Maataloustieteellinen Aikakauskirja Vol. 63: 321—40, 1991 Competition and yield performance in mixtures of oats and barley nitrogen fertilization, density and proportion of the components 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 and yield performance in mixtures of barley and oats were evalu- ated from addition series experiments (three experiments) in 1983 and in 1984. Three doses of nitrogen fertilization (10 kgN/ha, 40 kgN/ha and 80 kgN/ha) were applied. In the first year the components were Agneta barley and Veli oats and in 1984 in addition to the previous com- bination also Ida barley and Veli oats were included. The competitive relationship between components was analysed by replacement series model and by regression analysis. The results showed that the dominant component according to the regression analysis was also dominant according to the indices of the replacement series model independently of density and proportion. Barley was generally more competitivethan oats. The dominance of barley usually increased with increasing nitrogen fertilization, especially in the mixture of Agneta and Veli. All the yield components of the barley plants increased with the decreasing proportion of barley in the mixture. In 1983, some mixtures overyielded significantly (p<0.05). The relative yield total being usually greater than one indicated yield advantage. In 1984, oats suffered from insect damage and neither barley cultivar was able to compensate enough so no overyielding occurred. The relative yield total was lower than one and thus no yield advantage was achieved. Index words: Competition, yield advantage, barley, oats, mixtures INTRODUCTION interest has been paid to crop mixtures for two main reasons: an increase in yield brought about by the complementary habits of as- yield over locations and seasons due to the ability of at least one genotype in the mixture to yield well in adverse conditions (Taylor 1978). Approximately 50% of the barley and oats grain produced in Ontario is from mix- sociated genotypes, and greater stability of tures of the two components (300 000 ha) 321 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=qNSOUbNAW2UF-Jts.sPKS0ZvdGres7ikUb4QNdg.LNzj6C_X0Wgvuj2xmqiPTXgSj0RaMtMuUaLymJYSLFI-HyyChCEzBB3YdidFUNaRfRfP4fI0-3_8NZ8S7mKWSFWjLtlnID4P_HN3cbGeiYXgpQ52Rj7pVZy9QBJuD_IOc6J5r7MaXvrxQRndR8ZR1CE1z4UApc8fd4YudGx23k56dZKqeIk_jEdKDSiVHApttO-0GSrZn6NTFcGtbQWZ (Fejer et al. 1982). In several studies of barley-oats mixtures grown for feed, grain yield increases over the mean of the components in monoculture have been observed and even overyielding has oc- curred (Salminen 1945, Van Dobben 1953, Bebawi and Naylor 1978, Taylor 1978, Fejer et al. 1982). Ontario provincial agricul- tural statistiscs show that mixed grain consis- tently outyielded pure stands as reported by Fejer et al. (1982). In trying to combine the two species so that there was less mutual com- petition at critical stages, Syme and Bremner (1968) found that mixture yields did not ex- ceed the better component and were usually similar to mid-component. In most cases of mixtures of oats and bar- ley the yield of the mixture is compared with the average of the yield of the two monocul- tures. A higher yield of the mixture is inter- preted as an argument for mixed cropping. This indicates that the yield advantage of mix- tures is not always completely assessed. This is because without calculation of relative yield total the interpretations based on the ratio of actual and expected yields can be misleading, especially in cases where compensation occurs (Willey 1979). Compensation seems also to be the most common situation with mixtures of barley and oats, i.e. the competitive abili- ties of barley and oats differ (for example Salminen 1945, de Wit 1960, Syme and Bremner 1968, Fejer et al. 1982). A mixture of species might more efficient- ly utilize the resources and therefore yield more than the pure stand. This may indicate that intraspecific competition is more severe than interspecific interference with growth. For these reasons mixtures might be expected to show a yield advantage (Spitters 1983). To achieve an accurate assessment of the rela- tive strengths of intra- and interspecific com- petition in mixtures of barley and oats, these experiments were conducted. In the experiments described here, replace- ment series (substitutive) (de Wit 1960, Harper 1977, Connolly 1986) at three total plant densities of barley-oats mixtures and monocultures were used to assess the competi- tional relationship between species and the yield advantage of mixtures. The design is characterized by the term addition series (Spitters 1983). Two approaches were used to analyse com- petition. The first approach was to use mea- sures of competitive abilities and combining abilities of varieties based on the relative yield responses according to the de Wit model (de Wit 1960). The other approach is based upon linear regression with the reciprocal of aver- age plant grain yield as the dependent varia- ble and density as the independent variable. The reciprocal yield model was expanded for multiple genotypes by Wright (1981) and Spitters (1983). MATERIALS AND METHODS The addition series field experiments were carried out in 1983 (one experiment) and in 1984 (two experiments) at the experimental farm of the University of Helsinki in Helsinki Viikki (60° 13'N, 25° 00'E) with barley and oats sown separately and in mechanical mix- tures. In 1984, the experiments situated side by side. In 1983, the soil was silty clay with pH 5.6 and in 1984 finer fine sand with pH 5.4. Experimental design and management. A split-split-plot design (nitrogen levels in main plots, total densities in subplots and genotypic composition of stand in subsubplots) was used with three blocks. The