Effect of salinization and desalinization on the uptake, distribution, and assimilation of fertilizer nitrogen by nodulated soybeans

Abstract

Soybean plants were grown in water culture, to study the effect of salinization and desalinization on the uptake, distribution, and assimilation of fertilizer nitrogen using ¹⁵N as a tracer. The following results were obtained:

1.	Up to 8 days after NaCl application, 15N uptake by the salt-affected plants was lower than that by the control plants, but higher after NaCl removal.
2.	During the time course of 16N absorption, the incorporation of 15N into the leaves was depressed by salinization, even after NaCl removal. On the other hand, the nodulated roots of the salt-affected plants accumulated higher amounts of 16N than the control plants, even after NaCl removal. Pods and stem followed the general trend of the whole plant.
3.	The proportion of absorbed 15N in the pods which decreased by salinization, was similar to that of the control plants at the end of the desalinization period. An opposite trend was observed for the nodulated roots.
4.	Assimilation of fertilizer 15N into the various nitrogen fractions of pods was depressed by salinization, although the assimilation of absorbed 15N into the cationic fraction, as a percentage of total 15N incorporated into the pods was increased by salinization, i.e. the assimilation of absorbed 15N into the insoluble nitrogen fraction (protein) was depressed by salinity.

Based on these findings, it is suggested that, a) the irrigation of soybean plants with fresh water after salty water may alleviate the depressed effect of salinity on nitrogen nutrition and b) salinity may decrease the seed yield due to the inhibition of protein synthesis

Key Words:

• desalinization
• ¹⁶N assimilation
• ¹⁵N uptake
• salinization