English

Flora Maria De Melo Villar,Daniel Marçal De Queiroz,Gracielly Ribeiro De Alcântara,Dilermando Miranda Da Fonseca,Francisco De Assis De Carvalho Pinto

doi:10.14393/bj-v31n5a2015-26338

Abstract

In addition to be absorbed by plants, nitrogen (N) applied in the soil is subject to loss by leaching, volatilization and microorganism immobilization. The spectral characteristics of plants have been used for defining the N fertilizer rate. However, it has been a challenge to translate the sensor readings into the N rate. Thus, the aim of the present study was to evaluate three spectral variables to recommend variable rate N fertilization in Brachiaria decumbens using the Nitrogen Sufficiency Index (NSI). The five treatments consisted of a control plot (without nitrogen application), a reference plot with a fixed N rate of 150 kg ha -1 and three different spectral readings for applying N at variable rates. In the variable rate plots were initially applied a N rate equal to 50% of that in the reference plot, and the following rates were defined based on NSI. The three spectral variables were: a portable chlorophyll meter readings, Visible Atmospherically Resistant Index (VARI RedEdge ) and the ratio between Modified Chlorophyll Absorption Ratio Index and Optimized Soil Adjusted Vegetation Index (MCARI/OSAVI). The experiment was conducted in randomized block design with five replicates during three plant harvesting. The forage was harvested when the plant height was 25 cm in the reference plot. The variable rate treatments presented better nitrogen use efficiency than the fixed rate treatment. The portable chlorophyll meter was more suitable than the used vegetation indices to recommend variable N rate fertilization since their plots produced the same dry biomass matter as in the fixed rate plot with less amount of fertilizer applied.

Highlights

The livestock producers are moving to fields where the soil has lower fertility due to agriculture demands since grain crops have more financial advantage than growing pastures
The American Potash & Phosphate Institute (PPI), in one of its recommendation bulletin for site-specific management for corn and wheat, presented a methodology for N variable rate prescription based on the comparison of chlorophyll readings on a reference plot with the readings on the areas where N would be applied (FRANCIS; PIEKIELEK, 1999)
If the nitrogen sufficiency index (NSI) of an area, evaluated by Equation 1, is less than 95%, the N should be applied on this area (FRANCIS; PIEKIELEK, 1999)

Summary

Introduction

The livestock producers are moving to fields where the soil has lower fertility due to agriculture demands since grain crops have more financial advantage than growing pastures. A factor of pasture management that has impact in the productivity and potential for improving the economic performance of livestock activity is the nitrogen (N) management, which has a positive effect on production and nutritional value of the forage (ANDRADE et al, 2003). Site specific management has been proposed by applying variable rates of agricultural inputs with possible reductions in production costs (DURIGON, 2007). The American Potash & Phosphate Institute (PPI), in one of its recommendation bulletin for site-specific management for corn and wheat, presented a methodology for N variable rate prescription based on the comparison of chlorophyll readings on a reference plot with the readings on the areas where N would be applied (FRANCIS; PIEKIELEK, 1999). If the nitrogen sufficiency index (NSI) of an area, evaluated by Equation 1, is less than 95%, the N should be applied on this area (FRANCIS; PIEKIELEK, 1999)

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Results