2 Maataloustieteellinen Aikakauskirja Vol. 63: 287—305, 1991 Yield and competition in barley variety mixtures KARI JOKINEN Department of Crop Husbandry, University of Helsinki, SF 00710 Helsinki, Finland Present address: Kemira Oy, Espoo Research Centre, P.O. Box 44, SF 02271 Espoo, Finland Abstract. Competition between spring barley varieties and yield performance of two-, three- and four-variety mixtures were studied in two replacement series field experiments. In the first experiment, repeated in three successive years (1983 —85) the components were the six-row var- ieties Agneta, Arra, Hja-673 and Porno. In the second experiment (1984), including two nitro- gen doses (50 and 100kgN/ha), both six-row (Agneta, Pomo) and two-row (Ida, Kustaa) vari- eties were used. Arra in the first and Agneta in the second experiment were the most competitive varieties. The results suggested that the fast growth of Arra at the beginning promoted its competitive ability. Increase in available nitrogen usually strengthened the competitiveness ofAgneta. The observed competitive differences between varieties were not related to the earliness of a varie- ty, neither to the morphological characters (two- and six-row varieties) nor to the grain yield of a variety grown alone. The competitive ability was not always a stable character, the dominant- suppression relationship varying from one environment to another (e.g. growing season, nitrogen dose). The observed overyielding was not statistically significant. The ratio of actual to expected yield and the relative yield total of several mixtures exceeded slightly one. As a conclusion, the yield advantage of mixtures was marginal. As a rule, the mixtures were not more stable than monocultures as determined by the coefficient of variation. However, the yield of some mixtures varied less than the yield of the most stable monoculture. Index words: Competition, yield, barley, mixture INTRODUCTION Mixtures of field crops are still extensively grown in traditional agriculture, but where more mechanized methods are used, monocul- tures are more common. The plant commu- nities with some degree of genotypic heter- ogeneity may have advantages over pure stands. These alleged advantages have includ- ed one or more of the following: higher yields, 287 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND lower variability of yield from season to sea- son, an even distribution of production over the growth period, less susceptibility to dis- ease or lodging, and an improved quality of the crop product (Trenbath 1974). Also growing of variety mixtures, multi- lines or bulk hybrids instead of pure line var- ieties has been proposed as a means of obtain- ing higher and more stable yields. The mix- ture represents an obvious agronomic advan- tage in cases where the yield of the mixture exceeds the yield of the highest-yielding com- ponent grown in pure stand but in most cases the yields of the mixtures have been reported to be about the same as or slightly higher than that of the weighted mean of their components (Simmonds 1962, Allard and Adams 1969, Clay and Allard 1969, Sandfaer 1970, Blijenburg and Sneep 1975, Lang et al. 1975, Eisenberg 1980, Nitzshe and Hesselbach 1983, Aufhammer et al. 1984, Baker and Briggs 1984, Harrabi et al. 1986, Hou- moller et al. 1986, Karjalainen and Hnvo- la 1987, Mcdonald et al. 1988, Aufhammer and Stutzel 1989). In many experiments on varietal mixtures the yield advantage is not thoroughly assessed. This is because an analysis performed accord- ing to the de Wit model (relative yield total) (de Wit 1960, de Wit and van den Berg 1965)is in most cases impossible because only the total yield of a mixture is measured. In mixtures with relative yield total values (RYT) or land equivalent ratio values (LER) equal to unity where the highest-yielding component is the strongest competitor, the yield of the mixture will exceed the weighted mean of the components. However, this does not involve an agronomic advantage (Willey 1979, 1985). Only when RYT is greater than one is an agronomic advantage obvious. The replacement series experiments described here were made to test the hypoth- esis that mixtures of different spring barley varieties contrasted in terms of maturity, and morphological properties would yield more than the same varieties grown separately, pos- sibly through more efficient use of resources. Different ways (see above) to evaluate the yield advantage of mixtures are to be consid- ered. Besides the agronomically important yields also competitional interactions among barley varieties are elucidated. MATERIALS AND METHODS Two experiments were carried out between 1983 and 1985. Experiment 1 was repeated in three successive years. Experiment 2 was car- ried out once in 1984. The trials were located on the Viikki trial field, Helsinki University (60° 13', 25° 00'E). The soil pH varied from 5.4 to 5.8 (soil types are presented in the sec- tion on crop husbandry). The size of the plot was 10 m 2 (1.25 m x 8 m). Experimental design. Experiment 1 was laid out in a randomized block design with four blocks, the plots containing 15 variety/mix- ture treatments. Experiment 2 was in a split- plot design with four blocks, each of the two main plots containing the nitrogen fertilizer treatments were split for the 15 variety/mix- ture treatments. In both experiments the var- ieties were mixed mechanically before sowing in all possible combinations(two-, three- and four-variety mixtures) in equal proportions (number of plants per area). Thus, eleven mix- tures and four individual varieties were com- pared. Varieties. In experiment 1, four high- yielding six-row varieties (Arra, Hja 673, Agneta, Pomo) of contrasting maturity were chosen. The choice of varieties was made in order to harvest all the plots of the experiment at the same time. In experiment 2, the varie- ties were Ida and Kustaa (two-row), and Agneta and Porno (six-row) having different morphological characters (for example height, tillering capacity and grain size). The