subplot size was 10 m 2 (1.25 m x 8 m) with rows spaced 12.5 cm apart. In 1983, the varieties were Agneta bar- ley and Veli oats and in 1984, in addition to previous combination, also Ida barley and Veli oats were included. The general charac- ters of the cultivars are described elsewhere (Jokinen 1991 a). The total densities in 1983 were 200, 400 and 600 seeds/m2 and in 1984 200, 500 and 800 seeds/m2 . The proportions based on plant numbers were 25/75, 50/50 and 75/25. Granular NPK (N 2%, P 8%, K 12%) (500 322 kg/ha) combined withcalcium ammonium ni- trate (CAN) (N 27%) was applied at the rate of nitrogen 10, 40 and 80 kgN/ha. Sowing dates were 5 May in 1983and 18 May in 1984. The crops were kept free of weeds by one ap- plication of the herbicide Actril S (2—3 liters/ha mixed with 300 liters of water) con- taining MCPA (235 g/1), dichlorprop (184 g/1), ioxynil (38 g/1) and bromoxynil (24 g/1) at the time of shoot emergence. At maturity the total area of each plot was harvested (10 August in 1983 and 6 September in 1984) and the grain yields were determined (kg/ha at 15% moisture content). Sampling and analyses. The number of plants in each plot were determined by count- ing the number of seedlings in four randomly selected 1-m-long rows/plot about three weeks after sowing before the start of tillering. Simi- larly the number of generative shoots in 1983 was determined after the complete ear emer- gence of the cultivars. The height of the stands was estimated visually as well as the emergence time of seedlings. Four weeks after sowing in 1984 samples were taken in three randomly selected 1-m-long rows/plot for determination of the total above ground dry matter of the plants. From each mixture yield a 50 g sample was taken for determinationof the seed yield of the barley and oats components. The separat- ed samples of each mixture as well as samples of each pure stand yield were used for deter- mination of 1000 grain weights (g) (3 x 100 seeds/sample) in 1983. The number of grains/head was calculated using the data of yield, number of generative shoots and 1000 grain weight. Relative yield (RY) and relative yield total (RYT) were calculated according to the meth- od of de Wit and van den Berg (1965). Com- petitive ratio (CR) was determined according to the method of Wiley and Rao (1980). The mean yield/area was calculated before com- puting the indices. Details of the calculations are described elsewhere (Jokinen 1991 b) A discussion of the use of hyperbolic yield- density equations in various situations has been given elsewhere (Wright 1981, Spitters 1983, Firbank and Watkinson 1985, 1990, Connolly 1987, Roush et al. 1989). The method used here was described previously (Jokinen 1991 c). Data on the plant dry weights, the grain yields, 1000 grain weight and the number of generative shoots were subjected to analyses of variance for split-split-plot design (Steel and Torrie 1980). Mean separation was ac- complished by Tukey’s honestly significant difference test (HSD) (P = 0.05) (Steel and Torrie 1980). Table I. The influence of nitrogen fertilization and proportion of oats in the stand on the phytomass accumulation (dry weight mg/plant) of Veli oats during the first month ofgrowth in 1984 in two barley-oats experiments (Veli/Ida and Veli/Agneta). The analysis of variance is done separately for each experiment. Dry weight means in the average columns and in the average rows followed by the same letter are not significantly different at the 5% level (HSD test). The component of oats in the mixture Ida barley Agneta barley Proportion Nitrogen (kgN/ha) Nitrogen (kgN/ha) Oats/barley 10 40 80 Average 10 40 80 Average 100/0 144 179 190 171 c 151 188 185 175 d 75/25 134 167 173 158bc 133 174 172 160 c 50/50 134 147 160 147 b 125 140 146 137 b 25/75 124 139 137 133 a 105 127 130 121 a Average 134 a 158 b 165 b 152 129 a 157 b 158 b 148 323 RESULTS Vegetative development and lodging In both years the barley seedlings emerged first, about three days earlier than the oats. The first leaves of barley were larger than those of oats (data not given). The number of seedlings in each plot was about the same (0.95—1.05) as expected (data not given). The average phytomass of the oats was ap- proximately the same in both experiments (Ta- ble 1). Both barley varieties were over twice heavier than the oats (Tables 1 and 2). The average phytomass of all the varieties de- creased with increasing density (data not giv- en). The seedlings of Agneta were heavier than those of Ida. Unlike the oats, the phytomass of the barley varieties increased with decreas- ing proportion of the species in the mixture. Both barley varieties were more competitive than the oats competitive ratio varying from 1.21 to 1.52 (data not given). The relative yield totals varied from 0.96 to 1.05 (data not giv- en). No lodging occurred in 1983. In 1984, the pure stands of barley at the highest density and the highest level of nitrogen fertilization were the most lodged (Table 3). Grain yields In 1983, the mean yield of the experiment of Veli oats and Agneta barley was 5446 kg/ha (Table 4). The analysis of variance showed sig- Table 2. The influence of nitrogen fertilization and proportion of barley in the stand on the phytomass accumulation (dry weight mg/plant) of Ida barley and Agneta barley during the first month of growth in 1984 in two barley-oats experiments (Veli/Ida and Veli/Agneta).The analysis of variance is done separately for each experiment. Dry weight means in the average columns and in the average rows followed by the same letter are not significantly different at the 5% level (HSD test). Ida barley Agneta barley Proportion Nitrogen (kgN/ha) Nitrogen (kgN/ha) Barley/Oats 10 40 80 Average 10 40 80 Average 100/0 271 348 353 324 a 317 397 455 390 a 75/25 296 341 334 324 a 336 431 453 407 b 50/50 315 384 362 354 b 353 445 476 425 c 25/75 326 359 390 358 b 364 490 466 440 d Average 302 a 358 b 360 b 340 343 a 441 b 463 b 416 Table 3. Lodging of the stands (Vo of area) in 1984.