CALIBRATION OF NEUTRON PROBE IN A HAPLOXERANDS SOIL

Abstract

The neutron moisture meter is the indirect sensor more accuracy for soil water- monitoring that require calibration for site specific.The experiment was conducted in a silt loam soil Diguillín serie (Haploxerands ). The objective of this study was to calibrate a neutron probe CPN 503-DR Hydroprobe. The water volumetric contendt and count ratio was measured to 20-40-60-80 and 100 cm depth in aluminum tubes inserted to 1.20- m depth. The results showed a low accuracy for the 20 cm-depth (R²=0.62 and RMSE=25.08) by escape of neutrons into the atmosphere and the hydrogen thermalizing of the soil organic matter. A high accuracy was obtained at 40 (R²= 0.94 and RMSE 9,32), 60 (R² 0.91 and RMSE 9.12) and 80 (R² 0.90 and RMSE 7.34) cm depths due to uniforms physical properties. The accuracy decreased to 100-cm depth (R²=0.66 and RMSE=23.05), by presence of iron and manganese concretions. The calibration curve for all depths have a low accuracy (R²=0.59 and RMSE=18.75). Separate calibration by horizon improve the determination of soil water content as compared with the use of single calibration equation for the entire profile and permitted the use in horizon with similar texture, decreasing the error by depth, chemical elements and physical characteristics. The neutron probe used with strict observances of safety and training, is a key tool to get a better accuracy in scientific works on water use efficiency, water balance and irrigation scheduling.