charac- ters of the varieties shown in Table 1 are from long-term field trials (1979 —86) carried out by the Agricultural Research Centre in south- ern Finland (Rantanen and Simojoki 1987). Crop husbandry. The plots were fertilized at the rate of 500 kg/ha with compound fer- 288 tilizer NPK (N 2%, P 8%, K 12 %). The amount of nitrogen was adjusted to 80 kg N/ha in experiment 1 and in experiment 2 to 50 and 100 kg N/ha by calcium ammonium nitrate (CAN) (N 27%). The fertilizers were applied between seed-bed preparation and sowing with a fertilizer drill to a depth of B—l 28—12 cm. Seeds were sown at a density of 500 viable seeds/m2 by machine in rows with 12.5 cm spacing between rows. The crops were kept free of weeds by one application of the herbi- cide Actril S (2—3 liters/ha mixed with 300 liters of water) containing MCPA (235 g/1), dichlorprop (184 g/1), ioxynil (38 g/1) and bromoxynil (24 g/1) at the timeof shoot emer- gence. The trials (total area of each plot) were harvested by a combine harvester at the time when the latest variety reached its maturity stage (the analysed moisture content was un- der 30%). The sowing dates, harvesting dates, number of days from sowing to harvesting and soil types were the following: Exp. Year Sowing Harvesting Number Soil type date date of days 1 1983 5 May 4 August 92 Muddy clay 1984 4 May 9 August 98 Muddy clay 1985 27 May 26 August 91 Sandy clay 2 1984 22 May 24 August 94 Sandy clay Sampling and analyses. The number of seed- lings was determined before the start of tiller- ing and the number of generative shoots af- ter the complete ear emergence in randomly chosen rows along 3 x 1 m in each plot (or sub- plot). The density of all the stands correspond- ed to the amount of viable seeds sown (0.95 to 1.05 times as expected). Four weeks after sowing in 1983 (exp. 1) samples were taken from three random 1-m- -long rows/plot for determination of varietal characters (early growth and development) grown in monocultures. The same amount of plants was removed from mixture stands to avoid grain yield errors. The characters recorded were dry weight per plant, dry weight per main stem, leaf area of the four fully ex- panded growth leaves of the main shoot and height of the main shoot. The height of the main shoot (pseudostem) was measured from the point where adventitious roots start their growth to the point of the stipule of the latest leaf. Also the developmental stage of the var- ieties was evaluated by determining the num- ber of tillers and number of fully expanded leaves. The grain yields were determined (kg/ha at 15% moisture content). From each mixture yield samples of 400 seeds were taken for de- termination of the seed yield of the compo- nents. The separated samples of each mixture as well as samples of each pure stand yield were used for determination of 1000 grain weights (g) in 1983. The grain weight in mix- tures was determined by dividing the weight of the fraction by the number of seeds. The grain weight of each monoculture was deter- mined from samples of 3xloo seeds. Dry weight per plant, leafarea, grain yields and 1000 grain weight were subjected to ana- lyses of variance (randomized block design and split-plot design). Mean separation was accomplished by Tukey’s honestly significant difference test (HSD) (P = 0.05). The analyses were performed according to Steel and Tor- rie (1980). Relative yields (RY) based on grain yields (weight/area) were calculated according to the formula (de WIT and van den Berg 1965) : RY = O/M, where O is the yield of the variety (species) in mixture and M the yield of the variety (spe- cies) in pure stand. Relative yield total (RYT) was calculated ac- cording to the formula (de Wit and van den Berg 1965): RYT = RYI + RY2... + RYx, where RYI, RY2 and .. . RYx are the relative yields of variety (species) 1, 2.. ,x respectively. Competitive ratio (CR) is used as a measure of intercrop (-varietal) competition. The com- petitive ratio is calculated according to the for- mula (Willey and Rao 1980) CRI = (RYI/RY2)x(Z2/Zl), where Z 1 is the proportion of intercropped 289 Table 1. General characters of the varieties (Rantanen and Simojoki 1987). Variety Grain yield kg/ha Growing time days Height 1000- Grain protein content % cm grain weight g Agneta (6-row) (Svalöv 1978) Arra (6-row) (Jokioinen 1982) Hja 673 (6-row) (Hankkija 1973) Pomo (6-row) (Jokioinen 1969) Ida (2-row) 5100 (=100) 92 87 81 37.2 12.0 83 84 38.1 12.9 92 83 85 34.0 11.7 90 90 83 37.5 11.9 97 91 70 44.9 12.8 (Weibulsholm 1979) Kustaa (2-row) 92 93 67 42.9 11.9 (Svalöv 1980) area initially allocated to variety (species) 1 and Z 2 is the proportion of intercropped area initially allocated to variety (species) 2. Thus the CR term is therefore simply the ratio of the individual RYs of the two component crops, but corrected for the proportions in which the crops were intially sown. 290 Actual yield (A) is the harvested yield of the mixture. Expected yield (E) of the mixture is the average of the yield of the monocultures included in a given mixture. RESULTS 1. The effect of the variety and growing seasons (Exp. 1) Vegetative and generative development Evaluation of the early growth characters of the plants revealed significant differences between the varieties. Arra emerged first, fol- lowed by Pomo, Agneta and finally Hja 673. The early variety Arra contained the greatest Table 2. Phytomass accumulation (dry weight in mg) of different barley cultivars grown in monocultures during the first month of growth in 1983. Dry weight means in the columns followed by the same letter are not signifi- cantly different at the 5% level (HSD test). Cultivar Phytomass/plant Phytomass/main shoot Agneta 193 a 166 ab Arra 277 b 241 c Hja 673 186 a 145 a Porno 235 ab 183 b Figure I. Height of the main stem of different barley cul- tivars grown in monoculture for four weeks in 1983. Means followed by the same letter are not significantly different at the 5% level (HSD test). Table 3. Leaf area (LA in mm2 ) of different barley cultivars grown in