The influence of fertilization and environment on some nutritionally important quality criteria in vegetables - a review of research in the Nordic countries Aino-Maua Evers Evers, A.-M. 1994. The influence of fertilization and environment on some nutritionally important quality criteria in vegetables - a review of research in the Nordic countries. Agricultural Science in Finland 3: 177-188. (Agricultural Research Centre of Finland, Institute of Horticulture, FIN-21500 Piikkiö, Finland. Present address: Department of Plant Production, P.O. Box 27, FIN-00014 Univer- sity of Helsinki, Finland.) To understand the phenomena caused by nutrient applications on the quality of vegetables, some research has been done in Finland and in Scandinavia during the last decades. Purpose of this review is to evaluate this data against the information available on genetic and environmental factors. Genotype and light intensity highly affect the vitamin C content of plants. Opti- mal nitrogen level has a small effect, but excess of nitrogen decreases vitamin C content. Genotype, developmental stage of the plant, adequate photosynthesis, vig- orous growth and relatively high temperature increase the carotene content of carrots. The effects of fertilization on the carotene content of plants have been contradictory and warrants more research. No research results could be found of the effects of fertilization or growing practices on the vitamin B content even though vegetables are an important source of vitamin B in diets. Increasing nitro- gen fertilization, genotype, low light intensity, low temperature and drought in- crease the nitrate content of vegetables, but the levels are low in vegetables grown in the Nordic countries, except in lettuce grown under glass with the aid of lights during the dark season. The effect of fertilization on the sugar content is small, and the effect on dietary fibre warrants further study. Key words: nutrient, growing practice, climate, dry matter, vitamin, carotene. sugar, fibre, nitrate Introduction The marketable yield and quality of vegetables are influenced by genotype, environment, grow- ing practice, harvest, storage and marketing. Also fertilization can be manipulated by the grower and thus it is important to understand the phe- nomena caused by nutrient applications. The amount, type and form of nutrients, and the method of nutrient application will influenceplant growth patterns, yield, maturation, nutritional val- ue and post harvest physiology. The trend in ag- riculture and horticulture is towards ’sustainable’ farming which means more economic fertilizer application for ecological and economic reasons. In that context it is important to understand the effects of nutrients and nutrient amounts on the marketable yield and nutritional quality of veget- ables. During the last decades, some research has been 177 Agricultural Science in Finland 3 (1994)Literature Review https://www.c-info.fi/en/info/?token=XCrpUogAJXLs4bTx.7qmh2dJNbyOv1GWbQkcnPw.mHCV_jVCw6S9IMPltw4v43tXFIwgRc2zsmMOcySDgRaKztC8GEs9OVKahgfUB2d2kix3UUjhfckrQjwTj4iNQwFx0HqWu5VEqlOdLU08JdAUX2SYWauGZG3RtUVfiul299Rcv8vJaw59u_ksdEDzMgU2_YCHiq9eIjVBrY_0j-Ge8hte9PjLOn8NME_7UPt5bmNxN4y0vFTjbRHuOGTmWPfTvKCi41tD9eVdJCDQCIeUB6seYTsixa7OSH7880I-MLcOwdRe conducted in the Nordic countries on fertilization and quality of vegetables (e.g. Balvoll 1969, Rosenfeld 1978, Nilsson 1979, Lehtinen 1984, Nygaard Sorensen 1984, 1988, Aura 1985, Evers 1989a, b, c, d, e, Balvoll 1992). In the Nordic countries, the growing conditions are ex- treme compared to Central and Southern Europe. The growing period is short, summer days are long and temperatures are relatively low. These environmental factors affect the quality of veget- ables (Åberg 1946, Dragland 1969, Härdh and Hårdh 1972, Balvoll et al. 1975, Härdh et al. 1977) and they must be taken into account when interpreting the results of experiments on fertili- zation. The purpose of this review is to assemble and analyse this data to provide a basis for modi- fying agronomic practice in Nordic countries to- wards a more ’sustainable’ system without im- pairing nutritonal quality. Vitamin C / ascorbic acid in plants Genotype has a very strong influence on the vita- min C content of plants and thus plant species dif- fer greatly in their vitamin C composition. Exam- ples of high