Structure and Function in Agroecosystem Design and Management - Chapter 19 pps

CHAPTER 19 Effects of Climatic Change in Finland on Growth and Yield Formation of Wheat and Meadow Fescue Kaija Hakala CONTENTS Climatic Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 Climatic Change in Finland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 Agriculture in Finland Today . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 Implications of Climatic Change for Finnish Agriculture . . . . . . . . . . . . . . 400 Effects of Climate Warming and Increased CO 2 Concentration on Growth and Yield of Wheat (Triticum aestivum L., cv. Polkka) and Meadow Fescue (Festuca pratensis Hudson, cv. Kalevi) — A Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 Simulation of Climatic Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 Determinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 Effects of Simulated Climatic Change on Photosynthesis and Rubisco Content of Wheat and Meadow Fescue . . . . . . . . . . . . . . 406 Effects of Climatic Change on Yield and Yield Quality of Wheat and Meadow Fescue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 Wheat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 Meadow Fescue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 397 0-8493-0904-2/01/$0.00+$.50 © 2001 by CRC Press LLC 920103_CRC20_0904_CH19 1/13/01 11:26 AM Page 397 CLIMATIC CHANGE Water vapor, carbon dioxide (CO 2 ), ozone (O 3 ), nitrous oxide (N 2 O), and methane (CH 4 ) form the natural greenhouse gas layer above the Earth. Short- wave solar radiation—part of UV-B, UV-A, visible light, and infrared radia- tion—penetrates this layer. The long-wave heat radiation from the Earth to the atmosphere is, however, partly absorbed by the greenhouse gases. The Earth’s atmosphere is thereby warmed. In this way, the temperatures on the Earth are high enough to maintain life in its present form. Human activities are increasing the concentrations of greenhouse gases, especially CO 2 . The main CO 2 emissions come from burning of fossil fuels and through land use changes that release carbon bound in trees and soil. The other greenhouse gases, O 3 , N 2 O and CH 4 , are also on the increase. In addi- tion to this, the concentrations of halogenated hydrocarbons, such as CFCs, have increased. These are long-lived gases which will stay in the atmosphere long after their emissions have stopped. They are very effective in absorbing the long-wave heat radiation of the Earth. On the other hand, they destroy the stratospheric ozone layer, which has an opposite effect on the radiation balance. The increase in the greenhouse gases caused by human activity is about to lead to warming of the climate. According to a report of the Intergovernmental Panel on Climate Change (IPCC, 1998), the mean annual temperature on the Earth may increase by 1–3.5°C by 2100. At the same time, there may be big spatial and temporal changes in precipitation, and the mean sea level may rise by 15–95 cm. CLIMATIC CHANGE IN FINLAND A scenario of climate change in Finland (the central scenario, assuming central emissions and central climate sensitivity; Carter, 1996) states that the CO 2 concentration may be doubled (733 ppm) and the temperatures may be 4.4°C higher than now by the year 2100. According to the scenario, precipita- tion will increase by 11% and the sea level will rise 45.4 cm by 2100. Because the change is gradual, the CO 2 concentration would be 426 and 523 ppm, and the temperature 1.2 and 2.4°C higher by 2020 and 2050, respectively (Carter, 1996). While the average temperature will increase 0.4°C per decade, the increase is greatest (0.6°C) in winter and smallest (0.3°C) during the growing season. The increase in the mean temperature will also affect the length of the growing season. According to the scenarios of Carter (1996, 1998), the grow- ing season would be 25 days longer than at present in southern Finland (Turku) and 23 days longer in northern Finland (Kajaani) by 2050. With an increase in temperature of 4°C (approximately by the year 2100), the growing season would be 48 days longer in southern Finland (Turku) and 37 days 398 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH19 1/13/01 11:26 AM Page 398 longer in