monocultures after the first month of growth in 1983 (N = 120). Leaf area means in the columns followed by the same letter are not significantly different at the s0.05) differences between the yields of mixtures existed, whereas the yields of monocultures differed from each other (p<0.05) (Table 5). The yield of Porno var- ied the most as determined by the coefficient of variation (Table 5). The yield of the mix- ture of Agneta, Arra and Hja 673 was the most stable. In general, the yield of a mixture was be- tween the yields of the components grown in pure stand. Overyielding of some mixtures took place, but the difference was not statisti- cally significant. In every year the actual yields of the mix- tures correlated with the expected yields of the mixtures (1983 r = 0.841**, 1984 r = 0.672* 291 Table 5. The grain yield (kg/ha) ofmonocultures and mixtures ofbarley cultivars in 1983 —1985. A/E is of the ratio the actual and expected yield of the mixtures. CV =Coefficient of variation of grain yields (all the yields in groups are included, e.g. in monocultures N= 12etc.). Grain yield means in year columns, grain yield means in the average column and grain yield means in the average row followed by the same letter are not significantly different at the 5% level (HSD test). Year Stand 1983 1984 1985 Average Grain yield A/E Grain yield A/E Grain yield A/E Grain yield A/E CV Agneta(Ag) 4752 be 5613 be 4508 bede 4958 b 9.6 Arra (Ar) 4679 abc 5212 ab 4540 bede 4810 ab 6.0 Hja673 (Hj) 4276 a 5618 be 4716 de 4870 ab 11.5 Pomo (Po) 4560 abc 5369 abc 3608 a 4512 a 16.0 AgAr 4865 e 103 5299 abc 98 4440 bede 98 4868 ab 100 7.2 AgHj 4611 abc 102 5691 c 101 4618 bede 100 4973 b 101 10.2 AgPo 4735 bc 102 5554 bc 101 4349 bed 107 4879 ab 103 10.3 ArHj 4590 abc 103 5457 abc 101 4430 bede 95 4825 ab 100 9.4 ArPo 4761 bc 103 5049 a 95 4303 bc 106 4704 ab 101 6.5 HjPo 4369 ab 99 5244 ab 95 4154 b 100 4589 ab 98 10.3 AgArHj 4767 bc 104 5273 ab 96 4787 e 104 4942 b 101 4.7 AgArPo 4796 e 103 5570 bc 103 4274 bc 101 4880 ab 102 10.9 AgHjPo 4692 bc 104 5528 bc 100 4300 bc 101 4840 ab 102 10.6 ArHjPo 4646 abc 103 5598 bc 104 4196 b 98 4813 ab 101 12.1 AgArHjPo 4502 abc 99 5579 bc 102 4206 b 97 4762 ab 99 12.4 Average 4640 a 5453 b 4362 a 4815 Mono 4567 100 5453 100 4343 100 4788 100 11.7 2- 4655 102 5382 99 4382 101 4806 100 9.5 3- 4725 103 5492 101 4389 101 4869 102 10.0 4- 4502 99 5579 102 4206 97 4762 99 12.4 and 1985 r = 0.703*). Examination of the ra- tio between theactual and the expected yields of two- and three-variety mixtures revealed that the ratio was more likely to be above one (55% of the two- and 75% of the three-variety mixtures) than under one (33% of the two-and 17% of the three-variety mixtures). The ac- tual yield of the four-variety mixture was low- er than expected in two cases out of three. The relative yields (R Y) and the relative yield totals (R YT) The relative yield of the variety should be 0.50 in two-variety, 0.33 in three-variety and 0.25 in four-variety mixtures if they occupy the same space in the mixture as in the monoculture. The variety Arra was always able to occupy more space in mixtures than in monocultures (Tables 6, 7 and 8). Also the relative yields of Arra varied the least. In general, Hja 673 occupied less space in mix- tures than in monocultures. In 1985, howev- er, the relative yields of Hja 673 exceeded the expected in some mixtures. The relative yields of Agneta and Porno fluctuated above and be- low the expected value. In two-variety mixtures the correlation (RYj > RYi) between the increase and decrease of the relative yields of the components was ob- vious ( r = —0.792 ***, df= 16). In three- variety mixtures the correlation (RYj > RYi > RYz) between the increase and the decrease of the relative yields of the components was not clearly explicable (RYj/RYz r =—0.311 ns, RYj/RYi r =—0.322 ns, RYi/RYz r = —0.470 ns). The relative yield total of a given mixture was close to one (Table 9). The relative yield total of 55% of two-variety mixtures and 67% 292 293 Table 6. Relative yields of different barley varieties grown in two-variety mixtures in 1983—1985. CV=coefficient of variation due to the year (y) and the mixtures (m). Component in the mixture Variety Year Ag Ar Hj Po Average CV(y) CV(m) Agneta 1983 0.370.57 0.460.47 (Ag) 1984 0.390.58 0.580.52 1985 0.370.45 0.520.45 Average 0.380.53 0.520.48 6.114.3 Arra 1983 0.670.66 0.570.63 (Ar) 1984 0.590.67 0.620.63 1985 0.610.58 0.600.60 Average 0.620.64 0.600.62 2.32.6 Hja 673 1983 0.450.36 0.370.39 (Hj) 1984 0.430.35 0.460.41 1985 0.550.38 0.520.48 Average 0.480.36 0.450.43 9.011.9 Pomo 1983 0.550.45 0.600.53 (Po) 1984 0.430.34 0.490.42 1985 0.550.44 0.470.47 Average 0.510.41 0.520.48 9.510.3 Table 7. Relative yields of different barley varieties grown in three-variety mixtures in 1983—1985. CV =coefficient of variation due to the years (y) and the mixtures (m). Components in the mixture Ar Ar Hj Ag Ag Ag Variety Year Hj Po Po Hj Po Ar Average CV(y) CV(m) Agneta 1983 0.300.32 0.340.32 (Ag) 1984 0.320.33 0.390.35 1985 0.300.27 0.280.28 Average 0.310.31 0.340.32 9.04.4 1983 0.440.49 0.410.45 Arra 1984 0.500.42 0.470.46 (Ar) 1985 0.410.45 0.440.43 Average 0.450.45 0.440.45 2.81.0 1983 0.220.26 0.250.24 Hja 673 1984 0.280.29 0.230.27 (Hj) 1985 0.290.39 0.300.33 Average 0.260.31 0.260.28 13.48.4 1983 0.350.42 0.280.35 Pomo 1984 0.260.31 0.260.28 (Po) 1985 0.280.32 0.300.30 Average 0.300.35 0.280.31 9.59.5 Table 8. Relative yields of different barley varieties grown in four-variety mixtures in 1983—85. CV =coefficient of variation due to the years. Variety Year 1983 1984 1985 Average CV Agneta 0.24 0.28 0.16 0.23 21.7 Arra 0.33 0.36 0.34 0.34 3.7 Hja 673 0.17 0.20 0.23 0.20 12.3 Porno 0.23 0.19 0.23 0.22 8.6 of three-variety mixtures was above one. In one case out of three the relative yield total of the four-variety mixture was above one. It is important to note that in the three succes- sive years any individual variety did not con- sistently contribute positively or negatively to the relative yield