EFFECT OF THE SOWING METHOD, DATE AND ROW SPACING ON THE YIELDING OF ´STADION´ PERENNIAL RYEGRASS (LOLIUM PERENNE L.) CULTIVATED FOR SEED

Małgorzata Szczepanek, Zbigniew Skinder

ABSTRACT

The aim of the present research was to evaluate the yielding of perennial ryegrass (Lolium perenne L.), 'Stadion' lawn cultivar grown for seed, depending on the sowing method, date and row spacing. The research was carried out at the Experiment Station for Cultivar Testing at Chrzšstowo, in the vicinity of Bydgoszcz. The experiment was carried out over 1998-2002 in three series; each of them included the sowing year and two years of full use for farming purposes. The experimental factors included: I - sowing method/date: autumn pure stand, spring pure stand, undersown perennial ryegrass in spring barley cultivated for green matter and undersown perennial ryegrass in spring barley grown for grain, II - row spacing: 12 cm - narrow, 24 cm - average wide, 36 cm - wide and 48 cm - very wide. In the first year of full use for farming purposes, the seed yields were lowest when ryegrass was sown in autumn. Furthermore the yield of perennial ryegrass sown in spring in pure stand was significantly lower than that of undersown perennial ryegrass in barley in both its growing variants. The seed yield in the second year was significantly higher for sowing together with a cover crop, as compared with the yields obtained for autumn sowing. The application of varied row spacing showed a significant effect on the seed yield neither in the first nor in the second year of full use for farming purposes.

Key words: perennial ryegrass, sowing date, cover crop, row spacing, seed yield..

INTRODUCTION

Out of all the non-cereal grasses, perennial ryegrass (Lolium perenne L.) is of the greatest economic importance in Europe, which comes from its various applications. Fodder cultivars of this species are the main components of different mixtures of meadows and pastureland. Due to its very high nutritive value, feed palatability, easiness of leaf picking, resistance to trampling, to animal grazing and early mowing, the grass is allocated to feeding all species of farm animals. It is perfect for enhancing the condition of permanent grassland using undersown crops. It constitutes a precious component of grass mixtures and grass-and-papilionaceous plant mixtures to be grown on arable land. Lawn cultivars of perennial ryegrass are used to establish ornamental, recreational and sports lawns, as well as sodding difficult areas (banks, transport routes) and degraded areas (mine dumps, waste dumps). The demand for seed of this species is then very high and steady in nature [6].

In 2001 mean perennial ryegrass seed yields from plantations in Poland amounted to 0.54 tˇha^-1 and accounted for only half of the yields obtained in the countries of Western Europe [3,17]. One of the reasons of low yields are technological mistakes made during cultivation and harvest. Perennial ryegrass seed production profitability and competitiveness, as compared with other plantations, can be enhanced by a selection of agronomic factors which would allow using the biological potential of the cultivars. All that calls for comprehensive research which could be a real springboard for modernization of grass seed production [11,19].

The main aim of the present research was the evaluation of 'Stadion' lawn cultivar perennial ryegrass yielding evaluation, depending on the sowing method, date and row spacing. The following working hypotheses were made:

• application of spring barley as a cover crop limits the development of undersown perennial ryegrass as compared with pure stand,

• an earlier harvest date of barley grown for green matter, as compared to that of barley grown for grain, can enhance the seed yield over the years of full use for farming purposes,

• postponing the date of perennial ryegrass sowing until late summer shortens the time of plant development before winter and can limit yielding in the first year of full use for farming purposes,

• applying different row spacing affects the development of morphological-and-biological characters in plants which define the productivity when used for seed.

MATERIAL AND METHODS

The research was carried out at the Research Station for Cultivar Testing at Chrząstowo, in the vicinity of Bydgoszcz. The experiment was carried out over 1998-2002 in three series; each of them included the sowing year and two years of full use for farming purposes. Field experiments were set up on good wheat complex soil, III b class, in split-block design, with four replications. The plot for harvest was 12 m². Winter rape constituted the fore-forecrop, and winter wheat - forecrop. The following experimental factors were applied: I - sowing method/date: autumn pure stand, spring pure stand, undersown perennial ryegrass in spring barley grown for green matter and undersown perennial ryegrass in spring barley grown for grain, II - row spacing: 12 cm - narrow, 24 cm - average wide, 36 cm - wide and 48 cm - very wide.

