Zago et al (1999) also reported that the application of urea resulted in higher N concentration in the collard leaves when compared to the cattle manure addition. The higher N uptake with the mineral fertilizer application was due to the high solubility of the urea, resulting in an increase in the availability of this nutrient in the soil.…”

“…In addition, the adequate N supply improves the nutritional quality of collard green for promoting the increase in carotenoid content (KOPSELL et al, 2007). However, the high application rates of N fertilizer can provide excess N, with consequent nitrate accumulation and decreased quality of the product (ZAGO et al, 1999), as well as the production cost burdening. Thus, studies aimed at establishing adequate N rates are of extreme importance so that the total quality is achieved in the productive process.…”

“…Manure application provides an excellent nutrient source for plants providing conditions for obtaining higher yields (ABREU et al, 2010). In addition, organic fertilizers have a process of decomposition and release nutrient slower favorable condition for the increased production of collard (ZAGO et al, 1999), due mainly of the synchronization between the nutrients released from manure and greater demand of the crop. This inference is justified due to the long cycle of the crop, which can remain productive for over a year.…”

“…Studies have shown that organic fertilization has provided collard green yield similar to mineral fertilizer application (ZAGO et al, 1999;SHINGO;VENTURA, 2009). However, the effects of 'in nature' manure application on collard yield are still unknown.…”