(— =no lodging, 100=completely lodged, Ag=Agneta/Veli, Id =Ida/Veli). Nitrogen fertilization (kgN/ha) 40 80 Density (plants/m 2 ) Density (plants/m J) 200 500 800 200 500 800 Proportion Stand Stand Oats/barley Id Ag Id Ag Id Ag Id Ag Id Ag Id Ag 100/0 ______ ______ 50/50 ______ ___lo 25/75 10 20 47 33 18 77 0/100 3 22 32 52 47 33 83 83 93 324 nificant (p<0.05) interaction between the nitrogen fertilization and the proportion of the components, and between the density and the proportion of the components. At the lowest level of nitrogen two out of three mixtures yielded significantly more (approximately 9%) than the pure stands, i.e. the mixtures over- yielded. At the highest density all the mixtures overyielded significantly (approximately 7%). Comparison between the actual and expected yields of the mixtures (50:50) shows that all the mixtures were more productive than monocultures. In 1984, the mean yield in both experiments was lower than in the previous year (Tables 5 and 6). This was due to the very low yield of oats because of frit fly {Osdnella frit) dam- age. In general, the grain yield of the stands increased with increasing proportion of bar- ley in the mixture and no overyielding oc- Table 4. The influence of nitrogen fertilization, density and the proportion of barley (Agneta) and oats (Veli) in the mixture on the grain yield (kg/ha) of the stands in 1983. A/E is the ratio of the actual and expected yield of the mixture of 50:50. Grain yield averages within each treatment (nitrogen fertilization, density and proportions) followed by the same letter are not significantly different at the 5% level (HSD test). Comparison between the grain yield averages of different proportions is done at different levels of nitrogen and density (interaction statistically significant). Proportion Density Nitrogen fertilization (kgN/ha) Oats/barley (plants/m 2) ~ ~ ~ 710 40 80 Average 100/0 200 3941 4344 4383 4223 a 400 4829 5332 5608 5256 a 600 5138 5397 5973 5503 a Average 4636 ab 5024 a 5321 a 4994 a 75/25 200 4682 5044 5331 5022 b 400 5237 5670 6093 5667 be 600 5198 6130 6368 5899 b Average 5039 c 5614 b 5931 b 5528 be 50/50 200 4576 5179 5494 5083 b 400 5316 6009 6396 5907 c 600 5325 5690 6742 5919 b Average 5072 c 5626 b 6211 be 5636 c 25/75 200 4294 5313 5772 5126 b 400 5068 5894 6582 5848 be 600 5228 6048 6557 5944 b Average 4863 be 5752 b 6304 c 5640 c 0/100 200 4290 5585 5754 5210 b 400 4676 5727 6274 5559 ab 600 4508 5891 6206 5535 a Average 4491 a 5734 b 6078 be 5434 b Average 200 4357 5093 5347 4932 a 400 5025 5726 6191 5647 b 600 5079 5831 6369 5760 b Average 4820 a 5550 b 5969 b 5446 A/E 200 111 104 108 107 400 118 109 108 109 600 110 101 111 107 Average 111 104 109 108 325 curred. It is important to note that in 1984 in both experiments the actual yields of mixtures (50:50) were higher than expected in some cases (Tables 5 and 6). Relative yields (RY), relative yield totals (RYT) and competitive ratio (CR) in 1983, the relative yield of Veli oats was higher than expected only at the lowest level of nitrogen fertilization (Fig. 1). In 1984, the relative yield of oats was always lower than expected (Figs. 3 and 5). In both years the rela- tive yields of barley were usually higher than expected (Figs. 1, 2 and 3). In general, barley was more competitive than oats (CR> 1) (Figs. 2, 4 and 6). Only in 1983 at the lowest level of nitrogen fertiliza- tion were oats as competitive as barley in some cases (Fig. 2). In 1984, Agneta was more corn- Table 5. The influence of nitrogen fertilization, density and the proportion of barley (Agneta) and oats (Veli) in the mixture on the grain yield (kg/ha) of the stands in 1984. A/E is the ratio of the actual and expected yield of the mixture of 50:50. Grain yield averages within each treatment (nitrogen fertilization, density and proportions) followed by the same letter are not significantly different at the 5% level (HSD test). Comparison between the grain yield means of different proportions is done at different levels of nitrogen and density (interaction statistically sig- nificant). Proportion Density Nitrogen fertilization (kgN/ha) Oats/barley (plants/m 2 ) ~ ~ “ 710 40 80 Average 100/0 200 2762 2303 2748 2604 a 500 2674 2444 2368 2495 a 800 2852 2179 2817 2616 a Average 2763 a 2309 a 2644 a 2572 a 75/25 200 2288 3452 2751 2830 a 500 3701 3368 3478 3516 b 800 3215 3947 3693 3618 b Average 3068 a 3589 b 3307 b 3321 b 50/50 200 3476 4317 3987 3927 b 500 4069 4628 4551 4416 c 800 3631 4758 5042 4477 c Average 3725 b 4568 c 4527 c 4273 c 25/75 200 4446 4883 4440 4590 c 500 4832 5160 5506 5166 d 800 5274 5797 5342 5471 d Average 4851 c 5280 d 5096 c 5076 d 0/100 200 5255 5856 5694 5602 d 500 6095 6162 6228 6162 e 800 5789 5841 5425 5685 d Average 5713 d 5953 e 5782 d 5816 e Average 200 3645 4162 3924 3911 a 500 4274 4352 4426 4351 b 800 4152 4504 4464 4373 b Average 4024 a 4340 a 4271 a 4212 A/E 200 86 106 94 96 500 93 107 106 102 800 84 119 122 108 Average 88 111 107 102 326 Figure I. The influence of density (plants/m! ), nitrogen fertilization (kg N/ha) and proportion of the components on the relative yields (RY) of Agneta barley and Veli oats, and on the relative yield totals (RYT) of the mixtures in 1983. Figure 2. The influence of density (plants/m;), nitrogen fertilization (kg N/ha) and proportion of barley on the competitive ratio (OR) of Agneta barley over Veli oats in 1983. 327 Figure 3. The influence of density (plants/m 2), nitrogen fertilization (kg N/ha) and proportion of the components on the relative yields (RY) of Agneta barley and Veli oats, and on the relative yield totals (RYT) of the mixtures in 1984. Figure 4. The influence of density (plants/m 2), nitrogen fertilization (kg N/ha) and proportion of barley on the competitive ratio (CR) of Agneta barley over Veli oats in 1984. 