SIGNIFICANCE OF MIXED INTERCROPPING OF SPRING WHEAT AND LINSEED AS A POTENTIAL COMPONENT OF PLANT CULTIVATION IN SUSTAINABLE AGRICULTURE

Agnieszka Klimek-Kopyra, Tadeusz Zając, Andrzej Oleksy, Bogdan Kulig
Institute of Plant Production, University of Agriculture in Krakow, Poland

ABSTRACT

Trends in global agriculture are expected to move towards an increase in the productivity of linseed, as an oil crop with a valuable composition of unsaturated fatty acids. It is thought that a new agrotechnical approach diversifying linseed cultivation may increase crop yields. The aim of the study was to compare linseed cultivation in pure stand and in mixture with wheat in new sowing proportions (75+25%, 50+50% and 25+75%).

Mixed intercropping of linseed with wheat significantly decreased the length of the inflorescence, which was followed by a decrease in the number of branches and capsules. The spikes of spring wheat were longer in the two-species mixture, which resulted in a greater number of spikelets and grains. In the pure stand, the seed yield (g m^-2) for linseed was 297.7, while that of spring wheat was 546.4. The percentage of linseed in the seed yield for the mixtures with a 75, 50 and 25% share of linseed in the mixture was 41.1, 17.7 and 4.9%, respectively. High productivity of linseed in a mixture can be obtained only when its share is optimal (at least 75%). However, the total productivity of components in two-species mixture is lower by about 28% in comparison to pure stand which, from practical point of view, is not excellent agrotechnical solution. The correct proportion of species in a two-species mixture is the most important aspect of plant productivity.

Key words: competition indices, morphological traits, yield components.

INTRODUCTION

Cultivation of Linum usitatissimum L. is currently dominated by its oilseed form (linseed), while the economic importance of the fibre form (flax), supplying straw fibre, has declined [32]. Linseed is sown at a lower density, 25–55 kg ha^-1, to stimulate branching, in order to obtain more flowers and increase seed yield [14]. As the seeding rate was increased, plant density and seed yield increased linearly, while plant height decreased linearly [32]. However, Easson and Molloy [11] conducted a study under European conditions that indicated little increase in straw and fibre yields with a higher than normal seeding rate. Flax seed oil contains approximately 50% α-linolenic acid (ALA), an omega-3 fatty acid. The oil has a ratio of 1:3 between omega-3 and omega-6 fatty acids, which is not easily found in other seed oils [6]. Despite the fact that linseed yields are highly variable, both in Europe [26, 32] and in other parts of the world [6, 15], there is a lively interest in this species due to its numerous economic applications. Linseed seed yields are systematically rising on a global scale, which demonstrates the increase in the production potential of the species, but the level of yields is still low [12].

Productivity of linseed can be increased through mixed intercropping with pulse crops [25, 33] or spring cereals [27]. Gooding et al. [13] report that the popularity of mixed intercropping of cereals with pulses continues to rise in Western Europe. Other examples include two-species intercropping of linseed or Camelina sativa with wheat [27]. In the conditions of the Indian subcontinent (Pakistan), studies have been conducted on mixed intercropping of linseed with fenugreek [25] and linseed with rapeseed [1], which proved to be more productive at lower costs. Trends in global agriculture are moving towards increased productivity of crops in biologically varied agrophytocenoses [14, 22]. Promotion of sustainable crop production and organic farming is increasingly important in terms of crop productivity and protection of the natural environment [5, 20]. However, Dore et al. [10] claim that an agroecosystem requires selection of species aimed at regulating ecological and biological processes. Agroecology is expected to make a significant contribution to the development of sustainable plant production in the 21^st century [8].

The advantages of agroecological cultivation of linseed and wheat were studied by Pridham and Entz [29]. The authors found that mixed intercropping significantly reduced wheat yield, but on the other hand significantly reduced the degree of infection of the flag leaf by fungal diseases. The results of the study demonstrate the pro-ecological value of this crop mixture, but the study lacked methodology aimed at optimization of the proportions of the plants. The economic efficiency of intercropping of flax with wheat was evaluated by Carr et al. [7]. The authors report that intercropping of red spring wheat (Triticum aestivum L.) with flax (Linum usitatissimum L.) may offer advantages in comparison with sole cropping only in dry regions of the world (northern latitudes). At the same time, the authors found that a 50–50 share of each plant has little economic value and suggested that further studies are needed. Agrobiodiversity, treated as different proportions of plants in a mixed canopy, should be considered the basis for a change in the design of field experiments to more closely imitate a natural ecosystem [21, 22]. It seems that high plant productivity can only be obtained in a sustainable system when further work in this area combines analysis of the morphological traits of the plant with an innovative agrotechnical approach. Plant productivity can be assessed through simplified plant model approach [16] or presented by competition indices study. Various indices such as land equivalent ratio (LER), competitive ratio (CR), competitive balance index (Cb), aggressivity (A) have been used to describe the productivity and plant-plant relations in mixed intercropping [3, 4, 9, 23, 30, 31].