northern Finland (Kajaani) than at present (Tim Carter, personal communication). (Growing season is defined here so that it starts when the average daily temperature stays permanently above 5°C, and ends when the temperature stays permanently below 5°C.) In 2050, with 2.4°C higher aver- age temperature, the growing season would start 10 days earlier in both southern and northern Finland and end 15 and 13 days later than at present in southern and northern Finland, respectively. With 4°C higher temperature, the growing season would start 21 and 16 days earlier and end 27 and 21 days later than at present in southern and northern Finland, respectively (Tim Carter, personal communication). The increase in growing season length may be greater than when defined solely by the 5°C-threshold temperature. At present, even when the mean temperature has permanently risen over 5°C, the sowings of the spring cereals have to be delayed because of deep ground frost, or because the ground is too wet and soft to carry heavy agricultural machinery. In the warmer future climate, ground frost may be absent or melt earlier, and the ground may dry earlier because of shorter duration or absence of snow cover. AGRICULTURE IN FINLAND TODAY Agriculture in Finland is at present limited by low temperature and short growing season. In addition to this, late spring and early autumn frosts limit agriculture in areas where the average temperatures would be high enough for successful agriculture (Mela, 1996). Low temperatures may damage over- wintering crops, especially when the snow cover is thin during the winter. On the other hand, pathogens thriving under a thick snow cover also present a major problem for overwintering crops. Cultivation of spring-sown cereals, again, is often complicated by delay in sowing because of long duration of snow cover, ground frost, or too wet soil. Because of late sowing (usually in early May in southern Finland), the crops fail to benefit from the conditions of high radiation in early spring. In addition, the harvest of spring-sown crops is often impeded by early autumn rain. Because of the short growing season, the varieties of spring-sown cereals cultivated in Finland are bred for a short growing period. The growing time and time for grain filling of these varieties are short, and they are thus less productive than varieties of cereals bred for warmer climates, having slower growth rate and longer growing time. Despite the difficulties in cultivation of spring-sown cereals, they are nevertheless often preferred to autumn-sown cereals because of the unpre- dictable overwintering conditions. The area of Finland stretches from 60° to 70°N. The great variation in cul- tivation conditions in the different latitudes requires careful selection of crops for cultivation in the different areas. The recommended cultivation area of many grass and potato varieties covers the whole of Finland. The EFFECTS OF CLIMATIC CHANGE IN FINLAND 399 920103_CRC20_0904_CH19 1/13/01 11:26 AM Page 399 recommended cultivation area of cereals is, however, quite limited. Thus, some barley and oats varieties can be cultivated up to the polar circle in the west of Finland, where the Gulf of Bothnia warms the local climate. Otherwise, their cultivation is limited to areas south of 64°N. Spring wheat and winter rye can be cultivated on areas south of 63°N, and winter wheat on areas between 61° and 62°N (Komulainen, 1998). The actual cultivation area of spring wheat is depicted in Fig. 19.1a. IMPLICATIONS OF CLIMATIC CHANGE FOR FINNISH AGRICULTURE Increase in growing season temperature and growing season length would expand the cultivation area of crops. With mean annual warming of 2.4°C (by the year 2050), the regional suitability of spring wheat (Triticum aestivum) cv. Ruso would shift 270 km north from the present baseline (calculated suitabil- ity at present) in the west of Finland, and 460 km in the east (Figure 19.1c). The figures for spring barley (Hordeum vulgare, cv. Arra) and oats (Avena sativa, cv. Veli) would be 230 and 280 km north in the east and 340 and 500 km north in the west, respectively. Mean rate of shift to the north of these spring-sown cere- als by the year 2100 would be 45–58 km/decade (Carter et al., 