Sufficiency index for defining nitrogen recommendation in brachiaria grass pasture

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.

Mombaça grass yield as a function of nitrogen fertilization based on the use of the chlorophyll meter

“…As in the first cycle, the NSI90% treatment was also superior to the others in the second cycle, producing 47.52 kg DB kg N -1 . The use of a chlorophyll meter and the NSI, in the management of nitrogen fertilization, in brachiaria grass pasture, also allowed for greater efficiency in the use of nitrogen (Villar, Pinto, Fonseca, Queiroz & Alcântara, 2015).…”

Recomendações De Adubação E Desfolha Do Capim Mombaça Para a Região De Carajás – Pará: Eficiência E Efeitos No Solo

“…There is the possibility of compensatory production, and that nutrients do not need to be at their maximum levels in the soil to have high yields. Siri-Prieto et al, 2020 state that there need to be minimal nutrients to improve crop yield and warn of use of small amounts of P and K. Villar, Pinto, Fonseca and Alcântara (2015), when studying fertilization sufficiency index, and variable fertilization, they also realized that plots with medium fertilization produced equal to plots with higher fertilizer doses. Mean followed by uppercase letters in columns compared heights, and tiny, on the lines, compare fertilization strategies, do not differ statistically by the Tukey test at 5% probability.…”

Nitrogen variable rate in pastures using optical sensors

“…SPAD-502 (Minolta Corporation, Japan) has been used in much agricultural crop research to assist in decision-making for the application of nitrogenous fertilizers, including pastures (NETTO et al, 2005;PAGOLA et al, 2009;SABERIOON et al, 2013;VILLAR et al, 2015;WIDJAJA PUTRA et al, 2017). In each plot, 30 readings were performed by measuring different randomly selected, new and completely expanded leaves, with the equipment positioned in the intermediate portion of the leaf.…”

“…l Content PAD-502 (Minolta Corporation, Japan) has been used in much agricultural crop research to assist -making for the application of nitrogenous fertilizers, including pastures (NETTO et al, 2005;SABERIOON et al, 2013;VILLAR et al, 2015;WIDJAJA PUTRA et al, 2017). In e of SPAD 30 readings were used to calculate NSI using Equation 1. elopment and harvesting lant development was monitored using an AccuPAR LP-80 ceptometer (Decagon) by quantifying ted photosynthetically active radiation (IPAR) by the plant canopy.…”

“…This methodology was initially proposed for grain crops (corn and wheat), but due to its practicality and low cost, it can also be presented as a viable alternative to pasture management in Brazil. Villar et al (2015) used this methodology in crops of Brachiaria decumbens, obtaining satisfactory results in terms of productivity and economy of input. There is a predominance of grasses of the genus Brachiaria, representing approximately 80% of the total pasture cultivated in Brazil (CASTRO et al, 2013).…”