A perspective for setting the research priorities for the productivity of future crop production in Finland

The author proposes that future research work on crop production should concentrate on alleviating the problems associated with overwintering and frost, early summer drought and rainy autumn in order to enhance the competitiveness of field crop production in Finland. Further, more detailed knowledge on the crops is required to understand the genotypic differences in potential yield formation in order to optimize management practices. Increasing the nitrogen (N) fixation efficiency of leguminous species should be considered as an important target. Naked oats, sunflower, and leguminous plants might be advantageous species for future crop production in Finland. The bioenergetic implications of increasingcrop productivity are discussed.

Crop production forms the basis ofagriculture, i.e., there would be no agriculture without crop production.Therefore, when discussing the future ofFinnish agriculture, crop production research has a significant role in maintaining the competitive position ofFinnish agriculture.
The competitive position could be achieved through sustaining environmentally sound agriculture featuring economic productivity while main- taining high yield and good quality.Furthermore, production should involve limited risks, taking into account the biological factors in addition to the environmental ones.Thus, an understanding of management practices as well as crop physiology has a key role in sustainable agriculture as defined above.Crop research should primarily be carried out in field experiments because the interactions between the phenomena studied and the environ- ment are emphasized in northern latitudes.
Intensified productivity -a future prospect When adjusting to European integration, Finnish agricultural productivity must be considerably increased in order to improve competitiveness (Kola et al. 1992).Regarding crop production this can be attained either by breeding or more precise use of management practises.The improved pro- ductivity should result from optimization of inputs rather than increasing inputs (Kurppa 1992).The intensification of management practices by econo- mical, technological and biological methods is effi- cient only if the genotype-dependent yield potential of a plant from sprouting to harvesting is known (Peltonen and Peltonen-Sainio 1991).Thus, more precise information is needed on the critical plant growth stages in which the management practices are most favourable (Peltonen 1992 b).
The ecological cropping systems probably have no future in Finland, because the use of inputs (no industrial inorganic fertilizers and pesticides allo- wed) in these cropping systems cannot be as con- trolled biologically as in the intensive cropping systems.Moreover, the quality of Finnish agricultural products is very high and they are free from pesticide residues according to international standards (Kumpulainen 1992).This is because only a limit- ed number of pests and diseases are of importance in the marginal growing conditions prevailing in Finland (Karjalainen 1985).It is often claimed that yields cannot be sustained in monocultures based on repeated applications of inorganic fertili- zers and pesticides.The Rothamsted long-term experiments in the U.K. during the period 1852 - 1986 showed, however, that they can (Jenkinson   1991), although these experiments also indicated the importance ofcrop rotation.
Within this context, resistance breeding in Finland has hardly ever resulted in significant yield improvements as has been the case in other Euro- pean countries (Karjalainen 1985, Doodson 1981).The geographical location of Finland offers, however, special challenges for crop production research, alleviating the problems associated with overwintering and frost, early summer drought, and rainy autumn (Mukula and Rantanen 1989 a,b,c).Further, more precise information is needed on the physiological traits underlying a good crop ideo- type (Hovinen 1988 a, Peltonen-Sainio 1991)and its adaptation to long day and low light intensity (Pulli 1988).

