During the last three years, 1964—66, investigations on sprinkler irrigation of spring cereals have been carried out. The experimental fields were clay soils in Southern Finland. Neutral river and lake waters containing small amounts of soluble salts were applied in the nighttime. The application rate of the rotary sprinklers used was 2.5—4 mm per hour with the radius of 12±2 m. With this technique the experimental soils having poor structure endured the irrigation without any crust formation. It was found that the sprinklers equipped with two nozzles distributed the water more uniformly than those with one nozzle. With the former sprinklers a fairly good uniformity was attained: The amount of water usually varied between 25 and 35 mm with an average of 30 mm, except in a relatively small area nearest to the sprinklers which received too much water and in the area at the greatest distance from the sprinklers with less than the average amounts of water. The soil water conditions were followed by gypsum blocks inserted at different depths. In each experimental year, within 2—3 weeks from sprouting, the available water in the top soils decreased to 50 per cent of the total capacity. This dry condition existed for two months in the years 1964 and 1966 and for one month in 1965. During these dry periods the top soils were near the wilting point for a long time, and in 1966 the available water was wholly exhausted. The influence of transpiration was effective also in deeper layers. In 1966, the soil reached the wilting point also at the depth of 40 cm and stayed at this condition for about one month. The effect of a 30—37 mm irrigation on the soil moisture conditions lasted only for 1—2 weeks. Thus, the rate of evapotranspiration was as much as 4 mm per day. The plants consumed water simultaneously from the whole root zone, yet, most effectively from the surface layers. The top soil (20 cm in thickness) which had reached the wilting point was not completely moistened by the amounts of water applied. This indicates the high capacity of clay soils to store water. It is also noteworthy that a part of irrigation water percolated to 40 cm before the soil at the depths of 10 and 20 cm had time to get to the field capacity. In experimental years, to ensure favourable moisture conditions to spring cereals several high applications of water would have been needed. This proves that also during the short growing season in Finland a serious shortage of water may occur.
In 1967 and 1968, in the month of June, irrigation of silty clay soil in southern Finland by a single sprinkling, which involved the application of 30 mm of water, increased the yields of spring wheat by an average of between 880 and 970 kg per ha, or 37—51 %, and the yields of barley by 1140—1340 kg per ha, or 37—42 %. Repeating the irrigation after about one week further increased the wheat yields on the average by from 670 to 800 kg per ha and the barley yields between 810 and 860 kg per ha. The effect of the irrigation on the size of the yields was virtually of the same magnitude both years in spite of the fact that in 1967 both June and July were extremely dry months, whereas in 1968 the dry June was followed by a rainy July. The sprinkling affected the ripening of the grain, on the other hand, differently each year: slightly retarding the ripening in 1967 but considerably hastening it in 1968. In the latter year, the irrigation prevented detrimental late tillering and thereby augmented the hectoliter weight and 1000-grain weight of the crops. In response to the one-time sprinkling, the protein content of the grains decreased in the case of the wheat by an average of 1.0—1.3 and of the barley by 0.1—0.7 %-units. The effect of two sprinklings was corresponding decreases of 1.9—3.1 and 0.8—1.0 %-units. The application to the seedlings as surface dressing immediately before irrigation of calcium nitrate containing 60 kg/ha of nitrogen increased the protein content of the wheat on the average by 1.6 and of the barley by 1.9 %-units. The nitrogen fertilization thus prevented excessive lowering of the protein content by irrigation and, furthermore, considerably intensified the salutary effect of the irrigation in augmenting the yield. A disadvantage of abundant nitrogen fertilization was a slight retardation of ripening. The placement of basal dressing with a fertilizer drill at a depth of 9 cm proved effective, particularly in 1967, when both the wheat and the barley yields increased 22 per cent in comparison with the effect of surface dressing. Use of the fertilizer drill, moreover, promoted the ripening process. Sprinkling did not appear to reduce the placement effect of the fertilizer; rather did these two methods form an exceedingly favorable combination.
In the dry summers 1964, 1965 and 1966, irrigation experiments of spring cereals were carried out on clay soils in Southern Finland. The soils having a rather poor structure because of the long-term cultivation without leys, endured without slaking the irrigation which was applied with »slow sprinklers» in the nigh-time. Neutral irrigation water containing small amounts of soluble salts was taken from a brook and a lake. One irrigation of 30—37 mm, applied at the optimum date, increased the grain yields of spring wheat 600—1000 kg/ha or 25—50 % and those of barley and oats 1600 kg/ha or 50 %. Barley and oats were the experimental plants only in 1966, when the relative increase in yields of all the three cereals were of the same order, namely 50 %. The optimum date of irrigation did not very closely depend on the state of development of the cereals, since within 2—5 weeks from sprouting about equal increases in yield could be obtained. Barley and oats responded, however, best to the irrigation applied one week before ear emergence. The late irrigation which was applied three days after ear emergence was best utilized by oats. Thus, the right order to irrigate cereals was in 1966: wheat, barley and oats, in spite of the reverse order of the ripening of the crops. An irrigation at the stage of sprouting had no effect on yield, because the sprouting occured well also without irrigation. Irrigation produced higher increases in yield when higher amounts of fertilizer were used. Thus, the profitable influence of irrigation was at least partly based on the better recovery of fertilizer nutrients by plants. Placement of fertilizer into the depth of 8—12 cm postponed the optimum date of irrigation some days, because the crops were able to make use of placed fertilizer also without irrigation in the early part of the summer. Placement of fertilizer and irrigation together formed an advantageous combination, because the influence of the placement of fertilizer was most effective immediately after sprouting whereas the best period of irrigation began 2—3 weeks later. With these both means, in the best cases, the yields could be almost doubled.
Typpilannoitusmäärän ja lannoitustapojen vaikutusta rehumaissin sadontuottoon ja raakavalkuaisen määrään tutkittiin vuosina 1976—1978 ja vastaavasti sadetuksen ja lannoituksen vaikutusta v. 1978 Suitian tilalla Siuntiossa. Koetekijöinä olivat rivi- ja sijoituslannoitus sekä typpilannoitustasot. Sadetuskokeessa tutkittiin N-lannoitusmäärien ja -levitysaikojen vaikutusta satoihin. Typpilannoitustavalla, rivi- tai sijoituslannoituksella, ei ole ollut merkittävää vaikutusta rehumaissin kuiva-ainesatoon, raakavalkuaissatoon ja raakavalkuaispitoisuuteen. Typpilannoituksella 150N kg/ha kylvön yhteydessä annettuna saatiin suurimmat kuiva-ainesadot. Sitä suuremmat lannoitemäärät 2—3 erässä levitettynä eivät ole lisänneet satotasoa. Typpilannoitustason noustessa 100 N kg:sta/ha 250 N kg:aan/ha lisääntyivät sekä raakavalkuaispitoisuus että raakavalkuaissato merkittävästi. Sadetus lisäsi yhden kasvukauden tutkimuksissa rehumaissin satotasoa merkittävästi. Kokeessa käytetyt typpilannoitemäärät 120 ja 170 N kg/ha ovat antaneet sadettaen ja sadettamatta keskimäärin yhtä suuret sadot kuin 240 N kg/ha yhdessä tai useammassa erässä levitettynä. Sadetuksella myös raakavalkuaissadot olivat suurempia, mutta raakavalkuais-% keskimäärin pienempi kuin sadettamatta.
Virtanen's studies the recommended seeding rate was 120 kg/ha (35 plants/ m 2) with a row distance of 40 cm and with a seeding depth of 7-B cm. In
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