evaluation of monocropped and intercropped grain legumes for cover cropping in no-tillage and...

7/24/2019 Evaluation of monocropped and intercropped grain legumes for cover cropping in no-tillage and reduced tillage or

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Europ. J. Agronomy 65 (2015) 8394

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European Journal of Agronomy

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / e j a

Evaluation of monocropped and intercropped grain legumes for covercropping in no-tillage and reduced tillage organic agriculture

Lars Rhlemann, Knut Schmidtke

Hochschule fr Technik und Wirtschaft Dresden, University of Applied Sciences Dresden, Faculty for Agriculture/Landscape Management, Pillnitzer Platz 2,

01326 Dresden, Germany

a r t i c l e i n f o

Article history:

Received 19 March 2014Received in revised form30 November 2014Accepted 18 January 2015Available online 16 February 2015

Keywords:

Organic no-tillCover cropNitrogen fixationIntercroppingOrganic farmingWeed suppression

a b s t r a c t

Intensive tillage by means of mouldboard ploughing can be highly effective for weed control in organicfarming, but it also carries an elevated risk for rapid humus decomposition and soil erosion. To developorganic systems that are less dependent on tillage, a two-year study at Reinhardtsgrimma and Kllitsch,Germany was conductedto determinewhether certain legumecover crops could be equally successfullygrown in a no-till compared with a reduced tillage system. The summer annual legumes faba bean (Vicia

fabaL.), normal leafed field pea (Pisum sativumL.), narrow-leafed lupin (Lupinus angustifoliusL.), grasspea (Lathyrus sativusL.), and common vetch (Vicia sativaL.) were examined with and without sunflower(Helianthus annuusL.) as a companion crop for biomass and nitrogen accumulation, symbiotic nitrogenfixation (N2 fixation) and weed suppression. Total cover crop biomass, shoot N accumulation and N2fixation differed with year, location, tillage system and species due to variations in weather, inorganicsoil N resources and weed competition. Biomass production reached up to 1.65 and 2.19Mg ha1 (bothintercroppedfield peas),and N2fixation upto 53.7 and 60.5kgha1 (both commonvetches)in theno-tilland reduced tillage system, respectively. In the no-till system consistently low sunflower performancecompared with the legumes prevented significant intercropping effects. Under central European condi-tions no-till cover cropping appears to be practicable if weed density is low at seeding. The interactionsbetween year, location, tillage system and species demonstrate the difficulties in cover crop species

selection for organic conservation tillage systems. 2015 Elsevier B.V. All rights reserved.

1. Introduction

Organic farming practices commonly include conventionalmouldboard plough tillage with deep soil inversion as one of themost effective weed control methods (Gruber and Claupein, 2009).However, this labor- and energy-intensive technique reduces thesoils aggregate stability and organic matter content (Hermawanand Cameron, 1993; Schjnning and Rasmussen, 1989)leading tosoil erosion. Thiscontraststhe preservation of soil fertility, which isone basic principle of organic farming. No-till practices can dimin-

ish erosion to tolerable rates (Montgomery, 2007), stabilise soilaggregates and increase soil organic carbonclose to the soil surface

Abbreviations: a.s.l, above sea level; cv, cultivar; DM, dry matter; DWD,Deutscher Wetterdienst (German meteorological service); IC, intercropped; K,Kllitsch; MC, monocropped; RG, Reinhardtsgrimma. Corresponding author at: Hochschule fr Technik und Wirtschaft Dresden,

Pillnitzer Platz 2, 01326 Dresden, Germany. Tel.: +49 351 462 3017;fax: +49 351 462 2167.

E-mail addresses:[email protected](L. Rhlemann),[email protected](K. Schmidtke).

(Carter, 1992; He et al., 2009; Madari et al., 2005 ).Nonetheless, todate, organic no-till systems have not been widely adopted undertemperate central European conditions.

The most prominent barrier to implement a no-till system isthe yield reduction in the transition period (Reicosky and Saxton,2007), due to poor crop emergence, increased weed infestationand reduced nitrogen (N) mineralization. Poor crop emergence isoften a resultof unfavorable seed placement, whichleaves theseedexposed or embedded in hairpinned residue, resulting in reducedcrop emergence in dry conditions due to poor seedsoil contact

(Baker and Saxton, 2007).This can be avoided with the seedingtechnology of the inverted T-cross slot opener, which places theseed into horizontal slots below the residue covered soil surface,creating water vapor rich conditions that favorably affect germina-tion (Baker, 2007; Wuest, 2002).

