Relationships between root activity and N, P, K, Ca, and Mg contents in roots of field crops

Based on the previous paper (Osaki et al. 1995, Soil Sci. Plant Nutr., 41, 635-647), crops were classified by root characteristics for nitrogen uptake as follows: Group I (small root dry weight (RW) and high specific absorption rate of nitrogen (SAR(N))): legumes, potato, and beet; group II (large RW and low SAR(N)): cereals; and group III (large RW and high SAR(N)): sunflower. In the roots of field crops subjected to various treatments in a held of Hokkaido University, the nitrogen, calcium, and magnesium contents in roots were relatively higher in group I than in groups II and III. Potassium content in roots was high in maize and sunflower. Phosphorus content in roots in groups I and II increased linearly with the increase of the nitrogen content, and the contents of both minerals were higher in group II than in group I. However, the phosphorus content in group III remained constant or increased slightly with the increase of the nitrogen content. Potassium content in roots in groups I and II did not change with the increase of the nitrogen content up to a value of about 20 mg g(-1), then it increased slightly with the increase of the nitrogen content above a value of about 20 mg g(-1), especially in group I Potassium content; in roots in group III was constant regardless of nitrogen content. Calcium and magnesium contents were not related to the nitrogen content in groups I and II, but increased with the increase of the nitrogen content in group III. SAR(N) increased exponentially with the increase of the nitrogen content in the roots of groups I and II. In group I, the values of SAR(N) were generally higher than in group II for a similar nitrogen content, while in group III, SAR(N) increased linearly with the increase of nitrogen content in roots. Consequently, it appears that nitrogen and phosphorus nutrition in roots is very important for the maintenance of root activity (SAR(N)).