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European Journal of Agronomy
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he development competition and productivity of linseed and pea-cultivarsrown in a pure sowing or in a mixture
adeusz Zajaca, Andrzej Oleksya, Agnieszka Stokłosab,∗, Agnieszka Klimek-Kopyraa, Bogdan Kuliga
Department of Plant Production, H. Kołłataj University of Agriculture, Mickiewicza 21, 31-120 Krakow, PolandDepartment of Agrotechnology and Agricultural Ecology, H. Kołłataj University of Agriculture, Mickiewicza 21, 31-120 Krakow, Poland
r t i c l e i n f o
rticle history:eceived 5 September 2011eceived in revised form 10 July 2012ccepted 6 August 2012
ey words:lant developmentrowth stagesieldompetitive indices
a b s t r a c t
A field experiment was undertaken to study the growth and productivity of linseed and pea cultivarsgrown in either a pure sowing or mixture in the vegetative seasons, 2004–2006. Two different mixtureswere studied: oil-linseed cv. ‘Flanders’ with grain–peas cv. ‘Ramrod’ (mixture I) or oil-linseed cv. ‘Barbara’with fodder–peas cv. ‘Phönix’ (mixture II). The cultivars chosen for both mixtures were characterized bysimilar height. In the mixed sowings, a substitutive model was used, with 50% share of each of thecomponents. Growth and productivity of both species and cultivars grown in a pure sowing or mixturedepended on the weather conditions during vegetation. Non-typical weather conditions in the vegetativeseasons 2005 (wet) and 2006 (dry) resulted in a decreased 1000 seed mass (MTS) of linseed cv. ‘Barbara’grown in the mixture, by about 19% and 25%, respectively. Moreover, in 2005 a decreased share of seedsof cv. ‘Barbara’ in mixture I was stated, as compared with the seed share of cv. ‘Flanders’ in the mixtureII. Edible peas cv. ‘Ramrod’ grown in the mixture I had reduced the fruiting part of the shoot by about37%, the lowered number of pods by about 33% and the MTS by about 6%, as compared to its pure sowing.Mutual aggression between the linseed and peas in the mixtures was higher during the seasons of less
favorable weather conditions. The significantly higher aggression towards the companion plant in themixture showed peas cv. ‘Ramrod’ sown in the mixture I. At the same time, the harvest index value of‘Ramrod’ grown in the mixture I was higher by about 15%, as compared to its pure sowing, which was dueto using linseed as supporting plants. The mixture II of fodder peas cv. ‘Phönix’ with linseed cv. ‘Barbara’,proved to be significantly more reliable, as evidenced by the value of the land equivalent ratio (LER = 1.20).
. Introduction
In recent years, growing crops in mixtures has become an impor-ant element of sustainable and organic farming (Lithourgidis et al.,011a). Mixed cropping is especially popular in parts of Asia, and –o a lesser extent – in Europe, with the exception of Poland, wherehe total harvested area of mixtures is 1,329,000 ha (FAOSTAT,010), which accounts for 87% of total area of mixtures grown inhe European Union. A special role is played by mixtures whichnclude some species, usually peas, from the Fabaceae family. Ithould be noted that most of the acreage of peas is sown in the
orm of cereal–legume mixtures. The theoretical basis for interpret-ng the results of this sowing method were introduced by Willey1979). Growing peas in mixtures, mainly with cereals, such as
barley, oats or wheat, can increase the yield of abovegroundbiomass, as indicated by the land equivalent ratio (LER) (Chen et al.,2004; Lithourgidis et al., 2011b). The mixture of cereals with peas isalso an effective growing solution, raising the yield of nitrogen andsulfur from the unit area and reducing the water-induced leach-ing of nitrogen compounds from the soil (Andersen et al., 2007;Neumann et al., 2007). At the same time, semi-leafless pea-cultivarsare less competitive species in the mixture (Semere and Froud-Williams, 2001). Growing mixtures of peas with cereals helps toreduce the level of weed-infestation (Hauggard-Nielsen et al., 2006;Corre-Hellou et al., 2011). The mixed-sowings of legumes withcereals lies at the heart of current research, as demonstrated bythe work undertaken by the team of Authors from few EU coun-tries (Gooding et al., 2007). Compared to conditions in Poland, thestability of the yield of peas in the mixtures with barley or triticale,depended strongly on the soil quality (Rudnicki and Wenda-Piesik,
2008). Cereal–legume mixtures grown both for the green fodderand seeds are valued for the important role they play in sustain-able agriculture in Europe (Uzun et al., 2005; Andersen et al., 2007;Gooding et al., 2007). In this paper, the authors introduce a new
ixture, composed of oil linseed (Linum usitatissimum L.) and peaPisum sativum L.).
