Prediction of phosphorus sorption index and availability by NIRS and MIRS in soils in Madagascar

The development           of techniques for           the rapid, inexpensive and accurate determination of the           phosphorus (P)           availability and sorption index (PSI) in soils is important           for P management in           highly weathered tropical soils. The applicability of near-           and mid-infrared           reflectance spectroscopy (NIRS and MIRS) as tools for           estimating P availability           and PSI was assessed over a wide range of highly weathered           soils in Madagascar.           The predictions were based on chemometric methods using           multivariate           calibration models with partial least squares (PLS)           regressions, and           pedotransfer functions (PTF). Chemometric methods failed to           predict available P           (Presin). However, a P             sorption index,             determined as the P remaining in solution (Prem),           was estimated           with acceptable accuracy with both NIRS and MIRS (R2cv           =           0.70 - 0.73; R2v = 0.50 - 0.53). The PTF           showed that the PSI           was well explained by iron oxide, gibbsite and sand contents,           all of these           compounds being well predicted by NIRS or MIRS (R2v>           0.70). These results indicate that NIRS and MIRS can be           helpful for a rapid           estimate of PSI of highly weathered ferralitic soils.