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 nitro gen uptake as follows: Group I (small root dry weight (RW) and high sp ecific absorption rate of nitrogen (SAR(N))): legumes, potato, and bee t; group II (large RW and low SAR(N)): cereals; and group III (large R W and high SAR(N)): sunflower. In the roots of field crops subjected t o various treatments in a held of Hokkaido University, the nitrogen, c alcium, and magnesium contents in roots were relatively higher in grou p 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 in creased linearly with the increase of the nitrogen content, and the co ntents of both minerals were higher in group II than in group I. Howev er, 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 n itrogen 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 ab out 20 mg g(-1), especially in group I Potassium content; in roots in group III was constant regardless of nitrogen content. Calcium and mag nesium contents were not related to the nitrogen content in groups I a nd II, but increased with the increase of the nitrogen content in grou p III. SAR(N) increased exponentially with the increase of the nitroge n content in the roots of groups I and II. In group I, the values of S AR(N) were generally higher than in group II for a similar nitrogen co ntent, 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 maintenanc e of root activity (SAR(N)).