totals of all its mixtures. Competitive ratio (CR) The results presented in Tables 10, 11 and 12 show clearly that the earliest variety Arra was the most dominant variety (CR> 1). The competitive ratio of Arra was the most stable Table 9. The relative yield totals of barley variety mixtu- res in 1983—1985. (Ag =Agneta, Ar =Arra, Po =Pomo, Hj =Hja 673) Mixture Year 1983 1984 1985 Average AgAr 1.04 0.98 0.98 1,00 AgHj 1.02 1.01 1.00 1.01 AgPo 1.011.01 1.071.03 ArHj 1.021.02 0.961.00 ArPo 1.02 0,96 1.041.01 HjPo 0.97 0.95 0.99 0.97 AgArHj 1.04 0.97 1.05 1.02 AgArPo 1.01 1.06 1.01 1.03 AgHjPo 1.02 0.99 0.99 1.00 ArHjPo 1.01 1,04 0.98 1.01 AgArHjPo 0.97 1.03 0.96 0.99 Average 1.01 1.00 1.00 1.00 2- 1.01 0.99 1.01 1.00 3- 1.02 1.02 1.01 1.02 4- 0.97 1.03 0.96 0.99 compared to other varieties (Table 13). The other early variety Hja 673 was in general the subordinate one. However, in 1985 Hja 673 was equal to or more competitive than Agne- ta or Porno. The competitive relationship be- Table 10. Competitive ratio of different barley varieties grown in two-variety mixtures in 1983—1985. Component in the mixture Variety Year Ag Ar Hj Po Average Agneta 1983 0.55 1.26 0.83 0.88 (Ag) 1984 0.66 1.35 1.35 1.12 1985 0.61 0.82 0.95 0.79 Average 0.61 1.14 1.04 0.93 Arra 1983 1.81 1.83 1.26 1.65 (Ar) 1984 1.51 1.91 1.82 1.75 1985 1.65 1.53 1.36 1,51 Average 1.67 1,76 1.48 1.64 Hja 673 1983 0.79 0.55 0.62 0.65 (Hj) 1984 0,74 0.52 0.94 0.73 1985 1.22 0,66 1.11 1.00 Average 0.84 0.58 0.89 0.77 Porno 1983 1.20 0.79 1.62 1.20 (Po) 1984 0.72 0.55 1.07 0.79 1985 1,06 0.73 0.90 0.90 Average 0.99 0.69 1.20 0.96 294 Table 11. Competitive ratio of different barley varieties grown in three-variety mixtures in 1983—1985. Mixture Variety Year Ag Ar Hj Ag Ar Po Ag Hj Po Ar Hj Po Avg. Agneta 1983 0.61 1.20 0.70 1.14 1.31 0.81 0.96 (Ag) 1984 0.76 1.39 0.70 1.27 1.34 1.26 1.12 1985 0.67 1.00 0.61 0.90 0.72 0.88 0.80 Average 0.68 1.20 0.67 1.10 1.12 0.98 0.96 Arra 1983 1.63 1.96 1.28 1.45 2.00 1.26 1.60 (Ar) 1984 1.31 1.83 1.42 1.81 1.79 1.92 1.68 1985 1.50 1.50 1.67 1.47 1.41 1.46 1.50 Average 1.48 1.76 1.46 1.58 1.73 1.55 1.59 Hja 673 1983 0.83 0.51 0.76 0.62 0.50 0.63 0.64 (Hj) 1984 0.72 0.55 0.74 0.94 0.56 1.06 0.76 1985 1.00 0.67 1.39 1.22 0.71 1.04 1.01 Average 0.85 0.58 0.96 0.93 0.59 0.91 0.80 Porno 1983 0.88 0.68 1.24 1.62 0.80 1.56 1.13 (Po) 1984 0.79 0.55 0.79 1.07 0.56 1.08 0.81 1985 1.11 0.68 1.14 0.82 0.68 0.97 0.90 Average 0.93 0.64 1.06 1.17 0.68 1.20 0.95 tween the latest varieties Pomo and Agneta was rather inconsistent. In general, the rank between the competitive ratio of the varieties in a given year was rather constant irrespec- tive of the number of components in the mix- ture. Table 12. Competitive ratio of different barley varieties grown in four-variety mixtures in 1983—1985. Mixture Variety Year Ag Ar Hj Po Average Agneta 1983 0.73 1.41 1.03 1.06 (Ag) 1984 0.78 1.40 1.47 1.22 1985 0.47 0.70 0.69 0.62 Average 0.66 1.17 1.06 0.97 Arra 1983 1.38 1.94 1.43 1.58 (Ar) 1984 1.29 1.80 1.89 1.66 1985 2.13 1.48 1.48 1.70 Average 1.60 1.74 1.60 1.65 Hja 673 1983 0.71 0.52 0.74 0.66 (Hj) 1984 0.71 0.56 1.05 0.77 1985 1.44 0.68 1.00 1.04 Average 0.95 0.59 0.93 0.82 Porno 1983 0.93 0.70 1.35 0.99 (Po) 1984 0.67 0.53 0.95 0.72 1985 1.38 0.68 1.00 1.02 Average 0.99 0.64 1.10 0.91 295 Table 13. The variation of competitive ratio of different barley varieties as determined by coefficient of variation (CV) due to the years (y) and the mixtures (m) in 1983—1985. Variety Mixture CV(y) CV(m) Agneta two-variety 15.0 24.7 three-variety 13.6 21.9 four-variety 26.2 22.8 Arra two-variety 6.0 7.3 three-variety 4.6 7.2 four-variety 3.0 4.0 Hja673 two-variety 22.6 17.6 three-variety 19.3 19.7 four-variety 19.5 20.2 Pomo two-variety 18.0 21.8 three-variety 14.2 23.8 four-variety 14.8 21.6 Grain weight The environmental conditions in the mix- tures reduced the grain weight of Agneta and Hja 673 compared with their monocultures (data not shown). The grain weight of Arra was usually higher in mixtures than in monoculture. There was no relationship be- tween the grain weight of Porno whether grown in monoculture or in mixtures. 2. The effect of the variety and the level of nitrogen fertilization (Exp. 2) Actual and expected grain yields Increasing nitrogen fertilization from 50 kg/ha to 100 kg/ha had a negative effect on the mean yield (p<0.05) (Table 14). The aver- age yield of the monocultures was the lowest. The average yield of the mixtures (two-, three- and four-variety mixtures) increased when the numberof components in the stand increased. The yield of mixtures varied less than the yield of monocultures. Table 14. The grain yield (kg/ha) ofmonocultures and mixtures of barley cultivars at two levels of nitrogen fertiliza- tion. A/E is the ratio of the actual and expected yield of the mixtures. CV = Coefficient of variation of grain yields (all the yields in groups are included). Grain yield means in the average column and grain yield means in the average row followed by the same letter are not significantly different at the 5% level (HSD test). Stand Nitrogen fertilization (kg N/ha) 50 100 Average Grain yield A/E Grain yield A/E Grain yield A/E CV Agneta(Ag) 5884 5255 5570 be Ida (Id) 6058 5417 5738 c Kustaa (Ku) 6070 5210 5640 be Pomo (Po) 3828 3871 3850 a Agld 5801 97 5800 109 5801 c 103 AgKu 6041 101 6040 115 6041 c 108 AgPo 5272 109 4842 106 5057 be 107 IdKu 5679 94 5410 102 5545 be 97 IdPo 5662 115 4878 105 5270 be 110 KuPo 4848 98 4451 98 4650 ab 98 AgldKu 6167 103 5801 110 5984 c 106 AgldPo 5613 107 4967 103 5290 be 105 AgKuPo 5044 96 5170 108 5107 be 102 IdKuPo 5852 110 4934 102 5393 be 106 AgldKuPo 5832 107 5352 108 5592 be 108 Average 5577 a 5160 b 5370 Mono 5460 100 4938 100 5199 100 16.2 2- 5551 102 5237 106 5394 104 9.4 3- 5669 104 5218 106 5444 105 8.1 4- 5832 107 5352 108 5592 108 4.3 296 The yield of a given mixture was usually be- tween the monoculture yields of the compo- nents. The overyielding which occurred was not statistically significant. The correlationbe- tween the actual yields