contents (mg/100 g fresh edible mat- ter) are rose hip (840), sea buckthorn berry (200), parsley (190), black currant (181), horse radish (152), sweet pepper (144), kale (110), brussels sprout (85), broccoli (83) and cauliflower (73). Some plant species are quite important sources of vitamin C because of the high consumption in Finn- ish diets. Examples of these are strawberry (68), white cabbage (44), Chinese leaves (27), tomato (17), potato (11) and cucumber (8). Root crops often have a low vitamin C content (mg/100 g fresh edible matter), e.g. celeriac (11), beet root (8) and carrot (5) (Kansaneläkelaitos 1993). Light is the most important exogenous factor influencing the ascorbic acid content of veget- ables, fruits and berries (Åberg 1946, Murneek et al. 1954. Brown 1955, Mapson 1955). Åberg (1949) in Sweden showed that the ascorbic acid content decreases quickly when a plant leaf is shaded but increases again when the plant leaf gets light. At low light intensities the increase of ascorbic acid content is linear to the increase of light intensity, and increased daylength has the same effect (Åberg 1946). No other Scandinavian or Finnish study was found on this subject, but in other countries it has been shown clearly that light increases the ascorbic acid content in apple (Johansson 1939, Kessler 1939, Murneek and Wittwer 1948, Murneek et al. 1954), strawber- ry (Schuphan 1942, Hansen and Waldo 1944, Ezell et al. 1947, Robinson 1949) and tomato (Kaski et al. 1944, Brown 1955, Hamner et al. 1945, McCollum 1946, Somers et al. 1950, Murneek et al. 1954). These studies showed that it is important that the apple, strawberry and to- mato fruit itself is exposed to light, not only the plant leaves, and the amount of light close to the harvest period is especially important for high ascorbic acid content. The correlation between temperature and ascor- bic acid content of the plant is negative (Åberg 1946,Rosenfeld 1975, 1979). Thus low temper- atures increase the ascorbic acid content in plants, probably due to lower carbohydrate consumption in plant metabolism. Plant dry matter content cor- relatied positively with ascorbic acid content in all eight plant species studied by Rosenfeld (1975, 1979). Many studies have been conducted in the Nor- dic countries on the effect of latitude on the qual- ity of plants, but no obvious effect of latitude have be seen (Hårdh 1964, 1975, Kuusi 1965, Nilsson 1969, Dragland 1969, Hårdh and Hårdh 1972). Most of the differences in quality were assumed to be due to the developmental stage of the plants studied, and the ascorbic acid content is most likely affected by the light condi- tions close to the harvest period. Linden (1989) suggests that due to long summer days and rela- tively low temperatures ascorbic acid content is the quality criterion which is most likely to be affected positively by the northern conditions. The effect of fertilization on the vitamin C / ascorbic acid content There are only few studies on the effect of fertili- zation on the ascorbic acid content of vegetables, 178 Literature ReviewAgricultural Science in Finland 3 (1994) Agricultural Science in Finland 3 (1994) fruits and berries in the Finnish and Scandinavi- an literature. In his review Rosenfeld (1978) con- cludes that both structural and metabolic changes affect ascorbic acid levels. Intensive use of car- bohydrates in protein synthesis may compete with ascorbic acid production leading to decreased ascorbic acid content in plants. The competition seems to be absent in high light intensities. A high amount of nitrogen fertilizer results in a leaf structure similar to that in plants grown in shad- ow. The effect of irrigation is clear according to Rosenfeld (1978): drought increases and irriga- tion decreases the ascorbic acid content in plants. Nilsson (1979) studied the effects of organic and mineral fertilizers at normal and half doses on the yield, storability and chemical composi- tion of carrot, white cabbage and leek. Neither fertilizer nor fertilizer level affected the vitamin C content in freshly harvested or stored cabbage and leek. The different fertilizers had no influ- ence on the yield of carrots and leeks, but organ- ic fertilizers decreased the yield of cabbage sig- nificantly the first year but not the second year. Half the amount of fertilizer resulted