Abstract
The low efficiency of nitrogen (N) fertilizers impels the innovation of current N management strategies in cereal production. Site specific N management is an emerging field providing novel alternatives to current nutrient management practices through canopy sensing. Barley N use efficiency can be enhanced with GreenSeeker proximal sensors, whose optimal utilization requires algorithms. The design of such algorithms required four N rates (0, 50, 100 and 150 kg N ha-1) and in-season sensing of barley canopy reflectance using a handheld GreenSeeker sensor as well as crop N analysis. The N rates produced enough variability in yields, N uptake and normalized difference vegetation index (NDVI) readings together with strong determination coefficients between in-season NDVI values on one hand and on the other hand in-season N uptake (R2=0.68, p<0.001), forage yield (R2=0.84, p<0.001), forage N uptake at harvest (R2 = 0.65, p<0.001), grain yields (R2=0.88, p<0.001), and grain N uptake (R2 = 0.84, p<0.001). These factors enabled the development of in-season N fertilizer algorithms for barley grain and forage production. The built algorithms will enable farmers using GreenSeeker sensors to better manage barley N fertilization with positive outcomes for their financial returns and environmental contamination. Key words: Barley canopy reflectance, nitrogen fertilizer algorithm, GreenSeeker, N use efficiency, normalized difference vegetation index (NDVI), nitrogen uptake.
Highlights
Barley (Hordeum vulgare L.) is a highly valued cereal around the world but especially in Australia
With the exception of the two highest N rates where no significant differences were noticed, forage yield (FY), grain yield (GY), FNUPi, forage N uptake at harvest (FNUPh) and grain N uptake (GNUP) significantly increased with increasing N rates, delivering enough variability in data to make possible the derivation of N fertilizer algorithms
Barley canopy reflectance increased with increasing N levels
Summary
Barley (Hordeum vulgare L.) is a highly valued cereal around the world but especially in Australia. In the 2013 world food commodity ranking, barley was the 12th most important and the 4th major cereal right behind wheat, rice, and maize (Food and Agricultural Organization (FAO), 2016). The 2014 world production was estimated at 144 million tons, with Australia ranked 4th for its 9.1 million tons (FAO, 2016). Some of these strategies were grounded on the reflectance properties of crop canopies and their correlations with agronomic quantities such as crop biomass, grain yield, and crop N content. These correlations have been used to develop N fertilizer algorithms for in-season fertilization of cereal crops with the aim of maximizing yield and minimizing N losses
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