Resposta espectral do capim-tanzânia à adubação nitrogenada e densidades de plantio / Spectral response of Tanzania grass to nitrogen fertilization and planting density

AUTOR(ES)

Selma Alves Abrahão

DATA DE PUBLICAÇÃO

2007

RESUMO

The use of variable nitrogen rate application is more efficient, avoiding losses by lixiviation. Assuming that it is possible to discriminate nitrogen rates by the spectral response of forage crops, it becomes necessary the knowledge of this variable effect on the forage spectral response. The goal of the present research was to evaluate the effect of four nitrogen rates (0, 80, 160 e 320 kg ha-1) and three planting densities (9, 25 e 49 plants m-2) on the spectral response of the Panicum maximum cv. Tanzânia, on the correlation between the vegetation indices (NDVI, VARIRedEdge, VARIGreen, WDRVI(0.05), WDRVI(0.1) e WDRVI(0.2)) and on the chlorophyll measurements (SPAD readings) and on the dry mass (MS). The research was developed with the treatments arranged in a factorial of four N rates and three planting densities, according to the randomize block design, in the Animal Science Department of UFV, Viçosa-MG, at the Forragicultura field, from November of 2006 to January of 2007. Four data evaluations were accomplished in the field using two spectroradiometers SD2000 for spectral data sampling in 400 and 900 nm wavelengths, with spectral resolution of 0.34 nm. Using the bidirectional reflectance factors the blue (460 to 480 nm), the green (545 to 564 nm), the red (620 to 670 nm), the transition of the red to near infrared (700 to 710 nm) and the near infrared (840 to 880 nm) bands of the satellites MODIS and MERIS were simulated to calculate the six vegetation indices. In agreement with the obtained results, it was obtained that, the spectral response of the Tanzânia grass crop along the evaluations, presented a characteristic behavior of green vegetation. In the visible region, there was general tendency of the spectral reflectance of the Tanzânia grass crop to decrease with the increasing of the nitrogen rates. While in the near infrared region, the spectral response was opposed to the visible region one. The planting density, one year after its establishment, in two spectral bandwidths (visible and near infrared), did not influence the reflectance, as well as it did not influence the following variables: N content, vegetation indices and dry mass production. For 30 days after the first cut and 20 days after the fertilizer application, the WDRVI(0.05) was the best index to discriminate rates of nitrogen. For 15 days after the second cut and 13 days after the first fertilizer application, the VARIRedEdge was the best index to discriminate rates of nitrogen. For 26 days after the second cut and 11 days after the second fertilizer application, the WDRVI(0.05) and VARIRedEdge were the best indices to discriminate rates of nitrogen. The results indicated that there was not a unique index that can be used for discriminating all the N rates applied on different dates of application. For all dates of data evaluations, the index that presented the highest correlation with SPAD values and MS was the VARIRedEdge.

ASSUNTO(S)

precision agriculture nitrogênio radiometria de campo nitrogen agricultura de precisão maquinas e implementos agricolas field radiometry

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