Nutritional management

• Recommended dose for Nepal: FYM = 6 ton/ha

NPK 60:40:20 kg/ha Sulphur 20 kg/ha Zinc 20-25 kg/ha Boron 2-5 kg/ha

Nutrient to be supplied before the grand growth period (45-60 days).

100 kg seed cotton  produced depletes the soil by 6-7 kg N, 1.9-2.5 kg K and 1.2-2.0 kg S.

Water logged condition increases denitrification.

1.1 Nitrogen:

• Nitrogen is most common, high demanded, good responsive and kingpin fertilizer nutrient to crops in early growing period .
• It is essential for plant establishment, vegetative growth, improving fruiting quality and seed cotton yield.
• Nitrogen helps to increase plant height, no. of fruiting nodes, boll load(no. of boll /plant), LAI, Dry matter yield, cotton yield and seed index.

Deficiency symptoms: N deficiency symptoms first appear on the older leaves at the bottom of the plant. N is a mobile element and is rapidly translocated to the young developing parts.

❖ Early season deficiency results in plants with pale green yellowish leaves and stunted growth.

❖Late season deficiency leads to reduced boll retention.

Management

• It is most often the major limiting factor to cotton production, after water.
• Both the excess and deficit conditions  are  harmful to the plants.

• Excess amount of nitrogen causes in more of vegetative growth and delay maturity, more susceptible to infestation by sucking pests, weakening of fiber and thereby affects quality.
• For varieties, 50-60 kg N/ha is adequate and 90-120 kg N/ha is recommended for hybrids.

Various management options are available to enhance the NUE which are listed below.

• Use of coated urea fertilizers and nitrification inhibitors
• Split application.
• Spot or band placement

1.2 Phosphorous (p)

• The form of uptake is largely governed by PH. Most of the cotton is grown on high pH soils and the form preferred for its uptake is HPO42-.
• The most important role of P is in energy transfer(as ATP).
• Cotton has low P requirement but has a definite role in improving root development, water use efficiency, seed production, protein and oil content of seed.
• It assists to increase boll wt. , no. of seeds per boll and percent of matured boll at first picking.

Deficiency symptoms: P is mobile in the plants and the deficiency symptoms are reflected in the lower leaves of the plant.

• Plants are stunted , have dark green leaves and accumulation of anthocyanins, imparts the leaf a purplish colour.
• It also causes delayed flowering and fruiting and shedding of boll.

Management:

• Next to nitrogen, P is considered to be the most limiting nutrient. Response to P has been inconsistent.
• Most of the P requirement of crop is met through DAP (diammonium phosphate) and use of complex fertilizers. In the vertisols, calcium is the dominant cation and the soils are mostly calcareous.
• The added P is rapidly transformed to calcium phosphates (CaHPO4, Ca3(PO4)2 etc.) of low water solubility. This is the main reason which necessitates annual P application inspite of positive balance in the soil.

For efficient P fertilizer use the following points need to be followed:

• Placement of P fertilizers is a superior method due to less P fixation
• 40 kg P2O5 ha-1 is adequate (Pundarikakshudu, 1981)
• Need for P is high where more N is applied
• In calcareous soils, yearly application is needed.

1.3 Potassium (K)

• Potassium remains in an ionic form in the plant cells and tissues and plays an important role in osmoregulation. K plays an important role in fibre development and the turgor driven expansion of fibre cells ultimately determines the fibre length .
• Equally important is its role in enzyme activation. There are more than 50 enzymes which either completely depend on or stimulated by K+.

Deficiency Symptoms: K is a mobile element in the plant and deficiency symptoms appear on the lower leaves.

• Deficiency of K causes pale-yellowish green leaf, brown necrotic spot and reddish brown, dry and fall off.
• The pre mature senescence of the leaves prevents normal development and maturation of the bolls, reduces fiber quality and stem becomes weak and lodges easily.