Agricultural and Food Science in Finland, Vol. 11 (2002): 153–161 153 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 153–161. © Agricultural and Food Science in Finland Manuscript received February 2002 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 153–161. Yield formation of spring rye at high latitudes with reference to seeding rate and plant growth regulation Pirjo Peltonen-Sainio, Ari Rajala and Susanna Muurinen Department of Applied Biology, PO Box 27, FIN-00014 University of Helsinki, Finland. Current address: MTT Agrifood Research Finland, Plant Production Research, FIN-31600 Jokioinen, Finland, e-mail: pirjo.peltonen-sainio@mtt.fi Aspects of crop physiology and agronomy of spring rye were evaluated at Viikki Experimental Farm, University of Helsinki in 1996–1998 to get baseline information on its potential as a novel cereal crop in southern Finland. The German spring rye cultivar Ovid was fertilized with 80 kg N ha-1. Seeding rates were 300, 500, and 700 viable seeds m-2. Chlormequat chloride (CCC) was sprayed at the two-node stage of the main shoot and its effects on lodging and yield formation were studied. Various traits were assessed that characterised tiller and main shoot growth and productivity, growth duration and plant stand structure. Spring rye responded differently over years and among CCC treat- ments. CCC increased grain yield by about 200 kg ha-1compared with the control. Spring rye has long straw (130–140 cm) and tended to lodge under heavy rainfall. Thus, grain yield was maximum (ca. 5200 kg ha-1 in 1997) when rainfall was minimum. Partly because high seeding rates enhanced lodg- ing, no seeding rate effects on grain yield were recorded. At 300 seeds m-2, yield formation of both main shoot and tillers was enhanced to compensate for the reduced number of main shoots m-2. Rip- ening was not delayed at low seeding rates. Grain and hectolitre weights were not affected by seeding rate. Thus, spring rye is a potential crop for Finland if low seeding rates are used. Key words: crop yield, lodging, precipitation, sowing rates, Secale cereale, stems, tillering, yield components Introduction In Finland the harvested area of autumn sown rye (Secale cereale L.) fluctuates greatly from year to year. For example, during the last dec- ade it ranged from 9,000 to 81,000 hectares (http://www.fao.org/). According to Mukula and Rantanen (1989a), the major reason for large fluctuations in harvested area in Finland is ex- cessive precipitation in the autumn. The optimal sowing period for winter rye is brief and it may be passed not only due to heavy rains in autumn, but also due to delayed harvesting of the pre- ceding crop. In addition, the risk analysis of Mukula and Rantanen (1989a) indicated that winter damage, flooding of fields and heavy rains at harvest, reduced the harvestable area. mailto:pirjo.peltonen-sainio@mtt.fi 154 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Peltonen-Sainio, P. et al. Yield formation of spring rye In the 1990s the total annual harvested grain yield of winter rye in Finland ranged from 22,000 to 250,000 t and the average grain yield was 2.5 t ha-1 (http://www.fao.org/). Productivity of rye has not improved markedly during the last 50 years: the yield gains have averaged 1.38% per year, which is less than for the other cereal crops grown in Finland (Slafer and Peltonen-Sainio 2001). Even though winter rye is far better adapt- ed than winter wheat to high latitudes (Mukula and Rantanen 1989b), problems related to sow- ing and over-wintering cause instability in yield formation and have yet to be overcome. There- fore, this study was done to make crop physio- logical and agronomic evaluations of spring rye and thereby get preliminary information about the potential of spring rye as a substitute crop for winter rye when weather conditions are un- favourable for sowing winter