Nutrition

Mineral nutrition

Uptake and export of nutrients

For growth and production, passionfruit requires an adequate nutritional state at all stages of growth and this requires a fertilization plan to permit the maintenance of an adequate nutritional state of the crop. From the start of fruit formation there is a great demand for energy by the plant and a strong translocation of nutrients from the leaves to the developing fruits and this reduces the vegetative growth of the plant.

The total quantities of nutrients taken up and exported by the entire plant, including the fruits, at 370 days, with 1,500 plants/ha, are shown in Table 3. The macro-nutrients N, K and Ca are taken up in the greatest quantities, followed by S, P and Mg. Of the micro-nutrients, Mn and Fe are absorbed in the greatest quantities, followed by Zn, B and Cu. Of the nutrients removed in the harvested fruits by far the largest quantity is K followed by N. Although only small quantities of Mg, S, Ca and P are removed, the amounts of P and Mg represent 40% and 29% of the total taken up, respectively. Of the micro-nutrients, Mn is taken up most, but by percent Zn, followed by Cu, are the most exported. In spite of the large amount of Mn found in the fruits, it represents only 6.4% of the total taken up; however 34% of Zn, 32% of Cu, 13% of B and 11% of Fe are accumulated in the fruit and, thereby, removed at harvest. In this way for a crop yielding about 25 t/ha, the export of macro-nutrients in the fresh fruits, in kg/t, is 1.82 of N, 0.28 of P, 3.01 of K, 0.28 of Ca, 0.17 of Mg and 0.17 of S; while that for micro-nutrients, in g/t, is 1.54 of B, 2.61 of Cu, 3.59 of Fe, 7.35 of Mn and 4.41 of Zn.

Table 3. Quantities of nutrients absorbed by the whole plant and exported in the fruits of the yellow passion-fruit, at 370 days of age, at the yield level of 13 t/ha.

Nutrient	Quantity
	Absorbed	Exported
Macro-nutrient (kg/ha)
N	205	44.6
P	17	6.9
K	184	73.8
Ca	152	6.8
Mg	14	4.0
S	25	4.0
Micro-nutrient (g/ha)
B	296	37.8
Fe	779	88.0
Mn	2,810	180.2
Zn	317	108.2
Cu	199	64.0

Source: Haag et al., 1973.

Functions and importance of nutrients

Nitrogen (N): It is fundamental for the growth of all plant parts. It stimulates the development of floral and fruit buds, as well as increasing the amount of protein. In its absence, growth is slow and the plant's size is reduced, with thinner and fewer branches. There is a greater quantity of total soluble solids and lower acidity in yellow passionfruit juice, as well as higher productivity, with the application of larger amounts of N to the soil.

Phosphorus (P): In its absence passionfruit growth is reduced, affecting the quantity of dry matter, root growth and fruit production.

Potassium (K): Its deficiency reduces the weight of the plant and the production of fruits, which fall prematurely or shrivel. Increases in length and diameter of the fruit were observed with the application of larger amounts of K.

Calcium (Ca): Its deficiency results in deformed leaves due to the breakdown of leaf tissue structure, because Ca affects cell elongation and the process of cell division.

Magnesium (Mg): In nutrient culture experiments, the absence of Mg affected the nutrient state of the plant, resulting in a greater absorption of P, K and Ca, relative to plants grown using a complete solution.

Boron (B): Boron deficiency results in an increase in N, P and S in the tendrils and Mn in the stem and leaves of passion-fruit.

Visual diagnosis

Based on the fact that each nutrient has a specific role in the physiological functions of plants, then excesses or deficiencies, i.e. imbalances, often result in characteristic symptoms, which permit the identification of the cause of the disorder. To establish the cause of visual symptoms requires knowledge of the symptom and its cause determined in both controlled experiments, which simulate the nutritional disorders systematically, and from soil and plant analysis. In Table 4 symptoms of nutritional deficiencies are described.

Table 4. Visual symptoms of nutrient deficiency in passionfruit leaves

Nutrient	Leaf age	Leaf symptoms and causes
N	Oldest	Light green and smaller area. Yellowing and premature falling. Cause: low composition of organic matter, acidity (lower mineralization), leaching, prolonged drought.
P	Old	Dark green, later yellowing from the edges to the centre. Cause: low composition of P in the soil, low pH (lower availability).
K	Old	Progressive chlorosis from the edges to the centre, necrosis and tissue "burn". Cause: low composition of K in the soil, leaching and excessive liming.
Mg	Old	Yellowish spots between the veins, wizened lamina curling down. Cause: soils low in Mg, acidity and excessive potassium in fertilization.
Ca	Young	Death of apical sprout, interveinal chlorosis and necrosis. Cause: low Ca composition in the  soil,  excessive potassium in fertilization.
S	Young	Chlorotic, yellowish veins on the bottom side of the leaves. Cause: low soil S composition, low organic matter content.
Cu	Old	Large and wide leaves, dark green in color and partially shrivelled, thickening of the veins on the upper side, curved downwards. Cause: low soil Cu composition, excessive liming and high levels of organic matter.
Mo	Old	Interveinal chlorosis. Cause: acidity, excessive sulphate.
B	Young	Plants atrophied, necrosis of the terminal sprout. Smaller and shrivelled leaves with waves along the edges. Cause: low soil B composition, low organic matter content, excessive acidity, leaching.
Fe	Young	Interveinal chlorosis. Cause: Excessive liming, elevated organic matter content, low soil Fe composition and elevated moisture.
Mn	Young	Chlorotic spots between the veins. Cause: excessive liming, elevated organic matter content, low soil Mn composition.
Zn	Young	Small leaves, gaunt and pointed lobes, milky white spots with yellow edges Cause: low soil Zn composition, excessive liming and phosphatized fertilization.

