Interactions between pre‐ and post‐emergence weed harrowing in spring cereals

Abstract

SummaryPre-and post-emergence weed harrowing were studied in spring cereals in different environments and with two types of harrows in Norway during [2004][2005][2006]. The objectives were to investigate interactions between preand post-emergence weed harrowing and the importance of harrow type. We hypothesised that pre-and post-emergence harrowing interact positively, that a combination gives more stable weed control effects than pre-and post-emergence weed harrowing used alone, and that a harrow type with bent tines is more aggressive and suitable on hard-packed soils than a harrow with strait tines. The results only supported the last of these hypotheses. Post-emergence weed harrowing controlled a certain percentage of the present weeds, and this percentage was not dependent on pre-emergence weed harrowing. On average, pre-emergence harrowing reduced weed density by 26% and weed biomass by 22%, while the average effect of postemergence harrowing was 47% on weed density and 41% on weed biomass. The combined effect of pre-and post-emergence weed harrowing was 61% on weed density and 54% on weed biomass. The combination did not give more stable weed control effects than preand post-emergence weed harrowing used alone. Preemergence harrowing increased the average crop yield by 6.2%, post-emergence harrowing by 4.0% and the combined effect was 10%. Crop yield was mainly increased on hard-packed soils. Weed and crop responses varied strongly among experiments, but the efficacy of pre-and post-emergence weed harrowing was positively correlated across experiments. Weed species composition was of minor importance regarding weed control. The study indicates that one aggressive postemergence cultivation may be as good as one preemergence and one less aggressive post-emergence cultivation. However, little is known about the interactions between cultivation at different crop and weed growth stages.Keywords: integrated weed management, machinery, mechanical weed control, non-herbicide weed management, organic farming.

Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

“…A recently published study by Brandsæter et al . (), however, did not support this view. In their study, both pre‐emergence and post‐emergence weed harrowing independently reduced weed biomass compared with the untreated control, by 22% and 41% respectively.…”

“…On average in our study, pre‐emergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while the combination of pre‐ and post‐emergence weed harrowing reduced weed density by 59% and weed biomass by 67%, compared with the control. Several studies have documented similar weed reductions from weed harrowing once or twice (Rasmussen & Rasmussen, ; Lundkvist, ; Brandsæter et al ., ). Post‐emergence weed harrowing controls a certain percentage of the weeds present, independent of whether it was preceded by pre‐emergence weed harrowing or not (Brandsæter et al ., ).…”

“…This is supported by Brandsæter et al . (), who found that pre‐emergence harrowing increased the average crop yield by 6.2%, which was more than post‐emergence harrowing (4.0%). However, pre‐ and post‐emergence harrowing combined gave the highest yield increase (10%).…”

“…Experiments conducted before 1930 predate fertiliser use and have shown greater crop yield increases and reduction in weed parameters due to weed harrowing (e.g. Korsmo, ) than more recent studies (Brandsæter et al ., ). It is possible that well‐fertilised crops are less affected by competition from weeds and would therefore not benefit as much from removal of weeds by harrowing as an unfertilised or insufficiently fertilised crop.…”

Robotic weeding's false dawn? Ten requirements for fully autonomous mechanical weed management

“…Weather, is the main driver of soil moisture, which as noted above, can dramatically modify soil physical properties, but, in addition, many weeders (e.g. spring tine harrows) achieve a much higher weed kill in hot dry weather than cold, wet weather (Kurstjens & Perdok, ; Brandsæter et al ., ), while a few can perform regardless of soil moisture and weather (e.g. brush weeders and mini‐ridgers (Merfield, )).…”