and the expected yields was obvious (r =o.Bo2***, df=2o). The ratio of the actual to the expected yields of mixtures was more frequently above one (67% n = 12 of the two- and 87% n = 8 of the three-variety mixtures) than below one (33% Table 15. Relative yields of different barley varieties grown in two-varietymixtures at two levels of nitrogen fertiliza- tion. CV =coefficient of variation due to the nitrogen fertilization (n) and the mixtures (m). Component in the mixture Variety Nitrogen Ag Id Ku Po Average CV(m) CV(n) (kg N/ha) Agneta 50 0.52 0.61 0.57 0.57 (Ag) 100 0.65 0.67 0.59 0.64 Average 0.59 0.64 0.58 0.60 4.4 5.8 Ida 50 0.45 0.47 0.57 0.50 (Id) 100 0.44 0.54 0.53 0.50 Average 0.45 0.51 0.55 0.50 8.2 0.0 Kustaa 50 0.41 0.47 0.50 0.46 (Ku) 100 0.49 0.48 0.47 0.48 Average 0.45 0.48 0.49 0.47 3.6 2.1 Porno 50 0.50 0.58 0.48 0.52 (Po) 100 0.45 0.53 0.53 0.50 Average 0.48 0.56 0.51 0.52 6.4 1.9 Table 16. Relative yields of different barley varieties grown in three-variety mixtures at two levels ofnitrogen fertili- zation. CV =coefficient of variation due to the nitrogen fertilization (n) and the mixtures (ra). Components in the mixture Variety Nitrogen Id Id Ku Ag Ag Ag Average CV(m) CV(n) (kg N/ha) Ku Po Po Ku Po Id Agneta 50 0.430.41 0.360.40 (Ag) 100 0.480.43 0.450.45 Average 0.460.42 0.410.43 8.55.8 Ida 50 0.370.33 0.300.33 (Id) 100 0.37 0.30 0.29 0.32 Average 0.37 0.32 0.30 0.33 8.9 1.5 Kustaa 50 0.36 0.26 0,27 0.30 (Ku) 100 0.31 0.29 0.32 0.31 Average 0.34 0.28 0.30 0.31 8.1 1.6 Porno 50 0.37 0.35 0.36 0.36 (Po) 100 0.33 0.34 0.30 0.32 Average 0.36 0.35 0.33 0.35 3.6 5.7 297 Table 17. Relative yields of differentbarley varieties grown in four-variety mixture at two levels of nitrogen fertili- zation. CV = coefficient of variation due to the level of nitrogen fertilization. Variety Nitrogen fertilization (kg N/ha) 50 100 Average CV Agneta Ida 0.33 0.35 0.34 2.9 0.21 0.25 0.23 8.7 0.25 0.23 0.24 4.2 0.29 0.25 0.27 7.4 Kustaa Pomo of the two-and 17% of the three-variety mix- tures). It is important to note that the actual yields were usually higher than expected more frequently at low yielding conditions (i.e. at high nitrogen level) than at high yielding con- ditions (Table 14). The relative yields (R Y) and the relative yield totals (R YT) The six-row variety Agneta occupied more space in all the mixtures than in monoculture (Tables 15, 16 and 17). Increasing nitrogen fertilization intensified the use of the space by Agneta. The two-row variety Kustaa was Table 18. The relative yield totals of barley variety mix- tures at two levels of nitrogen fertilization (Ag =Agneta, Po =Pomo, Id =Ida, Ku =Kustaa). Nitrogen fertilization (kg N/ha)Stand 50 100 Average 0.971.09 1.011.15 1.071.04 0.941.02 1.151.05 0.980.99 1.031.10 1.071.02 0.971.08 1.101.02 1.081.08 Agld AgKu AgPo IdKu IdPo KuPo 1.03 1.08 1.06 0.98 1.10 0.99 1.07 1.05 1,03 1.06 1.08AgldKuPo 1.041.03 1.06 1.02 1.06 1.04 1.06 1.08 1.08 Average 2- 3- 4- 1.04 1.05 1.08 usually able to use the space less efficiently in mixtures than in monoculture. The relative yields of the six-row variety Porno and the two-row variety Ida varied both above and be- low the expected value. The reader should observe that at the high nitrogen level almost all the relative yield to- AgldKu AgldPo AgKuPo IdKuPo Table 19. Competitive ratio of different barley varieties grown in two-variety mixtures at two levels of nitrogen ferti- lization (kgN/ha). Variety Nitrogen Component in the mixture Ag Id Ku Po Average Agneta 50 1.15 1.49 1.14 1.26 (Ag) 100 1.49 1.38 1.31 1.39 Average 1.32 1,44 1.23 1.33 Ida 50 0.87 1.00 0.99 0.95 (Id) 100 0.67 1.14 1.00 0.94 Average 0.77 1.07 0.96 0.95 Kustaa 50 0.67 1.00 1.02 0.90 (Ku) 100 0.72 0.88 0.89 0.83 Average 0.70 0.94 0.96 0.87 Porno 50 0,88 1.01 0,98 0.96 (Po) 100 0.77 1.00 1.13 0.97 Average 0.83 1.01 1.06 0.97 298 tals were greater than one (Table 18). At low level of nitrogen fertilization 50% of the two-, 75% of the three-variety mixtures and the four-variety mixture had an advantage over monocultures (RYT>I). The six-row variety Agneta was the domi- nant component in all the mixtures (CR> 1) (Tables 19, 20 and 21). The competitive ratio of Agneta was also the most stable in differ- ent mixtures compared to other varieties (Ta- ble 22). The dominance of Agneta usually in- creased as nitrogen fertilization increased. Al- most without exception the two-row variety Kustaa was the subordinate variety. The com- Table 20. Competitive ratio of different barley varieties grown in three-variety mixtures at two levels of nitrogen fertilization (kgN/ha). Variety Mixture N Ag Id Ku Ag Id Po Ag Ku Po Id Ku Po Avg. Agneta 50 1.28 1.61 1.35 1.13 1.41 1.03 1.30 (Ag) 100 1.59 1.48 1.50 1.44 1.55 1.30 1.48 Average 1.44 1.55 1.43 1.30 1.48 1.17 1.40 Ida 50 0.78 1.25 0.74 0.84 1.01 0.98 0.93 (Id) 100 0.63 0.93 0.67 0.96 1.20 1.13 0.92 Average 0.71 1.09 0.71 0.90 1.11 1.06 0.93 Kustaa 50 0.62 0.80 0.71 0.73 0.99 0.97 0.80 (Ku) 100 0.68 1.07 0.65 0.84 0.83 0.94 0.84 Average 0.65 0.94 0.68 0.79 0.91 0.96 0.82 Porno 50 0.88 1.20 0.97 1.37 1.02 1.03 1.08 (Po) 100 0.70 1.05 0.77 1.19 0.89 1.06 0.94 Average 0.79 1.13 0.87 1.28 0.96 1.05 1.01 Table 21. Competitive ratio of different barley varieties grown in four-variety mixtures at two levels ofnitrogen fer- tilization (kgN/ha). Variety Nitrogen Component in the mixture Ag Id Ku Po Average Agneta 50 1.55 1.27 1.12 1.31 (Ag) 100 1.41 1.51 1.46 1.46 Average 1.48 1.39 1.29 1.39 Ida 50 0.64 0.82 0.72 0.72 (Id) 100 0.70 1.06 1.03 0.93 Average 0.67 0.94 0.88 0.83 Kustaa 50 0.78 1.21 0.87 0.95 (Ku) 100 0.66 0.94 0.96 0.85 Average 0.72 1.08 0.92 0.90 Porno 50 0.88 1.38 1.13 1.13 (Po) 100 0.68 0.96 1.03 0.89 Average 0.78 1.17 1.08 1.01 299 Table 22. The variation of competitive ratio of different barley varieties as determined by coefficient of variation (CV) due to the mixtures (m) and the nitrogen fertiliza- tion (n). Variety Mixture CV(m) CV(n) Agneta two-variety 6.5 4.9 three-variety 8.9 6.4 four-variety 5.6 5.4 Ida two-variety 13.3 0.5 three-variety 18.2 0.5 four-variety 