This study was conducted to compare the productivity and competitiveness of linseed and spring wheat grown in pure cropping or mixed intercropping at different plant densities. The comparison was extended to include an analysis of the morphological traits of both species and competition indices.

MATERIAL AND METHODS

Experiment design
A field experiment was conducted in 2006 and 2007 on lessive soil at the Research Centre for Cultivar Testing in the village of Pawłowice, Silesian Voivodeship (50° 28’N, 18° 31’E, 250 m asl). The soil is classified as quality class IVb, which is characterized by pH 7. The content of nutrients in soil reached 66 kg ha^-1 Nmin, 14.7 mg 100 g^-1 P₂O₅, 19.2 mg 100 g^-1 K₂O, 8.2 mg 100 g^-1 Mg.

The forecrop in both years was pea harvested for seeds. Fertilizer was applied in the spring following pre-sowing cultivation (kg ha^-1): N – 60, P – 50 and K – 72. Seeds were sown with an Oyjord® plot drill on optimal dates (22.03.2006 and 28.03.2007). Linseed cv. ‘Szafir’ and spring wheat of the ‘Koksa’ variety were sown in the amount of 400 (100%) germinating and dressed seeds per m². Row spacing was at 20 cm, and the seeds were placed in the soil at a depth of 3 cm. Three mixtures of linseed and spring wheat were compared, with the following proportions of the two species: linseed (Lin.) 75% + spring wheat (Swh.) 25%; Lin. 50% + Swh 50%; and Lin. 25% + Swh 75%. The number of seeds per m² for each species was as follows: Lin. 300 + Swh 100; Lin. 200 + Swh 200; and Lin. 100 + Swh 300. Five treatments were compared in the experiment, in four replications, and the area of the plot for harvest was 10 m². Dicotyledonous weeds were controlled with the herbicide Chwastox Extra 300SL at 1.5 dm³ ha^-1 during the herringbone stage (BBCH 12–14). Before harvesting, plant density was determined on each plot and then 10 shoots were collected from each species. The length of the stems and inflorescences of linseed and spring wheat were measured. The plant material was dried in a barn over the month of August and then the following were determined for the linseed shoots: number of first-order branches per inflorescence, number of capsules, and the number of seeds per capsule. This made it possible to estimate the number and weight of seeds per shoot, the weight of a single seed, and the harvest index. Similar measurements were made for spring wheat: shoot weight, number of spikelets per spike and number of kernels per spike. The weight of a single kernel, total kernel weight per spike, and harvest index were determined. Yield per unit area (1 m²) and per inflorescence were calculated, as well as the percentage of linseed in the yield of the mixtures. The plants were harvested during the full maturity stage, on 27.07.2006 and 02.08.2007. Seed yield was determined at 15% moisture content.

Weather conditions
Weather conditions during the growing period of the linseed, spring wheat and mixtures were similar in the two seasons (Fig. 1). In 2006 a warmer March enabled earlier sowing. Beginning in April, the air temperature was similar in both seasons, and similar to the long-term average. A wetter April in 2007 led to higher shoot density than in the previous year. No lodging of either linseed or spring wheat was observed in either year, in either the sole cropping or intercropping.

Fig. 1. Monthly average temperature and total rainfall during the (a) 2006 and (b) 2007 growing seasons and long-term averages.

Competition indices
The seed yield was used to calculate competition indices:

• Land equivalent ratio, LER = (LERa+LERb)=(Yab/Yaa) + (Yba /Ybb) [28],
• Competitive ratio, CR=CRa+CRb={(LERa/LERb)x(Zba/Zab)} [29],
• Competitive balance index; Cb = ln[(Yab/Yaa)/( Yba /Ybb)] [29],
• Aggressivity A=[(Yab/(Yaa x Zab)) − (Yba/(Ybb x Zba)] [21].

