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 of the 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:

Fertilizing papaya with zinc containing chemicals is uncommon.  However, those farmers who are applying zinc as fertilizers to soils have continued to apply every year leading to accumulation of high levels of zinc in such soils.  This has caused imbalance in plant nutrition leading to induced phosphorus and other deficiencies. Keeping this in mind and the pattern of fertilizer use in papaya and the crop ability to absorb nutrients it is advisable to go for foliar application of zinc rather than soil application as a precaution to avoid unnecessary accumulation in the soils leading to nutrient imbalances. A general spray of 0.25 to 0.40% solution of ZnSO₄.7.H₂O would take care of the zinc requirement of papaya.  Use of Arka papaya micronutrient formulation developed by IIHR, Bengaluru @ 2g per litremeets the micronutrient requirement of papaya including zinc.

Manganese (Mn): Manganese deficiency is not common in papaya.  Under deficiency there will be marginal chlorosis of young leaves, which later turn brown. Leaves give striped appearance from the edges.  Leaves also show typical gallery type interveinal chlorosis on younger and recently mature leaves. Leaves desiccate prematurely causing poor fruit development. Manganese supply is very restricted  under dry conditions. If plants face manganese deficiency, under such circumstances, normal size fruit is produced by the plant but the fruits are covered with raised dark brown or black spots.

Management of manganese in papaya: Manganese deficiency in papaya being uncommon, farmers do not apply manganese to papaya crop.  Since papaya growing regions are well supplied with soil Mn, it is also advised not to render to soil application of Mn. Only if need arises by way of expression of deficiency symptoms growers may undertake foliar application of Mn.  Though rare, if deficiency appears during dry period a simple spray of 0.2% MnSO₄ will correct the deficiency .

Copper (Cu): Copper deficiency in papaya is not reported in India.  This is mainly because the soils of papaya growing regions are well supplied with copper and further to this many of the agrochemicals and organics added to papaya contain sufficient copper to meet the copper requirement of the crop.  However,  if papaya is grown in high organic matter soils and peat soils, under such situations papaya can show copper deficiency. Deficient papaya plant show midrib and main veins bending backwards giving plant an umbrella appearance. Leaves turn to a yellow bronze color. Cu toxicity is possible, in particular where copper oxichloride and Bordeaux mixture are in use for plant protection.

Management of copper: Copper is not reported as deficient in any of the papaya growing regions.  Hence copper application to papaya may be avoided.  Sufficient copper is supplied to crop through the addition of organic matter and also through the copper containing fungicides and as a contaminant with other agrochemicals.  Hence soil application of copper to papaya may be avoided.

Iron (Fe): Iron deficiency appear first on younger leaves and  expressed as gradual interveinal chlorosis and stunted growth.  Leaves may become yellow-white. The chlorosis is more acute in the  months of March-April and continues till rains are received and may reappear after soils dry in post monsoon period before onset of winter.  In most of the areas deficiency gets corrected during rainy season. It is also expressed on trees grown on alkaline and calcareous soils soon after rains after a dry spell because of increase in the bicarbonate content in the soil solution.

Management of iron in papaya: Iron chlorosis is a major production concern for papaya production on calcareous soils and soils irrigated with waters containing high bicarbonates.  Application of iron to such soils may not be fruitful unless a chelated form of iron is applied. Foliar application of iron will be necessary to grow a healthy tree on these soil types. Iron fertilizer formulations are available that can correct chlorosis; however, the required application rate and frequency make the treatment expensive. If plant exhibits iron deficiency then foliar application of 0.25-0.4% ferrous sulfate (FeSO4) corrects the deficiency but care should be taken to see that the spray solution pH must be in the range of 6.25 to 6.75. Synthetic organically chelated forms of Fe like Fe-EDTA, Fe-HEDTA, Fe-DTPA, and Fe-EDDHA are available in the market. The effectiveness of these fertilizers varies greatly, depending on soil pH. Fe-DTPA may be used on mildly alkaline soils (with pH values of 7.5 or less), whereas Fe-EDDHA is the chelate of choice for use on highly calcareous soils (with a pH value greater than 7.5).