The aim of the present research was a diploid lawn perennial ryegrass cultivar, 'Stadion', representing mid-late cultivars of slow growth, tolerance to partial shade and of thousand seed weight of 1.1 g [25]. The cover crop was made up by spring barley, 'Nagrad' which is highly resistant to lodging, shows a good productivity and health status [2].

Spring sowing coincided with the second decade of April, while the autumn sowing was conducted by September 5 [25]. When sown with a cover crop, perennial ryegrass was sown directly after barley sowing. 'Stadion' basic seeds were sown at the amount of 10 kgˇha^-1, 2 cm deep. In barley cultivation for green matter 120 kgˇha^-1 was assumed as the seeding rate, and when grown for grain - 20% lower [25]. Barley grown for green matter was harvested in the second or the third decade of June, while the harvest of barley grown for grain from the third decade of July to the second decade of August. When sown in spring and in autumn in pure stand 30 kgˇha^-1 N, 120 kgˇha^-1 P₂O₅ and 100 kgˇha^-1 K₂O were used before sowing. In objects with a cover crop the following were applied before sowing: 15 kgˇha^-1 P₂O₅ and 40 kgˇha^-1 K₂O as well as 80 kgˇha^-1 N wh en grown for green matter and 70 kgˇha^-1 N when grown for grain. After barley harvest 30 kgˇha^-1 N and in the third decade of September 120 kgˇha^-1 P₂O₅ and 100 kgˇha-1 K₂O were used. Over the years of full use for farming purposes in the third decade of March there were applied 60 kgˇha^-1 N and 60 kgˇha^-1 K₂O and nitrogen at the amount of 30 kgˇha^-1 over shooting stage, and in the second year of full use for farming purposes - also 30 kgˇha^-1 at the beginning of tillering. In the first year of use in autumn there were applied 120 kgˇha^-1 P₂O₅ and 100 kg K₂Oˇha^-1.

Weed control followed the guidelines of the Institute of Plant Protection, using MCPA + mecoprop, over the sowing years at the beginning of tillering of perennial ryegrass, while over the years of full use for farming purposes - in the second or the third decade of April. Over the years of full use, in the first or the second decade of May tridemorf + epoxyconazole were applied to control Erysiphe graminis. A higher intensity of occurrence of rust caused by Puccinia ssp. species fungi in the third decade of June 1999 required chemical control, using tridemorf + epoxyconazole. Over the years of full use pests were controlled with deltametryn only in 2000 in which there was observed white ear caused by Thysanoptera.

Over each year of sowing and successive years of full use phenological plant development observations were made. Prior to perennial ryegrass seed harvest, biometrical measurements were taken: the number of generative tillers on the area of 0.25 m², generative tillers length, ear length, and the number of grains per ear based on 20 randomly sampled tillers from each plot. Right prior to tillering lodging was evaluated on each plot using a 9-degree scale. The seeds were harvested in two stages from the end of the first to the third decade of July, over early dough stage, when 60-80% of the ears were affected by browning, and hand test showed the first shattering. A few days after mowing, threshing with plot combine-harvester followed. The seeds were weighed once they had been dried to 15% moisture and screened.

Weather conditions were carried out based on the observations made at the observation-and-measurement centre SDOO Chrząstowo. To calculate variance analysis, AWAR software was applied, developed by IUNG in Puławy. The analysis was carried out for 'split-block'. Significance of differences was determined with Tukey's confidence half-interval, at the confidence level of a = 0.05. The correlation relationships were calculated using Statistica software. In the present paper the results are presented as means of three series for: sowing year, the first and the second year of full use.

