Open access publications in the SLU publication database

Abstract

More than 1000 field experiments with nitrogen to spring barley conducted over a period from 1967 to 2004 were investigated. Only one year experiments were included. Yields and N off-take were measured. Three types of production functions were estimated on an experiment wise level. Second and 3rd degree polynomials were considered together with a 3rd degree polynomial combined with a straight line from the inflexion point of the curve. Yields are generally larger today than they were in the mid 60s. This holds both for control treatments and for N fertilized treatments. It implies that the efficiency of N has increased over the years. In other words, the yield increase kg-1 N has increased. Currently a yield increase with 600 kg grain 40 kg-1 N is obtained as an average in the range 40-120 kg N. Similarily, the grain N response to N fertilizer was 0.13 percentage units 40 kg-1 N equal to 0.8 percentage units protein. Yields decline from south to north Sweden while the highest grain N contents were observed in north Sweden. The N off-take averaged over all N-levels was the largest in south Sweden with 75 kg ha-1 N. In north Sweden it was just above 60 kg ha-1. It could be confirmed experimentally that barley after cereals required more N for economical optimum yields than after e.g. a leguminous crop or oil-seeds. The difference was approximately 15 kg ha-1 N. With today's prices applied on the current response curves and on those 30 years ago it was shown that the most economic N fertilization level today is nearly twice that of the 70ies.