The use of stable strontium as a chemical tracer for root penetration

Abstract

Stable strontium was used successfully, in the glasshouse and the field, as a tracer for root penetration and activity in some crop plants. Changes in strontium concentration in shoots were detected within a few days of roots coming into contact with soil enriched with strontium chloride, either mixed throughout a horizon as a powder or place at a particular depth as pellets.

In glasshouse experiments there was a close correlation between dry weight of roots in the enriched zone and strontium accumulated in the shoots. Of various sizes of pellets used, 100 mg pellets were effective in raising the strontium content of shoots, while diffusing through only a limited volume of surrounding soil. Movement of strontium from larger pellets was excessive for accurate monitoring of root penetration and soil strontium concentrations were undesirably high, while smaller pellets, or a narrow band of enrichment, were ineffective.

In the field, a technique of placing 100 mg pellets at 10 cm intervals in soil successfully monitored root penetration when wheat was grown under two systems of cultivation. Differences in shoot strontium concentration were greatest at early harvests and gradually disappeared. Hence it was essential to take frequent harvests in order to record root penetration with accuracy.