1996). However, when the growing season temperatures increase, the develop- ment rate of the cereals increases (Saarikko and Carter, 1996). When this hap- pens between anthesis and yellow ripening, the time of grain filling becomes shorter. This may lead to decreased yield because less time is available for carbohydrate production through photosynthesis. The effect of climate warming on the duration of grain filling of spring barley (cv. Pomo) is pre- sented in Figure 19.2, and the modeled effect on the yield in Figure 19.3. In addition to the adverse effects on grain filling, increased temperatures may increase the occurrence of pests and pathogens in Finland. For example, a potato pest, potato cyst nematode (Globodera rostochiensis), may expand its occurrence to Lappland, where it is not found at present (Carter et al., 1996). This and other pests and pathogens not known in Finland at present may cause yield losses of crop plants in the future warmer climate. Increase in the concentration of CO 2 not only affects the climate but has also direct effects on plant growth. Many investigations around the world have demonstrated that elevated CO 2 increases crop yield through increased photosynthesis and biomass production (Cure and Acock, 1986). Experimental and modeling studies of Finnish crop plants have also shown increases in yield in elevated CO 2 (Pehu et al., 1994; Hakala and Mela, 1996; Carter et al., 1996; Hakala 1998a). An example of this is shown in Figure 19.2c. Yield loss caused by increased growing season temperatures (Figures 19.2a and b) is changed to yield gain with the projected concomitant increase of CO 2 concentration to 523 ppm (Carter et al., 1996). 400 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH19 1/13/01 11:26 AM Page 400 EFFECTS OF CLIMATIC CHANGE IN FINLAND 401 Figure 19.1 (a) Actual cultivated area of spring wheat (Triticum aestivum) in 1990 as a percentage of total arable land, (b) estimated probability of success- ful ripening (percent) for spring wheat cv. Ruso under the baseline (1961–1990) climate and (c) according to the climate change central scenario (Carter, 1996) with 2.4°C warming of climate. Adopted from Carter et al., 1996. 920103_CRC20_0904_CH19 1/13/01 11:26 AM Page 401 402 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Figure 19.2 Simulated change in duration of the phase heading to yellow ripeness in barley (Hordeum vulgare) cv. Pomo relative to the baseline climate (1961–1990) for the climate change central scenario (Carter, 1996) by (a) 2020 (1.2°C warming of climate), (b) 2050 (2.4°C warming), and (c) 2100 (4.4°C warming). Adopted from Carter et al., 1996. 920103_CRC20_0904_CH19 1/13/01 11:27 AM Page 402 EFFECTS OF CLIMATIC CHANGE IN FINLAND 403 Figure 19.3 Modeled grain yield (tn ha Ϫ1 ) of barley (Hordeum vulgare) cv. Pomo (a) under the baseline climate (1961–1990), (b) according to the climate change central scenario (Carter, 1996) by 2050 (with 2.4°C warming of climate), and (c) according to the central scenario of climate change by 2050 with changes of CO 2 included. Adopted from Carter et al., 1996. 920103_CRC20_0904_CH19 1/13/01 11:27 AM Page 403 EFFECTS OF CLIMATE WARMING AND INCREASED CO 2 CONCENTRATION ON GROWTH AND YIELD OF WHEAT (TRITICUM AESTIVUM L., CV. POLKKA) AND MEADOW FESCUE (FESTUCA PRATENSIS HUDSON, CV. KALEVI)—A CASE STUDY Simulation of Climatic Change Climatic change was simulated so that the temperatures were increased by 3°C both during the growing season and in the winter, and the CO 2 con- centrations were increased to 700 µl l Ϫ1 . The experiments were carried out during four growing seasons in 1992–1995 at Jokioinen, southern Finland (60°49’ N, 23°30’ E). Spring wheat (Triticum aestivum L.) cv. Polkka and meadow fescue (Festuca pratensis Hudson) cv. Kalevi were grown under four treatment regimes: (a) present-day conditions in the field; (b) conditions of warmer climate (temperatures 3°C above ambient); (c) conditions with higher CO 2 concentration 700 µl l Ϫ1 , without warming of climate; and (d) con- ditions of both warmer climate (temperatures 3°C above ambient) and higher CO 2 concentration (700 µl l Ϫ1 ). The combination of experimental conditions was based on the SILMU climate scenario developed for Finland (Carter, 