To control the weed infestation, the transition to the no-tillsystem should be initiated after grain cash crop harvest in sum-mer with the establishment of no-till seeded cover crops. This canreduce the weed competition for the cover crop because the avail-able N resources for weeds have been depleted by the cash crop,whereas perennialweedsthatare favored bythe omission of tillage

http://dx.doi.org/10.1016/j.eja.2015.01.0061161-0301/ 2015 Elsevier B.V. All rights reserved.
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84 L. Rhlemann, K. Schmidtke / Europ. J. Agronomy 65 (2015) 8394

Table 1

Soil, experimental details and date of first daily mean below 0 C (end of g rowing season by temperature definition).

Site Reinhardtsgrimma (RG) Kllitsch (K)

2009 2010 2009 2010

Soil type (FAOclassification)a

Dystric Cambisol Dystric Cambisol Arenic Fluvisol Arenic Fluvisol(shallow) (shallow) (deep) (deep)

Soil texture Loamy sand Loamy sand Loamy sand Loamy sandField capacity (vol.%)b 34 34 32 32Soil pH (0.01M CaCl2) 6.1 5.6 5.6 5.6Soil P (CAL; mg kg1)c 71 29 31 35Soil K (CAL; mgkg1)c 156 135 41 40Soil Mg (0.01 M CaCl2; mgkg1) 88 84 159 131

Cover crop sowing dates 19 August 2009 24 August 2010 17 August 2009 15 August 2010Biomass harvest I 18 September 2009 24 September 2010 18 September 2009 20 September 2010Biomass harvest II 22 October 2009 25 October 2010 25 October 2009 27 October 2010End of growing seasond 31 October 2009 24 November 2010 13 December 2009 24 November 2010

a Soil type according toIUSS Working Group WRB (2006).b Estimated according to DIN 4220 (DIN Deutsches Institut fr Normung e.V., 2008).c Calcium acetate lactate (CAL) extraction method afterSchller (1969).d First daily mean temperature


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L. Rhlemann, K. Schmidtke / Europ. J. Agronomy 65 (2015) 8394 85

The cash crops were harvested during early August and the strawwas transported off the fields, with one exception at the K sitewhere the straw was chopped in 2010. No fertilizer was appliedafter cash crop harvest and during the cover cropping period.

As cover crops, the legumes faba bean (cv. Scirocco), field pea(cv. Livioletta normal leaf type), narrow-leafed lupin (cv. Azuro),grass pea (cv. Merkur) and common vetch (cv. Mery), (1000 seedweight: 437, 169, 145, 224, 46 g, respectively), were sown in MCand IC plant stands. The tested varieties are commonly used ascover crops in Central Europe. The seeding rate (viable seeds) inthe MC plant stands was 55seedsm2 for fababean, 110 seeds m2

for field pea, narrow-leafed lupin and grass pea, 165seeds m2 forcommon vetch, and 139seedsm2 for sunflower. In the IC plantstands an additive mixture was used which consisted of legumesat 100% of their full MC seeding rate plus sunflower (cv. Iregi; 1000seed weight: 65g) at 20% (28seeds m2) of the full MC sunflowerseeding rate. These seeding rates were in the upper range of theregional, experienced based seeding rates to ensure rapid groundcover and high weed suppression. The seed lots, which originatedfrom certified organic seed, differed between 2009 and 2010. Seedrates were adjusted to accommodate variations in the germina-tion ability of the individual seed lots and equal quantities of viableseeds were sown each year.

The design of the field trial was a completely randomized splitplot with four replications. The main plot factors were no-till andreduced tillage. Each main plot was divided into twelve sub plots(22.5 m2, 1.5 m wideand15 m long),fiveplotshadMC legumes,fiveplots had IC legumes with sunflowers, one plot had MC sunflowersas the reference crop for the calculation of the N2fixation, and onefallow plot was without any cover crop.

On the day of seeding, the reduced tillage plots received twopasses of tillage. The first pass was a shallow soil inversion(0.100.12 m depth) conducted with a stubble plough (Type Zobel,Germany)followedbytheseedbedpreparation(0.08mdepth)witha rotary harrow (Type Erpice Rotante, Maschio, Italy). At both loca-tions the reduced tillage cover crops were sown at 0.17 m rowspacing with a plot seeder (Type HEGE 80, Wintersteiger, Austria)

with shoe openers (Wintersteiger, Austria trial preparation in2009) and single disk coulters (RoTeC Control coulter, Amazone,Germany trial preparation in 2010). The direct seeding was con-ducted using a no-till plot drill with inverted T-cross slot openers(Baker No-Tillage Limited, New Zealand) at 0.17 m row spacing.

