Crop Nutrition in Papaya

Papaya is considered one of the most economically important and nutritious fruits, being a rich source of antioxidant nutrients such as carotenes, vitamin C and flavonoids; the B vitamins folate and pantothenic acid; the minerals potassium, magnesium and fiber.

Integrated Nutrient Management

For papaya, fertilizers should be applied once in every two months. Although fertilizer application in a particular region depends on the soil and leaf analysis, generally 90 g of Urea, 250 g of Super phosphate and 140 g of Muriate of Potash per plant are recommended for each application. Total requirement is 250 g N + 250 g P₂O₅ + 500 g K₂O per plant/year. Application of 7-10 kg farm yard manure / plant every six months is recommended in addition to fertilizers. The leaf analysis technique for papaya has also been standardized and recently matured 11^th leaf petiole was found optimum. Fertigation also can be followed with soluble fertilizers, which save about 25-30% fertilizers.  Apply 100% recommended N and K fertilizers through drip irrigation (50 g N and 50 g K₂O) in addition to soil application of 50 g P₂O₅ at bimonthly interval.

Nutrients removed by Papaya

Papaya has three distinct development phases:

(1) Initial growth; (2) Flowering and fruit formation; (3) Production.

Papaya takes up relatively large quantities of nutrients and the demand continues until the plants are about one year old. Because harvests are intermittent from the start of production, the plant needs frequent applications of water and nutrients to ensure the continuous production of flowers and fruits.

Percentage distribution, during the development of papaya, of the total nutrients in the crop at the end ofthe first year of growth, based on the rate of nutrient absorption estimated at IIHR and nutrient uptake by two year old whole plant of papaya.

Nutrient status

Nitrogen (N): Second only to potassium, nitrogen is the most used nutrient in papaya growth, development and fruit production. Regardless of soil, cultivar and climate the total nitrogen taken up by papaya is related to the total dry matter production.  Nitrogen is considered to be in short supply even when the crop is grown on highly fertile soils. Required for vegetative growth, N should not be limiting in the first 5 to 6 months after planting. Symptoms of N  deficiency appear first in the mature leaves, which have yellowish areas between the veins. Later, these leaves become yellow, aged and stands out from the trunk, and may even become necrotic with the centre turning brown and the edges purple. When N deficiency is severe, all of the leaves turn yellow, new leaves have slimmer stems and leaf laminas are not well developed. Application of excess N without balancing amounts of P and K would result in over vegetative growth, with a greater distance between fruits on the trunk and inconsistent quality of the pulp. The TSS of the fruit pulp reduces and the fruit become over soft on ripening.

Phosphorus (P): Although it is the macro-nutrient, this is required in very low quantity. Absorption by the plant increases uniformly during growth and is most important during initial root development. Thus it is necessary to give the young plants a source of readily plant-available P. It is also suggested that P has an effect on setting the fruit.  Hence basal application of phosphorus helps in better crop establishment. The deficiency of P causes reduced leaf production, complete cessation of elongation and older leaves becoming increasingly irregularly necrotic. P deficiency causes a blue or dark green coloration of leaves.  Marginal chlorosis and premature death are also caused. P deficient trees bear fewer fruits and hence also suggested that P has an effect on setting the fruit.  Plants raised on P deficient nutritive solution resulted in P deficiency symptoms initially in the oldest leaves, which have amottled yellow color along the edges. As deficiency progresses, the yellow areas become necrotic and the leaves have pointed lobes while the edges curlupwards. Later, the leaves turn completely yellow and fall from the trunk. New leaves are smaller and have a dark green coloring.