Source: Borges and Lima, 2003

However, it is not sufficient to just rely on visual symptoms, to confirm that an anomaly is due to a disorder provoked by a specific nutrient. Because many factors may act simultaneously, to rely on one diagnostic based only on visual symptoms is not prudent. Visual symptoms should be confirmed by leaf and soil analysis of samples taken from crops grown in the field. Once it has been confirmed that deficiency or excess of a specific nutrient is the cause of the problem appropriate corrections can be made.

Leaf diagnosis

This consists of the determination, via chemical analysis, of the nutrient composition of the leaf which is the organ that best reflects the nutritional state of the plant. To be successful appropriate leaves in relation to stage of growth and position on the plant must be taken for analysis. For passionfruit it is recommended to sample the 4^th leaf from non-shaded and non-pruned branch apices, taking four leaves per plant, from both sides, including the leaf stem. In the first year, samples should be taken between the 8^th and 9^th months and, in the following years, during the flowering period. Adequate ranges of macro- and micro-nutrient compositions are given in Table 5. 

Table 5. Adequate ranges of macro- and micro-nutrients in passionfruit leaves.

Nutrient Concentration
Macro-nutrient (g/kg) N 47.5-52.5 P 2.5-3.5 K 20.0-25.0 Ca 5.0-15.0 Mg 2.5-3.5 S 2.0-4.0	Micro-nutrient (mg/kg) B 2.0-4.0 Cu 5.20 Fe 100-200 Mn 50-200 Zn 45-80

Source: Borges and Lima, 2003

Manuring/Fertilization

A balanced fertilizer that supplies nitrogen, phosphorus and potassium in approximately equal proportions, as well as essential micronutrients (magnesium, manganese, copper, zinc and iron), is adequate for passion vines on the slightly acid, sandy soils. On the alkaline, rocky soils, phosphorus is needed less than nitrogen and potash, but micronutrients must be applied for normal growth and production. These can be applied 4 times a year in foliar sprays. In addition, iron chelates can be applied directly in solution to the soil near the roots.

Fertilizer should be applied in early spring before growth begins. Light applications should be given at 4-6 week intervals during active growth and production phases from July to October. Passion vines are heavy feeders, but over-fertilization will damage the roots, and possibly destroy the plant. The amount to apply depends on the size of the plant, and can be determined by experience. No more than 10 g each of NPK/plant should be applied at one time until it has been determined that more can be applied safely. It should be evenly spread in a circle of about 45 cm radius about the stem, and then irrigated. 

Organic manures

Using organic manures helps to maintain soil productivity, because it has beneficial effects on the physical, chemical and biological properties of the soil. The materials to be applied in the planting holes, especially in sandy soils and those of low fertility, depend on their availability. The quantities vary according to the nutrient composition of the materials available and may be, FYM/compost (10 to 20 kg),  poultry manure (5 to 10 kg) and neem cake (2 to 4 kg) amongst others.

Inorganic fertilizer

Fertilization consists of supplying nutrients in quantities sufficient for the plant to be able to reach its production potential. Fertilization aims to increase both productivity and quality, without compromising the fertility of the soil, especially in irrigated areas, keeping in mind that fertilization can degrade soil. Any fertilization programme should take into account the fertilizer to be used, the quantity, the time of year and the location of application relative to the plant. Thus, there is no single formula that would be the best for all conditions. It is important that, for each plant, one takes into account soil fertility, evaluated by soil analysis, and the expected productivity (Table 6). Amounts of fertilizer used during early growth of the plant are, to a certain extent, comparable amongst the different regions. Fertilizer recommendations are related to soil analytical data and the potential productivity of the site and the phenological phase of the plant.

Table 6. Fertilization recommendation at planting, growth and production phases of irrigated yellow passion-fruit.

	N (kg/ha)	P2O5 (kg/ha): P-resin (mg/dm3)			K2O (kg/ha):K-soil (cmol/dm3)
		0-15	16-40	>40	0-0.07	0.08-0.15	0.16-0.30	0.31-0.50	>0.50
At planting	150(1)	120	80	0	0	0	0	0	0
During growth
Days after planting
30	10	0	0	0	20	10	0	0	0
60	20	0	0	0	30	20	10	0	0
90	30	0	0	0	40	30	20	10	0
120-180	40	0	0	0	60	40	30	20	0
During fruit production
Expected yield (t/ha)
<15	50	50	30	20	100	90	70	50	0
15-25	70	90	60	40	160	120	90	70	0
25-35	90	120	80	50	200	160	120	80	0
>35	120	150	100	60	250	200	150	100	0

⁽¹⁾ In the form of bovine manure. Source: Borges and Lima, 2003

Taking into account all the factors the schedule of manures and fertilizers for passionfruit grown in the two premier belts of India is given in Table 7.