Narrow-leafed lupin seed inoculation took place just beforeseeding with Rhizobium lupinii (Radicin Nr. 6, JOST GmbH,Germany). Other legume species were not inoculated becauselegumes in the crop rotation maintained a natural level of Rhi-zobium leguminosarum. Field emergence was determined three tofour weeks after seeding at a row length of 1.5m with six repeti-tions per plot. The weed flora was determined visually by means ofplot pictures taken in the course of the study. In the no-till system,weeds were differentiated as weeds present at seeding or newly

germinated weeds based on their growth stage. In the reducedtillage system, tillage removed weeds before seeding, and all weedspresent in the study germinated or regrew after the cover cropseeding.

2.2. Sample collection and analysis

The cover crop and weed biomass were harvested twice; eachharvest sample contained the biomass produced between seedingand the individual harvest date (Table 1). The first harvest (harvestI) was performed four to five weeks after seeding to determine thecover crop and weed biomass production during the early covercropping phase. The second harvest (harvest II) was conducted inthe period between the first frost day (first daily minimum tem-

perature


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Table 2

Monthly mean and trial period mean temperature, monthly precipitation and cumulative precipitation during the cover crop trial period.

Temperature (C) Precipitation (mm)

Reinhardtsgrimma (RG)a Kllitsch (K)b Reinhardtsgrimma (RG)a Kllitsch (K)b

Month 2009 2010 2009 2010 2009 2010 2009 2010

January 4.2 5.3 3.2 5.1 22 31 8 36February 0.4 1.6 0.8 0.5 69 21 27 39March 3.9 2.9 5.3 4.9 76 48 48 73

April 11.2 7.5 12.2 8.9 18 41 9 31May 12.8 10.5 14.4 11.3 91 107 54 216

June 13.9 15.5 15.6 16.6 80 65 45 11July 17.6 19.2 19.0 21.4 108 134 91 63August 17.6 16.6 19.7 17.9 96 222 75 180September 13.8 11.0 15.3 12.9 24 138 29 144October 7.1 6.7 10.7 8.1 108 7 56 14November 6.7 4.2 8.0 5.3 44 107 99 117December 0.7 5.7 0.2 4.3 72 96 148 36

Mean temperature (C) during cover crop trial period Cumulative (mm)P1 15.6 12.3 17.4 15.1 43 90 38 146P2 9.4 7.1 13.7c 9.0 115 118 60 130P3 12.3 9.8 12.0 158 208 98 276

P1, mean temperature and cumulative precipitation during the first period from seeding to harvest I (from August to September).P2, mean temperature and cumulative precipitation during the second cover crop growth period between harvest I and II (from September to October).P3, mean temperature and cumulative precipitation in whole cover crop growing period (from August to October).

a

Climate data (DWD, 2012 personal communication).b Climate data (LfULG 2012),temperature data not available from 1027 October 2009.c Only timeframe 19 September9 October available.

1.5 interquartile range, and removed before conducting statisticalanalyses. Theunbalanced data set was accounted for in thestatisti-cal analysis. The cover crop shoot drymatter biomass of IC legumesand IC sunflowers were then combined to total IC plant stand drymatter production, so that subsequent analyses always comparedthe MC and IC cover crop plant stands as total values. This was alsothe case for total cover crop shoot N accumulation. Values of IClegumes and IC sunflowers were combined as a result of the lowIC sunflower biomass production. Data for field emergence, totalshoot dry matter at harvest I and II, inorganic soil N after harvestII, total shoot N accumulation and N

2fixation were subjected to

analysis of variance (ANOVA) using the MIXED procedure (SAS v.9.3 SAS Institute, Cary, NC). Statistical analyses were performed fortwo locations (RG and K) and two years (2009 and 2010) using alinear mixed model with location, year, tillage system and speciesas fixed effects andreplicatesas randomeffects. The fitof themodelwas tested using residual plots of the pooled data, and data trans-formations (Piepho, 2009),when necessary, were used to achievethe required assumptions for linear regression analyses (Ireland,2010).The arcsine transformation was applied to cover crop fieldemergence; the logarithmic transformation was applied to covercrop and weed biomass at harvest I as well as inorganic soil N afterharvest II; the BoxCox transformation (fixed 0.4) was applied tocover crop and weed biomass at harvest II; data for N2fixation didnot require any transformation.

Homogeneity of variance was tested and in the case of hetero-geneous variances the model was fitted for partitioned variances(Littell, 2011). The degrees of freedom were determined based onthe KenwardRoger method. Least squares means were calculatedand mean comparisons were conducted using the TukeyKramertest (P< 0.05) within the SAS procedure MIXED. A letter displayfor the mean comparisons was created with the %MULT macro byPiepho (2012). In the presence of significant four way interactionsbetween themain factors year, location, tillage systemand species,the slice option within the %MULT macro was used to test for sig-nificant simple main effects by comparing one specific factor atvariable levels of another factor (Schabenberger et al., 2000).Datathat had been transformed was transformed back to the originalscale for presentation.