in signifi- cantly lower yields of cabbage and leek for both years, but had no effects on the yield of carrots. In his discussion Nilsson (1979) states that potassium is the nutrient that affects the vitamin C content in vegetables the most, because potas- sium is important in the carbohydrate synthesis. The lack of potassium decreases photosynthesis and increases respiration (ref. Mengel 1972). Nilsson (1979) further claims that the N/K rela- tionship is important. Low potassium fertiliza- tion combined with increasing N/K decreases the vitamin C content. In such cases the fresh yield increases, but the dry matter content decreases. Thus organic and mineral fertilizers do not affect the vitamin C content if one uses N/K in the right proportion. According to Nilsson (1979), the vi- tamin C content is not influenced by any other macronutrient if there is no deficiency. The dry matter and vitamin C contents were higher in biodynamically cultivated potatoes than in conventionally cultivated potatoes (Petters- son 1982). This result has been criticised, be- cause Pettersson used 120 kg N/ha, which is too much for conventionally grown potatoes. Bio- dynamically grown potatoes did not suffer from excess nitrogen, because organic fertilizers re- lease their nutrients slowly over a period of years. In the study of Nygaard Sorensen (1988), increasing nitrogen amount decreased the vita- min C content in cabbage. The reduction is as- sumed to be due to the bigger outer leaves which shade the inner leaves and the head. Increasing potassium amount increased the vitamin C con- tent in white cabbage. There was a clear positive correlation between vitamin C and dry matter con- tent. Carotene in plants Carotenoids are tetraterpenes of the isoprenoid group (Gabelman 1974). Carotenoids include car- otenes and xanthophylls, and some carotenes are important for human nutrition because they are precursors of vitamin A (Devlin 1975). Geno- type, plant species and variety, are important fac- tors for plant carotene content (Simon et al. 1982, Simon and Wolff 1987, Heinonen 1990, Kansaneläkelaitos 1993). Examples of high (3- carotene content (|Xg/100 g fresh edible matter) are carrot (7600), parsley (5600), spinach (3300), celery (2900), red sweet pepper (2900), kale (2150), broccoli and leek (1000), lettuce (980) and tomato (660) (Kansaneläkelaitos 1993). Carrots grown in European coutries have usu- ally been selected for their root colour which is caused by the presence of ()- and a-carotene. Be- cause carrot is widely consumed it has become the major source of (3-carotene in Western Euro- pean diets. For these reasons the factors affecting the carotenoid content of carrot have been the subject of much research. These studies confirm that the carotene content of carrots is influenced by genotype (Gabelman 1974, Simon and Wolff 1987), environment (Barnes 1936, Banga et al. 1955, Habben 1972, Simon et al. 1982, Simon and Wolff 1987) and by the size and age of carrot (Barnes 1936, Banga et al. 1963, Banga and Bruyn 1964, Habben 1972, Phan and Hsu 1973). 179 Literature Review Literature Review Banga and Bruyn (1964) summarise that in carrot the enlargement of the root and maturation proceed simultaneously. Different conditions may favour one activity more than the other. With in- creasing root size the carotenoid concentration gradually increases up to a certain maximum. This is caused by the increase in the carotenoid con- tent in the individual cells of the maturing tissue, and the increase in the ripe upper part of the root. The carotenoid contents of carrot roots should therefore be determinend in relation to the size of the root. The carotenoid content depends pri- marily on adequate photosynthesis. If the roots are grown in a well-drained soil of good struc- ture, there are two types of growing conditions which may further modify the carotenoid content in relation to root weight. These are the factors that control the growth rate (plant density, soil moisture content, nutrient supply) and tempera- ture. High temperature favours maturation, where- as low temperature favours primary vegetative growth. Thus adequate photosynthesis (light), vig- orous growth (plant density, soil moisture, nutri- ent supply) and relatively high temperature are the exogenous factors that increase the (3-caro- tene content