Effects of nitrogen, calcium: potassium saturation ratio, and and electrolytic concentration on uptake of calcium and potassium by rice plants
Chaudhry, M.S.; Mclean, E.O.; Jr Franklin, R.E.
Agron J 56(3): 304-307
Rice plants were grown in a growth chamber under different nitrogen treatments, Ca:K saturation ratios of the soil exchange complex, and electrolyte (CaCl2) concentrations. Both short term (4-day) and long term (40-day) studies were made to investigate the effects of the various factors on Ca and K uptake by rice using Ca45 and Rb86 as tracers. Root cation exchange capacities of the rice seedlings were increased by N treatment, but the differences disappeared during the longer growth period; and only relatively small effects of the N treatment were evident on Ca and K uptake. The amounts of Ca and K taken up increased with saturation of each cation and with level of electrolyte present. Arithmetic increases in Ca saturation generally caused geometric increases in Ca uptake. The marked increases in uptake of Ca when relatively small increases in concentration of CaCl2 were made appeared to emphasize the competitive role of soil colloids for the Ca and the importance of free (active) Ca in Ca uptake. Smaller effects of electrolyte concentration on K than Ca uptake evidently resulted from relatively strong bonding of K at low K saturations and relatively weak bonding compared to Ca at higher K saturations. The uptake of Ca was relatively high in the short term study and remained so with time while the uptake of K was low initially and increased with time. The data indicate that a portion of the K was bonded very strongly, and thus became available to the rice plants only as the K saturation was increased or as increased root growth brought the plant in contact with more soil. The trends in amounts of Ca taken up from the soil according to cation saturation and electrolyte level were rather similar in the 4-day and 40-day uptake periods. Less similarities were evident in uptake of K in the two uptake periods. Sufficient saturation of the soil cation exchange capacity with K was essential for adequate uptake of K, but greater than 10% of the cation exchange capacity of soil was detrimental to Ca uptake. A higher concentration of electrolyte than 0.02 S was beneficial to uptake of Ca by rice plants.