1996; central scenario), according to which, in about 100 years from now (2090), the ambient CO 2 concentration will be approximately 700 µl l Ϫ1 and the growing season temperatures 3°C higher than at present. To raise the temperatures above ambient (conditions of warmer climate), a greenhouse (20 m ϫ 30 m) was built over part of an experimental field (Hakala et al., 1996). The experimental field outside the greenhouse, repre- senting the present-day conditions in the field (later referred to as the open field), was covered at a height of 3–4 m with the same plastic film as was used in the construction of the greenhouse. This resulted in radiation conditions comparable to those in the greenhouse. The greenhouse temperatures were regulated so that they were constantly 3°C higher than the temperatures in the open field. To increase the CO 2 concentrations to 700 µl l Ϫ1 , the experi- ments were conducted in open-top chambers (OTCs). The OTCs were big, 3 m in diameter, and 2 m high. Each OTC was divided in half. The northern half was occupied by the spring wheat stand, and the southern half used for experiments with meadow fescue. Four OTCs were set up in the greenhouse, and the same number in the open field. In each location, two of the OTCs were maintained at elevated CO 2 (700 µl l Ϫ1 ) and two at ambient CO 2 (two replicates per treatment). In addition, two replicate plots similar to those with the OTCs were sown in both temperature treatments, however with no OTC on (open air plots) to study the chamber effect in the experiments (Hakala et al., 1996). The CO 2 fumigation was started after the seedling emergence of the sown crops in 1992, 1993, and 1994, and after the beginning of the thermal growing season (before sowing of wheat) in 1995. The thermal growing season was defined to begin after the average daily temperature of five 404 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH19 1/13/01 11:27 AM Page 404 consecutive days had exceeded 5°C. There was no CO 2 fumigation during the winter. The crops were sown 9–10 May in the open field, the normal sowing time in the Jokioinen region. To simulate the future conditions with average tem- peratures 3°C higher than at present, and the growing season starting 2–3 weeks earlier than at present (Tim Carter, personal communication), the crops were sown about 3 weeks earlier inside the greenhouse than in the open field, as soon as the thermal growing season had started in the greenhouse. The experiments were conducted on a heavy clay soil mixed with 1000 m 3 ha Ϫ1 of peat containing 35% sand during 1992 and 1993. For growing sea- sons 1994–1995, the clay-peat soil of the experimental site was replaced with a lighter sandy loam soil brought from another field at Jokioinen. During all the experimental years, the soil nitrogen was adjusted to about 120 kg N ha Ϫ1 with a standard fertilizer (20% N, 6% P, 6% K), according to an analysis of the soil nitrogen before sowing. A detailed description of the soil and nutrient conditions is given in Hakala et al. (1996) and Hakala and Mela (1996). The crops were sown directly in the field. The sowing density of wheat was 600 germinating seeds m Ϫ2 in 1992 and 500 in 1993 and 1994. The sowing density of meadow fescue was 1250 germinating seeds m Ϫ2 in 1992 (first 2-year exper- iment) and, to find out if the effect of CO 2 enrichment would increase at lower sowing density, only 750 germinating seeds m Ϫ2 in 1994 (second 2-year exper- iment). For the same reason, the sowing density of wheat was lowered to 300 germinating seeds m Ϫ2 in 1995. In 1992 and 1993, the meadow fescue canopies were cut at about monthly intervals. In 1994 and 1995, the cuttings were done each time the leaf area index (LAI) of the stand reached a value of 5, as measured with an automatic LAI meter (Licor, U.S.). Cutting according to LAI was adopted to make sure that the effect of CO 2 enrichment on the photosynthesis and biomass accu- mulation of meadow fescue would not be affected by differences in the degree of canopy closure. An increase in the degree of canopy closure under CO 2 enrichment has been shown to decrease the effect of increased CO 2 con- centration (Nijs et al., 1989). LAI 5 was chosen as the cutting LAI, because previous investigations