RESULTS

Rainfall and its distribution over the vegetation period and quite mild winters in the vicinity of Bydgoszcz were favourable to perennial ryegrass seed production (Fig. 1). Over the sowing years of 1999 and 2000 the weather conditions were mostly favourable to perennial ryegrass growth and development. In 1998 throughout the vegetation period no water deficit was recorded. In 2000 low rainfall April through June was sufficient for the initial growth. High rainfall July through September stimulated perennial ryegrass growth and development which under the conditions of long and warm autumn was recorded by as long as December 17. The rainfall distribution in 1999 was unfavourable to perennial ryegrass sown in spring; in that year the water deficit July through September resulted in leaf wilting and a total plant growth inhibition.

Fig. 1. Hydrothermal conditions over 1998-2002 against the 1980-2003 multi-year means

The hydrothermal conditions in April, May and June showed a positive significant effect on most of the biological characters researched (except for 1000 grain weight) and on perennial ryegrass yielding and a negative effect on its lodging (Table 1).

Table 1. Correlation between the seed yield and selected biological characters and hydrothermal conditions in the first and the second year of full use of perennial ryegrass (correlation coefficients)

Item	Characters	1	2	3	4	5	6	7	8
1	Seed yield, tˇha-1	x
2	Number of generative tillers, pcs.ˇm-2	0.52*
3	Number of spikelets per ear	0.16*	0.14*
4	Number of seeds per spikelet	0.51*	0.27*	0.18*
5	Thousand grain weight, g	0.18*	-0.01	-0.14*	0.03
6	Tiller length, cm	0.82*	0.56*	0.31*	0.57*	-0.02
7	Ear length, cm	0.60*	0.43*	0.52*	0.47*	-0.10*	0.76*
8	Lodging, 9o	-0.85*	-0.40*	-0.03	-0.48*	-0.19*	-0.72*	-0.49*
9	Sielianinov’s coefficient value in April	0.72*	0.52*	0.31*	0.53*	-0.10	0.90*	0.73*	-0.65*
10	Sielianinov’s coefficient value in May	0.81*	0.49*	0.20*	0.55*	0.01	0.89*	0.67*	-0.82*
11	Sielianinov’s coefficient value in June	0.73*	0.57*	0.01	0.26*	0.25*	0.68*	0.43	-0.67*
12	Sielianinov’s coefficient value April through June	0.79*	0.58*	0.20*	0.47*	0.05	0.88*	0.66	-0.74*

* significant at α = 0.05

The dynamics of germination and emergence of perennial ryegrass sown in spring barley was similar with that observed in pure stand (Fig. 2). A delayed development of undersown crops as compared with the plants in pure stand coincided with the development of 2-3 leaves, and a total growth inhibition, which lasted until barley harvest, was recorded at early tillering stages. Perennial ryegrass sown in the first decade of September developed more slowly than that sown in spring. In 1998 and in 1999 by the end of vegetation (9 weeks after sowing) the plants completed their vegetation at the beginning of tillering (1 tiller), in 2000 only, with its longer vegetation period (15 weeks after sowing), 2-3 tillers were noted prior to winter. Over the years of full use, except for the year 2000, weather conditions were mostly favourable to generative development of perennial ryegrass. April through June, which determined the perennial ryegrass seed productivity, rainfall was suffic ient for an adequate plant development, the semi-drought period was noted only in June 2002 in which rainfall was considerably low but evenly distributed. In 2000 water deficit in the first three months of vegetation seriously limited the elongation of generative tillers of perennial ryegrass and resulted in leaf wilting in all the objects studied.

Fig. 2. Perennial ryegrass development over the sowing years

In the first year of full use over the beginning of vegetation period, perennial ryegrass sown in spring showed strong tillering, and the lawn was 12-15 cm high, while the plants sown in autumn developed 4-5 tillers, and the lawn was not more than 5-6 cm high. In spring the period of continued tillering of perennial ryegrass sown in autumn was 11 days longer, and that of shooting - 9 days shorter than that of ryegrass sown in spring (Fig. 3), which decreased the tiller length in perennial ryegrass sown in autumn by 11.2 cm. Ryegrass sown in autumn reached its seed harvest maturity 4 days later than that sown in spring. The beginning of lodging was usually observed over flowering, over successive development stages lodging was becoming more and more intensive and at the ripeness stage it covered almost the whole area of the plots. A lower lodging was observed for autumn sowing. In the second year of full use perennial ryegrass developed faster and reached harvest maturity 5-9 days earlier as compared with perennial ryegrass in the first year of full use. In the second year of use for autumn sowing there was recorded a slightly greater growth rate, and in 2002 also earlier and greater lodging than for spring sowing. Over the sowing years and the years of full use there were observed differences neither in the growth nor in reaching successive development stages of perennial ryegrass sown with different row spacing. In the second year of full use between the rows there appeared seedlings from shattered seeds in the first year of full use; most numerous for the wide and very wide row spacing. Their development ended over emergence or tillering, only few developed single generative tillers.

