Weed control by harrowing is an essential measure in organically grown cereals, but it is also known to be less effective against perennial weeds. Such problems might be solved by using a more effective hoeing which needs wider row spaces. On the other hand, there is a risk of low competi-tiveness in wide crop stands, particularly if mechanical control effects are unsatisfying.

Therefore, a new approach has been investigated by using a crop design with alternating crop bands and crop-free bands. Using hoes in the crop-free band as well as a higher crop competitiveness within the crop band are two possible effects in order to make weed control more effective

Verschwele, Arnd

English

Organic Eprints

times varying between early- and late-season over time toavoid proliferation of particular species. Perennial covercrops, on the other hand, may actually enhance thepersistence of seeds in the seedbank. The past decade hasseen considerable interest in manipulating seedbanks, withconsiderable interest in predation, and advances related tothe importance seeds availability and predator demand.Lastly, as evidence that progress is possible, there are thefew known examples of organic farmers who haveseemingly ’solved’ their weed problems. They share afocus on preventing seed production, reflecting the wisdomof the age-old adage (’a years seeding...’), and the morerecently proposed ’No Seed Threshold’ (Norris, 1999).They have experienced progress in their weed managementefforts, as their seedbanks decline over time. At firstconsideration, their tactics - intensive use of organicmulches and summer fallowing - may seem extreme,beyond practical. They argue, however, that practiceswhich simultaneously control weeds, improve soil quality,and permit available labor to manage other aspects of thefarm are critical to sustaining their enterprises. Thesefarmers exemplify the goal stated in the 2007 NationalOrganic Research Agenda, published by the U.S.-basedOrganic Farming Research Foundation: ’to understandand develop management systems that shift the focus ofpest management from use of external inputs to internalbiological controls arising from the system itself, leading towhole farm systemic resistance to weeds...’613. New Technologies Call for New Research Priorities inPhysical Weed Control with Low Selectivity. JesperRasmussen1, Michael Nørremark2, Bo Martin Bibby2;1The University of Copenhagen, Taastrup, Denmark;2TheUniversity of Aarhus, Horsens, DenmarkA web-based digital image analysis tool (IMAGINGCrop Response Analyser) has been developed, tested andmade public (www.imaging-crops.dk). This new technol-ogy makes possible objective estimations of crop-soil cover(i.e. how much crop is buried with soil) associated withpost-emergence weed control with spring tine harrows,rotary hoes and other weeders. Objective estimation ofcrop-soil cover offers new possibilities to improve decisionsupport of physical weed control practises with lowselectivity because trade-offs between weed control andresulting injury to the associated crop now may bequantified, communicated and incorporated into models.The objective of this presentation is to suggest keyparameters and research priorities for future researchand to suggest standards for estimation and statistical testof the analytical parameters. The overall aim is to helpresearchers deliver reliable parameter estimates that mayhelp to predict the optimal intensity and timing of physicalweed control with low selectivity and, thereby, contributeto the theoretical and methodological framework ofphysical weed control. Selectivity and crop recovery aresuggested as key parameters because they are crucial inpredictive models and are less influenced by site-specificsoil conditions and implement settings than other param-eters. Selectivity is defined as the ratio between weedcontrol and crop-soil cover and crop recovery is defined asthe ability of the crop to recover from soil coverage. Bothparameters depend on the intensity of tillage. To facilitatecomparisons between different studies, it is suggested thatthe crop soil cover associated with 80% weed control andthe relative crop yield loss associated with 25% crop-soilcover are calculated with 95%-confidence intervals.Experimental protocols needed to make such calculationsare outlined and factors that influence - or may influence -selectivity and recovery are listed and research prioritiesare given. Crop tolerance has previously been used toexpress the susceptibility of the crop to physical weedcontrol, but crop recovery is shown to be more useful indecision support models than crop tolerance. Recentstudies using the new digital image analysis tool and theabove suggested parameter estimation procedure showthat timing of weed harrowing is of lesser importance if theintensity of tillage is correctly adjusted to the growth stagecompared with prediction of the optimal intensity in site-specific conditions. This latter issue remains the majorchallenge for future development614. Effects of Sowing Measures on Weeds and Yield ofOrganically Grown Wheat. Arnd Verschwele1;1JuliusKu ¨ hn Institute, Braunschweig, Niedersachsen, GermanyWeed control by harrowing is an essential measure inorganically grown cereals, but it is also known to be lesseffective against perennial weeds. Such problems might besolved by using a more effective hoeing which needs widerrow spaces. On the other hand, there is a risk of lowcompetitiveness in wide crop stands, particularly ifmechanical control effects are unsatisfying.Therefore, a new approach has been investigated byusing a crop design with alternating crop bands and crop-free bands. Using hoes in the crop-free band as well as ahigher crop competitiveness within the crop band are twopossible effects in order to make weed control moreeffective.Three winter wheat experiments were conducted in 2005,2006 and 2007 (year of harvest) at the organic farmingresearch area. The trials were performed in a block designwith 4 replications and a plot size of 120 m2 including thefollowing row spacings:(a) narrow spacing: row distance of 100 mm,(b) band spacing: bands of 4 rows (400 mm width)alternate with crop-free