rye. An important factor causing fluctuation both in yield and grain quality of winter rye is the tendency of the long-strawed cultivars to lodge (Mukula and Rantanen 1989a). Plant growth reg- ulators (PGR) represent a method to control lodging in cereals, but experiments with PGRs have mainly focussed on wheat (Triticum aesti- vum L.) and barley (Hordeum vulgare L.) (Raja- la and Peltonen-Sainio 2000). In winter rye, both PGR induced increase in lodging resistance or grain yield (Kurten et al. 1972, Sturm 1975, Fro- ment and McDonald 1997) and absence of ef- fect or yield reduction have been recorded (Hey- land and Aufhammer 1973). Since the spring rye cultivar evaluated in this study was long strawed, we monitored the effects of the gibberellin bio- synthesis-blocking agent, chlormequat chloride (CCC), on stem elongation, lodging resistance, tiller growth and yield formation. Winter rye sown earlier in the autumn than winter wheat can tiller profusely prior to winter. Short days, low temperatures and high precipi- tation favour tiller bud release and tiller growth. In contrast to autumn sown rye, the contribution of tillers to grain yield is negligible for spring sown cereals in northern growing conditions (Mela and Paatela 1974, Peltonen-Sainio and Järvinen 1995). Thus, this study focussed on monitoring the role of tillers in yield formation of spring rye as well as studying the effects of seeding rate on tiller performance and yielding ability. Material and methods Field experiments were carried out at Viikki Experimental Farm, University of Helsinki, Fin- land (60ºN13’N) in 1996–1998. The trials were conducted with the German spring rye cultivar Ovid (supplied by Tilasiemen Oy) and were sown on 22 May in 1996, 14 May in 1997 and 21 May in 1998. Net plot size was 10 m2 (1.25 × 8 m, 12.5 cm between rows). 80 kg of N ha-1 as NH4NO3 was applied as a basal dressing. Weeds were controlled with MCPA [(4-chloro-2-meth- ylphenoxy) acetic acid] and dichlorprop. A two factor (sowing rate and PGR treatment) ran- domised block design with four replications was employed. Sowing rate was 300, 500 and 700 viable seeds m-2 with or without CCC treatment. CCC [(2-chloroethyl)-trimethylammonium chlo- ride] was sprayed on to the plant foliage at 1.1 kg a.i. ha-1 (at 300 l ha-1) when the second main shoot node was evident (GS32, Zadoks et al. 1974), 41, 36 and 35 days after sowing in 1996, 1997 and 1998, respectively. Soil type was ten- tatively classified as sandy clay. The following morpho-physiological traits were measured on plants from each plot: 1) grain yield (kg ha-1, calculated at 15% moisture), 2) days from sowing to heading, 3) days from sow- ing to yellow ripeness, 4) length of grain-filling period (d) from heading to yellow ripeness, 5) height from soil surface to the uppermost leaf ligule (cm), 6) length of visible peduncle (cm), 7) length of the head (cm), and 8) height from soil surface to the head tip (cm) at maturity, 9) lodging (%) when plant stands were irreversibly lodged at post-anthesis, 10) number of heads m-2 measured from 3 rows per plot, each 0.5 m long, 11) main shoot phytomass (g), 12) main shoot vegetative phytomass (g), 13) main shoot head 155 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 153–161. weight (g) as a total weight of grains per head, 14) tillers per main shoot (no.), 15) head-bear- ing tillers per main shoot (no.), 16) vegetative phytomass on tillers (g per main shoot), 17) to- tal weight of grains on tiller heads (g per main shoot), 18) contribution of tillers to grain yield (%) as a proportion of grain yield per plant pro- duced by head-bearing tillers, 19) main shoot HI (harvest index, %) as a proportion of total weight of grains over phytomass, 20) single grain weight (mg), 21) number of grains per main shoot head, 22) main shoot head-filling rate (HFR, mg per head d-1), and 23) main shoot