Jordbearbetning i mörker : inverkan av harvning med ljustät övertäckning på ogräsuppkomsten
Field experiments in Sweden and abroad during the last few years have shown that soil-disturbing operations such as seedbed preparation and sowing when carried out at night, reduced the subsequent emergence of weed seedlings, compared with the emergence after the same tillage operations in daylight. Earlier experiments at the Swedish University of Agricultural Sciences in Alnarp have shown that the number of weeds per m2 also decreases after cultivation in the daytime with a light-proof cover at the harrow. In the literary survey the possibility of amplifying the inhibiting effect on germination with an extra amount of dark red light (circa 735 nm) under the cover was investigated. The literary survey also contains one part about the effect of light on germination and one part about previous experiments of soil cultivation in darkness. The amount of dark red light required to reach an inhibiting effect is given in the literature with a great spectrum. During cultivation the seeds are exposed to the dark red light for only a short period of time. The lamp effect required under the cover will therefore be considerable, maybe as high as 70 kW m2. The conclusion is that with today's methods it will be hard, if not impossible, to obtain this high effect. Thus it is probably impossible to obtain an inhibiting effect on light-stimulated seeds with an extra amount of dark red light during cultivation. The purpose of the field experiments was to observe how light influences the weed emergence by carrying out the soil disturbance on different occasions, with and without a light-proof cover on the cultivator. I also wanted to study if a less light-proof cover than the one used by Ascard & Holmqvist (1993) could give a satisfactory effect and reduce weed emergence. Two field experiments were carried out on crop-free soil near Alnarp (55°39'N, l3°05'E) in the autumn of 1993. The harrowing was with and without a cover during the day and in twilight and with a cover approximately one hour after sunset. The experimental harrowings were carried out twice in each plot immediately after each other so as to correspond to a normal seed bed preparation. For economical reasons no crop was sown in the experiments. In the first experiment a simple cover made of tarpaulin was hung over the implement. In the second experiment the cover was elaborately made of two layers of black fibre mat, the same as in Ascard & Holmqvist (1994) Light measurements were made under the cover before every treatment. The insolation was measured continuously from the first to the last treatment. In the first experiment all weeds that emerged after the experimental cultivation two months before were recorded. In the second experiment the emerged weeds were recorded both one and two months after cultivation. In the later the weed species also were determined. In both experiments most weeds appeared after soil disturbance during the daytime without cover. Harrowing in the daytime with cover of tarpaulin gave a reduction of emerged weeds with 23% and with a cover of black fibre mat the reduction was 8% compared with cultivation in the daytime without a cover. The differences were not significant. Harrowing in twilight without a cover decreased the emergence of weeds in both of the field experiments compared with cultivation in twilight without cover. The differences were not significant and they were probably the result of a higher level of light when the cultivations were carried out without a cover while it was performed before the one with cover. In the experiments with a tarpaulin there were no significant differences of the weed emergence between the different treatments. Although all tree cultivations with a cover showed a lowered emergence of weeds compared with the harrowing in the daytime without a cover. In the experiment with black fibre mat harrowing at night decreased the emergence of weeds significantly compared with harrowing during the daytime without a cover, both one and two months after treatment. After one month the reduction was 25% and after two it was 20%. The relatively small reduction of weeds in my experiments can possibly be explained by the fact that the treatment was carried out in the autumn. In the experiment with the black fibre mat there was a connection between a reduced number of weeds and a low level of light. To make this connection more clear a light measuring equipment with higher sensitivity than the one used in this experiment is needed. In the literary survey and through my own calculations I studied whether an increased amount of germination-inhibiting dark red radiation (circa 735 nm) under the cover compared with germination-stimulating red radiation (circa 665 nm) could reduce the emerged number of weeds.
mörkerharvning; miljövänlig; ogräsbekämpning; frö; groning; fytokrom; ljus
Rapport - Sveriges lantbruksuniversitet, Institutionen för lantbruksteknik
Publisher: Institutionen för lantbruksteknik, Sveriges lantbruksuniversitet
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