in carrots. Banga et al. (1955), Banga and Bruyn (1964, 1968) have found that low temperatures (+B°C) delay root growth and cause low carotenoid content. At high tempera- tures (17 - 23°C), protein synthesis decreases and more photosynthases become available for carotenoid synthesis. Both Barnes (1936) and Banga et al. (1955) reported that high tempera- ture favours carotene synthesis. Evers (1989b) showed in Finland that the carotenoid content was higher in a warm summer than in a cold and rainy summer. Carrots produced in Southern Sweden (Lam- brecht and Svensson 1950, Nilsson and Hintze 1952), in Southern Norway (Balvoll et al. 1975) and in Southern-Finland (Hårdh 1975, Hårdh et al. 1977) contain more carotene than carrots pro- duced in the northern parts of the countries. Re- searchers assume this to be due to the fact that carrots in the north have not reached the same developmental stage and, consequently contain less carotenoids. The effects of fertilization on carotene content Only three studies from Scandinavia and one from Finland were found on the effect of fertilization on the carotene content of vegetables. Increased nitrogen fertilization increased the carotene con- tent in spinach (Balvoll 1969). Organic and min- eral fertilizers at normal or half rates did not affect the carotene contents of carrot either at harvest or after a storage period (Nilsson 1979). Nilsson claims that nitrogen is not a limiting factor and that it was the exceptional warmth in the summers of 1975 and 1976 that determined the carotene levels. The carotene levels were very high in that study (18-20 mg/IOOg fresh weight a + P -carotene) analysed spectrophotometrical- ly. Usually the carotene contents are lower: 6.1- 9.3 (Nygaard Sorensen 1988), 3.4-6.4 (Evers 1989b), 7.3-15.1 mg/100 g fresh weight (Hei- nonen 1990). Increasing nitrogen and potassium fertilization both increased the carotene content in carrots (Nygaard Sorensen 1988). Nitrogen increased the carotene content even at supra optimal levels, but potassium increased the carotene content at optimal level only. Evers (1989b) studied the effects of differ- ent fertilization practices. The best application methods increased the carotene content in two climatically different years. In 1985, which was climatically an unfavourable year, placement fer- tilization increased the carotene content by 35%, NPK fertirrigation with basic fertilization by 28%, and PK placement with three nitrogen fertiga- tions by 44% compared to no fertilization. In 1986, which was climatically a favourable year, the increases were respectively 9%, 9% and 10%. Thus placement of PK fertilizer is profitable es- pecially in poor weather conditions. In the unfa- vourable year 1985 the placement of PK fertiliz- er showed a tendency (p=o.l) to increase the car- otene content in carrots compared to other fertili- zation practices, but no other significant differ- ences were found between fertilizer application methods. The surplus nitrogen did not affect the carotene content as compared to the average of other fertilization treatments, where the N amount 180 Agricultural Science in Finland 3 (1994) Agricultural Science in Finland 3 (1994) applied was thought to be optimal on the basis of the yield. Thus Evers (1989b) could find no in- dication that the optimal or surplus nitrogen amount or application method would have any further effect. The variation in the carotene content of carrot mainly depends on the genotype (Gabelman 1974) and the climate (Simon et al. 1982). Also Evers (1989b) observed a clear difference in the mean carotene content between the two years. The average carotene content for all treatments was 41.2 % higher in the favourable year 1986 than in the cold and rainy year 1985. There is general agreement in the literature that the caro- tenoid content of carrots increases with matura- tion of the plant (Banga et al. 1963, Phan and Hsu 1973,Fritz and Habben 1975,Evers 1989b). The carotene content in carrots correlates pos- itively with the dry matter content and high shoot/ root ratio (Banga and Bruyn 1964,Evers 1989e). Banga and Bruyn (1964) summarise that high dry matter content can be regarded as an indica- tor of intensive photosynthesis, and carotene con- tent in carrots is dependent on the intensity of photosynthesis and the size of the foliage used for