O milho, var. Piranão, foi cultivado em solução nutritiva com níveis crescentes de N, R e K. Houve resposta linear à adição de N e assintótica às doses de R e de K. A determinação da atividade da reductase de nitrato se correlacionou melhor com a produção da matéria seca que a do N total nas folhas. O teor de potássio total nas folhas, por sua vez refletiu melhor o estado nutricional que a determinação de putrescina nas folhas.
Maize plants, Piranão cultivar, were grown in nutrient solution with 5 levels each of N, R and K till harvest. Nitrate reductase activity and putrescine level were determined in leaves of plants in the N and K series, respectively, at silking stage. Upper and lower leaves were analysed for N, R and K in the corresponding treatments at the end of the life cycle. The main conclusions were the following : 5.1 There was a linear effect of level of N in the substrate on dry matter production. 5.2. High activities of nitrate reductase suggest that under natural conditions the variety should be very responsive to N fertilization. 5.3. An asymptotic response curve was found in the treatments with increasing levels of R in the medium, as well as in the case of the K treatments. 5.4. Curves of response of roots (dry matter) showed a tendency to level of as a function of increasing levels of element at lower concentrations than the components aeral part of the plant (leaves, stems, ears). 5.5. Determination of leaf putrescine did not of prove a better indicator of the K status leaf K. 5.6. The variety under study seems to be relatively more efficient in the utilization of N for yield components; the efficiency for utilization of K, is rather low and that for R is intermediate, findings that should have a bearing on the fertilization in field conditions.
Estudos sobre a nutrição mineral do milho: II. efeito de doses crescentes de N, R e K no crescimento, produção e composição mineral da variedade Piranão em condições controladas*
Studies on the mineral nutrition of corn: II. efect of rates of N, P, and K on growth, yield and mineral composition of the variety Piranão under controlled conditions
E. MalavoltaI; L. C. BassoI; E G. D. OliveiraI; C. A. VasconcellosII; Z. G. SantosII; J. M. FortesII; J. FernandesII; N.P. StamfordII; J.O. LorenziII; N. F. SampaioII; F. J. HassII, J. C. FreireII; M. SouzaII; N. VentorimII; R. Victoria F.II; CA. RosalénII; E.A. ZagoII; M.T. MirandaII; S.A. LimaII, A.M.G. CastroII; A.P. SouzaII; E.S. LopesII; L.F. SobralII; L.A. LovatoII, M. MenezesII; E O. Tisselli F.°II
IDepartamento de Química, ESALQ - USP
IIEstudantes pós graduados de Solos & Nutrição de Plantas
RESUMO
O milho, var. Piranão, foi cultivado em solução nutritiva com níveis crescentes de N, R e K. Houve resposta linear à adição de N e assintótica às doses de R e de K. A determinação da atividade da reductase de nitrato se correlacionou melhor com a produção da matéria seca que a do N total nas folhas. O teor de potássio total nas folhas, por sua vez refletiu melhor o estado nutricional que a determinação de putrescina nas folhas.
SUMMARY
Maize plants, Piranão cultivar, were grown in nutrient solution with 5 levels each of N, R and K till harvest.
Nitrate reductase activity and putrescine level were determined in leaves of plants in the N and K series, respectively, at silking stage.
Upper and lower leaves were analysed for N, R and K in the corresponding treatments at the end of the life cycle.
The main conclusions were the following :
5.1 There was a linear effect of level of N in the substrate on dry matter production. 5.2. High activities of nitrate reductase suggest that under natural conditions the variety should be very responsive to N fertilization.
5.3. An asymptotic response curve was found in the treatments with increasing levels of R in the medium, as well as in the case of the K treatments.
5.4. Curves of response of roots (dry matter) showed a tendency to level of as a function of increasing levels of element at lower concentrations than the components aeral part of the plant (leaves, stems, ears).
5.5. Determination of leaf putrescine did not of prove a better indicator of the K status leaf K.
5.6. The variety under study seems to be relatively more efficient in the utilization of N for yield components; the efficiency for utilization of K, is rather low and that for R is intermediate, findings that should have a bearing on the fertilization in field conditions.
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LITERATURA CITADA
Entregue para publicação em 15/12/1976
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