328 petitive over oats than was Ida. In 1984, Agne- ta was more competitive than in the previous year. Especially Agneta barley was the most competitive at the highest level of nitrogen fer- tilization. In 1984, unlike the previous year, the competitive ratio of Agneta usually in- creased with increasing proportion of barley. As a rule, the relative yield totals exceeded one in 1983 (Fig. 1). In 1984, the relative yield totals of both mixtures were close to or lower than one (Figs 3 and 5). Regression models The regression equations accounted for 90—96% of the variation in grain yield of both species (R2 = 0.90—0.99) (Tables 7, 8 and 9). Only in 1984 in the mixture of Agne- ta barley and Veli oats were the regression coefficients of oats not statistically significant in regression equations for oats. As a rule, the intraspecific competition of barley was more severe than the interspecific competition and vice versa for oats. Barley Table 6. The influence of nitrogen fertilization, density and the proportion of barley (Ida) and oats (Veli) in the mixture on the grain yield (kg/ha) of the stands in 1984. A/E is the ratio of the actual and expected yield of the mixture of 50:50. Grain yield averages within each treatment (nitrogen fertilization, density and proportions) fol- lowed by the same letter are not significantly different at the 5% level (HSD test). Proportion Density Nitrogen fertilization (kgN/ha) Oats/barley (plants/nP) ~ ~ ~ T10 40 80 Average 100/0 200 2588 2657 2748 2664 500 2657 3292 2769 2896 800 2853 2908 2908 2890 Average 2689 2952 2808 2816 a 75/25 200 3342 3500 3473 3438 500 3469 3788 3979 3745 800 2992 3673 3993 3553 Average 3268 3654 3815 3579 b 50/50 200 4466 4372 4075 4304 500 4028 4944 4656 4543 800 4697 4564 4795 4685 Average 4397 4627 4509 4511 c 25/75 200 4679 5047 5149 4958 500 4546 5459 5643 5216 800 5615 5223 5441 5426 Average 4947 5243 5411 5200 d 0/100 200 5772 5741 5869 5794 500 6082 6155 6243 6160 800 5807 5789 5901 5832 Average 5887 5895 6004 5929 e Average 200 4169 4263 4263 4232 a 500 4150 4728 4658 4512 a 800 4393 4431 4608 4477 a Average 4238 a 4474 a 4509 a 4407 A/E 200 107 104 95 102 500 92 105 103 100 800 108 104 109 107 Average 102 104 102 103 329 Figure 5. The influence of density (plants/m! ), nitrogen fertilization (kg N/ha) and proportion of the components on the relative yields (RY) of Ida barley and Veli oats, and on the relative yield totals (RYT) of the mixtu- res in 1984. Figure 6. The influence of density (plants/m 1), nitrogen fertilization (kg N/ha) and proportion of barley on the competitive ratio (CR) of Ida-barley over Veli-oats in 1984. 330 331 Table 7. Multispecies reciprocal yield models (1/W =Bo+ BINI + 82N2) for interactions between barley (Agneta) and oats (Veli) grown at three levels of nitrogen fertilization in 1983. * Species Nitrogen B 0 B 1 B 2 RC 1/RC NDI (Bab x Bba)* a (b) BaO Baa Bab Baa/Bab Bab/Baa b (a) BbO Bbb Bba R 2 Bbb/Bba Bba/Bbb Ag (Ve) 10 —15.72 2.20 1.65 0.99 1.34 0.74 1.61 1.50 Ve (Ag) 10 192.59 1.63 1.36 0.99 1.19 0.83 Ag (Ve) 40 5.08 1.74 1.17 0.99 1.48 0.67 1.24 1.41 Ve (Ag) 40 223.06 1.41 1.70 0.97 0.83 1.21 Ag (Ve) 80 30.21 1.56 0.68 0.99 2.29 0.44 1.75 1.10 Ve (Ag) 80 233.34 1.37 1.77 0.94 0.77 1.29 * b-values x 10~3 . NDI (Niche differentiation index) =(Bbb/Bba)/(Bab/Baa). 1/W is the reciprocal yield of an in- dividual plant (grain yield/plant). B 0 is the reciprocal of the theoretical maximum yield of an individual, B 1 describes influences of intragenotypiccompetition, B 2 describes influences of intergenotypic competition, N is plant density and RC predicts relative competitive ability of each genotype. p< 0.001 for B 1 and B 2 in each model. Table 8. Multispecies reciprocal yield models (1/W = Bo+ BINI + 82N2) for interactions between barley (Agneta) and oats (Veli) grown at three levels of nitrogen fertilization in 1984.* Species Nitrogen B 0 B 1 B 2 RC 1/RC NDI (Bab xBba)* a (b) BaO Baa Bab Baa/Bab Bab/BaaBaO Baa Bab Baa/Bab Bab/Baa b (a) BbO Bbb Bba R 2 Bbb/Bba Bba/Bbb Ag (Ve) 10 19.22 1.71 1.04 0.95 1.64 0.61 0.21 3.45 Ve (Ag) 10 1635.70 1.43 11.47 0.90 0.13 8.00 Ag (Ve) 40 30.31 1.62 0.59 0.99 2.76 0.36 0.18 3.71 Ve (Ag) 40 1107.66 1.51 23.37 0.93 0.06 15.63 Ag (Ve) 80 37.51 1.68 0.50 0.99 3.34 0.3037.51 1.68 0.50 0.99 3.34 0.30 0.18 4.12 Ve (Ag) 80 2050.11 —1.77 34.09 0.91 0.05 19.23 * b-values x lO-3 . NDI (Niche differentiation index) =(Bbb/Bba)/(Bab/Baa). 1/W is the reciprocal yield of an in- dividual plant (grain yield/plant). B 0 is the reciprocal of the theoretical maximum yield of an individual, B 1 describes influences of intragenotypiccompetition, B 2 describes influences of intergenotypic competition, N is plant density and RC predicts relative competitive ability of each genotype. p 1)was at the lowest level of nitrogen fertilization in 1983 (Table 7). Then both components benefitted from mixed culture. In this case the asymptotic yields ofboth components grown in mixture (1/(B1 -I- B2)) were higher than the asymptotic yields of both components grown in monoculture (1/B1). Barley was a stronger competitor than oats as determined for the ratio of regression coefficients from barley (RC = 81/B2). Agne- ta was a stronger competitor in 1984 than in 1983. In 1984, Agneta was more competitive against oats than was Ida. In most cases the relative competitive ability of barley increased with increasing nitrogen fertilization. Only in 1983 was the overall intraspecific competition greater than the overall inter- specific competition (NDI > 1) independent of nitrogen fertilization. In 1984 the competition was more severe in the