engleski

Soil sampling with increased accuracy

Conventional soil sampling usually implemented in Croatia considers sample weight of 2 kg per 4-5 ha area, which means that representative sample in relation to soil mass up to 30 cm depth is presented through the ratio 1:10 000 000. New sampling method changes the ratio to 1:625 000, thus increasing amount of sampled soil 16 times with assumption that such sample better describes investigated area. Moreover, new soil sampling probe can be used for precision farming purposes where the central point of the probe ring is positioned with precision of ±1 cm and represented with 4, 8 or 16 samples taken in 50 cm radius from the center. Soil probe prototype was tested on agricultural land of 4 ha area with total number of 200 samples and on the 12 ha area with total of 12 samples. To justify application of new constructed probe, this study gives results of geostatistical analysis of spatial variability in soil pH values up to 30 cm depth. Ordinary kriging was used as interpolation method. Spatial structure of soil parameter was analyzed by calculating semivariograms and approximated by exponential model. Root-mean-square error (RMSE) of prediction was used as measure for the best model evaluation. Interpolation analysis of reduced number of samples per investigated area of 4 ha resulted in deviation in RMSE of 13, 2% when 50% less samples were randomly introduced, and 41% with 60 samples, compared to total of 200 samples. Using new soil sampling method for soil survey and applied geostatistical tools provides a solution for quantifying spatial variability of soil properties, possibilities for commercial activities and a way to introduce variable rate technology in agricultural input application which can optimize farm profitability through improving yield, reducing input costs and minimizing input losses to the environment.

soil pH; automatic circular soil probe; precision farming; kriging; spatial variability

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