DESIGN AND DEVELOPMENT OF A HIGH-SPEED DIBBER DRILL FOR IMPROVED CROPESTABLISHMENT

Field sowing is cheaper than transplanting, but the emergence is often erratic. One practical solution to this problem may be to achieve bet ter control of the soil physical environment in the seed zone by an ap propriate drilling technique. For example, the use of dibbers to place the seeds in intimate contact with the soil will help ensure optimal use of available soil moisture. Also, by covering each seed with a sma ll quantity of material other than soil, the emerging seedlings may be protected against adverse changes in soil conditions. This hypothesis was first tested with a low-speed fixed spacing drill. When used to s ow crisp lettuce this drill gave significant improvements in emergence compared with a conventional coulter drill. These improvements were g reatest in the absence of irrigation when an average 77% of the dibbed seeds, covered with a mixture of peak and vermiculite, emerged compar ed with 36% for the coulter drill. These results led to the developmen t of the second drill described in this paper, which offers both high- speed operation, up to 2 m/s, and variable spacing of successive seeds within the row. Despite achieving improvements in emergence in crisp lettuce, comparable with those recorded with the low-speed drill, init ial experiments with a brassica showed that the coulter drill performe d very much better (80% emergence compared with 57% for the dibber dri ll). Later experiments, following modification to the drill to reduce the consolidation of the soil around the seeds, eliminated the depress ion in emergence. However, further work is required to realize improve ments in emergence of brassica comparable with those recorded with let tuce and other crops.