mixture of Agneta and Veli than in the mixture of Ida and Veli (NDI Agneta/Veli < NDI Ida/Veli). The square root of the product of the in- terspecific competition coefficients [(Babxß- baf'/i] was less than the intraspecific compe- tition coefficients of barley and oats only in two cases in 1983. In these situations a mix- ture of optimum proportions will yield more than both monocultures, i.e. a mixture will overyield. Yield components In 1983, the addition of nitrogen, change Table 10. The influence of nitrogen fertilization, density and the proportion of barley (Agneta) and oats (Veli) in the mixture on the number of generative shoots per plant of Agneta barley in 1983. Shoot number averages within each treatment (nitrogen fertilization, density and proportions) followed by the same letter are not significantly different at the 5% level (HSD test). Comparison between the shoot number means of different proportions is done at differ- ent levels of density (interaction statistically significant). Proportion Density Nitrogen fertilization (kgN/ha) Barley/oats (plants/m 2) ’ 10 40 80 Average 100/0 200 1.00 1.28 1.30 1.19 a 400 0.74 0.83 0.90 0.82 a 600 0.70 0.75 0.78 0.74 a Average 0.81 0.95 0.99 0.92 a 75/25 200 0.89 1.45 1.59 1.31 a 400 0.67 0.86 1.03 0.85 a 600 0.67 0.75 0.82 0.75 a Average 0.74 1.02 1.15 0.97 ab 50/50 200 1.14 1.26 1.39 1.26 a 400 0.76 0.83 0.93 0.84 a 600 0.73 0.74 0.84 0.77 a Average 0.88 0.94 1.05 0.96 ab 25/75 200 1.37 1.57 1.74 1.56 b 400 0.67 1.10 1.02 0.93 a 600 0.71 0.73 0.82 0.75 a Average 0.92 1.13 1.19 1.08 b Average 200 1.10 1.39 1.51 1.33 a 400 0.71 0.91 0.97 0.86 b 600 0.70 0.74 0.82 0.75 c Average 0.84 a 1.01 ab 1.10b 0.98 332 of the total density of stands or the growth in a mixture as compared with pure culture affected all the yield components (the num- ber of generative shoots per plant, the 1000 grain weight and number of grains per head) of both species in certain extent (Tables 10—15). DISCUSSION Advantages of mixtures The results of the present experiment sug- gest that overyielding may occur in the mix- tures of oats and barley under certain condi- tions. Other studies of mixtures of barley and oats suggest that the yield of a mixture can be above that of the better component (Salminen 1945, van Dobben 1953, Bebawi and Naylor 1978, Taylor 1978, Jokinen 1991a). Syme and Bremner (1968) and Fejer et al. (1982) found that mixture yields did not exceed those of the better component. In addition to overyielding, mixtures can be advantageous over monocultures if the yield of the mixture exceeds the mid-component but are not necessarily so. For example in 1984 the actual yields of mixtures exceeded the expect- ed in many cases, however, theresults of rela- tive yield totalof a given mixture indicated no yield advantage. Thus when relative yield to- tal did not exceed one the same yield of bar- ley and oats might have been obtained with monocultures as with mixtures, without changing the total area of land (Willey 1979). At least from field experiments the rela- tive yield total could be assessed for the proper Table 11. The influence of nitrogen fertilization, density and the proportion of barley (Agneta) and oats (Veli) in the mixture on the number of generative shoots per plant of Veli oats in 1983. Shoot number averages within each treatment (nitrogen fertilization, density and proportions) followed by the same letter are not significantly different at the 5% level (HSD test). Comparison between the shoot number means of different proportions is done at differ- ent levels of density (interaction statistically significant). Proportion Density Nitrogen fertilization (kgN/ha) Oats/Barley (plants/m-) , Q 40 80 100/0 200 0.80 0.77 0.92 0.83 b 400 0.70 0.70 0.73 0.71 a 600 0.59 0.60 0.64 0.61 a Average 0.70 0.69 0.76 0.72 b 75/25 200 0.85 0.78 0.87 0.83 b 400 0.69 0.68 0.63 0.67 a 600 0.60 0.59 0.55 0.58 a Average 0.71 0.68 0.69 0.69 ab 50/50 200 0.66 0.67 0.69 0.67 a 400 0.70 0.68 0.64 0.67 a 600 0.62 0.66 0.44 0.57 a Average 0.66 0.67 0.59 0,64 a 25/75 200 1.01 0.92 0.80 0.91 b 400 0.64 0.72 0.67 0.68 a 600 0.66 0.57 0.52 0.58 a Average 0.77 0.74 0.66 0.72 b Average 200 0.83 0.79 0.82 0.81 a 400 0.68 0.70 0.67 0.68 b 600 0.62 0.61 0.54 0.59 b Average 0.71 a 0.70 a 0.68 a 0.69 333 evaluation of the mixture advantage. There are only a few published experimen- tal results with barley-oats mixtures from which it is possible to calculate relative yield totals. The relative yield total of the mixture of oats and barley was close to one (1.03) as calculated by the author from the results of eight experiments conducted by Salminen (1945). This indicates no or a very slight yield advantage. The results calculated by de Wit (1960) indicated that in general the yield of barley or oats is proportional to the relative space occupied by these crops. The relative yield totals calculated by the author from the experiments of Syme and Bremner (1968) varied from 0.90 to 1.15 with two out of sev- en values being lower than one. The calculat- ed relative yield totals (1.07, 1.15) from the two experiments of Fejer et al. (1982) as well as the results of the present experiment in 1983 suggest that cropping of mixtures of barley and oats may be of benefit. However, more experiments in different environments are needed to provide support for the practical use of mixtures. In addition to possible yield advantages there are otherbenefits of growing barley and oats in mixture such as prevention of lodging (de Wit 1960). The results of the present ex- periments in 1984 suggest that lodging may be reduced by growing mixtures. The decreased lodging of mixtures compared with monocul- tures may be because of shorter barley plants in mixtures (K.J. Jokinen unpubl.). The in- creasing light intensity during the growth of barley plants is