had shown that at this LAI the light interception of the sward is virtually complete, the net photosynthesis rate is at about maxi- mum, and the rate of dry matter accumulation of the sward has just reached a steady maximum (Brougham, 1956; Robson, 1973a and b). It was assumed that the effect of CO 2 enrichment would be greatest when the growth rate depended on the rate of photosynthesis of the canopy. Cutting according to LAI resulted in a different number of cuts being made in each treatment. Determinations The photosynthetic activity of the crops was measured with a LCA-3 CO 2 analysis system (ADC Co., England). The measurements were conducted throughout the growing season, on sunny days, when the photon flux EFFECTS OF CLIMATIC CHANGE IN FINLAND 405 920103_CRC20_0904_CH19 1/13/01 11:27 AM Page 405 density was not lower than 800 µmol photons m Ϫ2 s Ϫ1 . This photon flux den- sity was found to be close to light saturation for both wheat and meadow fescue. The content of the key enzyme of CO 2 assimilation, ribulose-1,5- bisphosphate carboxylase-oxygenase (Rubisco) in the flag leaves of wheat and in the leaves of meadow fescue was measured in material collected in 1993 and 1994. The piece of the leaf where photosynthesis was measured was cut off after the measurement and immediately frozen in liquid nitrogen. The leaf pieces were kept in liquid nitrogen until the end of each measuring period and then stored at Ϫ80°C. For determination of the content of Rubisco, the protein was separated by SDS-PAGE by the modified Laemmli (1970) method using 3.5% stacking gel and 13% separating gel. Purified spinach Rubisco was used as standard. The amount of Rubisco in the gels was determined densitometrically after staining with 0.1% Coomassie Brilliant Blue R solution. Samples for the determination of biomass dry weight, leaf area, yield com- ponents, and nitrogen content of wheat and meadow fescue were collected in connection with the cuts of meadow fescue and at anthesis and at harvest of wheat. The nitrogen content (% nitrogen of the dry weight) of the samples was determined in 1992 with the Kjeldahl method using a Kjeltec System 1026 Distilling Unit (Tecator AB, Sweden). Nitrogen content was not measured in samples collected in 1993. In 1994 and 1995, the nitrogen content was deter- mined with an automatic nitrogen analyzer, LECO FP-428 (LECO Corp., U.S.). Effects of Simulated Climatic Change on Photosynthesis and Rubisco Content of Wheat and Meadow Fescue It has been found in earlier studies that as CO 2 assimilation becomes more effective in increased CO 2 , the concentration of Rubisco is reduced (Schmitt and Edwards, 1981; Bowes, 1991; Sage, 1994; Nie et al., 1995; Rogers et al., 1998). The reduction may be due to accumulation of carbohydrates in the leaves in conditions where the sink for photosynthetic products is not in balance with the source (photosynthesis) (Stitt, 1991). Reduction in the amount of Rubisco in conditions of increased CO 2 is a good acclimation sys- tem for the plants, while it allows them to invest the nitrogen released from Rubisco in processes limiting photosynthesis (e.g., light harvesting or elec- tron transport) and in growth (Sharkey, 1985; Stitt, 1991; Quick et al., 1992; Sage, 1994; Rogers et al., 1998). Rubisco makes up 50% of the total soluble protein of plant leaves (Lawlor et al., 1989; Leegood, 1993). Therefore, a decrease in the Rubisco content in elevated CO 2 may decrease the nitrogen content of crops. Decrease in nitrogen content of grasses like meadow fescue might decrease the nutritional value of their biomass as animal feed. Moreover, a considerable part of the nitrogen of wheat leaves is used as a source of nitrogen for the grain (Dalling et al., 1976; Waters et al., 1980; 406 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH19 1/13/01 11:27 AM Page 406 [...]... rate in the higher temperatures during the growing season resulted in a 30–40% higher yield in the warmer climate simulation in the 920103_CRC20_0904_CH19 1/13/01 11:27 AM Page 411 EFFECTS OF CLIMATIC CHANGE IN FINLAND 411 years of sowing (199 2 and 199 4) The increase in yield in higher temperature was only 15% in the second growing season in 199 3, but 65% in 199 5 (Hakala and Mela, 199 6, Figure 19. 