Influence of soil surface disposal on precision of measuring soil water by near-infrared spectroscopy

In order to measure fertilizing indexes of soil quickly, precisely and in the field for precision farming, it is a key to improve the accuracy of soil water measurement by finding out the pattern influencing rules of soil surface on the measurement by the near-infrared reflectance spectroscopy, and is also helpful to measure soil nutrients by the reflectance technique. Six soil sample with different water level of soil samples were measured by near-infrared reflectance spectroscopy. By regression analysis, it was found that the correlation between the soil water content and the relative spectral absorptivity by using of a meshwork controlled surface finishing was better than by only ruler finishing. Among the different type of soils, the order of relative absorptivity from high to low is as following, medium loam, heavy loam and light loam. For different partied size of soil with the same surface disposal method, the correlation is the highest for the soil whose particle sizes are within the range of 0.5 to 1 mm. The results showed that the uniformly continuous soil surface was the dominant cause for the improved result and the surface flaw and scratches were the main factors to degrade the measurement accuracy.