photosynthesis. Vitamin B in plants The vitamin B complex comprises vitamin 81/ thiamine, vitamin 82/ riboflavin, niacin (nicotin- ic acid and nicotinamide ), vitamin 86/pyridox- ine, vitamin 812, folic acid, pantothenic acid and biotin. Vegetables are an important source of vi- tamin B in Danish diets: 19% of vitamin 81, 9% of vitamin 82, 14% of vitamin 86, 29% of folic acid and 13% of niacin are obtained from veget- ables. Fruits and berries are not so important for only 2-6% of the total vitamin B intake is ob- tained from fruits and berries in Denmark (Levnedsmiddelstyrelsen 1990). No studies have been conducted in the Nordic countries concern- ing the influence of environment, fertilization and growing practice on the vitamin B contents of vegetables. Vitamin B levels are relatively high in pea (both immature and dry seeds), parsley. spinach, Brussels sprout, bean (both immature pods and dry seeds), broccoli, lettuce, kale and leek, and higher than for instance in whole wheat flour or beef. Potato, carrot and tomato contain moderate quantities of vitamin B. The effects of fertilization on vitamin B No research results on the influence of fertili- zation on the vitamin B content of vegetables, fruits and berries could be found in Scandinavian and Finnish literature. Because vegetables are an important source of vitamin B in human diets, the effects of growing conditions should be stud- ied. Nitrates in plants Nitrate (N0 3 ") is undesirable in vegetables, be- cause it may be reduced to nitrite (N0 2“) which is hazardous to babies and may be involved in the development of gastro-intestinal cancer. Ni- trate accumulation in plants is attributed mainly to genotype, light intensity, daylength, tempera- ture, soil moisture content and nitrogen fertiliza- tion. Wide fluctuation has been observed also dur- ing a 24-hour period (Maynard et al. 1976, Corré and Breimer 1979). Nitrate contents ex- ceeding 2500 mg NOT kg fresh matter have been observed in celery, spinach, beetroot, radish and lettuce. In turnip, cabbage, parsley leaves, celeri- ac, leek and rhubarb, the nitrate contents usually range from 1000 to 2500 mg NO s/ kg fresh mat- ter (Corré and Breimer 1979). Butterhead let- tuce varieties differ considerably in their nitrate content, whereas spinach varieties differed only sightly (Behr 1988). It is well documented that high light intensity, high total radiation and long days decrease the nitrate content of vegetables. This is an important contributory factor for low nitrate content in spring and summer, and higher content in autumn and winter. The effect of tem- perature is complex and interrelated with light, soil moisture and nitrogen supply (Maynard et al. 1976). 181 Literature Review Literature Review Table 1. The effects of plant species, years and N fertilization on the nitrate-N content of carrot and red beet (Vuorinen and Takala 1987). Nitrate-N content nO3 -N mg /kg fresh matter Year Carrot Red beet kgN/ha kg N/ha 60 120 180 60 120 180 1980 16.8 46.6 55.3 205.6 392.9 438.3 1981 5.6 11.7 21.7 24.2 117.3 155.7 1982 27.2 60.0 87.6 43.0 201.9 284.5 1983 12.1 21.1 32.9 28.5 92.9 169.7 The effect of fertilization on the nitrate content The nitrate content of vegetables increases with increasing fertilizer nitrogen amount, and plenty of Scandinavian and Finnish literature can be found on this subject (Eppendorfer 1978, Nils- son 1979, Lehtinen 1984, Aura 1985, Bodin 1988, Nygaard Sorensen 1988, Evers 1989c, Jokinen and Tahvonen 1991, Andersen and Nielsen 1992, Salo 1992). Also genotype, light intensity, daylength, temperature, and soil mois- ture content clearly affect the nitrate content of vegetables (Maynard et al. 1976, Corré and Breimer 1979). Therefore research results should always be interpreted in the whole context. The research results in Table 1 (Vuorinen and Taka- la 1987) are very illustrative. The greatest varia- tion can be found between plant species; the var- iation due to climatic differences in differentyears and the variation caused by increasing nitrogen fertilization are considerable but smaller than var- iation between plant species. Even though the effect of increasing nitrogen amount is evident, the consequence is surprising. The absolute nitrate contents in Finnish and Scan- dinavian vegetables (Table 2) are clearly below the limit values applied in