Foliar Fertilisation with Primary Nutrients During the Reproductive Stage of Plant Growth

Foliar applications of micronutrients have been successfully used for a long time to correct nutrient deficiencies in plants. Although primary nutrients can also be absorbed by foliage, it has been difficult to apply effective amounts without damage to the plant.

Premature leaf senescence may occur during seed formation when photosynthate is translocated to the seed and roots are starved. Addition of nutrients to the leaves at this stage may delay senescence.

Recent experiments have shown that more phosphorus can be absorbed by the leaf without injury from polyphosphates than from orthophosphate. Preliminary experiments in 1974 and 1975 using potassium polyphosphates, urea, and a small amount of a sulphate source in concentrated solutions as a foliar spray on soybeans gave a 10 percent to 20 percent increase in yield. A large number of experiments in 1976 following the same procedures gave inconclusive results.

Some of the conditions necessary for successful use of foliar fertilisation during seed formation have ben established. High air humidity, adequate soil fertility, adequate soil moisture, and small spray droplet size are important. Further experimental work is necessary to identify other conditions favorable to yield increases from foliar fertilisation.