Determinação dos teores de nitrogênio na seiva do tomateiro por meio de medidor portátil¹

Determination of nitrogen on tomato sap using a portable meter.

Resumos

O presente estudo objetivou determinar teores e níveis críticos de nitrogênio na forma de nitrato (N-N0₃) na seiva do pecíolo de tomateiros utilizando-se medidor portátil, e estabelecer a relação destes valores com os teores de N-N0₃ na matéria seca dos pecíolos, e de N-orgânico e de N-total na matéria seca do limbo. Plantas de tomateiro (Lycopersicon esculentum), cv. Santa Clara, cultivadas em vasos contendo amostras de dois solos (argiloso = Vi; areia-franca = TM), foram submetidas a cinco doses de N (25, 125,225, 325 e 425 mg/dm³⁾ aplicadas parceladamente, via solução nutritiva. As folhas opostas ao 1° e ao 3° cacho foram amostradas por ocasião do início da antese das flores do respectivo cacho, e as concentrações de N- N0₃ na seiva dos pecíolos foram determinadas utilizando medidor portátil equipado com microeletrodo seletivo ao N-N0₃. Determi nou-se, também, as concentrações de N-N0₃ na matéria seca do pecíolo e do limbo, e as concentrações de N-orgânico na matéria seca do limbo, ambas por colorimetria. Os valores de N-total na matéria seca do limbo foram obtidos a partir da soma dos teores de N-N0₃ e de N-orgânico. Os níveis críticos das formas de N foram maiores no solo TM, e em ambos os solos, maiores na folha oposta ao 1° cacho. Os níveis críticos de N-N0₃ nas seiva das folhas opos tas ao 1° e ao 3° cacho foram, respectivamente 2.581 e 1.085 mg/L para o solo Vi, e 2.616 e 1.690 mg/L para o solo TM. Os teores de N-N0₃ na matéria seca dos pecíolos, e de N-orgânico e de N-total na matéria seca do limbo foram estimados com relativa precisão à partir dos teores de N-N0₃ na seiva, em ambas as amostragens fei tas nas plantas cultivadas no solo TM, e nas folhas opostas ao 3° cacho das plantas cultivadas no solo Vi.

Lycopersicon esculentum; nitrato; nível crítico.

The aim of this study was to determine concentrations and critical levels ofN0₃-N in tomato petiole sap by a quick test using a portable meter, and the relationship between these values and those of N0₃- N on petiole dry matter, and of organic and total N on leaf blade dry matter. Tomato (Lycopersicon esculentum Mill.) plants, cv. Santa Clara, grown in pots of two soil samples (clay = Vi and sand-course = TM), were submitted to five N rates (25, 125, 225, 325 and 425 mg/dm³⁾ sidedress applied as nutrient solutions. Leaves opposite to 1^st and 3 ^rd clusters were sampled at the onset of anthesis of each cluster, and petiole sap N0₃-N concentrations were determined with a portable meter equipped with a microelectrode selective to N0₃- N. Additionally, organic N (org-N) and N0₃-N were determined in leaf blade dry matter, and N0₃-N was determined in petiole dry matter. Total-N (tot-N) concentrations in blade dry matter were the sum of N0₃-N and organic-N. Critical N levels were highest on the TM soil, and for both soils, highest on the 1^st cluster. N0₃-N critical levels in petiole sap ofleaves opposite to 1^st and 3"¹ clusters were 2,581 and 1,085 mg/L on soil Vi, and 2,616 and 1,690 mg/L on soil TM, respectively. Concentrations of N0₃-N in petiole dry matter and of org-N and tot-N in blade dry matter were well estimated by sap N0₃-N concentrations in leaf samples taken from plants grown on soil TM, and in leaves opposite to the 3^d cluster from plants grown on soil Vi.

Lycopersicon esculentum; critical level; nitrate.

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Datas de Publicação

• Publicação nesta coleção
  Nov 1998

Histórico

• Aceito
  01 Out 1998