Many countries in Western Europe for example GermanyKaeufler, 1999), Britain, Ireland and Finland (Foster et al., 1998;ankari, 2000), have taken steps to expand the amount of landvailable for growing linseed. Linseed has come to be consideredhe third most productive oil crop, next to the winter oilseed rapend sunflower (Aufhammer et al., 2000; Diepenbrock, 2001). Soilith a permeable, medium-heavy or compact base, with a pH of
.0 or slightly alkaline, and good water retention is considered toe the best for this species (Hocking et al., 1997). According tourner (1991) the optimal plant density of linseed is about 400ieces per 1 m2. At this density, a good branching of shoots – theain and the lateral ones – is noted, and this stimulates the devel-
pment of a large number of capsules and increases the numberf seeds per shoot and per capsule. Bramm and Dambroth (1992)ecommend a dose of nitrogen for linseed of 60 kg N ha−1 and plantensity of 450 plants per 1 m2, as good yield indicators. However,
number of scientists point out that the yields of linseed betweenifferent European countries are highly variable (Diepenbrock et al.,995; Casa et al., 1999; Candrakova and Bakula, 2001). Bravi andommovigo (1997) observed that the yield of linseed is extremelyependent on climatic conditions in the two stages of development,
.e. during the sowing and the emergence and also the matura-ion stage. Flenet et al. (2006) have found that the germinationf juvenile linseed plants is between 50 and 60%, as compared tohe amount of seeds sown. These findings have been confirmedy other scientists (Casa et al., 1999; Strasil and Vorlícek, 2004;ajac, 2005). In the case of low plant density linseed tends toranch more intensively, compensating, in this way, for a decreasedumber of plants (Bazzaz and Harper, 1977; Diepenbrock and
versen, 1989; Zajac, 2004). On the other hand, too high densityf linseed usually causes early and severe lodging, leading to con-iderable decreases in the seed yield and lower harvests. To avoiduch a situation scientists have offered various solutions, such asower nitrogen fertilization (Hocking, 1995; Grant et al., 1999),he use of growth retardants (Leitch and Kurt, 1999) and a mod-rate amount of seed sown (Diepenbrock et al., 1995; Casa et al.,999).
Among the pulses, peas and beans are regarded as traditionalood crops in many parts of Europe (Smil, 1997; Stratmann et al.,004). In Europe, pea-seed and biomass-yields are character-
zed by high variability, influenced by quality of habitat, weatheronditions during the growing season and the potential yield-ng of cultivars (Jeuffroy and Sebillote, 1997; Poggio et al., 2005;nnicchiarico and Iannucci, 2008). There is a consistent belief that
he legumes, and among them peas, are invaluable species forrganic farming in a temperate climate (Corre-Hellou and Crozat,005). Currently, peas can also be of importance for sustainablegriculture, due to the high yields, which allow a yield nitrogenf 300 kg N ha−1, accumulated in the above-ground biomass, ofhich 70% is deposited in the seeds (Jeuffroy and Ney, 1997).igh yields of peas can be achieved since the duration of therowing season is longer, and because of the breeding of semi-eafless varieties which are resistant to lodging (Boros and Sawicki,997).
The growing of linseed as a two-species mixture with peas, canecome an effective agronomic option as compared to the pureowing of both species, the disadvantages of which were discussedarlier. For common growing with brown-seed oil linseed cultivarsoth, edible or fodder peas can be used, because growth and devel-pment of these species during the vegetation season is similar,
nd the plants of both species have similar dimensions (Zajac andorowiec, 2005). These species grown in mixture can be sown andarvested in a similar time-frame, and separating their seeds is notechnically complicated.
nomy 44 (2013) 22– 31 23
This study aimed at a comparison of the growth and productivityof linseed and peas grown either as a pure sowing or mixture. Thecomparison was extended to an analysis of the morphological traitsof both species and also the interaction between species occur-ring during their joint vegetation, as a reaction to these methods ofsowing.
2. Materials and methods
2.1. General design
One-factorial field experiment was carried over a two yearperiod between 2004 and 2006 in the Experimental Station of theAgricultural University in Prusy n/Krakow. The experimental fieldis located at the following geographical coordinates 50◦07′01′′Nand 20◦05′19′′E and is 270 m above sea level. The experimentwas set up on degraded chernozem (Umbrisols–FAO). This typeof soil is fine-grained with a moderate amount of nutrients –P, K and Mg; 1.21% organic carbon and 0.16% total nitrogen.The soil and water conditions within the experimental field areequal.
The growth, competition and yielding of oil linseed (Linum usi-tatissimum L.) and semileafless peas (Pisum sativum L.), sown aspure sowings or mixtures, was assessed. A 50:50 replacementdesign was used for the mixtures, where each species was sown at50% of its sole crop density. In the previous studies carried out byZajac et al. (2005) in the climatic conditions of southern Poland, twooil linseed cultivars: ‘Flanders’ (L1; breeder: AgriFood Canada); and‘Barbara’ (L2; breeder: Gabonatermesztesi Kutatointezet, Szeged,Hungary), were of high yielding and distinct morphological traits.Two semi-leafless cultivars of peas were included in the research:cv. ‘Ramrod’ (P1; breeder: Hodowla Roslin Szelejewo Sp z o.o.,Poland), which represent the edible type of peas and cv. ‘Phönix’(P2; breeder: Südwestdeustche GbR, Rastat, Germany), a foddertype of pea. It was believed that linseed will protect semileaf-less plants of peas from lodging. Two linseed-peas mixtures werestudied: (I) cv. ‘Flanders’ + cv. ‘Ramrod’ (L1 + P1) or (II) cv. ‘Bar-bara’ + cv. ‘Phönix’ (L2 + P2). The height of plants was a criterionin selecting cultivars for inclusion in each of the mixtures. Cv.‘Barbara’ has short stems, but is characterized by a large massof seeds and a large area of individual leaves, and it was there-fore mixed with lower peas cv. ‘Phönix’. On contrary higher peascv. ‘Ramrod’ was sown together with higher linseed plants cv.‘Flanders’.
