An investigation into the design of precision weeding mechanisms for inter or intra-row weed control

摘要

There is an increasing interest in the use of mechanical intra-row weeders because ofconcern over environmental degradation and a growing demand for organicallyproduced food. The aim of this study was to investigate the factors that influence thedesign of precision weeding mechanisms for inter-and intra-row weed control. Thepurpose is to increase the understanding of the dynamics of the soil-machineinteractions and to develop a system for either organic farming or to reduce theenvironmental loading of agrochemicals in conventional agriculture.Both the graphical computer simulation studies and the use of a mathematical model(O’Dogherty et al., 2007) for the kinematics of discs were used as tools to aid the discdesign to determine the optimum geometric characteristics for a rotating disc that willbe able to treat the intra-row area between the crop plants undisturbed circle. Themodel has wide applicability for the interactive design of discs for a range of crops.A force prediction model for shallow asymmetric static and rotating discs (about avertical axis) developed to predict the forces on rotating discs. The model takes intoaccount the geometric parameters of the discs, the speed of operation, the workingdepth and the physical properties of the soil based upon those required for the generalsoil mechanics equation which obeys the Mohr-Coulomb failure criterion. Acomparison of all experimental work encompassing the laboratory experiments withnon-rotating and rotating discs, incorporating the deflection effect of the shaft whenworking at 0o inclination angle showed that the model is able to predict the draughtforce with good accuracy. The predicted forces were 3.5% more than the measuredforces overall for a linear regression line (with a coefficient of determination of 0.7)and 61% of the data were within bounds of ± 25% a line of equal magnitude.The effect of working depth, inclination angle and disc geometry on draught andpenetration force requirements for flat and convex discs were assessed undercontrolled laboratory conditions. Because of its simplicity a flat disc was an obviousone to study as it is a circular blade with incorporating a cut-out sector, whilst the convex disc has the advantage of underside clearance. The effect of the concavity onsoil failure proved to be of interest by providing smaller aggregates. Four inclinationangles (0o - 15o) were examined at 0.5 m s-1 (1.8 km h-1) driving speed and 1 rev s-1rotational speed at 10 mm deep. Four depths (10 mm - 25 mm) were examined at 0.5m s-1 driving speed and 1 rev s-1 rotational speed at 10 mm deep and 0o inclinationangle were tested under controlled conditions. Inclination angle and disc geometryhad a significant effect on disc forces and soil failure. A small increase in inclinationangle to the direction of travel reduces the magnitude of draught and vertical force by70% and 80% respectively on average for both flat and convex disc geometries. Theconvex disc requires 15% less draught force than an equivalent flat disc. This allowedthe optimum working parameters for a disc to be selected to eliminate the weeds withthe minimum force requirements.The results of a field experiment after 16; 23; and 33 days transplanting with aworking speed of 0.5 m s-1 (1.8 km h-1) showed that the proposed novel mechanicalweed control system can achieve a weed reduction within the crop row up to 87%.The disc-hoe has a lower cost for an area of 125 ha of £81 ha-1,in comparison to £139ha-1 for the inter-row and hand weeding combination and £690 ha-1 for a six man gangmanual intra-row weeding, for two passes. It is also less expensive than the cost of the24 m tractor mounted sprayer of £100 ha-1The use of the rotating disc-hoe for mechanical weed control would have the benefitsof lower mechanical weeding cost, increased potential for organic production andreduction in the number of weeding operations through better targeting to minimiseproblems caused by frequent soil disturbance and reduced herbicide use having thebenefits of environmental advantage.