known at first to increase and Table 12. The influence of nitrogen fertilization, density and the proportion of barley (Agneta) and oats (Veli) in the mixture on thousand grain weight (g) of Agneta barley in 1983. Grain weight averages within each treatment (nitrogen fertilization, density and proportions) followed by the same letter are not significantly different at the 5% level (HSD test). Comparison between grain weight means of different proportions is done at different levels ofnitrogen fertilization (interaction statistically significant). Proportion Density Nitrogen fertilization (kgN/ha) Barley/Oats (plants/m! ) ~ ~ ~ T10 40 80 Average 100/0 200 36,3 35.7 35.4 35.8 400 33.5 32.4 32.2 32.7 600 30.9 30.6 29.7 30.4 Average 33.6 a 32.9 a 32.5 a 33.0 a 75/25 200 36.8 36.3 35.9 36.3 400 34.7 34.4 33.1 34.1 600 32.0 31.6 30.7 31.4 Average 34.5 ab 34.1 b 33.3 a 33.9 b 50/50 200 37.0 38.1 37,8 37.6 400 33.9 34.8 34.2 34.3 600 31.9 31.9 31.9 31.9 Average 34.2 ab 34.9 b 34.6 b 34.6 c 25/75 200 37,9 39.7 38.9 38.8 400 34.7 35.4 35.6 35.2 600 32.7 32.8 32.5 32.7 Average 35.1 b 36.0 c 35.7 c 35.6 d Average 200 37.0 37.4 37.0 37.2 a 400 34.2 34.2 33.8 34.1 b 600 31.9 31.7 31.2 31.6 c Average 34.3 a 34.5 a 34.0 a 34.3 334 then to reduce plant height (Briggs 1978 p.274). Thus in the monoculture of barley, plants might shade each other more than in mixed stands light being possibly a limiting factor especially at high levels of nitrogen fer- tilization and at high densities. Compensation in 1984, the dominant-suppression relation- ship between barley and oats was not always complete (RYT < 1). This indicates that in mixtures barley interfered with the yield for- mation of damaged oats more than expected without benefitting by itself. Thus barley was not flexible enough especially at low densities. According to de Wit (1960), the ability of un- damaged component to compensate depends on the time of damage. Thus the compensa- tion relates to the determination of the yield components and flexibility of the plants dur- ing the course of the development as well as the total density of the stands. One has to no- tice that in an extreme case the competition experiment can degenerate into a spacing ex- periment for one component. Competition models Although there were no profound dis- crepancies between the results of the two different approaches for analysing competi- tive interactions between components, the regression approach provided a more flexible framework for mixture studies than the con- ventionalreplacement analysis. The regression analysis uses a model of competition that al- lows the yields of both species in a binary mix- Table 13. The influence of nitrogen fertilization, density and the proportion of barley (Agneta) and oats (Veli) in the mixture on thousand grain weight (g) of Veli oats in 1983. Grain weightaverages within each treatment (nitrogen fertilization, density and proportions) followed by the same letter are not significantly different at the 5% level (HSD test). Proportion Density Nitrogen fertilization (kgN/ha) Oats/Barley plants/m !) IT ~ IIv ' 10 40 80 Average 100/0 200 31.5 31.5 30.0 31.0 400 31.4 32.6 30.9 31.6 600 31.7 32.2 31.6 31.8 Average 31.5 32.1 30.8 31.5 a 75/25 200 31.7 32.9 31.4 32.0 400 30.5 31.1 32.5 31.4 600 32.6 32.1 31.9 32.2 Average 31.8 32.0 31.9 31.9 ab 50/50 200 32.4 33.0 32.0 32.4 400 32.3 32.6 33.2 32.7 600 32.9 32.3 32.9 32.7 Average 32.5 32.6 32.7 32.6 c 25/75 200 31.4 32.6 31.2 31.7 400 31.7 33.2 32.3 32.4 600 33.6 32.6 32.5 32.9 Average 32.2 32.8 32.0 32.3 be Average 200 31.7 32.5 31.2 31.8 a 400 31.5 32.4 32.2 32.0 a 600 32.7 32.3 32.2 32.4 a Average 32.0 a 32.4 a 31.9 a 32.1 335 ture to be estimated at any combination of fre- quency and density. It was also able to parti- tion the influences of intra- and interspecific competition quantitatively. The competitive ratio was not always con- stant at different proportions with the same total density indicating that competitive ratio is dependent on frequency. For example in 1983 the dominanceof Agneta as determined by competitive ratio usually decreased whereas in 1984 it usually increased with increasing proportion of Agneta in the mixture. One has to note that this cannot be concluded directly from the competition indices of theregression model because the parameters in the regres- sion model are constant. However, from the regression models it can be predicted that when the intraspecific competition is greater than interspecific competition, the increasing frequency of an aggressor will increase its rela- five yield relatively less than the decrease in the relative yield of a subordinate. Then the competitive ratio of an aggressor will decrease as the actual values of the competitive ratio indicated. This also suggests that in the regres- sion model the equivalences between species (which the competition coefficients estimate) need not vary with frequency although the competitive ratio changes. Thus one should note that only when intraspecific competition is equal to interspecific competition in the mixture is the competitive ratio independent of the frequency of the components in the mixture. It is worth noting that different methods for analysing competitive relationship between species are unable to explain in detail the bio- logical backround of the effects. Thus the yields of the components of a mixture may also be influenced by other types of inter- Table 14. The influence of nitrogen fertilization, density and the proportion of barley (Agneta) and oats (Veli) in the mixture on the number of grains per head of Agneta barley in 1983. Proportion Density Nitrogen fertilization (kgN/ha) Barley/Oats (plants/m! ) ~ ~ “ T10 40 80 Average 100/0 200 59 61 63 61 400 47 53 54 51 600 35 43 45 41 Average 47 52 54 51 75/25 200 66 56 58 60 400 55 53 53 54 600 38 45 46 43 Average 53 51 52 52 50/50 200 58 73 72 68 400 56 63 67 62 600 36 45 54 45 Average 50 60 64 58 25/75 200 64 64 72 67 400 67 53 71 64 600 39 53 65 52 Average 57 57 69 61 Average 200 62 64 66 64 400 56 56 61 58 600 37 47 53 46 Average 52 55 60 56 336 337 specific interaction than competition for growth resources such as interference with pests (frit fly damage in 1984) and diseases. The models do account implicitly for this type of interaction. However, the biological in- terpretation when it is based on competition for resources, may be biased because of the other type of interactions as emphasized by Louda et al.