Development of a novel mechatronic system for mechanical weed ...

Introduction
than 40 years before germination. The timing and method of soil management
have a great influence on the dormancy or germination of the weed seeds.
Weeds compete with crops for moisture, light, nutrients and space, and
therefore their elimination is of high importance. An understanding of the crop-
weed competition combined with the knowledge of weed characteristics and
behaviour can be critical in establishing an optimal weed management system,
or more exactly the timing of weeding operations. For most crops there exist a
critical period during which weeds must be controlled to maintain the yield.
Studies to determine the critical weeding periods under conventional growing
systems have been done for almost all crops. However, in the period
immediately after emergence, experiments showed that weeds present on the
field had little effect on the crop yield, as also after the critical period. Crop
species are tolerant to early weed competition without yield loss in certain
periods during their growth, whereas weed-free periods are required in other
development stages of the crop plants to prevent yield loss (Zimdahl 1980;
Grundy et al. 2003). Besides, weed species have distinct periods of germination
and seasonal patterns of weed emergence, which are experimentally examined
under the conventional growing system (Lampkin 1990; Naylor 2002). This
information can help to choose the optimal timing for operations such as
cultivation, sowing and weeding, according to the peak time for germination
periods of the predominant species.
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1.4 Organic weed management
Successful organic weed control involves the combination of various operations
and cultural management methods. The right approach in organic weed
management planning has to be systematic and should start with the highest
system level and descend to the lowest. If some levels are omitted or missing,
the result will reflect on the yield directly or cause significant problems in the
next season. The ultimate aim for all organic farmers is to prevent development
of the annual weeds to the stage when they are able to produce seeds and to
restrict the dispersal and growth of perennial weeds (Taylor and Zenz 2006).