Spring wheat was a fore-crop for both pure sowings and mix-tures. The experiment was set up as a block design with fourreplications, each plot of a size of 10 m2. Four replications (plots)were used to assess the yielding, whereas the fifth one was usedto collect plants for the biometrical measurements in the specificstages of development. This procedure was possible because both,soil and water relations are equal along the whole experimentalarea. Soil cultivation in the proper time for both linseed and peas,was performed according to standard cultivation methods. MineralP and K fertilizers were applied in the pre-sowing term in the sameamounts for pure sowing and mixtures: 48 kg ha−1 of P, 72 kg ha−1
of K. The total amounts of N fertilization for pure sowings and mix-tures were as follow: 60 kg N for pure sowing of linseed, 20 kg N forpure sowing of pea and 40 kg N for mixtures. Differentiated doses ofN for peas and linseed resulted from the fact that peas, as a legume,utilize nitrogen provided by Rhizobium bacteria. For that reason inthe autumn, nitrogen for peas was applied only once, as a “start-
ing dose”, a technique commonly used by Polish farmers. For thelinseed grown as pure sowing or mixture, nitrogen was appliedtwo times: before sowing and later in the stem extension stage.The second dose of nitrogen was applied in the amounts of 20 or
24 T. Zajac et al. / Europ. J. Agronomy 44 (2013) 22– 31
Table 1The weather course during the vegetation of linseed and pea.
Year Months
Precipitation (mm) Temperature (◦C)
April May June July August April May June July August
0 kg ha−1, for mixtures and linseed in pure sowing, respectively. sowing into rows was performed using the plot sowing machineBratek”, at the depth of 2–3 cm or 5–6 cm, for linseed and peas,espectively, with 15 cm row-spacing, For the mixture technique,he sowing of seeds was performed separately, first the peas at aepth of 5–6 cm with rows of 30 cm spacing and later the sameay linseed at a depth of 2–3 cm, in the middle of peas interrows,o that the final row spacing was of 15 cm. The number of germi-ating seeds per area unit of pure sowings was 80 pcs 1 m−2 foreas and 480 pcs 1 m−2 for linseed. In both mixtures (I and II) a 50%f seed rate was used. Afterwards, plants in the phase of emer-ence were sprayed with lambda-cyhalothrin (insecticide ‘Karate’,yngenta Ltd., Poland) in the amount of 0.3 L ha−1 to ward off fleaeetles and snout beetles. Dicotyledonous and monocotyledonouseeds, in the pure sowings and mixtures, were managed usingerbicides: linuron (herbicide ‘Afalon Dyspersyjny’, Bayer Crop-cience, Poland) and quizalofop-P-ethyl (herbicide ‘Targa Super’,rysta LifeScience, Poland), in the amounts recommended by theroducers.
Peas were harvested in early August, whereas linseed as well ashe mixtures were harvested in the second decade of August, afterrevious desiccation of plants with diquat (‘Reglone®’, Syngenta,oland), applied in a dose of 4 L ha−1, using a plot combine-arvester (Wintersteiger).
.2. Sampling and analyses of plant material
In the phase of emergence the number of plants in both pureowings and mixtures, was counted from four middle rows of eachlot over a length of 1 m. In the phase of full maturity, 10 plantsf each of species and cultivar were torn from the soil by hand,nd then air-dried in the barn. For the air-dry shoots of linseed,easurements were performed for: plant length, length of stem to
he first branch, number of capsules, number of seeds per capsulend mass of seeds per shoot. The measurements of air-dry peaslants included: plant length, stem length to the first node, numberf nodes with pods, number of pods, number of seeds per pod, massf seeds per shoot.
In the samples of dry seeds a share of contamination, water con-ent and a mass of 1000 seeds (MTS) were determined. The contentf water in the dry mass of seeds was calculated after drying themn 105 ◦C for 72 h; the seed yield was recalculated for 15% of waterontent in peas seeds and 9% of water in linseed seeds.
