Mechanized ring-furrow fertilization of organic fertilizers in orchards

Ring-furrow fertilization is traditionally known as a precision fertilization for orchards. However, it is still lacking in the mechanism of high fertilizer efficiency. The mechanization also remains a huge challenge. This review aims to focus mainly on the agronomic theory that is related to the mechanized ring-furrow fertilization in orchards, in order to realize the mechanized equipment for organic fertilizers. The root distribution was also summarized using the dense planting dwarfing apple trees. The root system of dwarfing apple trees was usually distributed within 1-3 m² close to the trunk in the horizontal direction. The most vigorous root system was found at a depth of 150-300 mm, with the best nutrient absorption capacity. The transport of nutrients in the soil into the root was also attributed to the diffusion and mass flow. But the low transport rate of nutrients was about 0.3 mm per day. Therefore, the nutrient availability depended on the distance between the fertilization position and the root system. Ring-furrow fertilization has been one type of precision deep-root fertilization, in order to improve the fertilizer effectiveness with the less migration distance of nutrients into the root system. As such, there was an outstanding increase in nutrient absorption by roots. The base circle radius in the trajectory of the mechanized ring-furrow was determined to be 0.6-1.0 m at the fertilization depth of 300 mm. Meanwhile, mixing organic fertilizer into the soil profile was an essential aspect of precision fertilization in orchards, which positively improved the root zone environment of apple trees. The fertilizer-soil mixing was rapidly improving the soil physicochemical properties in the root zone, together with the soil organic matter content, as well as the water and fertilizer storage capacity. The circulation of water and vapor was then promoted in the root zone environment. Besides, the fertilizer-soil mixing can be expected to enrich the soil microbial community for the soil enzyme activity in the root zone. A healthy soil environment was created for the nutrient availability of root growth with the nutrient ion coupling, the mineralization and decomposition of soil organic matter. Therefore, it is necessary and beneficial for the ring-furrow fertilization combined with the fertilization-soil mixing. Mechanized ring-furrow fertilization in the dense planting apple orchards was constructed with the opening continuous curved furrows along each side of the tree row to surround the root zone, accompanied by fertilizer application and fertilizer-soil mixing. A tracked and self-propelled fertilizer applicator was developed to implement the proposed mode. The fertilizer applicator was mainly composed of the tracked self-propelled chassis, fertilizer box, and fertilizer implement. An auger bit was adopted to synchronously complete the curve furrowing, fertilizing, and fertilizer-soil mixing. The fertilizer applicator was selected to control the lateral motion of the auger bit using an electro-hydraulic furrowing trajectory control system, particularly with the detected positioning signal of the tree trunk. The curve trajectory was synthesized to integrate the lateral motion of the auger bit and the longitudinal motion of the fertilizer applicator. The field test showed that the developed fertilizer applicator can be expected to accurately detect the tree trunk for the continuous ring-furrow in the application of fertilizer around the trunk, and then the organic fertilizer can be mixed with the whole soil layer. The ring-furrow width and fertilizer applying depth were (210±6.3) and (300±19.5) mm, respectively. The furrowing resistance torque and power consumption were 127.32 N·m and 5.84 kW, respectively, indicating stable working conditions. The average errors of ring furrow and fertilization trajectory were 0.05 and 0.03 m, respectively, when the set base circle radius was 0.7 m. The mechanized ring-furrow fertilization was first realized for the organic fertilizer. The finding can also promote the precise and efficient fertilization of organic fertilizer in dryland orchards.