Potassium (K): Among the nutrients the requirement of potassium is the largest. Papaya takes up K continuously throughout the entire plant cycle. It is especially important after the fertilization of the flowers to produce larger, better quality fruit, with elevated levels of sugars and total soluble solids. A ratio of N:K₂O of 1:1 seems to be the most favorable to obtain good yields,which suggests that the fertilizers used should have N:K₂O ratios close to 1:1. Potassium deficiency appears first in the oldest leaves and under severe deficiency the leaves are shed resulting in a decrease in their number and the remaining leaves positioned obliquely to the trunk. Deficiency results in marked reduction in growth, leaves profusely smaller, leaf margins necrosis and premature yellowing of plant. Purplish brown patches appear at the base of the petioles. Fruits are badly shaped, poorly filled and unsuitable for marketing. The oldest leaves may also become  yellow between the veins and along the edges with a slight marginal necrosis on the extremities of the lobes. The leaves tend to dry from the tip to the centre. The developing leaves show chlorotic edges with small necrotic spots. When K deficiency is severe the growing point is affected

Calcium (Ca): It is the third most required nutrient and it also accumulates uniformly like potassium. Calcium  deficiency causes aninitial chlorosis of recently mature leaves which have curled edges, harming leaf development with small necrotic spots spread overthe leaf lamina. This chlorosis extends back to the youngest leaves and the affected leaves have twisted and folded stems. Calcium deficiency is also responsible for premature ripening of fruits on the tree leading to loss of fruits and softening of the fruit pulp, which results in problems in transport and a short commercial shelflife.    

Magnesium (Mg): Magnesium is emerging as a limiting nutrient in papaya cultivation especially on red soils.  The reasons for the emergence of magnesium deficiency in papaya is both soil and plant based problems.  Soil magnesium levels are depleting without external additions. Fertilizer application pattern skewed towards potassium causes imbalance between Mg and K.  This is a major reason for the appearance of Mg deficiency in papaya.  Intensive cultivation with high yield targets through modified fertilizer application through drip using Mg free fertilizers fails to meet the Mg requirement of the plants leading to Mg deficiency.  Magnesium deficiency  results in the mature leaves having an intense yellow color, while the regions in the proximity of the veins remain green. When Mg is very deficient, the new leaves also have similar symptoms.

Sulphur (S): Sulphur is a component of papain, a proteolytic enzyme, and, in general, performs functions in the plant that affect yield and quality of the fruit. When sulphur is deficient, new, expanding leaves are light green in color before becoming uniformly yellow. With increasing deficiency, the completely expanded leaves also become yellow. Before the appearance of visual symptoms in the leaves, the growth of the papaya plant is affected. Sulphur uptake may also be affected by the presence of chloride ions added to soil in fertilizer.

Management of sulphur in papaya: Papaya is generally grown in the humid tropics with typically high annual rainfall and free draining soils. Because sulphur is predominately found in the anion form (SO₄), which is easily leached under such conditions, a regular supply is required to maximise productivity. In many soils, a crop’s requirement for S is supplemented by a natural source coming from organic matter but since our soils are typically poor in organic matter the S requirement far exceeds the natural supply. The data base of Indian soils on availability of sulphur is very poor.  But, our soils are generally poor in sulphur supply.  Fertilizers containing sulphur like sulphate of potash and single super phosphate and amendments like gypsum and pyrites may be used for growing papaya in acidic and  highly leached soils. Judicious application of organic matter takes care of the sulphur requirement of the crop.  However, a general application of 20 to 40 kg sulphur indirectly through P or K fertilizers or as gypsum or pyrite may be done in growing papaya on light textured soils.

Zinc (Zn): Zinc acts as a cofactor of enzymes and is involved in the production of growth regulators responsible for the internode elongation and chloroplast development.  Zinc deficiency significantly reduces growth and yield potential of papaya. Low zinc levels also reduces fruit number per tree and to a lesser extent the fruit size, resulting in decreased yields. Zinc deficiency is seen in the expanding leaves as interveinal chlorosis that later become purple spots. With increasing deficiency, the youngest leaves remain small, possibly showing necrosis along the edges and on the lamina between the principal veins. The internodal space is also shortened. Zinc deficiency included pronounced raised light green veins on the upper and lower leaf surface distorted strap like leaf lobes and slight yellowing of youngest leaves.

Management of zinc in papaya: