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

Abstract

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 (SARN)): legumes, potato, and beet; group II (large RW and low SARN): cereals; and group III (large RW and high SARN): sunflower. In the roots of field crops subjected to various treatments in a field 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-l, then it increased slightly with the increase of the nitrogen content above a value of about 20 mg g-l, 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.SARN increased exponentially with the increase of the nitrogen content in the roots of groups I and II. In group I, the values of SARN were generally higher than in group II for a similar nitrogen content, while in group III, SARN 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 (SARN).Key Words: mineral absorption, mineral balance, root activity, root function, specific absorption rate of minerals.Since the amount of dry matter increased exponentially with the increase of the amount of plant nitrogen accumulated in cereals and root crops, and linearly in legumes, nitrogen is considered to be one of the determinant factors for the regulation of dry matter production in field crops (Osaki et al. 1992). Though nitrogen was absorbed by roots, the nitrogen 12 M. OSAKI et al. uptake was strongly regulated by shoot growth during the vegetative growth stage (Shinano et al. 1994). After the maximum shoot growth (MSG) stage, however, the nitrogen uptake was regulated by the root activity (Osaki et al. 1995b). In high-yielding crops, photosynthetic activity and root activity remained constant during the maturation stage (Osaki et al. 1991a(Osaki et al. , b, 1995b(Osaki et al. , 1996. In crops with standard yield, the mineral absorption rate decreased during the maturation stage, which was ascribed to the decrease of the root activity. Thereafter, nitrogen compounds in leaves and stems were retranslocated to harvesting organs, resulting in ...

Evaluation of a generic agro-hydrological model for water and nitrogen dynamics (SMCR_N) in the soil–wheat system

“…The simulated N incorporated in the roots could not be quantitatively validated due to unavailable experimental data, but the approach for considering N partitioned in roots was reasonable for many crops as demonstrated in Zhang et al (2009). Further, the critical %N curve for roots during growth is supported by the experimental evidence (Osaki et al, 1997). The used soil organic matter breakdown rate is similar to those used in other models (Mueller et al, 1996;Fu et al, 2000;Fang et al, 2005).…”