Towards the in-forest assessment of Kraft pulp yield: comparing the performance of laboratory and hand-held instruments and their value in screening breeding trials

The non-destructive prediction of Kraft pulp yield in standing trees using near infrared (NIR) spectroscopy has been typically performed by removing 5 mm or 12 mm increment cores from candidate trees in the forest and returning the samples to the laboratory for analysis. It would be desirable to perform in-field prediction using a portable NIR device; for example, to rapidly screen individual trees in a breeding trial prior to selecting trees for further sampling. This paper compares the performance of a laboratory-based full-range Fourier transform NIR system with two portable NIR devices operating at two different spectral ranges (950-1800 nm and 1600-2400 nm). Calibrations, explaining commercially useful amounts of variance in Kraft pulp yield (R-2 = 0.85-0.94) and cellulose content (R-2 = 0.92-0.96), were developed for the laboratory NIR and both hand-held portable NIR instruments using woodmeal. This demonstrates that the wavelength range and resolution of the portable instruments are suitable for the prediction of Kraft pulp yield and cellulose content. In an initial in-forest trial, calibration of Kraft pulp yield ranged between R-2 = 0.4-0.6 across two sites and two sampling periods. While there are still a number of in-forest sampling issues to be resolved around seasonal sampling, the implication is that low-cost, hand-held NIR systems are a feasible alternative to laboratory-based NIR systems for routine assessment of Kraft pulp yield.