the other European countries although in fertilization experiments high levels of nitrogen have also been used. Only in lettuce grown in greenhouses, the concentra- tions are close to the limit values. Carbohydrates, sugars and dietary fibre Plant dry matter mainly consists of carbohydrates i.e. sugars, starch and fibre. All plants contain sugars and fibre, but nuts, bananas, potatoes, maize and dried peas, beans and lentils contain also starch. Carbohydrates make up 50.6 % of the total energy intake in Finnish diets, and this is in accordance with the recommended dietary allowances (Kansaneläkelaitos 1993). Vegetables, root crops and leguminous crops make up 11% of the total carbohydrate intake, and their amount in diets should be increased. These crops are im- portant sources of fibre, they make up 19% of the total fibre intake in Finland (Kleemola et al. 1994). The effect of fertilization on the sugar and fibre contents The effect of fertilization on the sugar content of vegetables has been small in the experiments made in the Nordic countries (Dragland 1978, Nils- son 1979, Aura 1985, Vuorinen and Takala 1987, Nygaard Sorensen 1988, Takala et al. 1988, Evers 1989d), and often the variation be- tween plant species and years has been much greater than the differences between fertilization treatments (Aura 1985, Vuorinen and Takala 1987,Takala et al. 1988, Evers 1989d). Increased nitrogen level decreased the total sug- ar content in carrot, red beet, white cabbage and 1182 Agricultural Science in Finland 3 (1994) Table 2. Vegetable nitrate contents in fertilizer experiments conducted in the Nordic countries in 1978- 1992. The results are both in units given in the original papers and in mg N0 3/kg fresh matter. Researcher, year Original unit mg NO,/kg fm Plant species Eppendorfer, W. H. 1978 Spinach 0.06 - 1.36 % NO,-N in dry matter 270 - 1600 Kale 0.01-0.91 -"- 45-400 Cauliflower 0.02 - 0.08 -" - 90 - 350 Nilsson, T. 1979 Carrot 61-243 White cabbage 68 - 176 Leek 45 - 327 Lehtinen, S. 1984 Carrot 2.51 - 6.04 NO, mg/g dry matter 250 - 600 Red beet 15.98-26.21 -"- 1600-2600 White cabbage 11.52 - 16.42 - " - 920 - 1300 Leek 2.96 - 4.02 -" - 380 - 520 Aura, E. 1985 Carrot 17 -82 N mg/kg fresh matter 75 - 360 Red beet 106 - 430 - " - 470 - 1900 Onion 5-23 -" - 20 - 100 White cabbage 13 -97 -" - 60-430 Bodin, B. 1988 Potato 0.011 - 0.018 % N0 3-N in dry matter 110 - 180 NYGAARD SORENSEN, J. 1988 White cabbage 55 - 670 Carrot 50 - 94 Evers, A. M. 1989 c Carrot 0.01 - 0.16 % NO,-N in dry matter 45 - 71 0 Jokinen, R. and Tahvonen, R. 1991 Lettuce, in greenhouse 630 - 6600 -"- 1150-4680 - " - 2770 - 3880 -"- 1910-3150 Lettuce, on the open field 80 - 750 Andersen, L. and Nielsen, N. E. 1992 Lettuce, in greenhouse 1080 - 2000 - " - 2080 - 3280 Salo.T. 1992 Red beet 600 - 2400 cauliflower in the experiments conducted in Piikkiö in 1978-1983. Single fertilizer applica- tion at the begining of the growing season yielded higher sugar contents than split applications (three applications during the growing season) in red beet, white cabbage, cauliflower and celeri- ac. However, the variations between plant spe- cies and between years were greater than the variations between fertilizer treatments. The re- sults of these experiments show also a tenden- cy for the sugar content to be higher when the yield remained lower. This could be seen in car- 183 Agricultural Science in Finland 3 (1994)Literature Review Literature Review rot, red beet and white cabbage on clay soil, and in cauliflower, but early summer cabbage and ce- leriac did not show any such tendency (Lehtinen 1984). Increasing nitrogen fertilizer amount decreased the sugar content in carrot (Dragland 1978), red beet (Aura 1985, Vuorinen and Takala 1987) and in white cabbage (Nygaard Sorensen 1988). On the other hand, Aura (1985) found no effect on the sugar content in carrot, white cabbage and onion, and Nygaard Sorensen (1988) observed increased nitrogen amount to increase the sugar content in carrot. Broadcast, placement and split application did not affect the sugar content of carrot in Evers’ (1989d) study. Both Nilsson (1979) and Takala et al. (1988) have compared the effects of organic and inor- ganic fertilizers on the yield and quality of veget- ables. Neither the type of fertilizer nor the amount affected the sugar content of carrot