The Relationship Between the Phosphorus Status of Subterranean Clover Plants and Losses in Chlorophyll from Detached Leaves: A Basis for the Visual Diagnosis of Phosphorus Deficiency

Leaves detached from subterranean clover plants (Trifolium subterraneumL.), grown in solution cultures at different phosphorus levels,were placed in water and in phosphate solutions. Losses in totalchlorophyll (a+b) of leaves in water were greater the lowerthe previous phosphorus supply to the plants from which theywere detached. In comparable leaves placed in phosphate solutionschlorophyll was maintained at levels at least as high as inleaves from non-deficient plants. For the latter there wereno differences between treated and untreated leaves. The differencesin colour change between treated and untreated leaves, therefore,increased with the deficiency in the phosphorus supply to theplants from which the leaves were detached, thus visibly reflectingtheir phosphorus status. A light intensity of 300 ft c (27 lx) or higher was necessaryfor maximum differences in leaf colour between treated and untreatedleaves, mainly because lower light levels reduced chlorophylllosses from leaves in water. Differences in colour between treated and untreated deficientleaves decreased with their age. However, valid comparisonsbetween treated and untreated leaf tissue could be ensured bythe use of treated and untreated leaflets. It is suggested that the results provide the basis for a simple,direct and visual diagnostic method, requiring no laboratoryequipment. Trifolium subterraneum L., subterranean clover, phosphorus deficiency, chlorophyll     

Some Effects of Potassium and Magnesium on the Growth of Subterranean Clover (Trifolium subterraneum)

Subterranean clover plants (Trifolium subterraneum L., cv. Mt.Barker) were grown in culture solutions at optimum nutrientlevels and on the 23rd day after sowing transferred to solutionswithout magnesium or potassium. A third group remained at thesame nutrient levels as before (controls). Magnesium deficiency caused a particularly rapid decline inroot growth, followed later by a net loss of root dry matter.This, and the fact that leaf expansion declined relatively morethan the increase in laminae dry matter, resulted in an accumulationof assimilates per unit leaf area. Transfer of magnesium-deficientplants to complete solutions on day 35 caused a preferentialdistribution of dry matter to the roots, then to petioles andrelatively less to the laminae. These changes caused a pronouncedfall in the root: shoot ratio as the deficiency became moresevere and a rise in the ratio during recovery. Plants in solutions without potassium showed no marked shiftsin dry matter distribution between plant parts. The root: shootratio remained close to that for control plants, except duringthe recovery, when there was a decrease in the ratio. Net rates of CO₂ uptake by laminae from potassium-deficientplants showed little change during the first 10 days of thedeficiency although values were somewhat lower than those forcorresponding control laminae. After transfer to complete solutionsthere was a marked response in photosynthesis, rising to a finalvalue close to that for control laminae. Laminae of plants placedin solutions without magnesium showed a rapid decline in photosynthesisonly 4 days later; there was little response when plants weretransferred to complete solutions a week later. Trifolium subterraneum L., subterranean clover, growth, root: shoot ratio, potassium deficiency, magnesium deficiencies