Fig. 3. Perennial ryegrass development in the first and the second year of full use

The number of generative tillers of perennial ryegrass (Table 2) depended on the weather conditions; the correlation with Sielianinov's hydrothermal coefficient was always significant over generative development April through June. In the dry year 2000 the number of generative tillers was even 1/3 lower than over the other research years. In the first year of full use the mean number of generative tillers developed in perennial ryegrass sown in spring (both in pure stand and with a cover crop) was significantly higher as compared with the number of such tillers in autumn sowing. In the second year of full use the number of generative tillers of undersown crops in spring barley was significantly higher than in plants sown in spring pure stand. Over both years of full use the number of generative tillers developed in plants grown with the narrow row spacing was higher than with the average wide row spacing, while the lowest one - with the wide and very wide row spacing.

Table 2. Number of generative tillers of perennial ryegrass, pcs.ˇm-2

Year of full use/ years	Row spacing cm	Sowing method/date				Mean
		Autumn	Spring
			Pure stand	With barley
				For green matter	For grain
First (1999-2001)	12	2694	3354	3264	3600	3228 a
	24	2607	2964	3146	2995	2928 b
	36	2095	2843	2840	2823	2650 c
	48	1847	2879	2755	2698	2545 c
Mean		2311 B	3010 A	3001 A	3029 A	2838
Second (2000-2002)	12	2819	2487	2968	2878	2788 a
	24	2677	2484	2566	2698	2606 b
	36	2281	1947	2397	2562	2297 c
	48	2071	1964	2435	2345	2204 c
Mean		2462 AB	2220 B	2592 A	2621 A	2474

A, B, C... – means followed by the same letter constitute a homogenous group in the row a, b, c... – means followed by the same letter constitute a homogenous group in the column

The length of generative tillers (Fig. 4) depended mostly on weather conditions in April and May, which is seen by high values of correlation coefficients with Sielianinov's coefficient. Over the years with favorable weather conditions generative tillers were 40-50% longer than in the dry year 2000. In the first year of full use perennial ryegrass sown in autumn showed significantly shortest generative tillers. In the first and second year of use generative tillers of perennial ryegrass sown with barley grown for green matter were significantly longer than in spring pure stand. In both years of full use there was no significant effect of varied row spacing on the 'Stadion' tiller length.

Fig. 4. Length of generative tillers of perennial ryegrass depending on the sowing method/date in the first and the second year of full use (A, B, C... – means marked with the same letter constitute a homogenous group)

Similarly, long generative tillers showed long ears (Fig. 5). The greatest relationship between the ear length and Sielianinov's hydrothermal coefficient was shown in April and in May. In the first year of full use perennial ryegrass sown with barley grown for grain developed longer ears and more spikelets per ear than in spring pure stand. In the second year ears were significantly longer and usually the number of spikelets per ear of perennial ryegrass sown in autumn increased, as compared with the spring pure stand. In the first year of full use ears of perennial ryegrass with the wide row spacing were longer than with the narrow row spacing. The number of spikelets per ear reflected the ear length (Table 3), but the differences were not significant. In the second year of full use perennial ryegrass developed significantly more spikelets per ear with wide than with the narrow row spacing.