3. Results

3.1. Weather conditions

In 2009, the mean annual temperatures at RG and K were 8.3and 9.8 C, respectively (Table 2).This was similar to the ten yearaverage, whereas in 2010 temperatures were 2 C below the aver-age (8.8 and 10.1 C, at RG and K, respectively) (DWD, 2012 and2013 personal communication;LfULG, 2012).The total precipita-tion in 2009 was similar at RG and higher at K than the historicalaverage (773 and 473 mm, respectively). In 2010 the total precipi-tationwas substantially higherat RG (+244mm) and K (+487mm)thanthe historical average (DWD, 2012and 2013personalcommu-nication;LfULG, 2012).The first part of the cover cropping periodfrom August to September in 2009 was dry in both locations whilein 2010, there was considerably more precipitation. In the secondpart from September to October a particularly low mean tempera-ture of 7.1 C was reached at RG in 2010.

3.2. Cover crop emergence

The cover crop field emergence was influenced byinteractions between year location tillage system andyear location species (Table 3). The emergence at the RGlocation in both years was lower in the no-till system than in the

reduced tillage system (2009: 55 versus 64%; 2010: 58 versus66%, respectively; data not shown). At K the emergence wassignificantly reduced only in 2010 (57 versus 74%; 2009: 64 versus62%, respectively). Species specific emergence differences weresignificant at the two locations for both years (Table 4). For MC andIC faba bean at RG in 2010 emergencewas considerablyhigher thanit was for the other species. There was less variation demonstratedbetween the species at RG in 2009 and at K in 2010.

3.3. Cover crop shoot and weed dry matter production

The cover crops in the two tillage systems displayed a variableresponse to theconditions in 2009 and 2010 at RG and K resulting


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Table 3

Sources of variation, degrees of freedom and statistical significance of the sources of variation for field emergence (legumes and monocropped sunflower), total cover cropand weed dry matter production at harvest I and II, inorganic soil N 00.3 m soil core, shoot N accumulation (shoot N) and N2 fixation.

Harvest I Harvest II Harvest II

Dry matterproduction Dry matter production Inorganic soil N Shoot Nb N2fixation

Source of variation dfa Field emergence Cover cropb Weed Cover cropb Weed

Year (Y) 1 n.s. *** *** *** *** *** *** *Location (L) 1 n.s. *** n.s. *** n.s. *** *** n.s.

Tillage system (T) 1 *** *** *** *** *** * *** n.s.Species (S) 10, (11, 9) *** *** n.s. *** *** n.s. *** ***YL 1 n.s. *** n.s. *** * *** *** ***YT 1 ** * *** *** *** n.s. *** n.s.LT 1 n.s. n.s. *** ** ** * *** *YS 10, (11, 9) *** *** n.s. *** *** * *** ***LS 10, (11, 9) n.s. *** n.s. *** * n.s. *** ***TS 10, (11, 9) n.s. *** n.s. *** n.s. * *** n.s.YLT 1 ** * n.s. n.s. n.s. n.s. * **YLS 10, (11, 9) * *** n.s. *** n.s. n.s. *** n.s.YTS 10, (11, 9) n.s. *** n.s. * n.s. n.s. ** n.s.LTS 10, (11, 9) n.s. ** n.s. ** n.s. n.s. * n.s.YLTS 10, (11, 9) n.s. ** n.s. *** n.s. n.s. *** *

Total 351, (383, 319)

Component of variation: *, **, *** significant at Plevels ofP< 0.05, 0.01, 0.001, respectively; n.s., not significant.a Degrees of freedom (df), values in brackets correspond to weed dry matter production, and N2fixation, respectively.b

Intercropped cover crop data includes c ombined dry matter production of intercropped legumes and intercropped sunflowers.

in significant year location tillage system species interactionsforthe cover crop drymatter production atharvest I and II (Table3).Weed pressure varied between the two trial years concurrent withthe weather conditions, strongly influencing the cover crop drymatter production. In 2009, the weed biomass production in theearly crop development phase up to harvest I reached 1.16 Mgha1

and 0.11Mg ha1 in the no-till and reduced tillage system, respec-tively (Table 5).In 2010, the weed biomass at harvest I reached0.27 and 0.06 Mgha1 in the no-till and reduced tillage system,respectively.