Table 7. Schedule of manures and fertilizers for passionfruit grown in two premier belts of India

	Manures and	South India			Northeast India
	Fertilizers	Planting	2-4 years	>4years	Planting	2-4 years     >4 years
i.	FYM (kg/vine)	5	10	15	2	4              6
ii.	Nitrogen (g/vine)	25	80	150	20	60           80
iii.	Phosphorus (g/vine)	10	30	50	10	40           40
iv.	Potassium (g/vine)	25	60	100	10	50           50

Source: Sema and Maiti, 2006

Fertilization with micro-nutrients

In the absence of soil analytical data apply 50 g of micro-nutrients mixture in the planting hole. Zinc and B are the micro-nutrients taken up in largest amounts by the plant, followed by Mn and Fe. With Zn deficiency, apply 20 g of zinc sulphate (ZnSO₄.H₂O) per plant, and of B, apply 6.5 g of boric acid (H₃BO₃) per plant. Boron and zinc recommendations for the yellow passionfruit are given in Table 8. 

Table 8. Boron (B) and zinc (Zn) recommendation for the irrigated yellow passion-fruit. 

Nutrient	Soil composition (mg/dm3)	Classes of fertility	Nutrient dose (kg/ha)
	Hot water
B	<0.2	Low	2
	0.21-0.6	Medium	1.0
	>0.6	High	0
	DTPA
Zn	<0.5	Low	6
	0.6-1.2	Medium	3
	>1.2	High	0

Source: Borges and Lima, 2003 

Splitting fertilization applications

Deciding whether to split fertilizer application depends on the texture and the CEC of the soil, as well as the pattern of rainfall. In sandy soils and those with a low CEC, fertilizers should be applied weekly or biweekly. In more clayey soils, fertilizers can be applied monthly or bimonthly, especially when applied to the soil. With fertigation nutrients can be applied weekly or biweekly, depending on soil texture.

Fertilization position

Passionfruit has a shallow superficial root system, i.e. about 60% of the roots are found in the upper 30 cm of soil, and 87% between 0 and 45 cm from the base of the stem. In young orchards, fertilizers should be distributed in a 20 cm wide area around and 10 cm from the trunk, gradually increasing this distance with the age of the plants (Fig. 1). In mature vines it is recommended to apply fertilizer in a band 2 m long and 1 m wide, on both sides of the plants and 20 to 30 cm from the trunk.

Fertigation

The application of fertilizers via irrigation water results in more rational use of fertilizers in irrigated agriculture, because there is an increase in efficiency, and a reduction in labour and energy costs. In addition, it allows flexibility in the time of nutrient application, which may be divided according to the needs of the crop in various stages of development. Drip irrigation is the most appropriate for fertigation, because nutrients are applied directly to the zone of greatest concentration of active roots.

Nitrogen is the nutrient usually applied via irrigation, because it has high mobility in the soil, especially in the form of nitrate (NO₃^-), but care must be taken not to favor loss by leaching. In fertigation, N is applied accordingly to the demand of the plant to reduce losses, especially in sandy soils. Because it is so mobile in soil, N should be applied frequently at three to seven day intervals, except in sandy soils when the interval should be around three days. The recommended quantity should be distributed throughout the period between the first four months of growths, corresponding to the formation phase of the plant and the beginning of the production phase (first year). Solid N fertilizers are available in four forms: ammoniacal (ammonium sulphate), nitric (calcium nitrate), ammoniacal-nitric (ammonium nitrate) and amide (urea), all being soluble in water and adequate for fertigation, including drip irrigation. In general, these N sources behave similarly and can be applied with other nutrients. Their different effect on the soil pH has to be considered.

In general, P is not often applied with irrigation due to the low solubility of most P fertilizers and their tendency to precipitate, causing blockage of the lines and emitters. Phosphoric acid, apart from a risk of corrosion in metallic lines and connections, does not cause problems of emitter blockage, and is applied via irrigation water to promote cleaning of the lines and emitters in fertigation systems. Apart from this, diammonium phosphate (DAP) and monoammonium phosphate (MAP) can be used in fertigation.

Like N, the application of K via irrigation water is viable, because K fertilizers are soluble. When using split applications, it is important to consider its potential loss by leaching in very sandy soils and its adsorption by clay minerals in heavy soils. Potassium fertilizers normally used in fertigation are potassium chloride, potassium sulphate, potassium nitrate and potassium and magnesium sulphate. The application of K with irrigation may be done every six or seven days and it is recommended to continue the distribution throughout the growth of the plant. Starting from the second year, the recommended quantity of K₂O for the production period may be divided between the 5^th and the 12^th month after the seedlings have been transplanted.

Drip irrigation emitters are usually placed at two emitters per plant at a distance of 60 cm between them and each one placed 30 cm from the stem.