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The role of plant growth regulators (PGR) in nitrogen (N) fertilization of spring wheat and oats (CCC), fodder barley (etephon/mepiquat) and oilseed rape (etephone) in crop rotation was studied in 1993–1996 on loamy clay soil. Carry over effect of the N fertilization rates (0–180 kg ha-1 ) was evaluated in 1997. N fertilization rate for the best grain/seed yield (120–150 kg ha-1 ) was not affected by PGRs. The seed and N yields of oilseed rape were improved most frequently by recommended use of PGR. The yields of oats were increased in 1995–96. Even though PGR effectively shortened the plant height of spring wheat, the grain yield increased only in 1995. N yield of wheat grains was not increased. Response of fodder barley to PGR was insignificant or even negative in 1995. The data suggest that PGRs may decrease some N leaching at high N rates by improving N uptake by grain/seeds, if the yield is improved. The carryover study showed that in soils with no N fertilization, as well as in soils of high N rates, N uptake was higher than in soils with moderate N fertilization (60–90 kg ha-1 ), independent of PGRs. According to soil mineral N contents, N leaching risk is significant (15–35 kg ha-1 ) only after dry and warm late seasons. After a favourable season of high yields, the N rates did not significantly affect soil mineral N contents. ;

Field experiments on arable crops seldom account for more than one half of the nitrogen applied in fertilizers (Russell 1961, Cooke 1964, Kaila 1965. This may be attributed to leaching or denitrification, to volatilization or immobilization. In any case, a large part of the expensive fertilizer nitrogen is likely to be wasted.Lack of movement into the root zone of even nitrates applied as surface dressing to spring cereals was demonstrated in Finnish field experiments, and placement or working in of nitrogen fertilizers was recommended (Kaila and Hänninen 1961). Because of the usual dry period in the beginning of the summer in Finland, attention has also been paid to the possibilities of improving the efficiency of nitrogen fertilizers by irrigation (Elonen et. ai, 1967).In the present paper results are reported from a field experiment which was conducted to study the influence of sprinkler irrigation, and the placement and chemical composition of the nitrogen fertilizer on the uptake of nitrogen by spring wheat. ExperimentalIn 1969 a large field trial was carried out in southern Finland, in the neighbourhood of Helsinki, in cooperation with the Finnish Research Institute ofAgricultural Engineering.Sprinkler irrigation was studied at four rates, and three kinds of nitrogen fertilizers were either placed or applied as a surface dressing. The uptake of nitrogen by spring wheat was followed by collecting samples of the aerial parts during the growing period.The soil was silty clay with an average clay content of 50 per cent. The pH of the ploughing layer was about 6 (in 0.01 M CaCl 2 ), and the content of organic C was 4-5.5 per cent.The nitrogen fertilizers studied were a Finnish ammonium nitrate-limestone, »Oulun-

The present study was carried out in summer 1970, when a rainy July following upon a dry June caused abundant detrimental late tillering among spring cereals in large parts of South Finland, and in part also in Central and North Finland. In four irrigation experiments, established in the clay area of South Finland, the irrigation performed in the middle of June (2 x 30 mm) increased the yield of two rowed barley by 1750 kg/ha on an average or by 71 % (variation range 49—104 %). In addition irrigation improved the quality of barley significantly by preventing detrimental late tillering. The irrigated evenly ripened barley was at harvesting time on an average 12.3 per cent units drier, with a hectolitre weight that was 3,6 kg higher when compared to the non-irrigated green grained barley. Analyses of the sheaves collected from the fields indicated that irrigated barley when compared to non-irrigated barley contained: a) equally many individuals per square meter, b) 14% less ears per individual, c) 83 % more grains per ear, d) 9 % heavier grains; in fact the total result was a 70 % higher grain yield. Causes of late tillering and the significance of irrigation in preventing this detrimental phenomenon are discussed. It is further established that in years when no late tillering occurs, irrigation affects the grain yield components in ways that differ from those established in the present study.