Abstract
ABSTRACT Through the use of remote sensing, the productivity and the nutritional state of the plants can be estimated in relation to the nitrogen doses due to the modification of the canopy reflectance. In this study, values of the normalized difference vegetation index (NDVI) obtained by a terrestrial optical sensor were correlated with productivity and contents of nitrogen (N) and of foliar crude protein (CP) of Brachiaria brizantha cv. Marandu, fertigated with doses of sewage treatment effluent (STE) The NDVI average rates of the forage were obtained by the active terrestrial sensor (GreenSeeker) before the harvests that were realized every 28 days in 2014. Five fertigated treatments with the following fractions of STE in water were evaluated: E5 = 1.0; E4 = 0.87; E3 = 0.60; E2 = 0.31; and E1 = 0.11. During the 12 months of experiment, the treatment E5 received 1,132 kg ha-1 of N and the others received quantities proportional according to the application fractions defined in each treatment. The increasing application doses of STE resulted in higher yields of dry biomass and better leaf qualities in N and crude protein (CP). The productivity, the foliar N content and the NDVI index were increasing due to the gradual application of applied STE. There was a high linear correlation among the NDVI indexes and the productivity (r>0.9256) and with the N content (r>0.9570) and also for CP (r>0.8421) and leaf N (r>0.8339), demonstrating that the method can be used to estimate forage productivity and quality.
Highlights
One of the applications of the geotechnologies use is the estimation of agricultural productivity and the nutritional status of the crops in a fast and precise way, due to the close relation between these variables and vegetation indices (Zerbato et al, 2016)
The determination of leaf quality, defined in terms of leaf nitrogen content, is an example of the potential of the application of the vegetation indices, since this variable can be readily correlated with normalized difference vegetation index (NDVI) (Bredemeier et al, 2013), while most methods based on chlorophyll meters and leaf analysis require a large number of leaf samples to identify the nutritional status of the crop in the field (Povh et al, 2008)
Similar results were obtained in the other harvests in 2014, with decreasing mean values as a function of decreasing sewage treatment effluent (STE) application (Figure 4)
Summary
One of the applications of the geotechnologies use is the estimation of agricultural productivity and the nutritional status of the crops in a fast and precise way, due to the close relation between these variables and vegetation indices (Zerbato et al, 2016). The determination of leaf quality, defined in terms of leaf nitrogen content, is an example of the potential of the application of the vegetation indices, since this variable can be readily correlated with NDVI (Bredemeier et al, 2013), while most methods based on chlorophyll meters and leaf analysis require a large number of leaf samples to identify the nutritional status of the crop in the field (Povh et al, 2008). The obtaining of the NDVI data through terrestrial sensors allows fast assessment of productivity and foliage quality in relation to NDVI, without causing impacts by beddings on agricultural crops (Bredemeier et al, 2013)
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