Pomegranate Crop Management & Diagnosis!

Crop nutrition: Management of micronutrients

Research findings have indicated that optimum quantity of fertilizers and time of application for efficient utilization of nutrients can reduce decline in pomegranate due to diseases. Response of micronutrients like Zn, B and Mn has been noted for increasing the quality and yield of fruits.

Nutrient status

Nitrogen:

Nitrogen is one of the primary nutrients absorbed by pomegranate roots, preferably in the  form of nitrate (NO₃ ^- ). The pomegranate  fruit crop requirement for N is equal to the amount of N contained in the harvested fruit as residues are generally recycled in the pomegranate groves. Mature fruit contain approximately 0.25 kg  N per 100 kg of fruits. If the residues are not removed from the pomegranate groves then replacement of this N can meet the requirement of pomegranate fruits. Blooms, fruit, woody tissues (both above and below ground), and leaves all contain N and other nutrients. As these materials fall to the ground, some (approximately 50%) of the N they contain is recycled within the grove. Therefore, pomegranate trees must take up N in excess of the crop requirement for young trees to increase in size. Optimum leaf nitrogen concentrations  for pomegranate ranges from 1.5 to 2.0%.  If leaf N falls below this range then application of nitrogen is recommended.  A note of caution- since pomegranate crop is susceptible to wilts and blights, care should be taken to see that while recycling the residues, the disease inoculum should not build-up in the groves.

Pomegranate tree showing general yellowing of leaves starting from older leaves with some leaves in “Yellow vein state		A close up view of a branch showing chlorosis of older leaves, younger leaves remaining green.

In nitrogen deficient pomegranate trees, there is no distinctive leaf patterns.  Generally deficiency is expressed by light green to yellow foliage over the entire tree. As the deficiency intensifies foliage will change the colour from light green to yellow. New flushes usually emerge pale green in colour, but darken as foliage expands and hardens. During severe deficiency the leaf exhibit a symptom called “yellow vein chlorosis”. In Karnataka, the midribs and some lateral veins also turn yellow, while the rest of the leaf remains with normal green colour. It may also occur with the onset of cooler weather in winter, due to reduced nitrogen uptake by the plant from the soil. Nitrogen deficiency is also associated with senescing older foliage, which can develop a yellow-bronze appearance prior to leaf abscission. Nitrogen deficiency will limit tree growth and fruit production, while high nitrogen applications produce excessive vegetative growth at the expense of fruit production, reducing fruit quality.

Phosphorus:

Phosphorus is a very important nutrient required for obtaining satisfactory yield and quality of pomegranate.  But the quantity required is not as high as other fruit crops like apple, mango etc. as very little P  is removed by fruits.  P does not leach readily where the soil pH is 6 or higher and most of the pomegranate soils fall under this category.  As a consequence of this over the years, P applied to established  groves had accumulated in the soil at high level and is available slowly to the plants. Therefore, regular P applications are not necessary and fertilizer application should be done on the basis of soil test. Excess P in pomegranate can cause imbalance in other nutrient availability and affect fruit quality, cause irregular maturity, and increased expression of aril browning and wind scars on the fruits.

Some soils used for new plantings are naturally low in P particularly in highly calcareous soils of Telangana and Vidharba regions. In this situation, P fertilizer should be applied until a soil test P rating of medium to high is achieved. Phosphorus fertilizer should be applied each year in newly planted groves on previously non-fertilized soil until the groves begin to bear fruit. As the trees approach economic bearing stage, P applications may be reduced or omitted. Diagnostic information from leaf and soil testing must be considered to determine if P fertilization is necessary. Optimum leaf phosphorus concentration for pomegranate ranges from 0.1 to 0.2%.  If leaf P falls below this range then application of phosphorus is recommended. 

Phosphorus deficiency is not common in pomegranate groves except under soil adverse conditions like on highly acid and calcareous soils. If it does occur, it is more difficult to diagnose than nitrogen (N) deficiency or other nutrient element deficiencies. Growth is reduced when P supply is too low. Phosphorus is highly mobile in plants, so when it is deficient, it may move from old leaves to young leaves and other actively growing areas where energy is needed to form seeds and fruits. Deficiency symptoms appear first on older leaves, with a lustreless bronze discolouration. Some leaves later develop necrotic areas, and young leaves show reduced growth rate. Leaves shed prematurely, and fruit can drop before normal harvesting time. Trees exhibit limited flower development with reduced fruit set and fruit yield. The fruit turns rough in texture with poor aril development. The fruit maturity is delayed because of high acidity in proportion to total soluble solids. Usually, roots are stunted and poorly branched.

a lusterless bronze discolouration of both younger and older leaves and reduced size of younger leaves,	trees with limited flower development and  reduced fruit set and fruit yield. The fruit turns rough in texture with poor aril development

Potassium

Potassium deficiency in pomegranate groves is common as the crop demand for K is high.  Normal vegetative growth of pomegranate can occur under a wide range of K content in the leaves. On the other hand, the leaves should contain a certain level of potassium, if the tree is to provide fruit with high yield and quality. The potassium content of mature pomegranate trees sometimes exceeds  that of nitrogen (N), as K is the most abundant mineral in the fruit. The juice is a strong sink for K, which occurs there mainly in the form of soluble K salts of the organic acids. Therefore, it is essential to apply potassium fertilizers to replace the K removed by the fruit,  to improve fruit quality; and  to maintain soil productivity. Potassium does not usually affect tree growth over a wide range of variation, unless it falls below 0.3% in index leaves. Since yield is positively correlated with tree size (volume) it is essential to have adequate content of K in the tree. The K content in the leaves decreases during the fruiting season and fruit load can enhance this decrease as a result of K mobility towards fruits. Appropriate fertigation can prevent the decrease in K or reduce the negative effect of yield on K content.  Optimum leaf potassium concentrations for pomegranate ranges from 0.6 to 0.8%. If leaf K falls below this range then application of potassium is recommended. 

Unlike other fruit crops, potassium deficiency is not conspicuous in pomegranate. Generally it results in poor fruit retention, reduced fruit size, with scorched leaves.  But under extreme cases of potassium deficiency the leaves dry up  leading to shedding of all fruits and death of the twigs.

poor fruit retention reduced fruit size, with scorched leaves	trees in extreme cases of potassium deficiency with leaves drying leading to shedding of all fruits and death of the twigs.

Calcium:

Calcium deficiency in pomegranate is rare but occurs on acid and highly leached soils  like  in red soils of Deccan plateau.  Symptoms resemble those of boron deficiency.  Leaf lamina shows chlorotic mottles and under severe deficiency these extend from margins spreading downwards and inwards.  Fruits develop blossom end hardening and also fruits develop cracks(Plate 4A,B).  Excess potassium and magnesium application aggravates calcium deficiency in pomegranate.  Optimum leaf calcium concentrations for pomegranate ranges from 0.7 to 1.5%.  If leaf Ca falls below this range then application of calcium is recommended. 

pale yellow older leaves with lateral fruit cracking,		leaves curving inwards with lateral fruit cracking.