.3. Calculation of competition indices
The competition indices were calculated based on the seedield of pure sowings and mixtures, in 4 repetitions. Four differ-
nt competition indices were analyzed: land equivalent ratio (LER)Willey and Osiru, 1972); Aggressivity (a) of peas relative to linseedMcGilchrist and Trenbath, 1971); competitve ratio (CR) of peas rel-tive to linseed (Willey and Rao, 1980) and partial land equivalent
76.0 8.3 13.6 16.4 18.2 17.9
ratio (LL,P) (de Wit, 1960), using equations:
LER =(
Lmix
Lmono+ Pmix
Pmono
); a = 1
2
[(Pmix
Pmono
)−
(Lmix
Lmono
)];
CR =(
(Pmix/Pmono)(Lmix/Lmono)
); LL =
(Lmix
Lmono
)and LP =
(Pmix
Pmono
),
where L − linseed, P − peas
2.4. Statistical analyses
To determine the differences between the methods of sowing(pure or mixed) both an F-test and Tukey test (P ≤ 0.05) were used.Morphological traits of plants in the key-developmental phaseswere analyzed using ANOVA. All calculations were carried out usingStatistica® 9.0 software (StatSoft, Poland).
3. Results
During the field experiment, the weather conditions variedbetween the growing seasons (Table 1). Monthly rainfalls in thegrowing season of 2004 promoted the growth and developmentof plants. Radically different weather conditions were observed inthe growing season of 2005 especially in May and July. Drought wasrecorded in July 2006.
The dynamics of dry matter accumulation in the abovegroundbiomass of linseed and peas, grown in the pure sowings andmixtures, varied among the vegetation seasons and the types ofmixtures (I or II) (Fig. 1). The weather conditions during the growingseasons visibly influenced the growth of botanically and agricul-turally different species. The development of plants in a givenvegetative season depended on the method of sowing (Fig. 1). Thehigher yields of aboveground biomass were obtained in 2004 and2005 when, due to the higher precipitations in the months of vege-tative growth, there were higher and more abundant plants in thesubsequent stages of development. The opposite situation occurredin the last season of the experiment—2006-characterized by lowerrainfalls, higher air temperatures (Table 1). As a result, there wasa decrease in the size and weight of the individual plants duringthis vegetative season. The unfavorable temperature and humid-ity conditions – 2006 was dry and hot – limited the elongationgrowth of plants, resulting in a reduced yield of the above-grounddry matter of the linseed and pea canopies. More variability in theaccumulation of biomass in the succeeding stages of developmentand vegetation seasons related to the mixture I (L1 and P1) (Fig. 1).A high rainfall which occurred in July and August 2005 promotedlodging of the mixture I before the harvest, which significantly
reduced its final biomass yield. In 2004, a year characterized by anaverage amount of rainfall, mixture I accumulated lower amountsof dry matter, while in the dry and hot season of 2006, the accu-mulation of dry matter was significantly higher in the early stages
T. Zajac et al. / Europ. J. Agronomy 44 (2013) 22– 31 25
Fig. 1. Biomass concentration of pea and linseed c
Table 2Indices for linseed and pea interactions in mixture.
a, aggressivity of pea to linseed; CR, competitive ratio of pea to linseed.c L, linseed; P, pea.d Mean values with the same letter are not different at 5% probability level.
f the plants’ development. During the phase of flowering of P1,rown as the pure sowing, dry matter accumulated more efficientlyn comparison with mixture I (Fig. 1).
The aggressivity (a) index calculated for above-ground dry massas significantly different for the seasons during which the experi-ent was conducted (Table 2). Mutual aggression between linseed
nd peas in joint vegetation was higher in the seasons with less
avorable weather conditions. P1 showed a significantly higherggression towards the companion plant in mixture I. A simi-ar tendency was found in relation to the competitiveness indexCR), which was significantly higher in mixture I. Components of
ultivars grown as a pure stand or a mixture.
mixture II were less competitive, and significantly better utilizedthe habitat resources, as the LER value (1.20) shows (Table 2). PartialLER were in favor of linseed, both for seasons and for mixtures andalways exceeding 0.5. Significantly higher partial LER value (P) wasnoted for P2 as compared to P1, which explains the much higherLER value for mixture II (Table 2).
Because of the sowing method, the direct and indirect featuresof the linseed plants impacting the single plant yield were sig-nificantly different between the growing seasons (Table 3). Theplant height of the linseed cultivars compared during the exper-iment did not depend significantly on the method of sowing,but indicated a significant interaction with the vegetation sea-son. The part of the linseed stem, measured from the base tothe first branch, was strongly differentiated. In 2005 plants ofboth linseed cultivars, grown in the mixtures with peas, branchedlower (Table 3). The number of linseed capsules was higher inthe mixture, regardless of the pea-cultivars chosen. In the mix-tures, a higher number of capsules occurred when the linseed wasbranching lower. As for the number of seeds per capsule a sig-nificant interaction between the vegetation season and sowingmethod for L1 occurred (Table 3). In 2004, favorable for linseedgrowth and development, a higher number of seeds per capsulewas obtained from the pure sowing. A different reaction occurredin the dry and hot season of 2006, when the higher numberof seeds per capsule was derived from mixture I. On the con-trary, under these weather conditions, L2 developed a greater
number of seeds in capsules when grown in mixture II. Mixedsowing of L2 with P2 was a factor which significantly increasedthe mass of linseed stems, indirectly improving the supportingvalue of linseed for peas—the companion plant in the mixture.
26 T. Zajac et al. / Europ. J. Agronomy 44 (2013) 22– 31
Table 3Morphological traits of linseed plants grown in a pure stand or in a mixture with pea cultivars.