and white cabbage. The different farming systems did not affect the starch content of potato or the sugar content of red beet, but the sugar content of car- rot was higher in conventional systems than in biological systems (Takala et al. 1988). The fibre in vegetables is important to human health (Varo et al. 1984), but very few reports can be found of the effects of growing technique on the fibre contents of vegetables, berries and fruits. The increase in fertilizer nitrogen amount increased the fibre content in carrot (Nygaard Sorensen 1988, Evers 1989c). Evers (1989c) further reports that fertilization and irrigation in- creased the fibre content in carrot, and single application compared to split application also in- creased the fibre content. On the other hand, in- creasing nitrogen amount decreased the fibre con- tent in white cabbage (Nygaard Sorensen 1988). Flaami et al. (1989) have found that a rainy sum- mer increases the water-insoluble fibre and nitro- gen fertilization the water-soluble fibre in rye. Further they found that water-insoluble fibre and total fibre contents correlates positively with pro- tein content. These few research results imply that fertilization and irrigation affect the fibre content and the quality of fibre, thus this item should be studied more closely. Conclusions Genotype has a very strong influence on the vita- min C content of plants. Light is the most impor- tant exogenous factor influencing the vitamin C content of vegetables, fruits and berries. At low light intensities the increase of vitamin C is line- ar to the increase of light intensity, and increased daylength had the same effect. Temperature cor- relates negatively with the vitamin C content of plants. At the optimal nitrogen level nitrogen has a small effect on the vitamin C content of veget- ables. If there is enough nitrogen for biomass production and protein synthesis, vitamin C con- tent is mainly affected by genotype and light in- tensity. In nitrogen deficiencies the dry matter and vitamin C contents increase, but simultane- ously the yields and protein content are low. Over- dose of nitrogen causes a reduction in the vita- min C content, probably due to the shadowing effect of big leaves or due to the decrease of dry matter content. It is obvious that yield, dry mat- ter content and vitamin C content are interrelated and they should be considered together. Even sug- ars and dietary fibre could be considered togeth- er with yield, dry matter and vitamin C. More research on this topic should be conducted. Most of the carotene research has been done with carrot. Genotype has a very strong influence on the carotene content. Carotene content increas- es with maturing of the plant. Adequate photo- synthesis, vigorous growth and relatively high temperature increase the carotene content of car- rot. In the the Nordic countries no clear trend can be seen on the effects of fertilization on the caro- tene content; few studies have been conducted and the results are contradictory. The contradic- tory nitrogen results may be due to the fact that the genotype, the climate and the developmental stage of the plant highly affect the carotene con- tent of carrot and fertilization has a much smaller effect. More research should be done on the ef- fects of fertilization and other growing practices on the carotene content of vegetables, because carotene is nutritionally very important to hu- mans. No research results on the effect of fertiliza- 184 Agricultural Science in Finland 3 (1994) Literature Review tion on the vitamin B content of vegetables, fruits and berries have been found in Scandinavian or Finnish literature. Because vegetables are an im- portant source of vitamin B in human diets, the effects of fertilization and growing conditions should be studied. Increasing nitrogen amount increases the ni- trate content in vegetables. Also genotype, low light intensity, short daylength, low temperature and drought increase the nitrate content in veget- ables. When comparing the absolute nitrate val- ues of Scandinavian and Finnish fertilization ex- periments with the limit values applied in other European countries, it can be seen that the nitrate content in vegetables are low even at high nitro- gen fertilizer levels. Only in lettuce culture in greenhouses is there a need to find ways to