6)... low in ambient CO2 (Hakala, 199 8a) This is in agreement with earlier investigations, according to which the increase in yield in CO2 enrichment is a result of an increase in the number of ears and grains rather than grain weight (Krenzer and Moss, 197 5; Fischer and Aguilar, 197 6; Sionit et al., 198 1; Goudriaan and de Ruiter, 198 3; Havelka et al., 198 4; McKee and Woodward, 199 4) The grain weight increases... lower in elevated CO2 than in ambient CO2 Even though tillering was increased in elevated CO2 in 199 4 at elevated temperatures, the increase in yield may have masked the increases in nitrogen content, the nitrogen content being known to decrease with an increase in biomass in CO2 enrichment (Wong, 197 9; Hocking and Meyer, 199 1; Baxter et al., 199 4) In 199 5, when the rate of tillering decreased in CO2,... 414 Table 19. 1 Nitrogen Content (% Dry Weight) of Meadow Fescue (Festuca pratensis Hudson, cv Kalevi) Above-ground Biomass in 199 2, 199 4 and 199 5 920103_CRC20_0904_CH19 Page 414 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH19 1/13/01 11:27 AM Page 415 EFFECTS OF CLIMATIC CHANGE IN FINLAND 415 CONCLUSIONS The wheat varieties currently cultivated in Finland are adapted... 920103_CRC20_0904_CH19 416 1/13/01 11:27 AM Page 416 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Carter, T.R., Saarikko, R.A., and Niemi, K.J., Assessing the risks and uncertainties of regional crop potential under a changing climate in Finland, Agric and Food Sci in Finl., 5, 329 –350 Cure, J.D and Acock, B., Crop responses to carbon dioxide doubling: a literature survey, Agric and For Meteorol.,... aestivum L.) cv Polkka at Jokioinen, Finland, under different temperature (T) and CO2 treatments (e ϭ elevated, a ϭ ambient) The sowing rate was 600 germinating seeds mϪ2 in 199 2, 500 in 199 3 and 199 4, and 300 in 199 5 The columns represent the averages over two replicate OTCs In 199 3, the grain yield was harvested from one replicate only The growth of ear-bearing lateral shoots and the effect of CO2 enrichment... Wheat and Meadow Fescue Wheat The grain yield of wheat tended to be higher in elevated CO2 than in ambient CO2 The increase in yield was mainly due to increase in the number of ears mϪ2 (Figure 19. 5) An increase in grain number per ear sometimes also contributed to the increase in yield in CO2 enrichment, but an increase in grain weight was seen only at elevated temperatures in 199 3, when the grain weight... than in ambient CO2 in both ambient and elevated temperatures in 199 2 (Hakala and Mela, 199 6; Table 19. 1) The increase in the nitrogen content of the biomass may have been caused by increased tillering (Hakala and Mela, 199 6) and 920103_CRC20_0904_CH19 412 1/13/01 11:27 AM Page 412 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 199 2 g dw/15 cm of row 35 30 25 0.10 0.10 20 15 10 0.21 0.22... subsequent increase in leaf area (Langer, 197 9) and proportion of young leaf material in the biomass Also in 199 4 and 199 5, the nitrogen content was higher in elevated CO2 than in ambient CO2 at ambient temperatures This was probably caused by higher tillering rates in elevated CO2 throughout the growing seasons At elevated temperatures, in 199 4 and 199 5, when there was a clear increase in biomass in CO2... greater increase in yield in 199 5 than in 199 3 was probably due to the more frequent cuttings in 199 5 When the cuttings were done according to the growth of the grass, canopy closure restricted growth less than in 199 3, when the cuttings were done at about monthly intervals in both temperature treatments CO2 enrichment increased the yield of meadow fescue by 10% in both temperature treatments in 199 2 and . was 600 germinating seeds m Ϫ2 in 199 2 and 500 in 199 3 and 199 4. The sowing density of meadow fescue was 1250 germinating seeds m Ϫ2 in 199 2 (first 2-year exper- iment) and, to find out if the. longer in southern Finland (Turku) and 37 days 398 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH19 1/13/01 11:26 AM Page 398 longer in northern Finland (Kajaani). of the sown crops in 199 2, 199 3, and 199 4, and after the beginning of the thermal growing season (before sowing of wheat) in 199 5. The thermal growing season was defined to begin after the average