bands (300 mm width),(c) wide spacing: row distance of 400 mm.As a second factor we tested two winter wheat cultivarswith different crop competitiveness (1. Ludwig, 2. Pegas-sos). Pegassos is known as a cultivar fairly adapted to theconditions of organic farming. It is characterised by255  Archived at http://orgprints.org/2384/   prostrated and large leaves whereas Ludwig can bedescribed by a more upright growth and consequently alow weed suppressing ability.Because of a very high initial weed infestation it was notpossible to keep plots weed free. Depending on the weeddensity all plots have been harrowed 2-3 times, addition-ally the plots with the crop bands and wide rows (variant band c) have been hoed two times. Among others, thefollowing parameters have been assessed: weed coverage,weed biomass, weed number, crop yield and crop quality.Data were analysed by a multifactor analysis process usingStatgraphics Plus, version 5.1. Based on all data, meanvalues and confidence levels were calculated by consider-ing the 3 tested factors row spacing, cultivar and year.The initial weed density varied from 225 to 451 weedsm2 . The most frequent weed species were Lamium spp.,Veronica spp. Stellaria media and Urtica urens. The weeddensity assessed before mechanical control measures wasnot effected by row spacing (P=0,737) and year(P=0,069) but by cultivar (P=0,006). There were nosignificant interactions between these factors. However,compared to the number of weeds there were strongereffects on the weed biomass. Row distance and year dideffect the weed dry matter assessed at growth stage BBCH61-65 significantly (P=0,016 and 0,000). The followingweed biomass was estimated at the 3 row spacings: (a)21.9, (b) 2.61, (c) 45.9 g/m2. Differences between (a) and(b) were not significant, but the wide spacing (c) resulted insignificant higher weed infestation. In 2005 and 2006 therewas also a cultivar effect on weed infestation: Correspond-ing to a higher crop cover, Pegassos showed a strongerweed suppression rather than Ludwig, especially in thewide spaced crop stand. No differences between bothcultivars have been observed in 2007 and at the bandspacing.All factors (row spacing, cultivar, year) had a significanteffect on the grain yield of winter wheat (P,0.001). Thehighest grain yield averaged over the 3 years (6.24 t/ha)was measured at band spacing (b) compared 5.85 t/ha atnarrow spacing (a) and 5.28 t/ha at wide spacing (c). Thisindicates the high compensating ability of the both wheatcultivars. The results show that, at least under favourablesoil and weather conditions, good weed control efficacycan be combined with high grain yield by using a bandsown crop stand.615. Organic Vegetable Cropping Systems for PurpleNutsedge Management. Carlene Chase1, Rosalie Koenig1,Jeffery Pack2;1University of Florida, Gainesville, Florida,United States of America;2Escuela Agrı´cultural Panamer-icana, Tegucigalpa, HondurasInfestations of perennial weeds are significant obstaclesto organic production and can result in growers removinginfested acreage from production. Uncontrolled popula-tions of purple nutsedge (Cyperus rotundus) can causecomplete crop failure. An on-farm evaluation of serialintegrated crop management systems was conducted tomanage purple nutsedge in organic vegetables in north-central Florida. A multi-pronged approach that involvesyearlong management during fallow and cropping periodswas employed. Summer fallow techniques included sunnhemp (Crotalaria juncea) as a cover crop, soil solarization,clean fallow with weekly tillage, clean fallow with flaming,and were compared with a weedy fallow. Two sunn hemptreatments were used so that after 12 weeks of growthstems were cut just above the soil surface and eitherincorporated prior to transplanting the fall crops orretained on the soil surface as mulch. The persistence ofpurple nutsedge suppression was evaluated in two subse-quent fall cash crops (lettuce, Lactuca sativa and brocco-li,Brassica oleracea) and spring cash crops (zuccchinisquash, Cucurbita pepo and bell pepper, Capsicum annuum)with differing canopy sizes and rates of growth anddevelopment. The additional benefit that could beobtained from a weed-suppressive infrared-transmitting(IRT) mulch was also assessed. All summer fallowtreatments effectively suppressed purple nutsedge and thesuppression persisted within subsequent fall and springvegetable crops. Highest lettuce yields occurred withincorporated sunn hemp, solarization and tillage; andbroccoli yields were best with flaming, solarization, andtillage. Pepper yields were higher with tillage than with allother fallow treatments. Squash was very competitive withpurple nutsedge so that yields with the weedy fallow onbare ground did not differ from those of most of the otherfallow treatments. The use of IRT film further reducedpurple nutsedge infestation and increased squash andpepper yields. The most consistent and effective combina-tion of treatments appears to be weekly tillage in summerfollowed by IRT film in spring.616. Pre-Plant Composting of Organic Matter Helps WeedControl in Organically Grown Vegetables. Barakat AbuIrmaileh1, Azmi Abu Rayyan1;1Faculty of Agriculture-University of Jordan, Amman, JordanWeed management in vegetables is a must; otherwisesevere yield reductions are anticipated. Several methodsare normally applied for weed control including herbicides.However, chemical weed control is not a choice inorganically grown vegetables. Several experiments werecarried out to investigate the efficiency of pre-plantcomposting of several organic matters in reducing weedpopulations under natural weed infestations in variousvegetables. Composting was carried out by incorporatingorganic matter in 0.4m-band in the soil of the plantingrows. After incorporation, the rows were immediatelycovered by black polyethylene (BPE) sheets then drip-irrigated twice during a period of six weeks beforeplanting. In a split-plot experiment, the tested organicmatters were wheat hay, manures of cow, poultry or sheep,256

Effects of sowing measures on weeds and yield of organically grown wheat

Abstract

Similar works

Full text

Available Versions

Organic Eprints