Fig. 5. Perennial ryegrass ear length depending on A – sowing method/date, B – row spacing in the first and the second year of full use (A, B, a, b... – means marked with the same letter constitute a homogenous group)

Table 3. Number of spikelets per ear of perennial ryegrass

Year of full use/ years	Row spacing cm	Sowing method/date				Mean
		Autumn	Spring
			Pure stand	With barley
				For green matter	For grain
First (1999-2001)	12	19.9	19.9	21.2	20.4	20.4
	24	20.8	19.5	20.4	21.7	20.6
	36	21.1	20.2	21.1	22.1	21.1
	48	19.9	20.0	21.2	21.6	20.7
Mean		20.4 BC	19.9 C	21.0 AB	21.5 A	20.7
Second (2000-2002)	12	18.7	18.6	18.8	18.5	18.7 b
	24	19.4	18.8	18.9	18.7	18.9 ab
	36	19.8	19.0	19.0	19.8	19.4 a
	48	19.1	19.1	19.1	19.0	19.1 ab
Mean		19.2	18.9	18.9	19.0	19.0

A, B... a, b... – see Table 1

The number of seeds per spikelet (Table 4) was determined by weather conditions in April and in May, while the thousand seed weight - in June. Perennial ryegrass with long generative tillers developed also more seeds per spikelet. In the first year of full use in spring pure stand, the very wide row spacing showed more favorable to the number of seeds per spikelet than the average wide row spacing. With the average wide row spacing perennial ryegrass developed the lowest number of seeds per spikelet when sown in autumn. The number of seeds per spikelet in the second year of full use of perennial ryegrass sown with spring barley grown for grain was higher as compared with the number of seeds per spikelet in autumn sowing.

Table 4. Number of seeds per spikelet of perennial ryegrass

Year of full use/ years	Row spacing cm	Sowing method/date				Mean
		Autumn	Spring
			Pure stand	With barley
				For green matter	For grain
First (1999-2001)	12	3.58 aA	3.46 abA	3.41 aA	3.67 aA	3.53
	24	2.98 aB	3.17 bA	3.63 aA	3.62 aA	3.35
	36	3.58 aA	3.46 abA	3.67 aA	3.69 aA	3.60
	48	3.28 aA	3.80 aA	3.35 aA	3.73 aA	3.54
Mean		3.35	3.47	3.52	3.67	3.50
Second (2000-2002)	12	2.81	2.83	2.89	3.12	2.91
	24	3.13	3.15	3.16	3.48	3.23
	36	3.12	3.31	3.17	3.32	3.23
	48	2.84	3.16	3.54	3.18	3.18
Mean		2.98 B	3.11 AB	3.19 AB	3.27 A	3.14

A, B... a, b... – see Table 1

In the first year of full use multi-year thousand grain weight mean was significantly higher in autumn sowing as compared with spring pure stand and with spring barley (Table 5). In the second year of use thousand seed weight was significantly higher for the sowing with barley grown for green matter than with barley grown for grain and as compared with autumn sowing. For perennial ryegrass sown with barley grown for green forage, the narrow row spacing was more favourable to thousand seed weight than the average wide row spacing. For perennial ryegrass grown with the narrow row spacing, sowing with barley grown for green matter was more favourable as compared with the autumn sowing and sowing with barley grown for grain. With the narrow row spacing a similar thousand seed weight was recorded in spring and autumn pure stand.

Table 5. Perennial ryegrass thousand seed weight, g

Year of full use/ years	Row spacing cm	Sowing method/date				Average
		Autumn	Spring
			Pure stand	With barley
				For green matter	For grain
First (1999-2001)	12	1.24	1.11	1.14	1.16	1.16
	24	1.23	1.17	1.12	1.11	1.16
	36	1.25	1.14	1.16	1.14	1.17
	48	1.27	1.16	1.13	1.13	1.17
Mean		1.25 A	1.15 B	1.14 B	1.13 B	1.17
Second (2000-2002)	12	1.03 aBC	1.08 aAB	1.13 aA	1.01 aC	1.06
	24	1.09 aA	1.08 aA	1.06 bA	1.07 aA	1.07
	36	1.09 aA	1.09 aA	1.10 abA	1.05 aA	1.08
	48	1.07 aA	1.09 aA	1.12 abA	1.07 aA	1.09
Mean		1.07 B	1.08 AB	1.10 A	1.05 B	1.08