Cultivar Year Method of sowing PLa (cm) LFB (cm) NC NSC MSC (g) MTS (g) HI (g g−1)
Significance level between years ** ** ** * ** ** **
NS, not significant.a PL, plant length; LFB, shoot length to first branch; NC, number of capsules; NSC, number of seeds per capsule; MSC, mass of seeds per shoot; MTS, mass of 1000 seeds;
HI, harvest index.b L1, Flanders, L2, Barbara.
F(
iicvows
TM
N
i
c P, pure sowing; M, mixture.* Significant at 0.05 probability level.
** Significant at 0.01 probability level.
or L1 such direction of dependencies occurred only in 2005Table 3).
The linseed seed yield per plant showed a highly significantnteraction with the vegetation season and weaker with the sow-ng method – pure vs. mixed (Table 3). The L1 yield was greater inonditions of mixed sowing with peas only in 2005, but in the pre-
ious season a similar trend was noted. On the other hand, plantsf L2 systematically had higher yields in the mixed sowing. In theet season, the weight of a single L1 seed was higher in the mixed
owings (Table 3). In dry and hot conditions both linseed cultivars
able 4orphological traits of pea grown in pure stand or in mixture with linseed cultivars.
Cultivar Year Method of sowing PLa (cm) LFN (cm)
P1b
2004Pc 101.1 39.3
M 86.8 53.4
LSD(P≤0.05) 10.53 9.16
2005P 108.3 32.3
M 118.1 42.7
LSD(P≤0.05) NS 6.43
2006P 65.5 33.5
M 65.0 48.1
LSD(P≤0.05) NS 8.53
Significance level between years ** *
P2
2004P 83.1 43.2
M 93.4 56.0
LSD(P≤0.05) NS 11.48
2005P 120.8 40.5
M 108.7 34.7
LSD(P≤0.05) NS NS
2006P 63.7 48.1
M 74.5 54.8
LSD(P≤0.05) NS NS
Significance level between years ** **
S, not significant.a PL, plant length; LFN, shoot length to first node; NP, number of pods; NSP, number of
ndex.b P1, Ramrod; P2, Phönix.c P, pure sowing; M, mixture.* Significant at 0.05 probability level.
** Significant at 0.01 probability level.
grown in mixtures developed smaller seeds. A statistically highervalue of harvest index (HI) for L1 was achieved, when sown in themixture in 2005. HI of L2 depended on the weather conditions, i.e.in 2004, when there were favorable conditions for the growth oflinseed, significantly higher values of HI for mixed sowing werenoted (Table 3).
As evidenced by the majority of morphological features, pea-cultivars included in the study reacted differently to the methodof sowing – pure or mixed, especially for P1 (Table 4). At the endof the vegetation period, the height of peas depended mainly on
seeds per pod; MSP, mass of seeds per shoot; MTS, mass of 1000 seeds; HI, harvest
T. Zajac et al. / Europ. J. Agronomy 44 (2013) 22– 31 27
Table 5Number of linseed and pea seeds sown and plants per unit area after emergence and before harvest, including losses (%) during the vegetation period.
Factor Number of seeds sown (pcs m−2) Number of plants (pcs m−2) Losses(%)
ean values with the same letter are not different at 1% probability level.a E, after emergence; H, before harvest.b L1, Flanders; L2, Barbara; P1, Ramrod; P2, Phönix.
he climatic conditions in each of the growing seasons. In the sea-on of 2005, both pea- cultivars had long stems. P1 developed podsigher on the stem, when sown with L1, in all the growing sea-ons (Table 4). In 2004 a similar trend for P2, when grown in theixture, was recorded. In the other vegetation seasons, the spe-
ific sowing methods used did not significantly affect the height ofhe pod depositions on the shoot of P2 (Table 4). The dry season of006, when had the shorter fruiting part of the stem in the pureowing of P2 was the exception. In all the seasons during which thexperiment was conducted, P1 grown in the mixture had a smallerumber of whorls, as compared to the pure sowing (Table 4).imilar trends, but at a clearly smaller scale and therefore statis-ically insignificant were also noted for P2. The number of pods perea-shoot was always lower in mixtures, determined by shorteninghe part of shoot bearing fruits, and a significantly smaller number
f fruit-bearing whorls. The number of seeds per pod dependedn the conditions occurring during the growing season; significantffects of the sowing method on this trait appeared only in 2005,
Fig. 2. Seed yield of linseed and pea grown as pure or m
when a smaller seed number per peas pods within the mixture wasnoted (Table 4). At the same time, the productivity of a single P1plant was always significantly lower in mixed sowing, as comparedto P2 (Table 4). The single plant seed yield of P2 was not significantlydifferent between sowing methods, except for the 2004 season,when a tendency toward a reduced yield in the mixed sowing wasobserved. Mass of the seeds of both pea cultivars changed, depend-ing on the method of sowing. The weight of 1000 seeds of P1 in2005 and 2006 was lower in the mixed sowing, as compared tothe pure sowing. As for the seed mass of P2 grown in the mixture, itdepended on the vegetative season conditions; a significant declinein 2004 was followed by another decline in the following season of2005, and by an increase in the dry season 2006. A more favor-able ratio for the harvest index was noted for the P1 in mixture I(Table 4).The HI value of P2 was not significantly influenced by the
sowing method, except in 2006 when a reduction of P2 HI valuedue to the reduced number of nodes with pods, number of podsand mass of seeds per shoot in mixture II was observed (Table 4).
ixed stand in the different years of experiment.