lower the nitrate content in plants at harvest. It is there- fore not necessary to pay too much attention to the nitrate content of vegetables in future research. The effect of fertilization on the sugar content are small. In several studies the effects of plant species and years have been much greater than the effect of fertilization. Most of the available research data shows a tendency that increased nitrogen fertilization slightly decreases the sugar content. The effects of fertilization and irrigation on the fibre content should be studied more close- ly, because the few results available are interest- ing and the fibre in vegetables is important to human health. In summary, fertilization affects but little the vitamin C and sugar contents. Further research is needed on the yield, dry matter, vitamin C, sug- ars and fibres as one entity to understand more closely the partitioning of photosynthates. The effects of fertilization and growing practices on the carotene, vitamin B and fibre contents are important topics of research as they are essential factors of a healthy diet. The accumulation of nitrate in the plants is quite well understood, but there is a need to find ways to lower the nitrate content in lettuce grown in greenhouses in the dark season. Acknowledgements. The author thanks Maj-Lis Aaltonen and the personnel of the library of the Agricultural Re- search Centre of Finland for providing all the necessary information. 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Vuorinen, M. & Takala, M. 1987, Porkkanan ja puna- juurikkaan sadetus, typpilannoitus ja kalkitus pouti- valla hiekkamaalla. Maatalouden tutkimuskeskus, Tie- dote 10/87. 30 p. Manuscript received November 1993 187 Agricultural Science in Finland 3 (1994)Literature Review SELOSTUS Lannoituksen ja ympäristötekijöiden vaikutus kasvisten ravitsemukselliseen laatuun - yhteenveto Suomessa ja Skandinaviassa tehdyistä tutkimuksista Aino-Maija Evers Maatalouden tutkimuskeskus Avomaan puutarhatuotannossa edistetään kestävän kehi- tyksen mukaista viljelytekniikkaa, jossa lannoitteiden ja torjunta-aineiden käyttöä tarkennetaan taloudellisista ja ekologisista syistä. Tässä tilanteessa on tärkeää ymmärtää ne mekanismit, jotka määräävät tuotetun sadon laadun, jotta viljelytekniikalla opittaisiin vaikuttamaan sadon ra- vitsemukselliseen laatuun myönteisesti. Viime vuosikym- meninä Suomessa ja Skandinaviassa on julkaistu useita tutkimusraportteja mm. lannoituksen ja ympäristötekijöi- den vaikutuksista ravitsemukselliseen laatuun. Tämän ar- tikkelin tarkoitus on koota yhteen nämä tutkimukset ja selvittää voidaanko jo nähdä yleisiä trendejä ja mitkä seikat vaativat vielä lisätutkimusta. Genotyypillä ja valon intensiteetillä on hyvin voimakas vaikutus kasvisten C-vitamiinipitoisuuteen. Optimaalisel- la typpilannoituksella lannoituksen merkitys on vähäinen, mutta liian suuri typpimäärä alentaa C-vitamiinipitoisuut- ta luultavasti suurten lehtien varjostusvaikutuksen tai kui- va-ainepitoisuuden laskun vuoksi. Genotyyppi, kasvin ke- hitysvaihe, tehokas yhteyttäminen, voimakas kasvu ja suh- teellisen korkea lämpötila lisäävät porkkanalla karoteeni- pitoisuutta. Sensijaan lannoituksen vaikutukset karoteeni- pitoisuuteen ovat olleet ristiriitaisia eri tutkimuksissa, jo- ten lisätutkimuksia tarvittaisiin tästä asiasta, varsinkin kun kasvikset ovat erittäin tärkeä karoteenin lähde ruokava- liossamme. Kasvikset ovat myös B-vitamiinien tärkeä lähde, mutta ainoatakaan tutkimusta lannoituksen tai viljelytekniikan vaikutuksista kasvisten B-vitamiinipitoisuuuksiin ei löy- tynyt. Lannoituksella on vain vähäinen vaikutus kasvisten sokeripitoisuuteen. Lannoituksen vaikutuksia kasvisten kuitupitoisuuteen on tutkittu vähän, mutta alustavat tutki- mustulokset ovat lupaavia ja jatkotutkimuksia tarvittai- siin. Kasvisten nitraattipitoisuuksia on tutkittu paljon ja sii- hen vaikuttavat tekijät tunnetaan hyvin. Nouseva typpi- lannoitus, genotyyppi, alhainen valon intensiteetti, alhai- nen lämpötila jakuivuus lisäävät nitraatin määrää kasvik- sissa. Suomessa ja Skandinaviassa kasvatettujen kasvis- ten nitraattipitoisuudet ovat olleet lannoituskokeissa al- haiset, ainoastaan kasvihuoneessa kasvatettujen salaattien nitraattipitoisuudet ovat olleet korkeat ja tämä vaatisi li- sätutkimuksia. 188 Literature ReviewAgricultural Science in Finland 3 (1994)