Yab represents the yield of mixed intercrop wheat (a) in combination with linseed (b), Yba the yield of intercrop linseed (b) in combination with wheat (a). Yaa is the yield in pure stand of wheat and Ybb is the yield in pure stand of linseed. Zab represents the sown proportion of intercrop wheat (a) in combination with linseed (b) and Zba the sown proportion of mixed intercrop linseed (b) in combination with wheat (a).

Statistical analysis
All data were analysed statistically according to the field experiment model in STATISTICA v.10.0 (StatSoft Inc.). Standard analysis of variance was applied separately for each year and species. The least significant differences between means were calculated by Tukey’s test at α = 0.05.

RESULTS

The two species produced stems of different length, but the mixed intercropping system had no significant effect on this trait (Tab. 1). Irrespective of the cropping system – pure stand or two-species mixtures, the spring wheat culms were always longer than the linseed stems. Variation in this trait was influenced by the year. Sowing of linseed in mixtures with spring wheat caused a significant  decrease in inflorescence length in this species. The reverse situation was observed for the spring wheat, whose spikes in the intercropping with linseed increased in length as the proportion of wheat in the mixture decreased. Thus the length of the spikes was longest in the case of a 25% share of wheat in the two-species mixture. Shoot length in the two species was similar in the pure stand: 71.3 cm for linseed and 70.8 cm for wheat. In the two-species mixture conditions linseed shoot length was varied, decreasing significantly with the proportion of linseed in the mixtures.

Table 1. Comparison of length [cm] of components of shoots of linseed and spring wheat grown in sole cropping (100%) and in three mixtures

Species or  mixtures [%]	Stem/culm		Inflorescence		Shoot
	(Lin.)	(Swh.)	(Lin.)	(Swh.)	(Lin.)	(Swh.)
100	52.3	62.6	18.62	8.16	71.3	70.8
75	51.7	62.9	10.29	8.56	62.2	71.5
50	51.2	61.8	7.85	8.43	59.0	70.2
25	51.5	59.8	6.42	9.20	57.9	69.1
LSD(α≤0.05)	NS	NS	2.44	0.38	4.0	NS
Significance level between years	*	*	NS	NS	**	*
NS – not significant * Significant at 0.05 probability level ** Significant at 0.01 probability level (Lin.) –  linseed (Swh.) – wheat

The cropping system and the year of vegetation did not significantly differentiate the number of seeds in the capsules (Tab. 2). This demonstrates the developmental autonomy of linseed fruits, whose development was similar in both cropping systems following their formation on the plant. In the two-species mixture conditions, the weight of a single seed showed an upward trend. These values indicated that mixed cropping produces seed yield with favourable use parameters. However, the number of seeds per linseed shoot was highest in the pure stand. In two-species mixture of linseed with wheat, the number of seeds per shoot decreased substantially, particularly in the mixture with a small proportion of linseed (25%). These relationships are due to the significant decrease in the number of branches in the inflorescence. These changes were preceded by a decrease in the length of the linseed inflorescence, which was shown above in Table 1. The logical consequence of developmental changes progressing in this manner was a decrease in the number of capsules formed on a single linseed shoot. This entailed a dramatic reduction in seed weight per shoot, accompanied by a decrease in the weight of the entire linseed shoot. These values led to a significant decrease in the harvest index, which was particularly visible in the treatment with a small proportion of linseed (25%) in the mixture with spring wheat, whose share was 75%. The harvest index was highest in the mixture with a small proportion of spring wheat (25%), but the differences compared to the pure stand were not proven statistically.

Table 2. Changes in shoot characteristics of linseed depending on the cropping system – sole cropping (100%) and three mixtures with spring wheat

Species ormixtures [%]	Number				Weight			Harvest index [g g-1]
	Branches	Capsules	Seeds per capsule	Seeds per shoot	Single seed [mg]	Seeds per shoot [g]	Shoot [g]
100	7.7	21.3	7.1	149.2	5.74	0.789	1.926	0.42
75	6.2	10.1	7.2	73.3	6.30	0.453	0.977	0.45
50	4.9	6.7	7.4	49.6	6.31	0.315	0.756	0.40
25	4.0	4.7	7.3	34.2	6.48	0.222	0.581	0.37
LSD (α≤0.05)	1.1	4.5	NS	31.2	NS	0.166	0.367	0.04
Significance level between years	NS	NS	NS	NS	*	NS	NS	NS
* Significant at 0.05 probability level; NS – not significant