2 J. Agro
vtsohPo
awctew
es1
4
pTtpailfracibstliitta
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8 T. Zajac et al. / Europ.
The density of both species per unit area differed between theegetation seasons (Table 5). Relating to the number of seeds sown,he percentage of emerging plants was approximately 45% for lin-eed and 80% for peas. During the dry and hot 2006 season, the lossf plants between emergence and harvest time, was significantlyigher. On average, smaller losses of plants were noted for L1 and2. In the mixed sowings, the loss of plants during vegetation wasf an amount similar to the pure sowings (Table 5).
An interaction has occurred between the components of linseednd peas mixtures (Fig. 2). The seed yield of linseed and peas, asell as the seed yield of their mixtures depended on the choice of
ultivars grown. Each season the yield of mixtures was in betweenhe yield of each of the components grown as pure sowings. Asxpected, the yield of dry weight of seeds of the analyzed speciesas the lowest in the dry and hot 2006 season (Fig. 2).
The collected seeds of linseed and pea- mixtures can be dividedasily because of the different mass of seeds in both species. Theeed-weight ratio of L1, grown in mixture I ranged from 1:29 to:46. In mixture II, this ratio for L2 ranged from 1:28.5 to 1:66.
. Discussion
This field experiment showed that in the mixture with peas,lants of linseed have a tendency to reduce their shoot length.his may signify the dominance of peas during common vegeta-ion, where the linseed plants perform the functions of a supportinglant. The height of the linseed shoot depended significantly on thegro-climatic conditions of the vegetative season. Consequently,n the dry seasons (i.e. 2006) a significant reduction of the plantength was observed. Casa et al. (1999), showed a significant dif-erence in the length of the linseed shoots in central Italy (Viterbo),esulting from variable rainfall during the vegetative season. Bazzaznd Harper (1977), carrying out the experiments with flax underontrolled conditions in a greenhouse found that plants growingn more intense light and low density branched noticeably at theottom of the main stem, creating additional lateral shoots, whichignificantly increased the dry mass of plants. Flax growing in con-rolled day and night temperatures and with approximately 50%ess light, developed higher plants. The direction of this relationshipndicates that weather conditions may be a factor which stronglympacts the growth habit of flax and, consequently, also the traitshat determine the productivity of individual plans. In our study,he wet and cool season 2005 promoted the growth of both speciesnd the cultivars, which resulted in a greater length of the shoot.
It has been shown, in relation to Flanders grown with peas cv.hönix in mixture, that its leaf area increased, but only after reach-ng the budding phase. The majority of linseed research thus far hasot included any testing of the individual components of the shoot
oliage during the life cycle during the vegetative season, hence theata obtained in this experiment fill the gap. In greenhouse con-itions, Bazzaz and Harper (1977) calculated different number ofax leaves per plant, depending on their sowing density – loose,edium, and dense, in the number of: 435, 264 and 130 pieces,
espectively (Bazzaz and Harper, 1977). In field conditions, Zajac2004) has found that the intensity of linseed branching depends
ainly on the initial density of young plants per unit area, and onlyo some extent on the weather conditions in the months of April and
ay. In the linseed canopy 23–40% of plants branched and, withinhem, three groups were separated: plants of 2, 3 or 4 shoots (Zajac,004).
The accumulation of dry matter within a single flax shoot is con-
idered to be the result of leaf area index (LAI) during growth, but,n the other hand, it may be conditioned by environmental fac-ors, especially the average daily temperature (Bisco and Gallagher,977). According to Fageria et al. (2006) the maximum leaf area is
nomy 44 (2013) 22– 31
equal to the maximal production of active leaf area. The analysisof the growth of both tested species confirmed the earlier observa-tions of Hassan and Leitch (2001), who found that the maximumcanopy height and leaf area index for flax, are achieved 2–3 weeksafter the flowering stage, when the largest yield of photosynthe-sis in the leaves occurs followed by the defoliation process. Thedynamics of dry matter accumulation in the aboveground biomassof linseed and peas, grown in the pure or mixed sowings, varies dur-ing the vegetative season. It has been shown that during ontogeny,from phase to phase, the accumulation of both, fresh and dry weightin the shoots of linseed occurs. Mixed sowing had a targeted effectonly on the accumulation of biomass of Ramrod peas, when themass of the shoot of this cultivar, grown in mixture with linseedFlanders, has decreased and this tendency has been an indica-tor of reduced productivity of peas in the mixture. On the otherhand, Flanders linseed showed the opposite response to the mixedgrowing with peas, which served as the supporting-plant for peas.However the productivity of individual plants in the mixed canopysignificantly increased, especially in certain seasons, which clearlydemonstrates the effectiveness of this growing-technique for sus-tainable agriculture.
