The effects of nitrogen application on growth and nitrogen distribution within the potato canopy

Abstract

SUMMARYThe effect of applying nitrogen (N) fertiliser on the growth and distribution of N within the potato canopy was studied in 1983 and 1984. In both years N was applied either in excess of that required to produce maximum tuber yields, or not at all. The large application of N changed the pattern of canopy growth ‐ stimulating growth of leaves at the top of the stem, particularly lateral branches, for longer during the season, and accelerating the death of (shaded) leaves at the base of the canopy. The pattern of canopy senescence was, therefore, changed from a synchronous to a progressive type.Application of nitrogen fertiliser at supra‐optimal rates increased the N contents of leaves, stems and tubers. The extra N in the leaves of these plants was present as reduced N in all leaf positions, and as nitrate (NO‐3) in the lowermost leaves. In addition, substantial quantities of NO‐3 were also stored in the stems. Part of this extra N in the canopy was redistributed during subsequent growth, especially to the lateral branches as crop N uptake slowed towards the end of the season. In addition, substantial quantities of N were also potentially available for redistribution to the growing tubers. There was little redistribution of N from the leaves of N‐deficient plants.It is suggested that redistribution of N in the canopy of N‐replete plants allowed the growth of lateral branches towards the end of the season, thereby maintaining photosynthetically active leaves for longer than N‐deficient plants.