Silvicultural Requirement

A. niloticais essentially a tree of semi-arid and arid areas restricted below 450 m elevation. It is generally found in plains, ravines and undulating ground. The frost and droughts are common in its zone of occurrence. The annual rainfall in its natural habitat varies from 200 to 1270 mm. It thrives best in areas with annual rainfall of about 500 to 1250 mm. It does not grow in areas receiving higher than 1500 mm annual rainfall except on gravelly porous soils. It does not withstand severe frost, hence it is completely absent above 3000 m altitude (Luna, 1996). It grows well in two types of soil: riverine alluvial and black cotton. It will not grow in hard soils which obstruct the penetration of roots, but can grow on saline and alkaline soils. Babul can grow in areas having a pH< 7.9 under poor drainage conditions. it is usually from April to June in northern India and earlier in southern India. The trees begin to flower early from the age of three years and thereafter seed every year. The pods attain full size by February- March and ripen in May-June.

Nursery Techniques

By Seed –   A. nilotica seeds collected from natural fruit fall, from standing trees or from felled trees. About 5-7-year-old trees start producing seed. Seeds are black-brown, smooth, compressed, 7-8 mm in diameter with a hard seed coat. Seed weight may vary from 5500 to 11,600 seeds/kg. If seeds are to be stored for a long time, they need to be completely air dried and kept in air tight containers. The seed coat of babul is very hard and impermeable. It requires pre-treatment to hasten germination by one of the following four methods:

• Immersion in cold water for 48 hours
• Immersion in hot water (80⁰C) for 30 minutes. Seeds are then soaked in ordinary water for 24 hours prior to sowing.
• Soaking in sulphuric acid (90%) for 10 to 30 minutes. Seeds after soaking in sulphuric acid are washed and dried prior to sowing.
• Seeds collected from goat/sheep pens do not need any further treatment and can be sown immediately after collection. This is probably the most convenient method. Animals may be fed with A. nilotica pods for this purpose.

Out of the above treatments the hot water treatment is safe, quick and effective and thus recommended. The treated seeds are sown in nursery beds either by broadcast or dibbling method. However, the dibbling, method is preferred. A nilotica is generally raised in polythene bags. Two or three treated seeds are sown in each bag, about 1.5 cm deep during February-March, i.e. about 5 months before transplanting in the field. The soil mixture used in polythene bags consists of soil and compost in 2:1 ratio. Germination commences one to three weeks after sowing and mostly completes in a month. The germination of the seed is epigeal. The radicle emerges and descends.
By Vegetative- Vegetative propagation of A. nilotica is successful under mist chamber conditions. Success is reported in case of rooting of stem cuttings treated with indole acetic acid and indole butyric acid. Air layering has also been tried successfully. Tissue culture propagation of A. nilotica has been successful with callus formation only.

Planting Techniques

• Direct sowing is the easiest and most common method for raising babul plantation in the field.
• Several methods have given satisfactory results. The successful ones are by broadcast sowing (seed rate 2.5- 3 kg/ha), dibbling in lines, patches or mound sowing during June (seed rate 1 kg/ha).
• The seedlings are generally planted in 30 cm x 30 cm x 30 cm pits.
• The most common spacing adopted for plantation is 4 m x 4 m.
• Mound planting is practiced where there is a risk of waterlogging specially on dug up road sides.
• For proper growth and survival it is necessary to give one or two watering after planting.
• Higher survival rate and better rate of growth is reported when soil and water conservation measures are also adopted.

Tending Operation

Weeding-In areas where growth of grasses and understorey vegetation is dense, it is almost impossible to raise babul without proper weeding. In the first year of plantation, three weedings are usually necessary.

Mulching- When babul is grown in dry areas mulching is generally recommended in the first year. Mulching needs to be carried out during November-December for optimum results.

Thinning- When babul is planted in close spacing, cleanings and thinnings become necessary.

Tending- Tending operations must be carried out for the first five years for the seedlings to develop into a vigorous and healthy crop.

Suitable Agroforestry Models

1. A. nilotica + rice is a traditional agroforestry system in central India. The farms have an average of 20 babul trees per hectare in upland rice fields, while the tree-stand density being greater on smaller than on larger farms (>8 ha). Over a 10-year rotation period, the trees provide a variety of products such as fuelwood (30 kg/tree), brushwood for fencing (4 kg/tree), small timber for farm implements and furniture (0.2 cu m), and non-timber products such as gum and seeds. The babul + rice system was estimated to have a benefit/cost (B/C) ratio of 1.47 and an internal rate of return (IRR) of 33% at 12% annual discount rate during a 10-year period, though at a low level of income. Babul trees account for nearly 10% of the annual farm income of smallholder farmers (<2 ha) (Viswanath et al. 2000).