Fabrício Silva Coelho

Índice SPAD em função de diferentes horários e posições no folíolo da batata sob fertilização nitrogenada

Objetivou-se avaliar a influencia do nitrogenio (N) sobre a leitura do indice SPAD, verificar se as leituras SPAD na quarta folha sao sensiveis a variacoes com a posicao e o horario de avaliacao bem como o efeito da irrigacao sob as leituras SPAD na cultura da batata. O experimento foi conduzido de junho a setembro de 2008, no delineamento experimental de blocos casualizados, com quatro repeticoes. Os tratamentos constaram de cinco doses de N (0; 50; 100; 200 e 300 kg ha-1) aplicadas no sulco em pre-plantio, na forma de sulfato de amonio. As leituras do indice SPAD foram realizadas na quarta folha (QF) a partir do apice e na folha mais velha (FV) aos 7; 14; 21; 28; 35; 42; 49 e 56 dias apos a emergencia (DAE). Aos 21 DAE realizou-se a leitura do indice SPAD em diferentes horarios, posicoes no foliolo terminal da QF e determinou-se o indice SPAD antes e apos a irrigacao. As doses de N e os DAE influenciaram a leitura do indice SPAD na QF e FV durante o ciclo da cultura. Houve efeito das doses de N sobre o indice SPAD em todas as regioes do foliolo terminal da QF, exceto para a regiao distal. As doses de N e os diferentes horarios de avaliacao durante o dia influenciaram a leitura do indice SPAD na QF. Houve diferenca entre os valores do indice SPAD antes e apos a irrigacao. Assim, deve ser estabelecido um rigoroso protocolo para a determinacao do indice SPAD.

Valor e predição do nível crítico de índices para avaliar o estado nitrogenado da batateira

Regardless of the nitrogen (N) content used, the existence of values, accepted as a critical concentration, is necessary for use as a reference standard. The objective was to establish critical levels of the SPAD index, Hue angle, concentration of total N, and fourth-leaf dry matter of the potato plant, by two methods, and to use such critical levels for the prediction of the N-status of the plant, based on the relative yield. The experiments were conducted on crops from the winter and rainy seasons. The treatments consisted of five dosages of N, applied in the form of urea when planting (0, 50, 100, 200 and 300 kg ha-1 of N). The design was of randomized blocks with four replications. The potato cultivar used was Agata. At 21 days after emergence (DAE) the SPAD index, concentration of total N, Hue angle and dry weight of the fourth leaf from the apex of the plant (MSQF), were all determined. To calculate the critical level, the Cate-Nelson graphical procedure and a mathematical procedure were used. The prediction errors of the diagnosis of the N-status determined from the critical levels were estimated using the Cate-Nelson graphical method, by quantifying the percentage of observations which were located in negative quadrants. There was an apparent discrepancy in the critical-level values of N when using the two calculation procedures. The critical levels determined at 21 DAE are suitable for making relatively accurate assessments of N sufficiency at an early stage of evaluation.