Abstract
The application of dibble fertilizers has been considered as a starter fertilizer application technique to improve the growth uniformity of winter lettuce. This paper describes the development of an automated dibble fertilizer applicator mounted on a commercial semiautomatic lettuce transplanter (Chidorisan) and examines whether the device could automatically deliver a precise amount of slow-releasing coated granular fertilizer into a lettuce transplanting hole without negative effects on the transplanting operation. Two volumetric metering devices with readily adjustable metering rates were designed and tested with metering volumes of 2ml to 7ml and metering speeds of 31, 47 and 70 rpm. Laboratory test results indicated that the applicator could offer both precision metering and application uniformity, which were evaluated using the coefficient of variation (CV) of the discharged amounts of fertilizer. The CV values for the metering devices ranged from 0.9% to 5.3%, whereas the overall CV values of the applicator were less than 7%. In addition, in a functional field test, the applicator was successfully operated in conjunction with practical lettuce transplantation; it completely delivered approximately 3.6g of a granular fertilizer into each transplanting hole.