The total cover crop dry matter production in the no-till sys-tem in 2009 at harvest I was largest for MC field pea (0.37 and

0.31Mgha

1) at RG and K, respectively (Fig. 1).That same year,the IC field peaand MC sunflower produced up to harvest I the mostbiomass at both locations in the reduced tillage system. Betweenthe first and second harvest the cover crop species differed in theirbiomass production particularly in the no-till system at RG. At har-vestI, thecommon vetchdisplayed a lowinitialbiomassproductionin the no-till system, while it showed strong growth in the secondtrial period. Conversely, MC and IC narrow-leafed lupin showed

Table 4

Field emergence of legumes and monocropped sunflowers (averaged across tillagesystems).

Cover crop field emergence (% germinatedplants of viable seeds)

Reinhardtsgrimma Kllitsch

Cover crop speciesa 2009 2010 2009 2010

MC faba bean 68 d 79 e 67 cde 75 cIC faba bean 63 cd 82 e 63 bcd 73 bcMC field pea 65 cd 68 d 70 de 72 bcIC field pea 58 bc 65 d 67 cde 69 abcMC narrow-leafed lupin 68 d 46 a 59 abc 63 abIC narrow-leafed lupin 64 cd 63 cd 62 bcd 67 abcMC grass pea 63 cd 48 ab 74 e 61 aIC grass pea 56 abc 55 abc 67 cde 59 aMC common vetch 51 ab 49 ab 52 ab 57 aIC common vetch 48 a 58 bcd 49 a 61 aMC sunflower 52 ab 62 cd 62 bcd 65 abc

Within a column, lower case letters display significant differences between covercrops within years based on TukeyKramer means separation (P< 0.05).

a

Monocropped (MC) and intercropped (IC) cover crop.

weak growth in the second trial period. Between harvest I andII in the no-till system at RG, the MC and IC field pea showed astrong biomass increase, resulting at harvest II in a large differ-ence between MC and IC narrow-leafed lupin and the field pea.At harvest II within the no-till system at RG the MC and IC fieldpea produced the most biomass by a large margin ( Fig. 2).At Kat harvest II there were only small differences between the covercrops with the largest biomass production (MC and IC field pea andIC narrow-leafed lupin) and the biomass of other species. MC fababean and grass pea were within the group of species with the leastbiomass production in the no-till system.

In the reduced tillage system in 2009 at RG the same species

as in the no-till system (MC and IC field pea) displayed the largestbiomass production at harvest II withsignificantdifferences in rela-tion to the other species. The second largest dry matter productionwas shown byMC and ICgrasspea and MCsunflower.At K, the MCsunflower producedthe mostbiomassin thereduced tillage systemalthoughnot significantlydifferentto IC field peaand grass pea. Theconditions in 2009 favored the sunflower growth at both locationsin the reduced tillage system but the intercropping of legumes andsunflowers was only successful in thereduced tillage systemat K.In the no-till system the IC sunflower biomass production was lowand contributed not significantly to an increased total dry matterproduction in IC compared to MC plant stands.

In 2010 at RG the largest dry matter production at harvest I wasin both tillage systems shown by MC and IC faba bean, narrow-

leafedlupin and ICfieldpea.Up toharvestII the narrow-leafedlupinbiomass production fell behind the one by MC andIC faba bean andIC field pea. Both species displayed the largest dry matter produc-tion in the no-till and reduced tillage system at harvest II althoughit was consistently below 0.52Mg ha1. At K in 2010, the MC andIC faba bean, narrow-leafed lupin and MC common vetch showedwithinthe no-till andreduced tillage system the largest dry matterproduction at both harvest dates;reachingat harvest II a biomass ofup to 1.49 and 1.65Mg ha1, in the no-till and reduced tillage sys-tem, respectively. The sunflower was, at both locations, negativelyinfluenced by the conditions in 2010; the intercropping with sun-flowers was not successful and even the biomass production of MCsunflowers at RG and K remained below 0.13 and 0.55 Mg ha1,respectively.


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Table 5

Shoot dry matter production of weeds in no-till (NT) and reduced tillage (RT) cover crop plots and the fallow plot at harvest I and II, as well as weed dry matter productionat harvest II averaged over tillage systems and locations, lower case letters within a column indicate significant weed dry matter differences in the plots of the cover cropsand the fallow plot, based on TukeyKramer means separation (P


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Fig. 2. Shoot dry matter (DM) of legumes and sunflowers at harvest II. Each column pair represents monocropped (left) and intercropped (right) plant stands of faba bean(FB), field pea(FP),narrow-leafed lupin (NL), grass pea(GP), andcommon vetch (CV), respectively. Thesingle columnrepresents monocropped plant standsof sunflower (S).Lower case letters indicate cover crop specific significant differences within tillage systems, based on TukeyKramer means separation (P< 0.05).