Boron (B): It is the most important micro-nutrient for papaya because it affects both the yield and quality of the fruit. Low levels of soil organic matter, low levels of soil boron,  liming the soil, excessive soil acidity, water deficiency, high light intensities, are cited as causes of B deficiency. Best expression of boron deficiency is seen on fruits with complete misshapen fruits with tumor like appearance on surface of fruits. When B deficiency is severe, the growing points of both stems and roots are affected, the fruits are poorly formed and latex drains from distinct points on the skin because of leakage of potassium from cell membranes. Newer leaves are distorted and the growing point dies. Leaves show chlorotic symptom with inward cupping with stunted growth. Shoot show bushy appearance. Additional symptoms of B deficiency are that flowers abort in periods of drought, fruits alternate on the trunk, leaves are yellow with short stems and the vascular system may or may not appear darker. Once a plant shows signs of deficiency it cannot fully recover.  The symptoms are generally confused with ring spot virus infection. 

• Management of boron in papaya production:
  Correction of boron deficiency in papaya is easier than that of iron.  To correct a boron deficiency care should be taken to apply the right amount of boron to the soil or through foliage. Excess boron severely damage or kill a plant. At the same time too little boron will not resolve the deficiency. If sufficient boron is supplied through foliar spray, then do not re-apply boron for at least 3 months, as this much time is required to see the effects of a treatment. While using the commercial products of boron care must be taken to follow the following points:
   ·         Feed papaya at least twice per year with a fertilizer designed for papaya like Arka papaya special. It should contain all of the minor elements, including boron. Even if papaya fertilizers containing boron are applied regularly, however, boron-deficiency symptoms may still develop.
   ·         If orchards exhibit boron deficiency then spray foliage or drench the soil with a 0.25% Borax or boric acid solution. The effect can be seen after 3 months of treatment.
  ·         If the farmers intend to apply to soil then apply 0.5 g boric acid around the base of a papaya plant. If this amount fails to solve the deficiency, up to 5 g Borax per plant may be applied. For symptomatic plants a drench to the root systems of using boric acid @ 2g per litre may be applied followed by irrigation or application of 10 to 15 liters of water per plant so that  the roots can take up the boron-containing water. ·         Wherever soil application is done farmers must get the soil analysed before next application of boron to any crop in the system

Molybdenum: Molybdenum is involved in enzymatic reactions essential for growth and reproduction in papaya. It is involved in the conversion of nitrate nitrogen, taken up by the roots, into a form that the tree can use. It is also involved in fruit set; seed formation, fruit development and fruit yield.  Molybdenum deficiency may be exhibited as small leaves; the edge of leaves burn, poor leaf colour, papery feel to leaves; distorted or zigzag growth habit of shoots. Trees with these symptoms accumulate excessive nitrate-nitrogen in the petiole.

Management of Molybdenum in papaya:

Molybdenum deficiency in Indian papaya is rare. Hence application of molybdenum may be avoided unless tissue testing is done.  If petiole/leaf analysis shows excessive nitrate levels (about 10,000 ppm) and molybdenum deficiency symptoms are exhibited then only molybdenum should be applied.
However, molybdenum deficiency may be a major cause of poor fruit set, without any vegetative signs of deficiency. Care should be taken to see that fruit set problems caused due to other factors, such as periods of cold, wet conditions and zinc or boron deficiency must be cross checked and confirmed before taking up corrective measures for molybdenum deficiency.
Trees with petiole Mo concentrations at less than 0.09 ppm or nitrate nitrogen more than 10000ppm, needs molybdenum application. Molybdenum, as a soluble fertiliser  is available as ammonium molybdate (54% Mo) or sodium molybdate (39% Mo). As molybdenum is only required in a small quantity, one annual foliar spray of 500g ammonium or sodium molybdate per 1000L of water should be adequate to overcome a vegetative growth deficiency where vegetative symptoms have been observed or petiole tests indicate high nitrate-nitrogen concentrations.