grain-filling rate (GFR, mg per grain d-1). Traits 11 to 21 were measured from 40 randomly sampled mature plants in each plot. Traits 14 to 18 were meas- ured only in 1997 and 1998. Statistical significances of differences be- tween the effects of year, sowing rate and PGR treatment for grain yield and morpho-physiolog- ical traits were established using the SAS Mixed Procedure (Littell et al. 1996). Differences at P < 0.05 among least significant means were es- tablished. Results Year (F2 = 454, P < 0.001) and CCC treatment (F1 = 7.97, P < 0.007) significantly affected grain yield of spring rye, whereas seeding rate had no effect (F2 = 0.59, P < 0.556). The grain yield ranged from about 2,000 kg ha-1 in 1998 to 5,400 kg ha-1 in 1997, about a mean of 3,480 kg ha-1. The number of days from sowing to heading dif- fered significantly among years (F2 = 1878, P < 0.001). Time to maturity also differed (F2 = 9262, P < 0.001) as did length of grain-filling period (F2 = 285, P < 0.001). In 1997, growth phases were short (Table 1), but weather conditions (Ta- ble 2) favoured yield formation. In 1997, the main shoot head weight and HI were far higher than in the other two years and were associated with higher number of grains per head (Table 3). In 1997, plant stands principally consisted of main shoots, and the numbers of heads per square meter were 49% and 31% lower than in 1996 and 1998, respectively. Production of veg- etative phytomass did not differ greatly from year to year. The height of plant stands varied from 130 cm to 139 cm depending on year (Table 4). Use of CCC increased grain yield of spring rye by about 200 kg ha-1 (F1 = 7.97, P < 0.007). This was not due to CCC induced delay in rip- ening, as no consistent and marked effects on duration of pre- and post-heading periods were recorded (Table 1). CCC slightly reduced plant height (by 1–6% depending on year, Table 5). This was particularly due to inhibition of elon- gation of the visible part of the uppermost in- ternode, peduncle, whereas the effects of CCC on head length and height to the uppermost leaf Table 1. Seeding rate and CCC treatment effects on growth duration of spring rye in 1996–1998. Means within each year and treatment not followed by the same letter are significantly different at P ≤ 0.05. Treatment Days to heading Days to yellow ripeness Grain-filling period (d) 1996 1997 1998 1996 1997 1998 1996 1997 1998 Seeds m-2: 300 42a 35a 47a 99a 89a 105a 57a 54a 58ab 500 41b 35a 47a 98ab 88b 105a 58a 53ab 58ab 700 41b 35a 46a 98b 88b 105a 58a 53b 59a PGR treatment: Control 41b 35a 47a 99a 88b 105a 58a 53a 58a CCC 42a 35a 47a 98a 89a 105a 57b 54a 58a PGR = plant growth regulator, CCC = chlormequat chloride 156 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Peltonen-Sainio, P. et al. Yield formation of spring rye Table 2. Monthly mean temperature (°C) and precipitation (mm) for growing seasons 1996, 1997 and 1998 and the long- term means (1961–1990) at Kaisaniemi Meteorological Station, Helsinki. 1996 1997 1998 Long-term Mean temperature: May 8.6 8.5 9.9 9.7 June 13.3 16.5 14.0 15.0 July 15 19.2 16.4 17.0 August 18.1 18.9 14.1 15.7 September 9.8 11.7 12.2 11.1 Precipitation: May 68 17 38 31 June 58 44 102 41 July 122 12 93 60 August 1 25 122 74 September 28 52 34 73 Table 3. Effect of year and seeding rate on main shoot phytomass, head weight, HI, grain number, and number of heads per square meter for spring rye. Means within each year or seeding rate not followed by the same letter are significantly different at P ≤ 0.05. Vegetative Head weight Phytomass HI Grains per Heads m-2 phytomass (g) (g) (%) head (no.) (g) (no.) Year: 1996 1.42a 0.66b 2.08b 31.7b 30a 1229a 1997 1.46a 1.11a 2.56a 43.2a 32a 631b 1998 1.28b 0.48c 1.77c 27.0c 23b 921b Seeds m-2: 300 1.53a 0.81a 2.34a 33.5a 30a 798b 500 1.36b 0.75a 2.11b 34.3a 28ab 913a 700 1.27b 0.69b 1.96c 34.2a 26b 1071a HI = harvest