Zinc in subterranean clover (Trifolium subterraneum L. cv. Seaton Park). II. Effects of phosphorus supply on the relationship between zinc concentrations in plant parts and yield

Publisher Website
Google Scholar
Abstract
The effect of P on the relationship of Zn concentrations in various plant parts to yield of Seaton Park subterranean clover was examined. Plants were grown in a glasshouse at 3 levels of P (39, 65 and 130 mg P/pot; denoted P1, P2 and P3, respectively) and 6 levels of Zn added in factorial combination to a sand deficient in both P and Zn. At the lowest 3 levels of Zn supply, plants were severely to moderately deficient in Zn: in them, increasing levels of P depressed growth and induced high concentrations of P (> 1% DM [dry matter]) in several plant parts and symptoms of P toxicity in leaves. At the highest 3 levels of Zn supply, plants at P1 were P deficient: application of P2 and P3 increased growth and induced Zn deficiency primarily by diluting the available Zn. In addition, P3 appeared to depress slightly the Zn content of plant tops by another mechanism. In severely Zn-deficient plants, P supply changed the relationships between Zn concentrations in various plant parts and yield of whole tops, probably as the result of P toxicity. In the youngest open leaf blades, an asymptotic relationship at P1 changed at P2 and P3 to sigmoidal and to ''Piper-Steenbjerg'' relationships, respectively. These changes would not have invalidated the use of plant analysis for diagnosing Zn deficiency. In moderately Zn-deficient plants, P supply had little or no effect on the relationships of Zn concentration in plant parts to yield of shoots. As a result, critical concentrations in plant parts generally remained constant over the whole range of P supply. The data refute suggestions that high levels of P in plant part inactivate the Zn within them, thus removing a potential problem in the use of plant analysis for diagnosing Zn deficiency in subterranean clover. The results confirm the previous suggestion that a concentration range of 12-14 .mu.g Zn/g in the youngest, open leaf blade is critical for diagnosis of Zn deficiency in subterranean clover.