(1990). Competition and niche differentiation When grown in competition, barley usual- ly had the advantage over oats as determined by competitive ratio or relative competitive ability. The results of phytomass accumula- tion during the early stages of development in 1984suggest that barley might be able to claim the available space at an earlier stage as also shown by Baeumer and de Wit (1968), and Syme and Bremner (1968). Syme and Brem- ner (1968) suggested that the initial advan- tage in seedling size of barley was derived from larger source of reserve material in the seed. According to the results of Taylor (1978), barley was also a stronger competitor than oats, contributing more than proportion- ally to leaf area index, dry-matterproduction and total number of tillers of mixtures. However, in 1983 at low level of nitrogen, thepure culture yield of oats was higher than that of barley, oats being even a better com- petitor than barley as determined by competi- tive ratio. This result may indicate that Veli oats might be better adapted to low soil fer- tility (low nitrogen), whereas Agneta barley might be more responsive to added nitrogen both in mixtures and in monoculture. Tren- bath (1976) suggested that where competition for light as well as nutrients occurs, nutrient Table 15. The influence of nitrogen fertilization, density and the proportion of barley (Agneta) and oats (Veli) in the mixture on the number of grains per head of Veli oats in 1983. Proportion Density Nitrogen fertilization (kgN/ha) Oats/Barley (plants/nT) ~ ~ IT 710 40 80 Average 100/0 200 78 90 79 82 400 55 58 62 58 600 46 46 49 47 Average 60 65 63 62 75/25 200 74 80 71 75 400 58 57 57 57 600 44 49 48 47 Average 59 62 59 60 50/50 200 99 75 77 84 400 54 52 51 52 600 46 39 55 47 Average 66 55 61 61 25/75 200 66 58 66 63 400 59 50 55 55 600 45 46 52 47 Average 57 51 58 55 Average 200 79 76 73 76 400 57 54 56 56 600 45 45 51 47 Average 61 58 60 60 additions will give reversals of dominance. This is because the shoot growth of species adapted to high nutrient conditions (with in- tense shoot competition) usually responds more to increased nutrient supplies than does that of species adapted to low nutrient condi- tions (with intense root competition). It is important to note that in the 1984study the results did not show thoroughly the effect of the nitrogen gradient on competition. This was because of the weak response of the stands to the added nitrogen possibly due to the high release of nitrogen from the soil. The yields of oats were also depressed due to in- sect damage (frit fly). The results especially in 1983 demonstrat- ed the effect of nitrogen fertilization on the structure of mixed plant community. There will be a point along the gradient, where Veli oats and Agneta barley can stably coexist by producing the same absolute yields (either number of seeds/plant or weight/plant). From theoretical considerations it follows that a necessary condition for a stable coexistence is that the species populations are regulated in differentways (Braakhekke 1980). Thus bar- ley and oats might be able to coexist because they are not limited by the same resources (differentiation of their realized niches). This means that in mixtures intraspecific competi- tion of both species is greater than interspecif- ic competition which occurred at the lowest level of nitrogen fertilization in 1983. If, how- ever, there is no such differentiation of their realized niches, or if it is precluded by the hab- itat (high nitrogen in 1983 and in 1984), then one competing species (in this case barley) will eliminate or exclude the other (in this case oats). Exclusion occurs when the realized niche of the superior competitor fills those parts of the inferior competitor’s fundamen- tal niche provided by the habitat, and the weak interspecific competitor lacks a realized niche when in competition with the stronger competitor (Begon et al. 1986 p. 258—260). Although the overall intraspecific compe- tition is greater than the interspecific compe- tition in mixtures (NDI> 1), it does not neces- sarily mean that the species can stably coexist in that environment. This is because the strong interspecific competitor will gradually out- compete the weak interspecific competitor as the regression model predicts (in 1983 high nitrogen). Thus NDI when greater than one did not always express that the realized niches of both species differ from each other. The fundamental question is whether NDI is a rele- vant index for evaluating niche differentiation from a terminological point of view. Only when interspecific competition for both spe- cies is less significant than intraspecific com- petition the species coexist (81/B2>1), and coexisting competititors may then exhibit differentiation of realized niches. Yield components All the yield components of barley tended to associate positively with higher yields per plant obtained from mixtures. The higher grain weight of oats in mixtures did not al- ways compensate for a lower number of ears per plant and lower number of grains per ear, leading usually to a lower yield per plant of oats in mixtures. The results for yield com- ponents suggest that the type of the plants (in- dividuals of the same species or different spe- cies) and their relative amount in the neigh- bourhood are also significant in respect to the formation of different yield components and not only the total density. As arule, the yield formation of the individual plant seems to be a rather complex phenomenon in different microenvironments. 