The effect of climatic factors on production of spring wheat quantity to quality ratio in southern Finland

Interrelationships between climatic factors and spring wheat yield and quality were examined with 21 years field experiments. The formation of gluten was less at dry conditions (total precipitation under 50 mm) and total precipitation exceeded 130—140 mm. The optimum daily temperature for gluten production was some 15—17°C during grain filling. The gluten content decreased if daily minimum and maximum temperatures exceeded 11 —12°C and 21—22°C, respectively. The effect of temperature and rainfall were not, however, significant in early maturing varieties. The climatic factors and grain yield did not correlate. Grain yield and protein yield had strong positive relationship, which was perhaps a consequence of supply and utilization of nitrogen. It is concluded that climatic factors affecting yield to quality ration in wheat may be excessive rains before heading and high temperature during grain filling. Interaction between weather and nitrogen are discussed to optimize correct timing of nitrogen fertilization for amount and quality of economic wheat yield. Index words: Spring wheat, climatic factors, grain yield, protein content


Introduction
The wheat processing industry needs high quality wheat for milling. The flour mills in Finland have, however, limited access to imported high quality wheat to compensate crop of poor technological quality. There was little annual variation in protein content of wheat grain before 1974 (Suomela et ai. 1977), however since 1974 there has been a decrease in the protein content. An explanation for this could be increased cultivation of late high-yielding wheat varieties. However, the effect of the choice of wheat variety on the decrease in protein content was only 0.5-0.6 % and does not alone explain the declining trend in protein amount (Juuri 1985).
Another factor causing the decrease in protein content may be weather conditions during the growing season. Excessive rains in June has been observed to decrease grain protein content (Rekunen and Juuri, unpub-227 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND lished data), however, according to Konttori (1979) sufficient rainfall and high radiation during early summer seemed to increase protein content. This may be attributed to better uptake of nitrogen by wheat (Kaila and Elonen 1970). Rain during harvesting activates enzymes that split starch and proteins, but the protein quality only decreases when sprouting of the ear is advanced (Lallukka 1971).
The effect of climatic factors on the yield of wheat has been studied by many researchers in 1960-1970's (e.g. Lipsett 1963, Asana and Williams 1965, Stoy 1966, Campbell and Read 1968, Lallukka 1971, Peters et al. 1971, Bremner 1972, Horhikawa ref. Evans et al. 1975, Kontturi 1979, but the role of weather in the yield quantity quality ratio in spring wheat has not yet been carried out under northern growing conditions. The object of the present study was to evaluate the role of climatic factors in the relationship between wheat quantity and quality.

Test material
The study period covered the years from 1968 to 1988. The material was cultivated at Tammisto 1968-72 andAnttila 1973-88, at (Zadoks et al. 1974) and days to yellow ripeness (GS 85). The plots were considered to be fully ripened (GS 91) 5-7 days after the yellow ripeness. This was dependent on daily temperature after yellow maturation.
Grain yield and thousand grain weight were measured from harvested yield. The protein content was determined by using the common Kjeldahl procedure and multiplied by nitrogen conversion factor of 5.7. From 1983 Near Infrared Reflectance (NIR) analyser was used to measuring the protein content. Wet gluten content was used to estimate the quantity of storage protein. Measured grain yield and quality are given in Table 2.

Data of climatic factors
The basic daily climatic data for each year and locality was obtained from the Finnish Meteorological Institute. The following climatic factors were used; mean, maximum, and minimum daily air temperature (°C), precipitation (mm d -1 )> and daily global radiation (MJ m -2 ), measured at the Helsinki-Vantaa Airport, located between Tammisto and Anttila experimental farms. Data given in table 3.
The statistical analysis was carried out using regression analysis in order to clarify significance of individual climatic factor on proportion of grain yield, grain size and protein properties.