Table 6

Weed biomass compositions at Reinhardtsgrimma and Kllitsch in 2009 and 2010 in the no-till (NT) and reduced tillage (RT) system.

Present and newly emerged weeds at

Reinhardtsgrimma (RG) Kllitsch (K)

2009 2010 2009 2010

Weed species NT RT NT RT NT RT NT RT

Capsella bursa-pastoris(L.) Medik. Chenopodium albumL. + + Cirsium arvense(L.) Scop. + + + Polygonum convolvulusL. Lamium amplexicauleL. + + Matricaria inodoraL. + +Matricaria recutitaL. Medicago sativaL. Plantago majorL. Poa annuaL. + + Polygonum aviculareL. + Rumex obtusifoliusL. Stellaria media(L.) Vill. + + + + + +Taraxacum spp. Veronica persicaPoir. Viola arvensisMurr. Volunteer cereal grain + + + + +

- Weed not present.Weed present at seeding.Weed emerged after seeding.Existing and newly emerged weed.+Dominant weed species.


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Fig. 3. Inorganic soil N at seeding, after harvest II, and shoot N accumulation of legumes and sunflower at harvest II. The first column pair represents the inorganic soil Ncontent at seeding in the main plot for no-till (NT) and reduced tillage (RT), respectively; remaining column pairs represent monocropped (left) and intercropped (right)contents after harvest II of faba bean (FB), field pea (FP), narrow-leafed lupin (NL), grass pea (GP), and common vetch (CV), respectively. The single column representsmonocropped plant stands of sunflower (S). Lower case letters indicate cover crop specific significant differences within tillage systems, based on TukeyKramer meansseparation (P< 0.05).

the largest weed abundance was shown by Matricaria inodora L.in both tillage systems. In 2009 and 2010 at RG, Stellaria media(L). Vill., was the dominant weed species in both tillage sys-tems.

The weed biomass production up to harvest I and II was influ-enced by multiple two way interactions (Table 3). At harvest Iin both years the average weed biomass was larger in the no-tillthan in the reduced tillage system(2009: 0.73 versus 0.06 Mgha1;2010:0.16versus 0.05 Mgha1, respectively, derived fromTable5).ThiswasalsothecaseatharvestIIalthoughthedifferencesbetweenthe no-till and reduced tillage system were smaller (2009: 0.57versus0.23Mg ha1; 2010: 0.16 versus 0.10 Mgha1, respectively).

Independent from the tillage system, the weed biomass variedconsiderably between the plots of the different cover crops andthe fallow plot in 2009 (Table 5).The lowest weed dry matter pro-duction was found in plots of MC and IC field pea, MC sunflower, ICcommon vetch,grass peaand narrow-leafedlupin. In2009all covercrops, except IC faba bean, displayed a lower weed biomass thanin the fallow plot, while in 2010 there was no difference betweenthe cover crop plots and the fallow plot. IC compared to MC plantstands influenced the weed biomass production only marginally.

3.4. Cover crop shoot N accumulation

The accumulation of N in cover crop biomass was affectedby interactions between year location tillage system species

(Table 3).Within the no-till system in 2009 at RG the MC and IC

field pea (60.7 and 61.1kg ha1, respectively) showed the high-est N accumulation by a large margin, while at K the differencesbetween species were smaller and the N accumulation remainedbelow 28.7kgha1 (Fig. 3).In the reduced tillage system at RG theMC and IC faba bean and grass pea accumulated the most N whileat K this was the case for MC and IC grass pea, IC narrow-leafedlupin and field pea as well as MC sunflower.

In 2010 at RG the N accumulation was low, the MC and IC fababean and field pea displayed, in both tillage systems, the largest Naccumulation (between 15.0 and 19.1kg ha1) while both the MCandIC narrow-leafed lupin andthe MC sunflower accumulatedlessthan 4.2kgha1. Conversely at K, the MC and IC narrow-leafedlupin accumulated in both tillage systems more than 46 kg ha1

and displayed together with MC and IC common vetch and IC fababean the largest N accumulation.

A larger shoot N accumulation in the IC compared with the MCplant stands was shown only in 2009 at RG by the IC commonvetch in the reduced tillage system and at K by the IC faba beanin both tillage systems and by the IC field pea in the reduced tillagesystem. The weeds in the no-till system displayed large shoot Naccumulation, particularly in 2009 (data not shown).

