COVER CROP VARIETY AND SEEDING RATE EFFECTS ON WINTER WEED SEED PRODUCTION

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1 COVER CROP VARIETY AND SEEDING RATE EFFECTS ON WINTER WEED SEED PRODUCTION Nthn S. Boyd nd Eric B. Brennn, USDA-ARS, Orgnic Reserch Progrm, 1636 E. Alisl Street, Slins, CA Astrct Weed mngement is one of the most criticl yield-limiting fctors in orgnic crop production systems. Little is known out the impct of winter cover crops on winter weed popultion dynmics. The USDA-ARS orgnic reserch progrm in Slins, Cliforni hs conducted severl trils exmining the impct of cover crop mngement options on weed popultions. The reserch focused on cover crop seeding rte nd vriety, mixture composition, nd rotry hoeing. In comprison of 1X (industry norm) nd 3X seeding rtes of rye, mustrd nd legume-rye cover crops, chickweed seed production ws 224 seeds/m2 in the 1X legume-rye mix while seed production did not exceed 18 seeds/m2 in ny of the remining cover crops. In nother experiment, incresing the cerel component or dding mustrd to mix reduced the numer of weed seeds produced during the winter. Cover crop mixes with high plnt density tht cover the ground quickly fter plnting re the most effective t reducing weed seed production. In poorly competitive cover crops, the rotry hoe provided n lterntive mens to control emerging weeds. Introduction Most cover crop reserch in the centrl cost of Cliforni hs focused on nitrte leching nd nitrogen cycling. Little is known out cover crop effects on weed mngement. Preliminry work t the USDA-ARS certified orgnic site in Slins indicted tht legume-cerel mixes my excerte weed prolems llowing high weed seed production (Brennn nd Smith, 2003). Incresing the seeding rte increses crop competitive ility (Mohler, 2000) nd in csh crops reduces weed seed production (Tesdle, 1998). Seeding rte effects on weed suppression in cover crops hs received little reserch ttention. In poorly competitive cover crops, the rotry hoe my e used for weed control fter cover crop emergence. It hs een used to control weeds effectively in vriety of monocultures, ut to our knowledge, hs never een evluted in mixed plntings. Multiple psses with the rotry hoe my help control weeds tht germinte nd emerge within the cover crop over n extended period of time (Lelnc nd Cloutier 2001). The ojectives of this pper re to report the impct of cover crop seeding rte, mixture, nd rotry hoeing on weed iomss nd weed seed return. Mterils nd Methods The cover crop vriety nd seeding rte tril is designed to exmine the impct of cover crop vriety nd plnting density (Tle 1) on winter weed popultions nd summer vegetle production. Rye, mustrd nd legume-rye cover crop mix were plnted t two rtes in the fll nd mesurements of cover crop iomss nd ground cover were tken throughout the seson. Weed emergence, growth, nd seed production were monitored in ll cover crops. Cover crop growth nd iomss production s well s weed growth nd weed seed production were compred in vriety of existing nd novel cover crop mixes. This pper reports the results of 9 of 27 mixes. The rotry hoe tril exmined the effect of rotry hoeing on weed popultions within legume-rye cover crop.

2 Tle 1. Seeding rtes nd estimted plnt density for three seprte cover crop trils. Tril Cover crop mix Seeding Rte (kg/h) Seeding density (plnts/m2) Cover crop vriety nd seeding rte tril Merced Rye1 1X Merced Rye 3X Mustrd X Mustrd X Legume-rye X Legume-rye X Mixes tril 10% ot, 90% legume % ot, 60% legume % rye, 90% legume % rye, 60% legume Legume4 + 2ls mustrd Bell ens (Vici f L.) Mustrd Cyuse ots (Aven stiv) Rye Rotry hoe tril Legume-rye Secle cerele ( Merced ) 2 61% Brssic junce (L.) Czern. ( Id Gold ), 39% Brssic hirt Moench. ( Pcific Gold ) y weight. 3 10% Secle cerele L. ( Merced ), 35% Vici f L., 25% Pisum stivum L., 15% Vici stiv L., 15% Vici enghlensis L. y weight. 4 35% Vici f L., 25% Pisum stivum L., 15% Vici stiv L., 15% Vici enghlensis L. y weight. 5 23% Vici f L., 17% Pisum stivum L., 10% Vici stiv L., 10% Vici enghlensis L. y weight. 6 45% Vici villos (Ln vetch), 45% Vici enghlensis L. (purple vetch) y weight. 7 30% Vici villos (Ln vetch), 30% Vici enghlensis L. (purple vetch) y weight. Cover crop cnopy development ws estimted y holding 30 y 30 cm qudrt with 64 cross grids ove the cover crop cnopy nd counting the numer of grid crosses ove cover crop plnts. Weed seed production ws estimted y vcuuming the soil surfce of 0.5 m2 qudrt from ech plot. A crust hd formed on the soil surfce llowing removl of weed seeds nd surfce deris with miniml soil disturnce. The weed seeds were seprted from soil