13.9 12.7 Kustaa two-variety 13.6 4.0 three-variety 15.3 2.4 four-variety 16.4 5.6 Pomo two-variety 10.2 0.5 three-variety 16.1 6.9 four-variety 16.5 11.9 petitive relationship between the six-row va- riety Porno and two-row variety Ida was in- consistent. DISCUSSION Occurrence of yield advantage The comparison between the average yields of mixtures and monocultures in the second experiment of the present study suggests that the increasing number of components in the mixture might increase the yields. This agrees with the results of Nitszche and Hesselbach (1983) who grew six varieties of barley in all possible combinations. However, in the 3-year experiment in the present study the blend responses of 0.4% (two components), 1.7% (three components) and —0.5% (four compo- nents) did not support the argument that the yield increase of mixtures depends in general on the number of varieties combined. This agrees with the results of Gieffers and Hes- selbach (1988). In addition, Clay and Al- lard (1969) also found no apparent relation between the number of components and the degree of deviation from expectation. The present results showed that the yield of the mixture was often equal to the means of the components grown in monoculture but also exceeded them. Occasionally the yield of the mixture even exceeded the highest yield- ing component grown alone, i.e. the mixture overyielded. However, it should be empha- sized that the overyielding was never statisti- cally significant. It was uncommon for a mix- ture to yield less than the mean of its compo- nents. These results agree rather well with the earlier work reviewed by Simmonds (1962), Trenbath (1974) and Wolfe (1985). The present results are also in accordance with re- cent published studies of barley variety mix- tures by Baker and Briggs (1984), Hou- moeller et al. (1986), Karjalainen and Hu vola (1987), Gieffers and Hesselbach (1988), Ibenthal et al. (1988) and Aufham- mer and Stutzel (1989). The results of the first experiment show that the performance of a mixture can be predict- ed at least reasonably well from the perfor- mance of the pure variety components. This rather close positive relationship between pure variety and mixture performance suggests that any complementary or compensatory effects that do occur are of minor importance. The range of individual blend responses observed in the second experiment (—6.7% to 14.5%) may imply certain complementary and com- petitional effects but may also be partly due to the large random variation, which occurred in the experiment (differences over 1072kg/ha between the yields of the stands having differ- ent compositional structure were significant at the level of 5%). In addition to the comparison of the actu- al and expected yields of the mixtures, the de Wit model (RYT-value) was used to evaluate the productivity of mixtures. The six varieties used in the present experiments were selected in respect to contrasting agronomic types differing in yield structures, morphological characters and growing time. The mixtures were also grown under varying environmen- tal conditions. The results of these experi- ments in most cases are well compatible with the de Wit competition model agreeing with the results of earlier barley varietal experi- 300 ments (e.g. Sandfaer 1970, Blijenburg and Sneep 1975). Thus, the results suggest that competition solely for the same space is rath- er common in mixtures of barley varieties and the yield advantage is marginal. It should be emphasized that the RYT- values of the mixtures of Agneta and Porno in both experiments exceeded one. Also the RYT-values of several other mixtures in the second experiment exceeded one. This sug- gests that some varieties might partly occupy different spaces in certain conditions. Results from the experiments by Allard and Adams (1969) calculated by Sandfaer (1970) also in- dicated that some genotypes of barley may partly occupy different spaces. Reasons for yield advantage When deviations of RYT-values from uni- ty occur, as at the high level of nitrogen fer- tilization in the present trial, some form of complementary use of resources (annidation) may be suspected (Trenbath 1974). The mechanisms resulting in the RYT-value being greater than one have been shown to be vari- ous (Trenbath 1974), but the data collected from the present experiments is limited in this respect. Theoretically, a mixture of varieties may benefit from the association by production of a more uniform leaf distribution or by reduc- tion of competition among integrated root sys- tems resulting in either temporal or spatial differences of use of growth factors. The evi- dence from the experiments of Palvakul et al. (1973) and Lang et al. (1975) suggests that such effects are likely to be small, or they do not favour mixing provided disease buffering is not an important factor. However, Auf- hammer and Stutzel (1989) reported that the yield advantage of barley mixtures could not be explained by the observed levels of disease or lodging. This suggests that also other mechanisms may operate. Competitive ability and consequences of competition In addition to the growing season and the level of nitrogen fertilization, neighbours in the mixture were also found to influence the competitive ability of the varieties. For exam- ple, the competitive relationship between Porno and Hja 673 varied from year to year. Increasing nitrogen fertilizationalso increased the dominance of a strong aggressor, Agne- ta. Thus competitive ability was a relative character of a variety. In other experiments the competitive ability of barley varieties var- ied also due to the environment (Sandfaer 1970). These results also showed that the use of resources in mixtures is not at equilibrium in different environments. No consistent relationship was observed be- tween competitive ability and yield ability in pure stands of different varieties. This agrees with the results of Sandfaer (1970) and Spit- ters (1979). The results of the present study, where the competitive