Payaya (Carica Papaya Linn.)
Description of Symptoms
Climatic Conditions Likely to Result in Boron Deficiency
The deficiency is common in high-rainfall areas with high temperatures (more than 33oC), on acidic soils with a coarse texture. Soil boron is highly soluble, and easily leaches out from such soils.
Soil Conditions Likely to Result in Boron Deficiency
Boron deficiency is common in calcareous soils (with a pH higher than 7.5), and soils with a very low soil boron content (less than 0.5 mg/kg hot-water soluble boron: HWS-B). The condition is also often found in sandy soils and acidic soils (pH lower than 5), soils with a very low organic matter (content lower than 0.75%), and soils derived from acid igneous rocks (granite). Boron deficiency may also be encountered in soils which have been given excessive applications of nitrogen and potassium fertilizers.
Diagnosis by Soil Analysis
Levels of boron (HWS-B) in low or deficient soils are less than 0.5 mg/kg. In soils with medium and adequate levels, the boron content is 0.5 – 2 mg/kg. Soils with high and excessive levels contain more than 2 mg/kg. Thus, soils with a level of boron (HWS-B) of 0.5 or less can probably not supply enough boron to support normal plant growth and yields.
Diagnosis by Plant Analysis
In most crops, a level of boron in plant tissue of 15-100 mg/kg is considered adequate for normal growth. More than 200 mg/kg is probably excessive, and have a toxic effect on crop growth and yields.
How to Correct Boron Deficiency
The problem of boron deficiency can easily be solved by applying boron, usually in the form of borax, a white crystalline salt. The quantities needed for the crop are very small. As little as 0.5 to 5 g/plant or 5-10 kg/ha can correct boron deficiency of papaya in Taiwan.
Alternatively, a foliar spray of 0.4 % of borax solution can applied repeatedly every 10 days until the deficiency is corrected. For calcareous soils, sulfur should be applied at a rate of 2 mt/ha, to reduce the soil pH to 6.0 – 7.0.
Information from Dr. Zueng-Sang Chen, National Taiwan University