Results and Discussion
individual climatic factors explained poorly the variation in grain yield per hectare and grain weight. The coefficient of determinations (R 2 ) between climatic factors and both grain yield and grain weight ranged 0.01 0.25, and 0.02-0.27, respectively (Table 4). Grain yield is the end-result of interaction of climatic factors and several plant characteristics (Miedema 1984). Thus any individual factor does not necessarily explain such a complex system as yield.
The coefficient of determination (R 2 ) between protein yield per hectare and minimum air temperature after sowing was 0.53 for early maturing varieties, and 0.51 for late maturing varieties, respectively. The lower the minimum air temperature was, the higher was the protein yield per hectare (Fig. 1).
Nitrogen absorption from the soil depends on soil moisture content (e.g. Kaila and Elonen 1970, 1971, Elonen et ai. 1975. According to figure 2a, it seemed that excessive rains before heading caused leaching of nitrogen which was followed the decrease in gluten con- Table 4. Coefficient of determination (R 2 ) in climatic data versus grain yield, thousand grain weight, protein content, protein yield, and wet gluten content in study period 1968-88. tent. When total precipitation exceeded 130 -140 mm, the gluten content decreased to below 25 %, and thus below that regular from bread wheat quality (Salovaara 1983). The heavy rains during grain filling contributes the decrease in wet gluten amount, too (Fig. 2b).
Rain fall under 50 mm before heading may cause the same type decrease in wet gluten content (Fig. 2a). The reason for this was perhaps that in dry soils the uptake of nitrogen was decreased (Kaila and Elonen 1971). The mean daily temperature during grain filling was below 20°C for the whole study period (Table 3). The optimum daily mean temperature for gluten formation appeared to be some 15-17°C in all wheat varieties (Fig. 3). The wet gluten amount decreased if daily minimum and maximum temperatures exceeded 11-12°C and 21 -22°C, respectively (data not shown). Temperatures exceeding 25-30°C have been found to cause decreases in grain yield and grain size (e.g. Asana andWilliams 1965, Peters et al. 1971 and Hoshikawa ref. Evans et al. 1975). According to Lawlor et al. (1988), the high temperature decreases protein synthesis more than it decreases carbon assimilation. It is concluded that high temperature during grain filling affects quantity to quality ratio in wheat.
The effect of temperature and precipitation on formation of wet gluten content was not significant in early maturing varieties 'Ulla' and 'Heta' (cf. Figs. 2 and 3), perhaps due to their better ability to utilize nitrogen effeciently and an advantageous weather during grain filling. Conversely, the late cultivars ('Ruso', 'Kadett', 'Drabant', 'Tähti') were more susceptible to lose their quality in unfavourable growing conditions (cf. data at Table 2, e.g. year 1987).
It has been suggested that grain yield and amount of protein in grain have a negative phenotypic relationship in Finnish cultivation conditions (e.g. Konttori 1979). This type of relationship was not, however, observed in Fig. 2b. The effect of precipitation on wet gluten content from heading to ripening. Fig. 3. The effect of mean air temperature on wet gluten content from heading to ripening. our examination (Fig. 4a). The present study showed that there was a strong positive correlation between grain yield and protein yield (Fig. 4b). According to Kramer (1979), within a wheat genotype the correlation between grain yield and grain protein content can be either close to zero, positive, or negative, depending on the level of fertilization. But between genotypes the correlation is strongly negative. It has also been suggested that grain  protein content can be used as an indicator to evaluate if nitrogen fertilization was sufficient (Goos et al. 1982 andGoos 1984). Perhaps, supply and utilization of nitrogen by wheat are the main factors changing quantity and quality proportion in wheat and the utilization of nitrogen is dependent of weather e.g. precipitation. However, more detailed experimental data is required to understand: the interaction between weather, nitrogen supply and quantity and quality of wheat yield. This would lead to a more efficient use of nitrogen in agricultural systems to optimize correct timing of nitrogen supply for amount and quality of economic wheat yield in Finland.