abilities of two- and six- row barleys were compared, suggest that an erect type combined with greater height, as in the case of Agneta, may be more favourable. However, the competitive relationship be- tween the six-row variety Porno (taller, erect) and the two-row variety Ida (shorter, prostate) was unpredictable. Thus caution should be ex- ercised in view of previous unsuccessful at- tempts (Sakai 1961, Valentine 1982) to relate competitive ability only to an individual plant character. The data collected in 1983 suggests that the superior competitive ability of Arra in all cir- cumstances might be related to the early ger- mination. Also the growth habit ofArra might favour its success in mixtures. The characters of Hja 673 during the early stages of growth were unfavourable in the course of competi- tion in 1983. The results of the competitive ability of the varieties in respect to the early growth agree rather well with the results of Blijenburg and Sneep (1975) and with the model constructed by Spitters and van den Berg (1982) and Spitters (1984). Spitters 301 and van den Berg (1982) concluded that the competitive ability of a plant is determined by the space it is able to occupy at the beginning of the growing season and the relative rate at which a single plant is able to expand the space it has already occupied. The varieties which were taller and had a larger leaf area during the early stages of development might shade the shorter plants, decreasing their root/shoot ratio (see Briggs 1978 p.274). The plants of the better competitor might have more light available in mixtures than in monocultures, thus increasing their root/shoot ratio. When the competitive relationship between two genotypes as in the case of Agneta and Porno, was rather inconsistent even the vigour of seed or the grain weight might determine the competitiveness of a genotype. This is be- cause both characteristics of a seed were shown (Kangasmäki pers.com.) to affect the growth rate of seedlings. In the present trial, some yield reductions and yield increases of the components grown in mixtures may partly be explained by the results of grain weight. Both Spitters (1979) and Valentine (1982) observed that compe- tition between barley varieties affected more strongly the number of ears/plant and the number of grains/ear than the grain weight. Limitation of replacement series design The fact that the competitive ability of the six barley varieties differed in many cases from each other shows that there occurred also intergenotypic competition in mixtures. However, the limitationof the indices like CR and RY based on the replacement design is their inability to separate intra- and intergeno- typic competition quantitatively from each other. Thus the results from replacement se- ries can give only qualitative insight into the relative magnitudes of the effects of intra-and intergenotypic competition (Firbank and Watkinson 1985, 1990, Häkansson 1988). The results of the experiments based on the de Wit model can be also biased, because only one density was used (Connolly 1986). In the present experiments the indices were based on the yields per unit area of the varieties, which typically change less rapidly as the monocul- ture density changes than does the yield per plant. According to Harper (1977 p. 152—4) the total plant yield is rather independent of density except when plants are very small or widely spaced (the law of constant final yield). The selected density used in these experiments was very likely near optimum in respect to achieve constant final yield of barley in north- ern growing conditions (see e.g. Erviö 1983). Stability of mixtures A frequently claimed advantage of mixtures is their capability to deal with environmental variability, implicitly equivalent to the avoid- ance of risk (Vandeermeer 1989). A number of authors reviewed by Trenbath (1974) and by Wolfe (1985) have noted the improved stability of mixtures compared with their com- ponents, but also the opposite effect has been noted. The results of the first experiment indicate that over years only few mixtures were more stable than their most stable component in monoculture; the remaining mixtures showed stabilities between those of their component monoculture. In the second experiment the high level of nitrogen fertilization induced stress in most of the monoculture stands, decreasing the yield whereas some mixtures were insensitive to nitrogen fertilization. This suggests that a mixture may adjust its geno- typic or phenotypic state in response to tran- sient fluctuations in environment in such ways that it gives high and stable return. The ad- vantage of mixtures in respect to stability may be partly due to the beneficial effects of com- pensation. Thus some mixed stands may ex- hibit populational buffering arising in inter- actions among different coexisting genotypes and show low »genotype»-environment inter- action. This suggests that mixtures might be universal instead of specialized producers ac- cording to the terminology introduced by Al- lard and Bradshaw (1964). 302 The greatest difficulty in discussing stabili- ty is the lack of any clear definition of an in- dex of stability of yield (Schutz and Brim 1971). The standard measurement of yield variability or yield stability is the coeffiecient of variation which was also used here. One common method of measuring stability of genotypes is to regress the yield of a particu- lar genotype to the mean yield of a group of genotypes over wide range of environments (see Eberhart and Russell 1966). This ap- proach has, however, been criticized, because dependency between genotypic means and en- vironmental means invalidates the analysis of variance of regression (Zhang and Geng 1986). This is rather obvious in mixture ex- periments where the independent variable in the regression is the average of a few yields. References Allard, R.W. & Adams, J. 1969. Population studies in predominantly self-pollinating species. XIII. Intergeno- typic competition and population structure in barley and wheat. Amer. Nat. 103:621—645. Allard, R.W. & Bradshaw, A.D. 1964. Implications of genotype-environmental interactions in applied plant breeding. Crop Sci. 4:503—508. Aufhammer, W. & Stutzel, H. 1989. Sorten- Mischungeffekte in Wintergerstenbeständenin Abhän- gigkeit von Standort und Produktionintensität. J. Agron. Crop Sci. 162:180—191. Aufhammer, W., Kubler, E. & Stutzel, H. 1984. Ef- fekte der Sortenmischung auf die Ertragsbildung von Gerstenbeständen. J. Agron. Crop Sci. 153:385—97. Baker, R.J. & Briggs, K.G. 1984. Comparison of grain yield of uniblends and biblends of 10 spring barley cul- tivars. Crop Sci. 24:85—87. Blijenburg, J.G. & Sneep, J. 1975. Natural selection in a mixture of eight barley varieties grown in six succes- sive years. 