Yields of dry matter and nitrogen in highly diverging genotypes of winter wheat in relation to N-uptake and N-utilization

The aim of the investigation was to find out if certain North American genotypes of winter wheat with exceptionally high grain protein concentrations (GPCs) are characterized by an extraordinary ability to take up and/or distribute nitrogen from the soil to the grains. Two of these genotypes were grown in a field trial in southern Sweden together with three 'normal' Swedish genotypes (two modern cultivars and one bid landrace). They were compared with respect to accumulation of dry matter and nitrogen in both grains and straw when cultivated at three levels of N-fertilization (0.75 and 150 kg N . ha(-1)). The results of this trial demonstrated that the yields of above-ground biomass (BY) and grain (GY) were significantly lower for the American genotypes than for the Swedish ones. Also the nitrogen yields in biomass (NBY) and grain (NGY) were significantly lower in the American types but the difference between the two groups was nor so pronounced as with respect to dry matter yields. The American types were thus superior to the Swedish ones in relative ability to take up nitrogen but not in absolute terms. The GPCs of the American wheats were very high also under Swedish growth conditions but a regression analysis of the relation between GPC and GY revealed a very strong negative correlation between these parameters (r = -0.95 at 0 N and r = -0.99 at 150 N). The correlation between GPC and HI was highly negative, too, (r = -0.83 at 0 N and r = -0.89 at 150 N). The specific ability to take up nitrogen was determined by estimating the changes in soluble soil nitrogen (NO3 + NH4) in the unfertilized plots during the vegetation period. These measurements indicated that the American types were less effective in retrieving nitrogen from the soil than the Swedish ones. The analysis of the soil in the fertilized plots also demonstrated that the American types were slightly inferior to the others in their ability to recover externally applied nitrogen. The efficiency to utilize absorbed N for production of above-ground and grain biomass was also estimated from the experimental data. The results demonstrated very clearly that the American genotypes exhibited a considerably lower nitrogen utilization efficiency than the Swedish types. Also the efficiency to allocate absorbed nitrogen into the grains (expressed as nitrogen harvest index, NHI) was examined and was found to be nearly identical for all genotypes and almost independent of the level of N fertilization. It is therefore claimed that the results reported in the present communication confirm the conclusions from parr I of this investigation, namely that the main reason for the high GPCs in the American genotypes investigated here are their relatively low dry matter production in the grain filling period. This fact does not exclude, however, that other high-protein genotypes may carry genes which in appropriate crosses can combine high-yielding ability with an improved GPC.