Improving Nitrogen Status Estimation in Malting Barley Based on Hyperspectral Reflectance and Artificial Neural Networks

Malting barley requires sensitive methods for N status estimation during the vegetation period, as inadequate N nutrition can significantly limit yield formation, while overfertilization often leads to an increase in grain protein content above the limit for malting barley and also to excessive lodging. We hypothesized that the use of N nutrition index and N uptake combined with red-edge or green reflectance would provide extended linearity and higher accuracy in estimating N status across different years, genotypes, and densities, and the accuracy of N status estimation will be further improved by using artificial neural network based on multiple spectral reflectance wavelengths. Multifactorial field experiments on interactive effects of N nutrition, sowing density, and genotype were conducted in 2011–2013 to develop methods for estimation of N status and to reduce dependency on changing environmental conditions, genotype, or barley management. N nutrition index (NNI) and total N uptake were used to correct the effect of biomass accumulation and N dilution during plant development. We employed an artificial neural network to integrate data from multiple reflectance wavelengths and thereby eliminate the effects of such interfering factors as genotype, sowing density, and year. NNI and N uptake significantly reduced the interannual variation in relationships to vegetation indices documented for N content. The vegetation indices showing the best performance across years were mainly based on red-edge and carotenoid absorption bands. The use of an artificial neural network also significantly improved the estimation of all N status indicators, including N content. The critical reflectance wavelengths for neural network training were in spectral bands 400–490, 530–570, and 710–720 nm. In summary, combining NNI or N uptake and neural network increased the accuracy of N status estimation to up 94%, compared to less than 60% for N concentration.

Plant composition, herbage yield, and nitrogen objectives in Arrhenatherion grasslands affected by cattle slurry application

Cattle slurry is commonly used to fertilize grasslands, so its impact on plant composition and herbage properties is important. Cattle slurry at annual rates of 60 (S1), 120 (S2), 180 (S3), and 240 kg nitrogen (N)/ha (S4) was applied to Arrhenatherion grasslands in moderately wet (WS), slopy (SS), and moderately dry (DS) sites cut three times a year over six years, to assess its effects on plant functional types, the Ellenberg N indicator value (Ellenberg N), herbage dry matter (DM) yield, herbage N content and offtake, N nutrition index (NNI), and N use efficiency (NUE). The site-specific changes in an increase in graminoid cover, Ellenberg N, herbage DM yield and N offtake, and NNI along with slurry application rates revealed, while cover of legumes, short forbs, and NUE decreased. In more productive sites (WS and SS), slurry application in the amount of 180 kg N/ha could be suggested as a slurry dose ensuring beneficial agronomic objectives. However, nature conservation requirements via maintaining plant biodiversity were not met. On the contrary, short-term slurry application up to 120 kg N/ha ensured on permeable DS not only sufficient agronomic objectives, but also plant biodiversity conservation requirements.