The effect of calcium supply on bur set and seed formation in subterranean clover (Trifolium subterraneum L.)

Abstract

In a glasshouse experiment subterranean clover plants were grown in soil at various levels of calcium nutrition. The developing burs were buried in separate soil containers to which no nutrients, calcium sulphate, calcium carbonate, or potassium sulphate were applied. When subterranean clover was growing in soil low in calcium, top yield was little affected; but bur and seed formation were greatly reduced. However, when the reflexed flowers were buried in soil to which a calcium salt had been added, bur and seed yield increases of up to 500% were obtained The increase in seed yield resulted from a greater percentage of flowers forming bur, more seed per bur, heavier seed, and less rotten seed.

Similar results were obtained in a second glasshouse experiment in which a different soil was used to grow the clover.

The beneficial effect of calcium ions around the developing bur was independent of the associated anions, or of the soil pH; nor could it be produced by the substitution of potassium or magnesium for calcium.

It seems likely that commercial seed yields and subterranean clover persistence in many areas may be reduced by calcium deficiency in apparently lush healthy pastures.

The similarity of this disorder to calcium deficiency in peanuts suggests that other crop and pasture species forming buried seed may also be especially susceptible.