3 nd orgnic residue y pssing ech smple through 1.7 mm sieve nd then floting the seeds in wter. All dt were nlyzed in SAS (Cry, NC) with the PROC GLM procedure nd Tukey s or lests squres mens comprisons. Only the first yer of multiple yer studies is presented. Results nd Discussion Cover crop vriety nd seeding rte tril. Chickweed (Stellri medi (L.) Vill.) comprised the mjority of the weed iomss. Weed iomss production ws significntly ffected y cover crop vriety nd seeding rte throughout the cover cropping period (Figure 1). The legume-rye 1X cover crop chieved 100% ground cover more slowly thn ny other cover crops nd hd significntly less iomss production erly in the seson. Mustrd nd rye 3X produced the most cover crop iomss erly in the seson. By erly spring (Mrch) there were no significnt differences in cover crop iomss production (dt not shown). Weed iomss ws inversely proportionl to erly seson cover crop iomss. Weed iomss in the legume-rye 1X incresed y more thn eight fold from Novemer to Jnury when it ws 11 times higher thn the verge weed iomss in ll other tretments. Aove Ground Biomss (kg/h) Legume-Rye Mustrd Rye 1x 3x 1x 3x 1x 3x 1x 3x 1x 3x 1x 3x 1x 3x 1x 3x 1x 3x Novemer 2003 Jnury 2004 Mrch 2004 Figure 1. Weed dry iomss production on 3 hrvest dtes in the cover crop vriety nd seeding rte tril. Brs re men ± SE. Within ech dte, rs topped with different letters re significntly different t < Chickweed seed production ws lso influenced y cover crop vriety nd seeding rte (Figure 2). The gretest chickweed seed production occurred under the legume-rye 1X (224 seeds/m2) nd the lest occurred under the legume-rye 3X (3 seeds/m2). Cover crop seeding rte did not influence chickweed seed production in mustrd or rye. Rotry hoe tril. One pss with the rotry hoe in the legume-rye cover crop reduced chickweed nd shepherd s purse seedlings y 64 nd 91%, respectively. At 36 dys fter plnting (DAP) there were totl of 474 emerged weeds/m2 in the no rotry hoe tretment. A single pss with the rotry hoe 14 DAP reduced totl weed density y 69% to 148 weeds/m2. An dditionl pss with the rotry hoe did not further reduce weed density. One pss with the rotry hoe reduced seed return y 81% for chickweed nd 93% for shepherd s purse (Figure 3). A second pss with the rotry hoe hd no dditionl ffect on weed seed return. Mixes tril. Ground cover, ove ground cover crop nd weed iomss nd weed seed production were compred for vriety of cover crop mixes. Chickweed ws the predominte weed. In single component cover crops the lowest weed seed production occurred in mustrd followed y rye (Tle 2). Ots nd ll other legumes exmined in this tril were less competitive. Incresing the cerel component of mix, nd consequently its density, decresed

4 weed seed production (Tle 2). Adding mustrd to legume mix reduced weed seed production nd survivl of the legume component (Tle 2). Weed iomss ws highly correlted with erly seson ground cover mesurements tken 43 DAP. Chickweed Seed Production (seeds/m 2 ) Legume-Rye 1x c c c Legume-Rye 3x Mustrd 1x Mustrd 3x Figure 2. Chickweed seed production y the finl cover crop hrvest in Mrch, 2004 of the cover crop vriety nd seeding rte tril. Brs re men ± SE. Within ech dte, rs topped with different letters re significntly different t P < Rye 1x Rye 3x Weed Seed Return (seeds m -2 ) Chickweed 0 Psses 1 Pss 2 Psses Weed Species Sheprd's Purse Figure 3. Weed seed return y chickweed nd shepherd s purse 134 DAP following 0, 1, or 2 psses with the rotry hoe. Brs within the sme weed species with different letters re significntly different t P<0.05.

5 Tle 2. Winter chickweed seed production within vrious cover crop mixes in the mixes tril. Cover Crop Mix Chickweed Seed Production 10% ot, 90% legume % ot, 60% legume % rye, 90% legume % rye, 60% legume 435 c Legume + 2ls mustrd 90 c Bell ens 1568 Mustrd 46 Cyuse ots 802 Merced Rye 310 1For further informtion on the cover crop mix plese see tle 1. 2Vlues followed with different letters re significntly different t P<0.05. Single components were not compred sttisticlly. The differences in weed suppression y the cover crop vrieties nd seeding rtes in these studies is prtilly explined y differences in cnopy development erly in the seson. As expected, incresing the seeding rte or the cerel component of legume-cerel mixes mrkedly improved their weed suppressive ilities. However, incresing cover crop seeding rte to improve weed suppression in legume mixes often suppresses oth weeds nd less competitive components like legumes (Brennn nd Boyd, unpulished dt). With single component cover crops, incresing the seeding rte my provide chep insurnce ginst weeds, considering tht cover crop seed ccounts for reltively smll prt 25%) ( of totl cover cropping costs (Klonsky et l., 1994). Alterntively, the rotry hoe my otin sufficient weed mngement in poorly competitive cover crops without incresing the seeding rte.

6 References Brennn, E.B., nd Smith, R Cover crop cultivr nd plnting density impcts on cover crop productivity, nd weed iomss nd seed production in n orgnic system in the Centrl Cost of Cliforni, p Proceedings of the Cliforni Chpter of the Americn Society of Agronomy, Modesto, Cliforni. Klonsky, K., Tourte, L., Chney, D., Livingston, P., nd Smith, R Culturl prctices nd smple costs for orgnic vegetle production on the Centrl Cost of Cliforni. Ginnini Foundtion Informtion Series, University of Cliforni Division of Agriculture nd Nturl Resources No. 94-2, 84. Lelnc, M.L., Cloutier, D.C., Susceptiility of dry edile en (Phseolus vulgris, crnerry en) to the rotry hoe. Weed Tech. 15, Lelnc, M.L., Cloutier, D.C., Susceptiility of row-plnted soyen (Glycine mx) to the rotry hoe. J. Sustin. Agric., 18, Mohler, C.L Mechnicl mngement of weeds, p , In M. Leimn, et l., eds. Ecologicl Mngement of Agriculturl Weeds. Cmridge University, Cmridge. Tesdle, J.R Influence of corn (Ze mys) popultion nd row spcing on corn nd velvetlef (Autilon theophrsti) yield. Weed Sci. 46,