Design, development and field evaluation of a map-based variable rate granular fertilizer application control system [Professional]
Scientific Article Abstract[1]
Site-specific application of agricultural chemicals including granular fertilizers is an effective way of resource saving and environmental protection. The objective of this research was to develop and to evaluate the performance of a map-based variable rate row crop granular fertilizer placement system.
The applicator system consists of an AVR microcontroller for controlling the driving step motor of the fertilizer metering screw and a ground driven wheel integrated with a rotary encoder for the applicator displacement and speed measurement. Initially, the applicator was calibrated in laboratory to derive a relationship among the step motor speed, the input frequency, and the rate of fertilizer application as a function of metering screw rotational speed. Laboratory evaluation included measurement of the lag time while changing the application rate from low to high and vice versa. In the field tests, a factorial experiment with a split-split design was used to investigate the effects of fertilizer type (urea and triple super phosphate), applicator forward speed (3, 6 and 9 km/s) and application rate (75, 125 and 175 kg/ha) on precision of application rate (the percent of deviation between actual and target rates).
The results showed that the forward speed and the application rate both had significant effect on precision of application rate, while fertilizer type had no significant effect. The precision of application rate decreased when forward speed and application rate were increased.
Analysis of variance on the field experiment data showed that the effects of applicator travel speed and application rate on accuracy of fertilizer application were statically significant, while the effect of fertilizer type was not significant. Comparison of mean errors for the effect of travel speed shows that the percent of application error at travel speed of 9 km/h is significantly larger than the other two lower speeds of 3 and 6 km/h.
Comparison of mean errors for the effect of fertilizer application rate, shows that the percent of application error increases with the increasing application rate. These phenomena could be attributed to several factors including the increasing transition distance from one application rate to another at higher travel speeds, incomplete filling of metering screw slots at higher rotational speeds needed for higher application rates and higher travel speeds. Two suggestions for improving the performance of the metering system include:
- employment of an application controller with the capability of looking ahead on the application map for advanced triggering of the application rate change with increasing the travel speed. This look-ahead procedure takes into account the time required for the metering device to change a flow rate after a decision is made to change the application rate.
- using a larger diameter feeding screw with deeper slots in order to have larger feed rates at lower rotational speeds. The overall mean values of application rate errors for urea and TSP fertilizers were 5.36 and 5.45%, respectively. This non-significant difference indicates that the variable rate applicator performs similarly for both fertilizer types.
Field evaluation tests showed that the developed VR fertilizer applicator was successfully able to respond to the target discharge rates with small delay time and acceptable accuracy. The overall mean value of application rate error was about 5.4%. In the most extreme case (highest discharge rate and highest travel speed), the application rate error was 9% equivalent to 15 kg/ha. With some compromise in travel speed, this VR fertilizer applicator could be integrated with row crop planters and seed drills to optimize the consumption of high demand crop fertilizers based on prescription maps.
References
[1]Ehtesham Forouzanmehr, Mohammad Loghavi. Design, development and field evaluation of a map-based variable rate granular fertilizer application control system. Agric Eng Int: CIGR Journal, 2012.