A Study on the Time Lag and Compensation of a Variable-Rate Fertilizer Applicator

Highlights A lag time detection system for variable-rate fertilization was developed. The lag time of a variable-rate fertilizer applicator was obtained and analyzed. A sigmoid equation was fitted to the data of rate change transition tests. The planar coordinates-based lag distance compensation method (LDCM) could reduce the lag distance effectively. Abstract. The location accuracy of fertilizer application is an essential aspect of the performance of variable-rate fertilizer applicators. The lag time of the fertilization system is an important cause of fertilizer rate transition lags. In order to obtain the lag time and make proper corrections, we developed a lag time detection system for a fluted roller-based variable-rate fertilizer applicator, taking into account the distance between the on-tractor GNSS antenna and the applicator furrow openers, and applied a planar coordinates-based lag distance compensation method (LDCM) to reduce the lag distance. To verify the performance of the LDCM, we conducted fertilization tests with and without LDCM at tractor forward speeds of 3.8, 5.5, and 8 km/h. First, the lag time detection sensors were installed on the fertilizer applicator, and the lag times were measured. Then, the corrected relative position coordinates of the fertilizer outlets were calculated according to the real-time speed and position data from the GNSS receiver. By implementing the control function of the applicator, the fertilization lags were corrected. A sigmoid equation was fitted to the rate change transition data. The results showed that for rate changes from 200 to 325 kg/ha, the delay distances were reduced from 1.10 to -0.84 m (at V = 3.8 km/h), from 1.97 to 0.09 m (at V = 5.5 km/h), and from 6.38 to 0.80 m (at V = 8 km/h). As a result, the LDCM can efficiently decrease lag distances of the variable-rate fertilizer applicator and meet the requirements of accurate fertilization in precision agriculture.