In the mixtures with linseed, spring wheat formed spikes containing significantly more spikelets. As a consequence, its spikes also had significantly  more kernels than in the case of pure stand of this cereal (Tab. 3). There was little variation in the number of kernels in a single spikelet of spring wheat. In the intercropping with linseed the wheat kernels were smaller, due to increased tillering of the plants, leading to a greater number of side shoots forming kernels of lower weight. For this reason the seed yield per spike of wheat was not significantly varied. Only where the proportion of wheat in the mixed intercropping was small (25%) did its spikes show a tendency towards greater yield. In this mixture the weight of the wheat shoot was greatest. The wheat from the pure stand had a significantly  higher harvest index. In the two-species mixtures the values for this quotient decreased, probably due to the increased weight of the culm. It should be emphasized that none of the wheat characteristics was influenced by the year, and the changes were exclusively due to the cropping system

Table 3. Changes in traits of spring wheat shoots depending on the cropping system – sole cropping (100%) and three mixtures with linseed

Species ormixtures [%]	Number			Weight			Harvest index [g g-1]
	Spikelets per spike	Kernels per spike	Kernels per spikelet	Single kernel [mg]	Kernels per spike [g]	Shoot [g]
100	15.6	33.7	2.1	33.6	1.144	2.239	0.55
75	16.7	36.1	2.1	30.1	1.103	2.212	0.49
50	16.4	35.6	2.2	32.7	1.172	2.298	0.51
25	17.3	39.1	2.2	32.4	1.269	2.573	0.49
LSD(α≤0.05)	0.8	3.7	NS	NS	NS	0.329	0.05
Significance level between years	NS	NS	NS	NS	NS	NS	NS
NS – not significant

In conditions of pure stand of the two species, spring wheat produced more shoots than linseed (Tab. 4). The density obtained for spring wheat culms can be considered satisfactory. In contrast, the density of linseed was lower than the sowing density. The seed yield of linseed was lower than that of spring wheat, as was expected. The yield in pure stand was 297.7 g m^-2 for linseed and 546.4 for spring wheat. The lower yield in the two-species mixture was due to a decrease in yield per linseed shoot, and the causative factors were presented above in Table 2. The linseed yield was satisfactory and stable over the two years. It should be emphasized that the mixture of linseed with wheat did not maintain a density corresponding to its share in the sowing, but substantially reduced it, to nearly twice as low as the sowing density. The decrease in the share of linseed in the yield was greater in the mixtures with higher proportions of spring wheat, 50 and 75%. In the treatment with 50% linseed sown, the proportion of seeds of this species was 17.7%, which was nearly three times lower than the sowing density. The proportion of linseed in the yield decreased even more dramatically – fivefold – in the case of the lowest proportion of linseed sown in the mixture.

Table 4. Comparison of density and production potential of linseed and spring wheat grown in sole cropping and intercropping

Species or mixtures [%]	Shoot density (number)		Yield [g m-2]		Percentage (Lin) of yield [%]
	2006	2007	2006	2007	2006	2007
Lin.100%	364*	382	278.6	316.7	–	–
Lin.75 + Swh.25%	278 + 145	278 + 141	317.0	293.5	45.1	37.1
Lin.50 + Swh.50%	209 + 254	194 + 251	381.3	339.3	20.7	14.6
Lin.25 + Swh.75%	92 +360	91 + 382	390.3	472.2	6.0	3.8
Swh.100%	459	499	521.7	571.1	–	–
LSD(α≤0.05)	24	31	45.5	50.6	3.6	4.6
* Figures in bold refer to linseed (Lin.) –  linseed (Swh.) – wheat

A value of CR> 1 means that the wheat was more competitive in the canopy than the linseed (Tab. 5). The CR value increased with the proportion of wheat in the mixture, attaining its highest level of competition in the case of the 75% share. This is confirmed by the positive aggressivity index (A), which indicates high dominance of wheat in the two-species mixture canopy. The A index increased linearly with the share of wheat in the mixture. The highest aggressivity was noted for the wheat plants when the share of wheat in the mixture was 75%. Despite the fact that linseed was completely dominated by the wheat, the land equivalent ratio (LER) increased with the proportion of the cereal in the mixture. LER< 1 indicates that plants grown in a two-species mixture do not utilize the resources of the habitat as well, and therefore utilization of the acreage was poorer in terms of production (Fig. 2). Total LER was greatest when the two species had equal shares in the canopy (0.89). In 2006 the total LER, for both linseed and wheat, was shown to be greater than in 2007, when the weather was less favourable. The LER for linseed decreased with its share in the mixture. A similar downward trend was observed for the LER in the case of the wheat.