index Table 4. Effect of year and seeding rate on height from soil surface to the uppermost leaf ligule and to the head tip and length of visible peduncle and head in spring rye. Means within each year or seeding rate not followed by the same letter are significantly different at P ≤ 0.05. Height to Length of Head length Height to leaf ligule visible peduncle (cm) head tip (cm) (cm) (cm) Year: 1996 104.1a 26.9a 8.3a 139.2a 1997 101.7b 24.1b 6.7b 132.5b 1998 99.3c 23.4b 7.5c 130.2b Seeds m-2: 300 102.7a 25.1a 7.7a 135.6a 500 102.4a 24.8a 7.5a 134.7a 700 99.9b 24.5a 7.2b 131.7b 157 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 153–161. ligule were negligible. In 1997, the 6% reduc- tion in plant height was associated with a re- duction in lodging of 35 percentage units (Table 6). In 1998, when heavy rainfall (Table 2) resulted in fully lodged plant stands, CCC treated plants lodged similarly to the control plants. There was significant year × PGR × seed- ing rate interaction for total number of tillers on main shoots (F2 = 2.56, P < 0.008), number of head-bearing tillers on main shoots (F2 = 3.34, P < 0.049), vegetative phytomass on till- ers (F2 = 2.91, P < 0.070), grain yield produced by tillers (F2 = 3.40, P < 0.047), and tiller con- tribution to grain yield (F2 = 3.37, P < 0.048). In 1997 when there was a drought (Table 2), CCC enhanced tillering, tiller growth and yield production at 500 and 700 seeds m-2, but inhib- ited them at 300 seeds m-2 in contrast to the general trend in 1998 when rainfall was heavy. CCC treatment did not affect any of the main shoot yield components. Seeding rate significantly affected many of the traits characterising the structure of the spring rye plant stands. Increase in seeding rate resulted in fewer tillers and head-bearing tillers, less vegetative phytomass and reduced grain yield on main shoots and tillers. There was low- er tiller contribution to grain yield, fewer grains per main shoot head, more heads m-2 (Tables 3 and 7), reduced plant height traits (Table 4) and increased lodging sensitivity (Table 6). Even though significant year × seeding rate interac- tion was established for length of pre-heading (F4 = 2.47, P < 0.056) and post-heading periods (F4 = 3.62, P < 0.011), only negligible effects on duration of growth phases were recorded (Tab- le 1). Table 5. Effect of CCC treatment on height from soil surface to the uppermost leaf ligule and to the head tip and length of visible peduncle and head in spring rye in 1996, 1997, and 1998. Means within each year not followed by the same letter are significantly different at P ≤ 0.05. Height to Length of Head length Height to leaf ligule visible peduncle (cm) head tip (cm) (cm) (cm) 1996: Control 103.2a 28.2a 8.1a 139.6a CCC 104.9a 25.6b 8.4a 138.8a 1997: Control 103.3a 25.8a 6.7a 135.8a CCC 101.7b 22.4b 6.7a 129.2b 1998: Control 100.1a 24.6a 7.5a 131.8a CCC 99.7a 22.2b 7.6a 128.7b CCC = chlormequat chloride Table 6. Effect of seeding rate and CCC treatment on lodg- ing of spring rye stands (%) in 1996, 1997, and 1998. Means within each year and treatment not followed by the same letter are significantly different at P ≤ 0.05. 1996 1997 1998 Seeds m-2: 300 34c 23c 90a 500 50b 40b 89a 700 70a 60a 91a PGR treatment: Control 55a 58a 90a CCC 48a 24b 90a CCC = chlormequat chloride 158 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Peltonen-Sainio, P. et al. Yield formation of spring rye Discussion The results indicated that under southern Finn- ish growing conditions, spring rye has high yield potential, but its realisation greatly depends on precipitation and lodging of the plant stands. The long-strawed rye cultivar Ovid lodged by 41%, 52%, and 90% (Table 6) and produced grain yields of 5,400, 3,100, and 2,000 kg ha-1 in 1997, 1996, and 1998, respectively. These annual dif- ferences in lodging sensitivity did not result from concomitant