Phosphorus toxicity in Subterranean clover and oats grown on Muchea sand, and the modifying effects of lime and nitrate-nitrogen

Abstract

Phosphorus supplied as mono-sodium phosphate depressed the growth of subterranean clover and oats grown on Muchea sand in pot culture. In both plants the detrimental effects appeared at phosphorus levels equivalent to about 2-4 cwt. per acre superphosphate, provided both nitrogen and lime were in very short supply. Adequate nitrogen, as sodium nitrate, invariably overcame the toxic effects of phosphorus within the range of levels examined. With the clover, nodulation was usually poor, but some evidence is presented in which "heavy" inoculation with Rhizobium markedly increased nodulation and alleviated the toxic effects. Nodule numbers in the clover were increased by addition of lime and in most instances the beneficial effects resulted from enhanced nitrogen supply. Lime was advantageous to the growth of oats, also, wherever applied nitrogen was low. Possible explanations of this are suggested. Phosphorus toxicity symptoms are described for both plants and the relation to percentage total phosphorus in the leaves is discussed. Figures in excess of 1.4 per cent. and 3 per cent. total phosphorus were found in affected leaves of subterranean clover and oats respectively. Identical symptoms were observed in clover with the mono- and dibasic phosphates of sodium, calcium, and potassium.

The Phosphorus-Iron Relationship in Genetical Chlorosis.

“…Similarly, symptoms of phosphorus deficiency (3), or phosphorus toxicity (12) were in accordance with the expected phosphortus-iron ratio in each case. An examination of chlorosis due to genetical and virological causes was therefore undertaken to ascertain the trend in phosphorus-iron and calcium-potassium ratios.…”

Effect of Phosphorus and Zinc Levels in The Substrate on 65Zn Distribution in Subterranean Clover and Flax

“…This depressive effect of phosphate was associated with high phosphorus concentrations in the tops of all P2 and P3 plants (Table 8). In this regard Rossiter (1952) found that subterranean clover showing incipient phosphorus toxicity symptoms contained a phosphorus concentration of 1·43%.…”

A Direct Test of the Ability of Vesicular‐arbuscular Mycorrhiza to Help Plants Take Up Fixed Soil Phosphate

“…At the highest levels of application (1000 mg P/pot) the plants were stunted and the leaves had necrotic tips. These are symptoms of phosphorus toxicity (Rossiter, 1952). As there is no satisfactory response function to include the descending part of the response curve yields from such treatments were not used.…”