Table 5. Comparison of competition indices in the canopy of intercropped linseed and spring wheat

Mixtures [%]	CR Lin.		CR Swh.		Cb		A Swh.
	2006	2007	2006	2007	2006	2007	2006	2007
Lin 75 + Swh 25%	0.55	0.36	2.06	2.92	0.45	0.05	0.61	0.84
Lin 50 + Swh 50%	0.54	0.31	2.18	3.34	-0.70	-1.19	0.57	0.70
Lin 25 + Swh 75%	0.38	0.21	2.90	4.79	-2.11	-2.65	0.58	0.84
LSD (α≤0.05)	0.17	NS	0.79	1.86	0.33	0.56	NS	NS
NS – not significant, (Lin.) – linseed, (Swh.) – wheat

Fig. 2. LER for the seed yield for linseed, wheat and total depending on proportions in the mixtures and years of vegetation, (Lin.) –  linseed, (Swh.) – wheat

DISCUSSION

Agrobiodiversity is becoming a new approach in sustainable agriculture, although further research in this area is required. The study showed that optimization of the proportions of each species in mixed intercropping is very important, because it determines the strength of interrelations in the canopy. One of the basic measures of the interrelations of crop plants in a mixture is biometric analysis of the plants. The biometric analyses show that the mixed cropping system had no significant effect on the length of the linseed or wheat stems. However, significant variation was found for shoot length in linseed, while no variation was found in wheat. This shows that wheat growth is controlled more by genetic than environmental determinants, as confirmed by Bajwa et al. [2]. Different results were obtained by Zając et al. [34], who studied the productivity of winter cereal mixtures. The authors demonstrated that the culm of cereals in mixed cropping adapts its length to the other plants in the canopy. In mixed cropping of winter cereals the short culms of barley and wheat grew longer while their weight decreased. The reverse was observed in cereals with long culms – rye and triticale – in which the culm was significantly shorter in mixed cropping.

In our study, in conditions of mixed intercropping of linseed with wheat, variation was noted in linseed shoot length. The length of the linseed shoot decreased significantly with the share of this species in the mixtures. Different results were obtained by Zając et al. [33] for mixed intercropping of linseed with pea. The authors demonstrated that linseed mixed intercropped with pea exhibited highly stable shoot length, which is considered to be one of the most characteristic features of competition of plants in a mixed canopy.

The study showed that shoot density was of greater importance in the dominance of plants in the canopy. More shoots were produced by both species in the pure stand. In the mixed intercropping, reduced density of linseed was observed in the mixtures with spring wheat in comparison to the amount sown. The 75% share of linseed in the mixture led to a 41.1% reduction in the final yield. This result is consistent with results obtained by Bajwa et al. [2].

The mixed intercropping system did not significantly differentiate the number of seeds per capsule, but did have a statistically significant effect on the number of capsules per shoot. The study showed a significant decrease in the number of capsules formed on a single linseed shoot as the share of linseed in the mixture decreased. This led to a dramatic decrease in seed weight per shoot, together with a decrease in the weight of the entire linseed shoot. Different results were obtained by Zając et al. [33] in a two-species mixture of linseed with pea. The authors demonstrated that the cropping system significantly affected the number of seeds per linseed capsule and the number of capsules per shoot. The number of seeds per capsule and the number of capsules was significantly higher in the mixed intercropping with pea than in the pure stand. The authors proved statistically that in the mixed intercropping of linseed with pea a greater number of capsules appeared when there was less branching of linseed shoots.

The number of kernels per wheat spike was significantly differentiated by the mixed intercropping system. Significantly more kernels per spike were obtained from plants intercropped with linseed. However, the kernel weight per spike was stable and independent of the cropping system. Bajwa et al. [2] showed that mixed intercropping of wheat with linseed did not differentiate the number of kernels per spike. However, they showed that growing wheat with linseed significantly decreased the kernel weight per spike, which led to a greater 1,000 kernel weight and greater wheat yield in the sole cropping. In our study the species grown in pure stand produced significantly higher yield in comparison to the intercropping mixtures (linseed 297.7; spring wheat 546.4). The lower yield in the mixtures was due to decreased yield of single shoots in the linseed crop. In a study by Paulsen et al. [27], mixed intercropping of linseed and wheat significantly reduced linseed yield, which indicates strong competition and dominance of wheat in the mixed canopy. Similar results were obtained by Carr et al. [7], who demonstrated a severe reduction in linseed yield in a mixture with wheat. Linseed yield in the mixed intercropping was reduced by 90% and wheat yield by 25%.

