IMPROVEMENT OF THE PREDICTION OF SOIL PARTICLE-SIZE FRACTIONS USING SPECTRAL PROPERTIES

Estimation of soil particle size fractions (percentage of sand, clay and silt) with sparse data can be improved by taking into account the spatial correlation with other variables. Reflectance of the near infrared band (0.76-0.90-mu-m) is used as an auxillary variable in the prediction of soil particle size fractions on a 100 m x 100 m grid in a 2200 m x 1300 m field. The results of kriging using the textural information alone are compared with those of cokriging with the auxiliary variable. Cokriging gives a higher correlation coefficient and a lower mean squared error between estimates and measurements than kriging. The most significant improvement of the estimation is in areas of the field with sparse data for the estimated variables. The relative improvement is up to 90% in terms of reduced kriging variance and up to 33% for the mean squared error between actual measurements and estimated values. Only 17-25% of the original observations of texture are needed to obtain relatively accurate estimates when cokriging with reflectance data.