Farm Mapping Techniques for Effective Soil Management in Large-Scale Farming

Abstract

Development of the RTSS has continuously advanced since 1997 (Shibusawa et al. 1999), keeping up with the current trend of the Japanese model for precision agriculture. However, the RTSS had not yet been used to measure fields larger than 1 ha. We developed a technique using the RTSS for efficient soil mapping of large-scale farms. Specifically, we developed an arrangement of RTSS soil scanning lines most suitable for use in large-scale farming, and we developed a method of presenting the data predicted by the RTSS on a farm map.
Soil scanning lines for farm crop management were arranged at an angle to the transect lines customarily used with conventional soil sampling methods, and the whole surface of the farm was scanned by the RTSS. The soil scanning lines for site-specific crop management followed the same intervals as a constant-width sprayer. The farm map is a grid-based map, which the grower can easily understand. A feature of the grid-map is that each grid cell shows the mean value, the maximum value, and the minimum value of various soil parameters.
The main improvement of the RTSS was made by doubling its customary speed to 0.56 m/s. We used partial least squares (PLS) regression techniques to analyze the change in the sensitivity of the calibration curves due to this increase in speed. The coefficients of determination (R²) between the values of parameters calibrated by the RTSS and measured values of soil samples were 0.77 for moisture content, 0.49 for soil organic matter, 0.53 for pH, 0.86 for total nitrogen, and 0.95 for total carbon. Owing to analysis error, the nitrate nitrogen data for many of the soil samples had to be omitted; therefore, the grid-map of nitrate nitrogen is shown for reference only. R² was 0.09 for nitrate nitrogen.
By such an increase in speed, RTSS scanning can now be carried out at 1 ha/h for large-scale farms. In this study we scanned 11 ha spread over four farms.
The best result from this study was that a grower was able to confirm from the pH grid-map an area where a large quantity of lime had been accidentally spilled in the past. Consequently, the grower accepted RTSS as a tool to assist him in making decisions.