The confrontation of linseed and peas plant density with theamount of germinated seeds sown, points to a partial loss of plantsduring the vegetation season. Poor germination of linseed in thepresent study corresponds with the findings of Flenet et al. (2006),who showed that, in the environmental conditions of northernFrance, it is difficult to maintain an appropriate density of plantsdue to a poor field emergence of seeds, since only half of the seedsof cv. ‘Oliver’ and cv. ‘Jupiter’ emerged. In south-west GermanyAufhammer et al. (2000) observed better-almost optimal flax emer-gence, as in their field experiment for 500 seeds sown, 476 seedsemerged in the first season, and 395 seeds emerged in the secondseason of experiment. Casa et al. (1999) points out that the linseedis able to compensate for the reduced densities of canopy mainlyby increasing the number of capsules per plant.
Peas are characterized by high soil and water requirements, andit is for this reason a lack of rainfall in the early stages of develop-ment inhibits growth, whereas drought, occurring later, restrictsthe number of pods, causing their premature falling (Davies et al.,1985). During the seasons examined, peas set a variable numberof fruiting nodes and consequently a variable number of pods eachyear. The agro-climatic conditions of 2005 season, with heavy rain-fall, stimulated the elongational growth of plants, but productivityof the shoot decreased. In the low-lying parts of Poland, significantfluctuations in the yielding of peas results from a strong reactionof this species to insufficient quantity and distribution of rainfallduring the vegetative season (Urbanowski et al., 1997). Accord-ing to the literature, the critical period for water requirementsfor peas is during the flowering-phase (Mahieu et al., 2009). Theincreasing density of peas plants in the canopy causes reductionin the shoot dry weight, due to mutual shading (Kruger, 1977),following the changes, such as a reduced number of leaves andpods (Lawson, 1982) and decreased yield as a consequence (Cousin,1997). Kruger (1977) and Cousin (1997) showed that intensive pro-duction of biomass, due to increasing intraspecies competition,leads generally to earlier and stronger lodging, which results in thereduced yield. Productivity of pea-shoots, growing in high densityper unit area decreases, resulting in their lower weight, as a resultof the competition for light (Bakry et al., 1984). Poggio et al. (2005)underline the significant role of light and temperature (photother-mal quotient) in the development of both pea-pods and seeds.Dore et al. (1998) fixed a threshold of 115 peas stems per m−2,
below which even a large seed number per stem does not com-pensate for low stem density. Growing peas in a mixture withlinseed was supposed to stabilize the productivity of the canopyof this mixture. During this experiment the lower density of peas
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er area in the mixture, resulting from the sowing plan, resultedn a higher weight of the pea-shoots. Heavy rainfall occurring inhe phase of maturity usually leads to a severe lodging of canopy,hich affects the seed development and also causes rotting, whenods come into contact with the soil. The authors of this studyecommend a new composition of species in mixture. Oil-linseednd semi-leafless peas were expected to improve the seed yieldnd content of nutrients in pea-seeds and would be an efficientption for agricultural practice. Studies by Patra et al. (2004) havehown that the mixed growing of flax with lentil and chickpeasesults in a lower accumulation of dry matter in the leaves andtems of flax, whereas legumes succeed more in this type ofowing.
In the studies of Paulsen et al. (2006), conducted in a region oforthern Germany (Trenthorst and Wilmerdorf), a variable sensi-ivity of mixture components to each other has been demonstratedith mixtures of wheat and flax or false flax. In the mixture of wheat
nd flax, a significant reduction in the yield of flax was noted, whichndicates strong competition in the canopy of mixture during theommon vegetation, due to the dominance of wheat over flax. Aimilar phenomenon, but of much lower intensity, was observedn the present study, because of the effect of the dominance ofeas in the canopy. Contrary results were obtained by Nazir et al.2000) who, in the climatic conditions of Pakistan (Faisalabad),tudied the growing of flax in a mixture with fenugreek (Trigonellaoenugraecum), with a diverse density of both components. Thistudy showed that variation in the flax-yield was mainly due tohe density of canopy (Nazir et al., 2000) and the adverse effectn flax yield was observed only in the conditions of high share ofenugreek in the mixture (1:4), suggesting competition for envi-onmental resources. This is confirmed by reports of Lamb et al.2007), who reported that the competition between plants in theanopy is unequal during the life cycle and usually is greatestetween the seedling and flowering stage. In the juvenile stages,lants strongly compete for limited habitat resources, determinedy the current meteorological conditions, and more precisely by themount and distribution of rainfall and specific trophic conditionsf a habitat resulting from the soil type, forecrop and fertilizerspplied. At the end of the growing season the strength of plantnteractions in the mixture weakens, as a result of different tim-ng of species maturation. In the present study, such strong bioticorrelation was not observed, but some of the trends were con-rmed; Ramrod peas accumulated significantly less biomass inhoots when grown in a mixture with linseed Flanders, especially inhe initial phases of vegetative growth, as compared to pure sow-ng. Similar observations were noted by Hauggard-Nielsen et al.2006) in a barley–peas mixture, where barley, due to the ear-ier seedling emergence, gained an initial growth advantage overeas, but peas were more growth-efficient in the later phases ofevelopment.