1. Competition between the varieties. Eu- phytica 24:305—15. Briggs, D.E. 1978. Barley. 612 p. New. York. Clay, R.E. & Allard, R.W. 1969. A comparison of the performance of homogenous and heterogenous barley populations. Crop Sci. 9:407—12. Connolly, J. 1986. On difficulties with replacement- series methodology in mixture experiments. J. Appi. Ecol. 23:125—137. Eberhart, S.A. & Russell, W.A. 1966. Stability parameters for comparing varieties. Crop Sci. 6:36—40. Erviö, L.-R, 1983. Competition between barley and an- nual weeds at different sowing densities. Ann. Agric. Fenn. 22:232—239. Eisenbero, B.E. 1980. Screening for competition effects amongst genotypes of barley, oats and lupins. Crop Production 9:39—47. Firbank, L.G. & Watkinson, A.R. 1985. On the analy- sis of competition within two-species mixtures of plants. J. Appi. Ecol. 22:503—517. Firbank, L.G. & Watkinson, A.R. 1990. On the effects of competition: From monocultures to mixtures. In; Grace, J.B. & Tiiman, D.(eds.). Perspectives on Plant Competition, p. 166—192. Academic Press, Inc. New York. Gieffers, W. & Hesselbach, J. 1988. Krankheitsbefall und Ertrag verschiedener Getreidesorten im Rein- und Mischanbau. 1. Sommergerste (Hordeum vulgare L.). Z. Pfl.krankheiten Pfl.schutz 95:46—62. Häkansson, S. 1988. Competition in stands of short-lived plants. Density effects measured in three-component stands. Swed. Univ. Agric. Sci. Dept. Crop Produc- tion Sci. Crop Production Sci. 3. 181 p. Uppsala. Harper, J.L. 1977. Population Biology of Plants. 892 p. Academic Press. London. Harrabi, M.M., Laribi, A. & Bouslama, M. 1986. Sta- bility and yield performance of some barley (Horde- um vulgare L.) cultivars and mixtures. Rachis, Barley and Wheat Newsl.s:ll— l6. Houmoller, M.S., Henneberg, U., Olsen, C.C., Stolen, O. & Welling, B. 1986. Sortsblandingeraf vinterbyg 1983—85. Tidskr. Planteavl. 90:15—26. Ibenthal, W-D., Göbel, M., Willnecker, G. & Bern- hold, L. 1988. Ertragsniveau, Krankheitsbefall und Mehltauvirulenz in Sortenmischungen von Sommer- gerste (1984 —1986). Z. Pfl.krankheiten Pfl.schutz 95:561—571. Karjalainen, R. & Hiivola, S.-L. 1987. Performance of cultivar mixtures under northern growing conditions in Finland. Barley Genet. V:7I9 —725. Lang, R.W., Holmes, J.C., Taylor, B.R. & Waterson, H.A. 1975.The performance of barley variety mixtures. Expl. Husb. 28:53—59. McDonald, 8.A., Allard, R.W. & Webster, R.K. 1988. Responses of two-, three-, and four-component bar- ley mixtures to a variable pathogen population. Crop Sci. 28:447—452. Nitzshe, W. & Hesselbach, J. 1983. Sortenmischungen statt Viellien-Sorten. 1. Sommergerste (Hordeum vul- gare L.). Z. Pfl.zuchtg. 90:68—74. Palvakul, M., Finkner, V.C. & Davis, D.L. 1973. 303 Blendability of phenotypically similar and dissimilar winter barley cultivars. Agron. J. 65:74—77. Rantanen, O. & Simojoki, P. 1987. Ohra. Peltokas- vilajikkeet 1987—88. Tieto tuottamaan 45:28—35. Hel- sinki. Sakai, K.I. 1961. Competitive ability in plants: its in- heritance and some related problems. Symp. Soc. Expl. Biol. 15:245—263. Sandfaer, J. 1970. An analysis of the competition be- tween some barley varieties. Risö Rep. 230. Danish atomic energy commission. 114 p. Roskilde. Schutz, W.M & Brim, C.A. 1971. Inter-genotypic com- petition in soybeans. 111. An evaluation of stability. Crop Sci. 11:684—689. Simmonds, N.W. 1962. 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SELOSTUS Ohralajikkeiden välinen kilpailu ja lajikeseosten sato Kari Jokinen Helsingin Yliopisto, Kasvinviljelytieteen laitos 00710 Helsinki Nykyinen osoite Kemira Oy, Espoon tutkimuskeskus, PL 44, 02271 Espoo Kahdessa korvaussarjaan perustuvassa kenttäkokeessa tutkittiin ohralajikkeiden välistä kilpailua ja seosten sadontuottoa seostenkoostuessa kahden, kolmen ja nel- jän lajikkeen yhdistelmistä. Ensimmäisessä kokeessa, joka toistettiin kolmena peräkkäisenä vuonna (1983—85), lajik- keet olivat monitahoiset Agneta, Arra, Hja-673 jaPomo. Toisessa kokeessa (1984), jossakäytettiin myös kahta typ- pilannoituksen määrää (50 ja 100 kgN/ha), lajikkeet olivat monitahoiset Agneta ja Pomo ja kaksitahoiset Ida, Kustaa. Lajikkeen valtauskyky ei yleensä ollut genotyypin stabi- ili ominaisuus lajikkeiden keskinäisten valtaussuhteiden muuttuessa ympäristöstä toiseen (kasvukausi, typpilan- noitus). Lajikkeen valtauskyky ei riippunut lajikkeen ai- kaisuudesta, morfologisista ominaisuuksista (kaksi- ja monitahoiset) eikä puhdaskasvustosadonmäärästä. Lajik- keen valtauskykyä edisti nopea alkukehitys Arran olles- sa vahaavin lajike. Ensimmäisen kokeen yhdenkäänseoksen kolmen vuo- den keskimääräinen jyväsato ei poikennut tilastollisesti 304 merkitsevästi seoksen komponentin puhdaskasvuston jyväsadosta. Toisessa kokeessa joidenkin seosten jyväsato oli tilastollisesti merkitsevästi suurempi kuin seoksen kom- ponenteista vähiten tuottaneen puhdaskasvustosato. Vaik- ka useiden seosten toteutuneen ja odotetun sadon väli- nen suhde ja seoksen suhteellinen kokonaissato oli hiu- kan suurempi kuin yksi, oli seosten satoetu marginaali- nen. Yksiselitteisesti seokset eivät olleet vakaampia sadon- tuottajia kuin puhdaskasvustotvaihtelukertoimella mitat- tuna. Joidenkin seosten jyväsato kuitenkin vaihteli vä- hemmän kuin vähiten vaihtelevan komponentin puh- daskasvuston jyväsato. 305