338 References Baeumer, K. & Wit, C.T. de. 1968. Competitive inter- ference of plant species in monoculture and mixed stands. Neth. J. Agric. Sci. 16:103—122. Bebawi, F.F. & Naylor, R.E.L. 1978. Yield performance of mixtures of oats and barley. New Phytol. 81:705—710. Begon, M., Harper, J.L. & Townsend, C.R. 1986. Ecol- ogy. Individuals, Populations and Communities. 876 p. Blackwell Scientific Publications. Oxford. Braakhekke, W.G. 1980. On coexistence: a causal ap- proach to diversity and stability in grassland vegeta- tion. Agric. Res. Rep. 902. 164 p. Wageningen. Briggs, D.E. 1978. Barley. 612 p. New York. Connolly, J. 1986. On difficulties with replacement- series methodology in mixture experiments. J. Appi. Ecol. 23:125—137. Connolly, J. 1987. On the use of response models in mixture experiments. Oecologia 72:95—103. Dobben, W.H. van. 1953. Proefnemingen met mengcul- tuur van haver en gerst in 1952. Report on inter- province trials 42 (mimeographed). Wagenin- gemCentral Institute for Agricultural Research. (Ref. Taylor, B.R. 1978) Fejer, 5.0., Fedak, G. & Clark, R.V. 1982. Experi- ments with a barley-oat mixture and its components. Can. J. PL Sci. 62:497—500. 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. Harper, J.L. 1977. Population Biology of Plants. 892 p. Academic Press, London. Jokinen, K.J. 1991 a. Influence of different barley vari- eties on competition and yield performance in barley- oats mixtures at two levels of nitrogen fertilization. J. Agric. Sci. Finl. 63:341—51. Jokinen, K.J. 1991 b. Yield and competition in barley va- riety mixtures. J. Agric. Sci. Finl. 63:287—305. Jokinen, K.J. 1991 c. Assessment of competition and yield advantage in addition series of barley variety mixtures. J. Agric. Sci. Finl. 63:307—20. Louda, S.M., Keeler, K.H, & Holt, R.D. 1990. Herbi- vore influences on plant performance and competi- tive interactions. In: Grace,J.B. & Tiiman,D.(eds.). Perspectives on Plant Competition, p. 413—444. Aca- demic Press, Inc. New York. Roush, M.L., Radosevich, S.R., Wagner, R.G., Max- well, B.D. & Petersen, T.D. 1989. A comparison of methods for measuring effects of density and propor- tion in plant competition experiments. Weed Sci. 37:268—275. Salminen, M. 1945. Onko ohrakaura-sekaviljan viljerai- nen puollettavissa. Koetoim. ja Käyt. 2:6—7. Spitters, C.J.T. 1983. An alternative approach to the analysis of mixed cropping experiments. I. Estima- tion of competition effects. Neth. J. Agric. Sci. 31:1 11. Steel, R.G.D. & Torrie, J.H. 1980. Principles and procedures of statistics. A biometrical approach. 2nd Edition. 633 p. McGraw-Hill Kogakusha, Ltd. Tokyo. Syme, J.R. & BREMNER, B.M. 1968. Growth and yield of pure and mixed crops of oats and barley. J. Appi. Ecol. 5:659—674. Taylor,B.R. 1978. Studies on a barley-oats mixture. J. Agric. Sci., Camb. 91:587—591. Trenbath, B.R. 1976. Plant interactions in mixed crop communities. In: R.I. Papendick et al. (eds.). Multiple Cropping. Am. Soc. Agron. Spec. Pubi. 27:126—169. Madison. Willey, R.W. 1979. Intercropping Its importance and research needs. Part 1. Competitionand yield advan- tages. Field Crop Abst. 32:1—10. Willey, R.W, & Rao, M.R. 1980. A competitive ratio for quantifying competition between intercrops. Exp. Agric. 16:117—125. Wit, C.T. de. 1960. On competition. Versl. Landbouwk. Onderz. 66.8:1—82. Wit, C.T. de & Berg, J.P. van den. 1965. Competition between herbage plants. Neth. J. Agric. Sci. 13:212—221. Wright, A.J. 1981. The analysis of yield-density rela- tionship in binary mixtures using inverse polynomi- als. J. Agric. Sci., Camb. 96:561 —567. 339 SELOSTUS Ohran ja kauran välinen kilpailu ja lajien seossato typpilannoitus, kasvutiheys ja seossuhteet. Kari Jokinen Helsingin Yliopisto, kasvinviljelytieteen laitos 00710 Helsinki Nykyinen osoite Kemira Oy, Espoon tutkimuskeskus, PL 44, 02271 Espoo Kenttätutkimuksissa selvitettiin ohran jakauran välistä kilpailua ja seosten sadontuottoa lisäyssarjakoemallin avulla (kolmekoetta) kahtena kasvukautena (1983 ja 1984) kokeen typpilannoituksen määrän muuttuessa (10 kgN/ha, 40 kgN/ha ja 80 kgN/ha). Ensimmäisenä kas- vukautena seoskomponentit olivat Agneta-ohra ja Veli- kaura ja toisena kasvukautena edellisen yhdistelmän li- säksi oli Ida-ohran ja Veli-kauran seos. Jyväsatoonperustuvien kilpailusuhteiden analysoinnis- sa käytettiin sekä korvaussarjamallia että regressioana- lyysia. Molempien mallien tulokset olivat samansuuntai- sia. Ohra oli yleensä dominoivampi kuin kaura. Kuitenkin ensimmäisenä vuonna kaura oli jokseenkinyhtä hyvä kil- pailija kuin ohra kasvuston typpilannoituksenmäärän ol- lessa matalin. Ohran dominoivuus lisääntyi kasvuston typ- pilannoituksen lisääntyessävarsinkin Agnetan ja Velin se- oksissa. Ensimmäisenä vuonna useiden seoskasvustojen jyvä- sato oli tilastollisesti merkitsevästi suurempi kuin satoi- simman puhdaskasvuston jyväsato. Useissa seoksissa myös suhteellinen kokonaissato oli suurempi kuin yksi, mikä merkitsi satoetua vastaaviin puhdaskasvustoihin ver- rattuna. Toisena vuonna kauran kärsiessä hyönteistuhois- ta kumpikaan ohralajike ei kyennyt kompensoimaan, se- oksen sadon ollessa pienempi kuin ohran puhdaskasvus- tosato. Toisena vuonna myöskään suhteellinen kokonais- sato ei ylittänyt yhtä vaikka joidenkin seosten (1:1) sato oli suurempi kuin komponenttien keskimääräinen puh- daskasvustosato. Siten satoetu ei toteudu aina ollen riip- puvainen ennalta-arvaamattomista ympäristötekijöistä. 340