The rate of above-ground mass production by particular speciesn the mixture depends on the rate of development of species grow-ng simultaneously; the value of specie dominance in the canopys best described by the land equivalent ratio–(LER) index. TheER index determines the effectiveness of mixtures in the relationo pure sowing and is determined by canopy density (Mead and
illey, 1980; Offori and Stern, 1987) and the competitive as wells complementary abilities of species in the mixture in relation tohe use of habitat resources. In our study, a much higher value ofER was found for the mixture II (LER = 1.20), which suggests a goodse of habitat resources, especially by Barbara linseed. Our resultshowed lower partial LER values for peas (P), which contradicts
he findings of Saucke and Ackermann (2006). Their study showedhat in a mixture composed of grain peas and false flax (Camelinaativa L.), partial LERs were in favor of peas. As shown by Nazirt al. (2000), the efficiency of mixture in tapping habitat resources
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is determined by the sowing method and density. Their study, in theclimatic conditions of Pakistan, showed that with increasing densi-ties of flax and fenugreek in the mixture the value of LER index wasalso growing. Mishra and Masood (2002) who sowed flax and lentilin a relation 6:2, with the maximum LER = 1.15 for flax, in relationto lentil as a component (LER = 1.09), showed a similar directionof changes of LER index, influenced by changes in the sowingrate.
Variable weather conditions shaped the linseed yield in a widerange from 0.82 to 2.76 t ha−1. Zajac et al. (2005), obtained simi-lar results observing that the linseed yields depend on the weatherconditions and on the traits of cultivars. During the wet seasons theaverage linseed yield was low and amounted to 1.67 t ha−1, whereasin the seasons of moderate weather conditions it was 2.84 t ha−1.Despite the large fluctuations in the yielding between seasons,three cultivars, namely ‘Flanders’, ‘Barbara’ and ‘AC Linora’ retainedyielding stability of 2.5 t ha−1 (Zajac et al., 2005). Diepenbrock et al.(1995) found the complex interdependencies influencing the lin-seed seed yield and resulting from the level of agronomic factors(nitrogen fertilization, plant density per unit area) and habitatconditions. Results of the study of Mishra and Masood (2002),who evaluated the yield of linseed sown in the mixture withlentils, have shown that an adequate share of linseed plants inthe mixture allows a high yielding of this species. According tothese authors, the highest seed yields were obtained when lin-seed: lentil ratio was of 6:2. Nazir et al. (2000) in the experimentthat aimed to determine the proportion of linseed in a mixturewith fenugreek, showed a significant reduction in the numberof capsules per linseed shoot, influenced by the increasing num-ber of fenugreek plants per unit area. In addition, these studiesalso demonstrated a significant reduction in linseed 1000 seedweight, as a reaction to the progressive increase of fenugreek den-sity in the mixture, as compared to linseed grown in the puresowing (Nazir et al., 2000).
Growing peas in mixtures with linseed, contributed to theincreased competitiveness of peas. A positive value of peas aggres-siveness index (A = 0.194) and high rates of competitiveness in thecanopy (CR = 1.10) were stated. Tofinga et al. (1993) and Hauggard-Nielsen et al. (2006) found that peas have a higher competitiveability, as compared to barley and wheat. However, the assessedrelative yield (RY) index for peas revealed that in a mixture withlinseed, a reduced interspecies competition in advantage to thecomplementary use of available resources appeared. The biolog-ical efficiency of the mixture was noted especially in 2007—a yearof relatively good water conditions, when the relative yield totalindex (RYT) was 1.22. A similar value of RYT = 1.17 was stated forthe mixture of long-strawed traditionally leafed peas cv. ‘Bohatyr’or cv. ‘Alf” grown with oats (Rauber et al., 2001).
In summary, weather conditions significantly influence thegrowth and productivity of both linseed and peas, grown as puresowing or mixture. In 2005, intensive rainfall stimulated elonga-tion growth of linseed and peas, nonetheless the sowing method.On the other hand, dry season 2006 reduced the species length.The productive results of wet season 2005 resulted in significantlylower share of linseed cv. ‘Barbara’ seeds in the mixture with fod-der peas cv. ‘Phönix’, as compared to the second mixture. Grainpeas cv. ‘Ramrod’ reacted negatively to the mixed sowing with lin-seed cv. ‘Flanders’ when inclement weather conditions occurred,and as a result there was a lower number of pods per shoot, lowerseed mass per shoot and lower mass of 1000 seeds. At the sametime, peas cv. ‘Ramrod’ showed a specific biological reaction, usinglinseed as a support plant. Peas cv. ‘Ramrod’ sown with linseedcv. ‘Flanders’ showed a significantly higher aggression towards acompanion plant in the mixture. The mixture of fodder peas cv.
‘Phönix’ with linseed cv. ‘Barbara’ proved to be more productive, asevidenced by the value of land equivalent ratio (LER = 1.20).
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