Responses of yield and N use of spring sown crops to N fertilization, with special reference to the use of plant growth regulators
L. PIETOLA | R. TANNI | P. ELONEN
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 19931996 on loamy clay soil. Carry over effect of the N fertilization rates (0180 kg ha-1 ) was evaluated in 1997. N fertilization rate for the best grain/seed yield (120150 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 199596. 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 (6090 kg ha-1 ), independent of PGRs. According to soil mineral N contents, N leaching risk is significant (1535 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. ;
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