H. Riley, G. Guttormsen
Reservations were made in a recent paper (Greenwood et al., 1996) about the validity of an equation used for calculating the critical %N of brassica crops. This parameter is crucial to the correct modelling of fertilizer requirements for such crops. Reference was made to our data on responses of cabbage to plant N-concentration. This paper presents an appraisal of that data, together with some comparisons of modelled and measured data from recent fertilizer trials.

Relationships were established between total above-ground dry mass of cabbage and crop N-concentration at periods ranging from 60 to 140 days from transplanting. Optimum levels of N-concentration were lower than those suggested by the equation used in the model of Greenwood et al. (1996), and only slightly higher than those indicated by the equation which he has previously proposed for arable crops. Use of the former equation probably suggests that crop N-contents would be considerably higher than is necessary for good growth. This may in turn lead to excessive leaching losses when the plant residues decay.

Our findings therefore indicate that the equation used for arable crops is probably also suitable for cabbage, except at the very early growth stage, when the maximum concentration measured in plants is always lower than that suggested by the equation.

Riley, H. and Guttormsen, G. (1999). ALTERNATIVE EQUATIONS FOR CRITICAL N-CONCENTRATION IN CABBAGE. Acta Hortic. 506, 123-128
DOI: 10.17660/ActaHortic.1999.506.16
Brassica oleracea var. capitata, critical %N, N-models

Acta Horticulturae