82 Papaya
The imbalanced application of nitrogenous fertilisers may induce boron defi-
ciency through crop growth dilution factors. Not many field trials have been con-
ducted to determine the micronutrient requirement of papaya. The boron deficiency
develops bunchy top and deformed fruit (Figure 6.2).
The ameliorative effect of boron application (as disodium octaborate tetrahydrate)
through foliar sprays is more effective than soil application (1–3 kg/ha). However,
it can start from 1 kg/ha for clayish soils, 1.5 kg/ha for rocky soils and 2–3 kg/ha
for sandy soils. Foliar application of the micronutrients, namely, ZnSO 4 (0.5%) and
H 2 BO 3 (0.1%) is done in order to increase the growth and yield. It will also help in
overcoming the deficiency. It is important to go for only one spray of boron in initial
fruit development stage, if both are combined, it may prove toxic to the plant (Figure
6.3). Therefore, balanced application of macronutrients is imperative for quality pro-
duction of papaya in boron deficient soils. The basal application of borax at 5 g/plant
at the onset of reproductive stage is very effective to control the bumpy fruit disorder
of papaya (Saran et al. 2014a, b, c, d).
TABLE 6.3
Critical Nutrient Levels in Petiole of Papaya
Nutrient Concentration (%) Nutrient Concentration (ppm)
Nitrogen 1.20–1.38 Iron 20–100
Phosphorus 0.17–0.21 Manganese 20–150
Potassium 2.70–3.40 Zinc 14–40
Calcium 1.00–3.00 Copper 4–10
Magnesium 0.40–1.20 Boron 20–50
Sulfur 0.30–0.80FIGURE 6.2 (See colour insert.) Bumpy fruits of papaya.