Berti et al. [6] showed that flax yields (Chile) were highly varied in five growing seasons, with the highest yield obtained in the 2003/2004 season, when the ‘Cathay’ and ‘Prompt’ varieties produced 5,746 and 5,742 kg ha^-1, respectively – the highest recorded in the literature. Papatheohari et al. [26] also obtained high linseed yield, ranging from 4,246 to 5,441 kg ha^-1. These results show that the yield-increasing potential of new varieties of linseed is high and determined by the environment. In our study we obtained no increase in linseed yield in the mixed intercropping due to the high competition from wheat, which was demonstrated by the high competition indices (CR) and aggressivity index (A).

The CR value increased with the share of wheat in the mixture with linseed, reaching the highest level of competition when its share in the mixture was 75%. This is confirmed by the positive aggressivity index (A) of the plants in the canopy, which proves the high dominance of wheat in the mixed canopy. The A index increased linearly with the share of wheat in the mixture. The highest aggressivity was noted for the wheat plants with a share of 75% in the mixture. Zając et al. [33] showed that mixed intercropping of linseed with pea increased intraspecific competition in the plants, which was confirmed by a positive A index and high CR index. Moreover, Zając et al. [33] found that mutual aggression between linseed and pea was greater in the season with less favourable habitat conditions.

In our study, we observed variation between years in the strength of the negative effects of plants in the mixture. Significantly higher values for the CR index were noted in 2006, with lower precipitation during the flowering and ripening stages.

The LER was less than 1, which means a lack of efficiency of cultivation of wheat and linseed in a mixture. The LER for linseed was lower than for wheat. Different results were obtained by Zając et al. [33], who showed a positive value for linseed intercropped with pea (LER 1.2) and a higher LER for linseed in the intercropping. Similar results were obtained by Mishra and Masood [24] for a mixture of linseed and lentil. The authors showed that a linseed and lentil mixture is more efficient than pure stand. Partial LER values were varied, with higher efficiency for linseed (LER = 1.15), and somewhat lower for lentil (LER= 1.09).

Wasaya et al. [28] noted a significant increase in LER in wheat-fenugreek mixed intercropping. The mixture led to a high LER value (1.78) and was considered very efficient for sustainable production, particularly in regions with a lot of rainfall. Many studies show that mixed intercropping may be more productive than pure stand due to the phenomenon of competition for water, space and nutrients [17–19, 21, 22]. It is very important to use the correct proportions of species in a mixed canopy. It appears that high production in intercropping is only possible when interspecific competition is lower than intraspecific competition. Further research is needed in this area.

CONCLUSION

Field experiment of linseed cultivated in pure stand and mixture with wheat indicated a large variation in yield among mixture combination. Results appears that high productivity of linseed in a mixture can be obtained only when its share is optimal (at least 75%), so that interspecific competition will be lower than intraspecific competition. High productivity of linseed in a mixture can be obtained only when its share is optimal (at least 75%). However, the total productivity of these two components of mixture is lower by about 28% in comparison to pure stand which, from practical point of view, is not excellent agrotechnical solution.

The correct proportions of species growing together in a mixed canopy are very important, thus further study in this area is needed.

Acknowledgments

Research supported by Poland’s Ministry of Science and Higher Education as part of the statutory activities of the Agriculture University in Kraków.

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Accepted for print: 19.11.2016

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Agnieszka Klimek-Kopyra
Institute of Plant Production, University of Agriculture in Krakow, Poland
Aleja Mickiewicza 21
31-120 Kraków
Poland
email: klimek.a@wp.pl

Tadeusz Zając
Institute of Plant Production, University of Agriculture in Krakow, Poland
Aleja Mickiewicza 21
31-120 Kraków
Poland

Andrzej Oleksy
Institute of Plant Production, University of Agriculture in Krakow, Poland
Aleja Mickiewicza 21
31-120 Kraków
Poland
email: rroleksy@cyf-kr.edu.pl

Bogdan Kulig
Institute of Plant Production, University of Agriculture in Krakow, Poland
Aleja Mickiewicza 21
31-120 Kraków
Poland

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Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.

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