A, B... a, b... – see Table 1

Perennial ryegrass seed yield (Table 6) was significantly correlated with weather conditions expressed with the Sielianinov's hydrothermal coefficient. In the first and second year of full use the vegetation year 2000 was least favourable; the seed yields were even 60% lower than in the years of favourable weather conditions. Perennial ryegrass seed yield was significantly correlated with morphological properties of plants; the greatest relationship was recorded with the number of generative tillers and the number of seeds per spikelet. Developing long tillers and ears, as well as numerous spikelets per ear was favourable to yielding, but it was always accompanied by a greater intensity of lodging. The difference in the seed yield over the years of full use was relatively low. In the second year of full use the yield was only 11.3% lower as compared with the first one. In the first year of full use seed yields were lowest in autumn sowing. Also the seed yield of perenn ial ryegrass sown in spring in pure stand was lower than that of undersown crops in barley in both variants of its cultivation. The seed yield in the second year of use was higher for sowing with a cover crop, as compared with the yields obtained from sowing in autumn. The application of varied row spacing did not show a significant effect on the seed yield in the first and in the second year of full use. A total seed yield from the first and the second year of full use was higher for sowing with a cover crop as compared with the yields obtained from spring pure stand, while the lowest seed yields were recorded for autumn sowing (Fig. 6), which was mainly due to the results obtained in the first year of use in which the differences in the seed yield for autumn and spring sowing, especially with a cover crop, were relatively high as compared with the second year of full use. A total seed yield was significantly lowest when perennial ryegrass was grown with the very wide row spacing.

Table 6. Perennial ryegrass seed yield, tˇha-1

Year of full use/ years	Row spacing cm	Sowing method/date				Mean
		Autumn	Spring
			Pure stand	With barley
				For green matter	For grain
First (1999-2001)	12	1.17	1.41	1.56	1.68	1.46
	24	1.19	1.45	1.60	1.59	1.46
	36	1.11	1.42	1.59	1.54	1.41
	48	1.08	1.39	1.45	1.56	1.37
Mean		1.14 C	1.42 B	1.55 A	1.59 A	1.42
Second (2000-2002)	12	1.22	1.27	1.31	1.31	1.28
	24	1.17	1.24	1.39	1.33	1.28
	36	1.17	1.22	1.30	1.32	1.25
	48	1.17	1.18	1.28	1.28	1.22
Mean		1.18 B	1.23 AB	1.32 A	1.31 A	1.26

A, B... a, b... – see Table 1

Fig. 6. Total perennial ryegrass seed yield from the first and the second year of full use depending on the sowing method/date and row spacing (A, B, a, b.. – see Fig. 5)

DISCUSSION

Fluctuations in the perennial ryegrass seed yields depending on the weather conditions can be very high [29]. Based on the results of the present research it was noted that the seed yield depended on the rainfall and its distribution over the period of generative tillers development and ripening and harvest of seeds. Weather conditions determined the development of structural yield components whose correlation with the seed yield was described earlier by others [8,11,21,34]. The years favourable to high productivity showed sufficient rainfall in April and May as well as in the first decade of June. Rainfall deficit over that period limited yielding, which was mainly due to a lower number of generative tillers, which is confirmed by the reports by Falkowski et al. [9] and a poor growth (shorter tillers and ears), which, as reported by Rutkowska and Dębska-Kalinowska [28], depends considerably on soil moisture. A favourable effect of high rainfall over tillering and shooting on the seed yield is also reported by Miazga [20] and Domański [5].

In the present research 'Stadion' seed yield in the first year of use was 2.6 higher than the mean yield obtained at home from production plantations [3]. In the second year of use a decrease in 'Stadion' yielding, as compared with the first year, was only 10.3%, which makes that cultivar special among others. A decrease in perennial ryegrass yielding in the second year of use reported in literature amounts to 30-50% [18,26], and so seed plantations are usually used one year only. Maintaining high reproduction potential of the cultivar researched in the second year of use can be a result of the cultivar representing a group of late cultivars which, according to Kelly [15], show a greater stability.