and marked differences in plant height, which varied only modestly, from 130 to 139 cm. Thus, the amount of precipitation dur- ing the growing season was considered to deter- mine lodging in these studies. In addition to this, the recorded absence of the height effect sug- gests that other traits such as strength of the ba- sal internodes and extent of the root plate per shoot had impact on lodging, shoot leverage and anchorage as recently shown by Berry et al. (2000). Heavy rainfall was likely to interfere with yield formation of spring rye under Finnish growing conditions. For example, grain yield was highest in 1997, when precipitation was below and temperature above the long-term av- erage for most of the growing season (Table 2). Under such growing conditions, the pre-head- ing period was up to 12 days and the post-head- ing period up to six days shorter than in 1998 (Table 1). In spite of this, the grain yield in a dry year like 1997 was more than double that in 1998, a year with ample precipitation. The results also indicated that the evident drought during post-heading in 1997 did not re- strict grain-filling. In 1996 the total weight of grains per main shoot head was only 60% and in 1998 43% of that recorded in 1997 (Table 3). This markedly contributed to the grain:straw ratio. In 1996 the main shoot HI was 11.5 per- centage units, and in 1998 16.2 percentage units, lower than in 1997. These results may indicate that the long-strawed spring rye culti- var Ovid has a root system able to penetrate into deep soil layers and thereby able to maintain water uptake even during drought periods. Such a high grain yield and main shoot head weight in 1997 could also result from less competition between plants, since a low numbers of heads m-2 were recorded compared to 1996 and 1998 (Table 3). In general, the long-strawed spring rye culti- var Ovid had high vegetative phytomass com- pared with grain yield and HI ranged from 27% to 43% depending on year. For the same years, 1996–1998, modern spring sown cultivars (10 Table 7. Seeding rate effect on tiller growth and tiller contribution to grain yield of spring rye in 1997 and 1998. Means within each and among both treatments not followed by the same letter are significantly different at P ≤ 0.05. Seeds m-2 Total number of Head-bearing tillers Vegetative Grain yield on Contribution of tillers per main per main shoot phytomass on tillers tillers tillers to grain yield shoot (no.) (g per main shoot) (g per main shoot) (%) (no.) Control CCC Control CCC Control CCC Control CCC Control CCC 1997: 300 1.16a 0.91b 0.68a 0.54a 0.84a 0.59b 0.57a 0.39b 0.32a 0.23b 500 0.70cd 0.78bc 0.26b 0.34b 0.25c 0.37c 0.15d 0.25c 0.12c 0.17bc 700 0.36e 0.62cd 0.12bc 0.31b 0.07d 0.26c 0.04e 0.16d 0.04d 0.13c 1998: 300 0.70a 0.74a 0.63a 0.70a 0.71a 0.72a 0.21a 0.23a 0.30a 0.33a 500 0.64a 0.68a 0.59ab 0.63a 0.57ab 0.56ab 0.17ab 0.17ab 0.26a 0.29a 700 0.56ab 0.48b 0.48bc 0.42bc 0.35bc 0.33bc 0.09b 0.10b 0.16b 0.17b CCC = chlormequat chloride 159 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 153–161. to 12 depending on species) of wheat had HI values of 35–47%, oat (Avena sativa L.) 43–53%, two-rowed barley 47–57%, and six-rowed bar- ley 50–61% in southern Finland (unpublished data). This inefficient translocation of pho- toassimilates to harvestable yield in long-strawed rye cultivars is likely to be one of the major rea- sons for the relatively modest yield gains in win- ter rye (1.38% p.a.) compared with other cereal species (1.78 to 1.91% p.a.) as shown by Slafer and Peltonen-Sainio (2001). Straw shortening and concomitant increase in the proportion of grain in the phytomass and lodging resistance in winter and spring rye may result in increased drought sensitivity. Plant growth regulation effects Treatments with anti-lodging agents to shorten and stiffen cereal straw may represent an effi- cient