At seeding, the inorganic soil N resources at RG in both yearsand at K in 2010 were below 14kg ha1 in both tillage systems,while at K in 2009 they reached 35kgha1 in the no-till and61kgha1 in the reduced tillage system (Fig. 3).After harvest II,the inorganic soil N contents displayed a highly significant interac-tion between year and location (Table 3). In 2009 the inorganic soil


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Table 7

N2fixation of legume cover crops in the no-till (NT) and reduced tillage (RT) system.

N2fixation (kgha1)

Reinhardtsgrimma (RG) Kllitsch (K)

2009 2010 2009 2010

Cover crop speciesa NT RT NT RT NT RT NT RT

MC faba bean 14.4 bc 15.2 abc 19.3 d 10.9 ab 7.3 ab 0.0 a 41.7 b 52.3 de

IC faba bean 14.4 bc 21.7 c 16.9 bcd 17.2 b 7.5 ab 0.0 a 44.5 bc 41.7 bcdMC field pea 46.5 d 53.2 d 18.7 cd 12.8 ab 33.8 c 0.1 a 22.4 a 36.0 abcIC field pea 44.3 d 53.2 d 15.0 bcd 17.3 b 17.8 b 0.0 a 23.7 a 24.5 aMC narrow-leafed lupin 2.2 a 9.7 ab 1.9 a 1.0 a 9.6 ab 3.6 a 40.9 b 43.1 cdIC narrow-leafed lupin 3.6 ab 6.8 a 2.1 a 1.9 a 16.3 ab 3.3 a 50.5b c 44.8 cdMC grass pea 23.3 c 53.9 d 5.8 ab 12.7 ab 10.4 ab 2.1 a 19.2 a 29.9 aIC grass pea 24.7 c 46.5 d 5.4 ab 9.4 ab 18.1 b 1.8 a 23.0 a 29.5 abMC common vetch 26.5 c 18.8 bc 7.5 abc 10.5 ab 6.6 ab 5.5 a 53.6b c 60.5 eIC common vetch 17.3 c 20.7 bc 11.7 abcd 12.7 ab 5.5 a 0.0 a 53.7 c 57.5 e

Within a column, lower case letters display significant differences between legume cover crops within tillage systems based on TukeyKramer means separation (P


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no-till andreduced tillage systemwas still lower than in a study byFranczuk et al.(2010) who used ploughtillage anda higherseedingrate (Franczuk, 2014 personal communication). Even at the lowerbiomass production rate in the present study, the N 2fixation washigh which makes the common vetch a very valuable cover cropfor an organic no-till system.

The grass pea biomass production in the no-till and reducedtillage system of the present study were similar to low and highdry matter yields, respectively, in a conventional no-till system inCanada (Martens et al., 2001).The reduced biomass production inthe no-till system of the present study canbe attributed to the highweed pressure and the grass peas poor competitive ability againstweeds (Wall et al., 1988).

The IC sunflowers could not be successfully established in theno-till system and there was no consistent increase of the totalabove ground dry matter production and N accumulation in the ICcompared with MC plant stands. This could be explained by thesunflowers sensitivity to seeding into wet and compacted soils(Bayhan et al., 2002; Carvalho and Basch, 1994)and to early com-petition (Johnson, 1971; Kandel et al., 1997).In the reduced tillagesystem under the warm conditions in 2009, especially the MC sun-flowers displayed their ability for a large dry matter production.By producing large amounts of biomass, MC sunflowers were able

to strongly suppress weeds and accumulate large amounts of N,emphasizing the potential of this species for cover cropping inorganic reduced tillage systems. The potential of sunflower wasalso shown through high sunflower yieldsin other organic reducedtillage trials (Berner et al., 2008). Nevertheless, the dry matter pro-duction of sunflower in the reduced tillage system can be stronglyimpaired by low temperatures and low inorganic soil N resources,as was the case at both locations in 2010.

Due to their importance for N2fixation, the legumes evaluatedin this study may prove useful in conventional systems as well.For instance, they can be used as annual green manure crops orshort term(frost killed) double cropswith winter cereals (Townley-Smithet al., 1993; Martens et al., 2001).The largest N2 fixationvalues shown by the legume cover crops were within the range

of other trials, but might have been higher had root material beensampled. The N2 fixation by faba bean at K in 2010 and by thefield pea in both tillage systems as well as by the grass pea in thereduced tillage system at RG in 2009 were similar to the N2 fix-ation averages between 40 and 49 kg ha1, which were estimatedby other methods in green manure trials in Canada ( Biederbecket al., 1996; Townley-Smith et al., 1993).The narrow-leafed lupinat K in 2010 displayed a larger N2 fixation than an undersownlegume catch crop with a similar dry matter production in Danishorganic farming trials (Askegaard and Eriksen, 2007). This might bebecause inthe Danishtrial the seedbed ofthe maincrop (spring bar-ley) was fertilized, increasing the availability and accumulation ofN from inorganic soil N resources for the later undersown narrow-leafed lupin. The N2fixation bycommonvetch at RG in2009 and at