In the first year of full use a higher seed yield was recorded when sowing involved spring barley in both of its cultivation variants than when sown in spring in pure stand. Similar results were reported by Hryncewicz et al. [14] who researched Italian ryegrass grown for seed. In the present research over tillering a development of undersown crops in spring barley grown both for grain and for seed was completely inhibited till the cover crop harvest, which was due to a limited intensity of photosynthesis of 'Stadion' perennial ryegrass sown with barley, as compared with that in pure stand [33]. Limiting growth and development made the undersown crops before winter less grown, as compared with the plants in objects with pure stand, however in the successive year they yielded higher. A similar relationship - a negative correlation between the plant status before winter and the seed yield in the successive year was reported by Prończuk [24]. One of the reasons, according to the author, is a li mited damage of lower and less-tillered plants of perennial ryegrass by snow mould in winter.

The results of research by Spiertz and Ellen [32] into the effect of light intensity on the morphological characters of perennial ryegrass show that poorly-tillered plants in autumn can, in spring, compensate for tillering; the number of reproductive culms can be even greater than that of well-tillered plants prior to winter. In the present research in the first year of use there was recorded no increased generative tillers density of undersown perennial ryegrass, however they usually had longer tillers, ears, a greater number of spikelets per ear and seeds per spikelet, as compared with the plants in pure stand, which can be enhanced by a strong root system developed by undersown crops exposed to competition for water with a cover crop, but also a lower transpiration and overdried soil in summer of less developed undersown crops, as compared with the luxuriant biomass of overground perennial ryegrass sown in spring.

One of the reasons of high yielding of perennial ryegrass grown with barley can be also, observed in the first year of vegetation period, a lower infection by Puccinia ssp., Drechslera ssp. and E. graminis [23]. A better health status of undersown crops was a result of a protective function of barley, which is seen by no differences in the intensity of occurrence of diseases after barley harvest. In the present research there was observed a greater infection by Puccinia ssp. and Drechslera ssp. than by E. graminis. A considerable importance of these pathogens in perennial ryegrass cultivation is confirmed by Prończuk [24] and Sadowski et al. [30].

In the present research there were noted no significant differences in the seed yield of 'Stadion' sown with barley grown for green matter and for grain. No differences in the seed yield of 'Stadion' perennial ryegrass sown with barley in the two cultivation variants could have been due to similar effects of a shortened vegetation period of barley grown for green matter and decreased sowing rate when grown for grain.

Mean seed yield in the first year of use was lowest in autumn sowing objects. Numerous research show that the yielding of plants sown in autumn depends on their reaching an adequate development state prior to winter defined as the number of leaves or tillers [22,31, 34]. Żyłka and Prończuk [35] report on sowing of September 1 which resulted in developing 4-5 tillers prior to winter and made it possible to obtain similar seed yields as in spring pure stand. In the present research perennial ryegrass sown by September 5 by the end of the vegetation had developed most frequently a single tiller, which had a negative effect on the seed yield in the first year of full use, by limiting the number of generative tillers developed, significantly correlated with the yield.

According to Hebblethwaite et al. [13], the seed yield formation also depends on the tillers produced due to spring tillering. Over their generative development they are shorter and show a lower seed setting in spikelets, as compared with tillers which appear in autumn already. In the present research in autumn sowing, a shorter shooting stage was accompanied by a significantly limited generative tillers length, as compared with spring sowing, which shows that the yield is formed mainly by less productive tillers formed in spring, which is confirmed by significant values of coefficients of correlation between the seed yield and generative tillers length as well as the number of seeds per spikelet.

Limiting the seed yields of perennial ryegrass from autumn sowing in the first year of full use could have been also due to a greater, than in spring sowing, number of entomophage (thrips, aphids and alfalfa plant bug) as converted into the generative tiller, mostly due to a lower number of such tillers per area unit [16].