way to increase yield stability in spring rye, in which lodging markedly interferes with build- up and/or realisation of yield potential. In this study, rye plants treated with CCC were shorter than the controls, but the reduction in height was modest: only 1–6%, corresponding to ca. 1–7 cm depending on year (Table 5). Moreover, Kurten et al. (1972) reported relatively slight reductions in straw length and stand capacity in response to CCC treatment in winter rye. Reduction in height of spring rye was principally due to CCC induced inhibition of elongation in the visible part of the uppermost internode, while no con- sistent effects on head length and height to the uppermost leaf ligule were established. Naylor (1989) reported that CCC restricted elongation of the upper internodes of triticale (X Triticose- cale Wittmack) stems. Even though the CCC induced shortening of straw was modest, it was associated with lodging resistance, which in- creased by 35 percentage units in 1997 (Table 6), when low precipitation did not cause severe lodging. However, in 1998, abundant precipita- tion (Table 2) resulted in completely lodged plant stands, and CCC treated plants lodged similarly to controls. Applying CCC increased the grain yield of spring rye by ca. 200 kg ha-1 (average grain yield for control stands was 3,400 kg ha-1 and for CCC treatment stands 3,600 kg ha-1). This was prima- rily due to reduced lodging, as CCC treatment neither prolonged the pre- and post-heading pe- riods (Table 1) nor altered yield components markedly. Both of these findings recorded un- der long day conditions are contrary to those of Naylor (1989), who found that CCC delayed leaf senescence and resulted in more grains per head in triticale. Kurten et al. (1972) also reported that CCC application resulted in more grains per head in winter rye. In addition to shortening the straw, CCC af- fected tiller growth, but the effect was depend- ent on year and seeding rate (Table 7). When there was drought, CCC treatment tended to en- hance tillering as well as tiller growth and yield formation at 500 and 700 seeds m-2, while in- hibiting them at 300 seeds m-2 when compared with the control. Under conditions of heavy rain- fall in 1998, a contrary effect, or lack of response to CCC treatment, was established depending on the trait measured. The cause of such differing responses to CCC treatment is, however, diffi- cult to explain on the basis of only two very con- trasting years. Seeding rate effects Plant stand structure of spring rye responded markedly to seeding rate without, however, af- fecting grain yield. Thus, spring rye was flexi- ble and well able to utilise the available space through tillering. The number of heads m-2 in- creased when higher seeding rates were used (Table 3). This indicates that even though tiller- ing and tiller growth were markedly enhanced at lower seeding rates (Table 7), tillers were un- able to fully compensate for the reduced number of main shoots m-2. However, in addition to stim- ulating tiller growth and productivity, as also indicated by Berry et al. (2000) and Whaley et al. (2000), a low seeding rate markedly enhanced grain yield of the primary heads (Table 3). For 160 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Peltonen-Sainio, P. et al. Yield formation of spring rye example, a decrease in seeding rate from 700 to 300 seeds m-2 resulted in four more grains per primary head, 17% higher head weight and a ten- dency of up to 18% increased head filling rate (data not shown). This enhanced tiller and main shoot growth at the lower seeding rates, which influenced that impact of seeding rate on grain yield, may result from greater radiation use effi- ciency following better radiation distribution through the canopy and increased canopy nitro- gen ratio as proposed by Whaley et al. (2000). Seeding rate only affected duration of