The yield potential of cultivated crops
In the present situation it is extremely important to identify which crop species can be economically produced in Finland in the future.The chemical composition of crop species varies greatly in their utility for either livestock, feedstock or "non-food" production.The amount of photosynthates needed by a crop is partly dependent on the chemical com- position of the economic yield.In northern condi- tions, the ability of crops to convert light energy into biomass is, however, limited (Åkerberg and  Haider 1976).Therefore, raising both quantity and quality simultaneously is increasingly difficult (Peltonen 1992 a).
In the following, the productivity of crop species is analyzed and drawn on the basis of their production related to the use of photosynthates.The results from the examination of the biochemical pathways (Penning de Vries et al. 1974) for the production of carbohydrates, proteins, and lipids from glucose were used as the basis.From 1 unit of glucose about 0.83 unit of carbohydrates, 0.40 unit of protein (assuming N0 3 -N to be the N source), or 0.33 unit of lipid could be produced.Based on these values it has been calculated how much energy produced in photosynthesis is consumed in the forma- tion of the economic yield of certain crop species (Table 1).The nitrogen requirement of the crop was estimated by calculating the protein produced from available photosynthate (Sinclair and de Wit  1975), in addition to N required for 1 % increase in the protein concentration (Bhatia and Rabson  1976).
To visualize more easily the differences between the crops, N requirements per gram of photosynthates were plotted against economic yield per gram of photosynthate (Fig. 1).In the lower right-hand part of Fig. 1 there are the carbohydrate rich crops (cereals, potato, sugarbeet).Of all the plant species examied, the productivity, defined as conversion of photoassimilates into economic yield, is the highest in sugar beet and potato.In addition to their importance as food crops they have become increasingly important in "non-food" uses; starch is used for glue and as a binder in the paper industry.The alternative use of starch as a raw material in producing decomposed plastics is also increasing, especially as plastic mulch for agricultural purposes (Doane 1981, Galliard 1986).The portion of domestic starch used as raw material for decomposed plastics is, however, only about 50% (Erikois-  kasvitoimikunta 1987).
The fate of cereals in future Finnish crop pro- duction has received most attention because cereals are "bulk" products and over-produced in the world market.In addition, it has been indicated that cereal production in particular suffers from the high production costs characteristic to of Finnish agriculture (Kola et al. 1992).Milk production has a bet- ter chance to adjust to European integration, but not withoutproblems, either.As an alternative, the pro- duction of naked cereals such as wheat, rye and naked oats for feed (Rekunen 1990) is suggested, because their feeding value is higher than that of ordinary hulled oats or barley.Naked oats is culti- vated relatively little in the world.The probable reason for this is its poor yielding ability as compar- ed with other cereals.The yield advantage ofhulled oats without husks over the yield of naked oats is still approximately 600 kg ha 1 (Peltonen-Sainio et al. 1992, manuscript).The limiting factor for the yield formation ofnaked oats is evidently the lower number of spikelets per panicle as compared with hulled oats (Peltonen-Sainio 1992, personal  communication).Naked oats has, however, a clear advantage in industrial processing by saving the cost ofhulling.Due to the "nakedness" of the grain the risk of harvesting damage increases (Rekunen 1990).Lipid and protein contents are also high in naked oats (Table 1).Therefore, its yield formation requires more N fertilization than that of other cereals.The biological value of the protein in oats is not reduced by N fertilization as is the case in other cereals (Lasztity 1984).Naked oats may be an alternative for cereal production in Finland fol- lowing the advances in breeding for better yields.
In the lower left-hand part of Fig. 1 there are the oil crops (turnip rape, rape, flax, sun flower).Sun- flower has the most effective yield formation of all of the oil crops.The reason for this may be its high potential maximum rate of leaf photosynthesis as compared to the other crops (Penning de Vries et al. 1989).Moreover, it requires less N for yield form- ation than turnip rape, rape or flax (Table 1).The high amount (57%) of polyunsaturated fatty acids Fig. 1.The requirement of nitrogen (mg) for yield per gram of available photosynthate (g) for 19 crop species.Regression functions for protein crops Y = 80.85 -82.38 X (R 2 =0.95"'), and for carbohydrate crops Y = 54.49-55.26 X (R 2 =0.96").
There is no significant relationship between oil crop species.
Table 1.Chemical composition, yield productivity (grams ofbiomass per gram ofphotosynthate), and nitrogen requirements (milligrams of N per gram ofphotosynthate) for crop yield of 19 crop species.Nitrogen requirement is calculated by assum- ing that protein is 16 % nitrogen by weight.The last column gives the percentage increase in nitrogen requirement for a 1 % increase in protein.
Composition*) in sunflower seed oil is an indicator of its good quality for human consumption.In contrast, rape seed oil contains some 25% of polyunsaturated fatty acids (Weiss, 1983).The rhizosphere pattern of sunflower is strong and deep.It can efficiently take up nutrients which may enable production even without application of chemical fertilizers.Harvest- ing of sunflower may be difficultbecause the mois- ture content of the seed seldom falls below 20% (FAO 1985).The inclusion of hybrids in crossing programs has been shown to lead to positive results with early maturity, good oil content, disease resistance and lodging resistance in breeding sunflower cultivars for northern latitudes (Dedio 1988).
In the upper right-hand part of Fig. 1 there are the protein rich crops (lupine, pea, field bean, red clo- ver, alfalfa, and grasses).The productivity of lupine is lower than that of pea and field bean.Furthermore, the high content of alkaloids in lupine lessens its use as feed (Alaviuhkola 1986).Due to the high lysine content of pea and field bean (Salo et al. 1990), they have a high value in feeding.In breeding, more stable yield formation is obtained with the help of the af-and defgene in pea and the //-gene in field bean (Hovinen 1988 a,b).The increase of pea and field bean cultivation is thus recommended to substitute the imported soyabean for industry.Owing to their capacity for biological N fixation, leguminous plants such as pea, field bean, red clover and alfalfa are independent ofinor- ganic N fertilizer.For this reason red clover and alfalfa have higher productivity than meadow fescue, cocksfoot, and timothy (Fig. 1).Many efforts have been made to improve the N fixation ability of Rhizobium bacteria (Uomala 1986), but more detailed studies from this research area are still needed.A research priority could be to attempt to increase the resistance of N fixation bacteria to soil acidity and early summer drought.