In the second year of full use the seed yield in autumn sowing was lower than when the sowing included a cover crop. In 2000 a lower yielding of perennial ryegrass sown in autumn was mainly due to poor tillering under water deficit, after seed harvest in the first year of use (1999). The dry spring in the second year of use also resulted in a decreased number of new generative tillers. The undersown perennial ryegrass reacted to water deficit less considerably, which could have been due to, just like in the first year, a greater health status and a stronger root system. A negative effect of semi-drought after seed harvest in the first year of use on the regeneration of plantation and seed yield in the following year is confirmed by Przygodzki [27]. In 2002 lower yielding was due to a very strong lodging of perennial ryegrass in autumn sowing already over flowering, which could have resulted in a worse pollination and a limited number of seeds per spikelet as well as made harvest more diffi cult and increased seed losses as a result of shattering. The losses can account for as much as 1/3 of the total seed yield produced [10].

The effect of row spacing on the seed yield in the first and the second year of use was not significant, although lower yielding usually coincided with the wide row spacing. The poor reaction to the row spacing widths applied could have been due to a low sensitivity of perennial ryegrass to light conditions when grown for seed [7] and to the effect reported by breeders of a partial tolerance of 'Stadion' to shade. The total yield of two-year use accumulated slight effects of the first and the second year and so the difference in the seed yield of perennial ryegrass grown with different row spacing showed significant. The main reason of lower yielding of plants grown with the wide row spacing was limiting the number of generative tillers, as compared with that noted with narrower row spacing. According to Harasim [12], perennial ryegrass is a species of a strong intraspecific competition, which can result in a poorer tillering of 'Stadion' plants with the wide row spacing, when exposed to a high plant density in a row. Limiting the number of culms as a result of plant competition in the field was also reported by Schöberlein [31]. Spiertz and Ellen [32] report on an increase in the light intensity stimulating perennial ryegrass tillering. Deregibus et al. [4] claim a greater importance of the light quality, namely the proportion of waves of a specific wavelength which depends on the field density. In generative development mutual shading does not inhibit the initiation of tillering, however it reduces a potential ear productivity [32]. In the present research, despite the formation of a greater number of generative tillers in plants grown with narrower row spacing, usually lower ear productivity was recorded (lower number of spikelets per ear, seeds per spikelet and thousand seed weight). A slight increase in thousand seed weight in perennial ryegrass grown with the wider row spacing was reporter by Acigkoz and Karagoz [1] as well as Goliński [11]. A decrease in the effectiveness of seed setting (a lower number of seeds per spikelet) is, according to Goliński [11], connected with deteriorated conditions of pollination with a greater density of generative tillers.

In the second year of use, mainly in the objects with the wide row spacing, between the rows there appeared perennial ryegrass plants grown from seeds shattered in the previous year. The plants developed single generative tillers only, however they can be a reason of obtaining sowing material of varied seed certification degree due to the share of seeds of successive generation in the seed yield.

CONCLUSIONS

1. Earlier spring barley harvest applied when grown for green matter did not affect 'Stadion' plants yielding significantly in the first and in the second year of full use.

2. Perennial ryegrass produced a significantly higher seed yield in the first year of full use and a total two-year yield when it was sown in spring with barley, as compared with pure stand. The significantly lowest seed yield was recorded from the autumn perennial ryegrass sowing.

3. Introducing a cover crop did not affect the seed yield in the second year of full use of perennial ryegrass sown in spring, however it increased the yield significantly, as compared with the autumn sowing.

4. Varied row spacing did not show a significant effect on the seed yield in the first and in the second year of full use; the total two-year yield of perennial ryegrass grown with the wide row spacing was lowest.

5. The cultivar researched, 'Stadion', showed a high applicability to seed production over two years of full use. The seed yield in the second year of full use was only 11.3% lower than in the first year of harvest.

6. Over the period of generative development the most critical period coincided with April, May and June. Drought over that period decreased the seed yield by 60%, as compared with the years of favourable weather conditions.

REFERENCES

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35. Żyłka D., Prończuk S., 1997. Wpływ terminu i sposobu siewu życicy trwałej na plon nasion [Effect of the perennial ryegrass sowing date and method on the seed yield]. Zesz. Probl. Post. Nauk Rol. 451, 279-286 [in Polish].

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Małgorzata Szczepanek, Zbigniew Skinder
Department of Plant Cultivation
University of Technology and Agriculture in Bydgoszcz
Kordeckiego 20 C, 85-225 Bydgoszcz, Poland
e-mail: szczepan@atr.bydgoszcz.pl

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