differ- ent growth phases by a maximum of one day (Table 1). Thus, growth duration of spring rye did not respond to seeding rate as markedly and consistently as did e.g. spring oat grown at high latitudes. Peltonen-Sainio and Järvinen (1995) indicated that the use of high seeding rates re- sulted in up to 5 days shorter duration of period from sowing to yellow-ripe. Our results indicat- ed that the enhanced tillering of spring rye at 300 seeds m-2 did not result in uneven ripening of plant stands. Even though there were no significant seed- ing rate effects on grain yield and single grain weight, it is interesting to note that there was a tendency that at the lower seeding rate, the grain yield and grain weight were higher, and not vice versa. This gives more emphasis to the finding that when spring rye is sown, there is no need to use seeding rates higher than 300 viable seeds m-2. This is far less than recommended for other spring cereals grown in Finland (e.g., Mela and Paatela 1974, Peltonen-Sainio and Järvinen 1995). Furthermore, it was evident that at high- er seeding rates the increased tendency to lodge was an important factor affecting yield forma- tion. When studying lodging-associated plant characteristics Berry et al. (2000) found that use of lower seeding rates in winter wheat increased stem diameter, but reduced the material strength of stem slightly. However, use of lower seeding rates increased anchorage of the wheat plants due to more spreading and deeper root plate (Berry et al. 2000). In this study, seeding rate did not affect grain weight (F2 = 0.63, P < 0.539) or hec- tolitre weight (F2 = 0.91, P < 0.411) suggesting that use of low seeding rates did not have ad- verse effects on spring rye quality. In conclusion, results from this study indi- cated that spring rye, a novel spring cereal in northern agriculture, has high yield potential, but lodging restricts its expression. By using low seeding rates of 300 viable seeds m-2, yield for- mation of both main shoots and tillers were en- hanced and lodging was prevented without de- laying harvesting and affecting grain yield, grain weight or hectolitre weight. 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SELOSTUS Kylvötiheyden ja kasvunsääteiden vaikutus kevätrukiin satoon Pirjo Peltonen-Sainio, Ari Rajala ja Susanna Muurinen Helsingin yliopisto Kolmivuotisessa kokeessa tutkittiin kylvötiheyden ja kasvunsääteiden vaikutusta kevätrukiin satoon Etelä- Suomen kasvuoloissa. Kokeet järjestettiin Helsingin yliopiston Viikin koetilalla. Kylvötiheydet olivat ko- keessa 300, 500 tai 700 itävää siementä neliömetril- lä, ja kasvustot joko käsiteltiin kasvunsääteellä [klor- mekvattikloridi (CCC)] tai ei. Tutkittu saksalainen kevätruislajike Ovid oli hy- vin pitkäkortinen ja altis lakoontumaan. CCC-käsit- tely lyhensi kortta ja vähensi lakoontumista vuosina, jolloin runsas sade ei aiheuttanut kasvustojen lähes täydellistä lakoontumista. Keskimäärin CCC-käsittely paransi satoa 200 kg ha-1. Paras kevätruissato (5200 kg ha-1) saatiin normaalia lämpimämpänä ja vähäsa- teisempana kasvukautena (1997), vaikka tähkälle tulo oli muihin vuosiin verrattuna enimmillään jopa 12 päivää ja jyvän täyttymisaika kuusi päivää lyhyem- pi. Kylvötiheys ei vaikuttanut sadon määrään, vaik- ka eri kylvötiheyksillä kasvusto olikin hyvin erilai- nen. Mitä alhaisempi kylvötiheys, sitä voimakkaam- min kasvusto versoi ja sitä enemmän versoista saa- tiin satoa, mutta myös pääverson sato parani olennai- sesti alhaista kylvösiemenmäärää käytettäessä. Tut- kimustemme perusteella kevätruista ei ole syytä kyl- vää tiheämpään kuin 300 siementä neliömetrille, kos- ka pitkäkortisena kevätruis on hyvin laonaltis, ja kos- ka versominen kompensoi muita kevätviljoja parem- min harvan kylvön ilman, että kasvusto tuleentuisi epätasaisesti. Title Introduction Material and methods Results Discussion References SELOSTUS