Abstract
The objective of the present work was to evaluate the use of spectral sensors to determine nitrogen fertilizer requirements for pastures of Urochloa brizantha cv. Xaraés in Brazil. The experimental design was a randomized block design with 4 replications of 4 treatments: a control treatment (TT) without application of N; a reference treatment (TR) with N applied at a standard predetermined fixed rate (150 kg urea/ha/cycle); a treatment using GreenSeekerTM (TG) to determine N requirement by the canopy normalized difference vegetation index (NDVI); and a treatment using SPAD 502 (TS) to determine N requirement by foliar chlorophyll assessment. For treatments involving spectral sensors, N fertilizer was applied at half the rate of that in the reference treatment at the beginning of each cycle and further N was applied only when the nitrogen sufficiency index dropped below 0.85. The sensors used in the work indicated that no additional N fertilizer was required by these pastures above the half rates applied. Applying N at the reduced rates to the pastures was more efficient than the pre-determined fixed rate, as both sensor treatments and the fixed rate treatment produced similar total forage yields, with similar crude protein concentrations. All fertilized pastures supported similar stocking rates, while the sensor treatments used less N fertilizer, i.e. 75 kg urea/ha/cycle less than the reference plot. Longer-term studies to verify these findings are warranted followed by promotion of the technology to farmers to possibly reduce fertilizer application rates, improve profitability and provide environmental benefits.
Highlights
One important characteristic of Brazilian livestock systems is the raising of pasture-fed cattle (Ferraz and Felício 2010), which is regarded as one of the most economical ways to produce beef and milk (Carvalho et al 2009; Deblitz 2009)
The objective of the present work was to evaluate the use of spectral sensors to determine nitrogen fertilizer requirements for pastures of Urochloa brizantha cv
The length of each growth cycle of Xaraés grass for the different treatments varied according to prevailing weather conditions and whether or not N fertilizer was applied
Summary
One important characteristic of Brazilian livestock systems is the raising of pasture-fed cattle (Ferraz and Felício 2010), which is regarded as one of the most economical ways to produce beef and milk (Carvalho et al 2009; Deblitz 2009) In this scenario, factors such as climatic conditions and availability of nutrients in the soil must be considered for the adequate development of the pastures (Fernandes et al 2015). Nitrogen is present in the amino acids that act in the synthesis of structural and functional proteins (Barbieri et al 2017), and directly involved within the photosynthetic process due to its participation in the chlorophyll molecule It increases tillering and improves the nutritional value of pastures (Marques et al 2016)
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