K in 2010 was within the range (2590 kg ha

1) of another Dan-ish organic system trial. Since the root material was not sampledin the present study, the total N2 fixation was probably 1025%higher (Mueller and Thorup-Kristensen, 2001).The calculation oftheN2 fixation only includedinorganicsoil N contents up to a depthof 0.3 m because the shallow soil at RG limited the soil sampling.PotentialN leaching at RG andK duringthe cover cropping periodwas not accounted for in the estimation of the N2fixation with theextended difference method.

4.3. Influence of available inorganic soil N level and weather

conditions

Low available inorganic soil N resources at RG in both years and

at K in 2010 impaired the growth of the non-legume cover crop

IC sunflower. Transfer of N from the legume to the IC sunflowerwas presumably negligible. The growing period was short, none ofthe legumes exceeded the early flowering period and, up to lateflowering, the N transfer from the legume to non-legume can beverylow(Jamontet al., 2013). Intheno-tillsystematKin2009,thepotential available inorganic soil N resources were higher, but thesunflowers were not able toacquire a larger amountof N due tothealready established weeds. The weedsaccumulated the majority ofthe available inorganic soil N resources, which further increasedtheir growth(Blackshaw et al., 2003). In the reduced tillage systemat K in 2009 without the early weed competition and with alle-viated soil compaction and even higher inorganic soil N resources,the intercropping was successful.

However, the large inorganic soil N resources at K in 2009 alsohad a negative effect on the N2fixation by the legumes, which wasreduced in theno-till system andalmost nonexistent in thereducedtillage system. The large available inorganic soil N resources likelyled to a depressed nodulation (Dean andClark, 1980) anda delayedonset of the N2fixation (Voisin et al., 2002).Intercropping did notincrease the N2 fixation in the present study, presumably due tothe short growing season in which the N immobilisation by the ICsunflower was not large enough to sufficiently reduce the availableinorganic soil N resources.

The preceding cash crops of the cover crops were cereal grains,winter rye and oat at RG and winter wheat in both years at K. Thedifference in grain species was caused by late harvest of organicwheatat theRG location,and could have influencedthe weed spec-trum and growing stage at cover crop seeding. The unfavorableclimate conditions at RG in 2010 resulted in late harvest of win-ter cerealgrains andthe cover crops were sown after a springsownoatscrop. The low weed biomass atRG in2010 inthe no-till systemcould be attributed to the seedbed preparation and oats seeding inspring but the equally low cover crop biomass production suggesta much stronger influence of the low late season temperatures atthis submontane location which displayed the limitations of lateseason cover cropping.

5. Conclusions

The present study under central European conditions indicatedthat no-till practices for legume cover cropping in organic farmingareonly applicable if theweed density at seeding is low; otherwise,the weeds will suppress the cover crop growth. In conditions witha high weed density, reduced tillage should be considered as analternative because it strongly reduces the early weed pressure.Significant year location tillage system species interactionsemphasized that the choice of species for late season cover crop-ping is difficult and the potential weed pressure, the inorganic soilN resources, as well as the expected weather conditions during thecover cropping period must be considered. The variable legume

performances indicated that under comparatively dry conditionswith moderate weed pressure, the normal leafed field pea couldbe suited for cover cropping in the no-till system while underwet conditions and with a low weed pressure, the faba bean, thenarrow-leafed lupin and the common vetch would be a betterchoice. The practical use of these legumes in the no-till systemshould be further investigated under different climate conditions,soils and within different weed communities. In the organic no-till system, the sunflower growth appeared to be impaired and theintercropping of legumes and sunflowers had no strong reductioneffect on the weed biomass production as a result of the absence ofan increased total cover crop biomass production. In the reducedtillage system legume intercroppingwith sunflowersor monocrop-ping of sunflowers could be successful if adequate inorganic soil N

resources are available and the weather conditions are favorable.


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Acknowledgements

This study was financially supported by the Schsisches Lan-desamt fr Umwelt, Landwirtschaft und Geologie on behalf oftheSchsisches Staatsministerium fr Umwelt undLandwirtschaft.Two anonymous referees and the editor are greatly acknowledgedfor theirimprovementsand valuable commentson the manuscript.Wethank MartinBecherand MarcelKubik fortheir assistance inthecollection of field data, Dr Jens Mhring (University of Hohenheim)for advice on the statistical analysis and Falk Bttcher (DeutscherWetterdienst DWD) for providing the climate information.

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