Introductory Agroforestry (1+1)

DESIRABLE CHARACTERISTICS FOR AGROFORESTRY

While selecting tree species for agroforestry systems, the following desirable characteristics should be taken into consideration. Though all desirable characters are not found in a single species, but their multiple uses are taken care of.

• Tree species selected should not interfere with soil moisture
• Tree species selected for agroforestry should have very less water requirement
• Should not compete with main agricultural crops for water.
• Tree species should be deep tap rooted so that they can draw water from deep strata of the soil.
• Tree species should not compete for plant nutrients
• Tree species should not utilize more plant nutrients
• They should help in building soil fertility,
• Leguminous tree species which fix atmospheric nitrogen in their roots should be prfer.
• The root system and root growth characteristics should ideally result in to exploration of soil layers that are different to those being trapped by agricultural crops.
• Tree species should not compete for sunlight
• Tree species should not interrupt sunlight falling on the crops.
• Tree species should be light branching in their habit.
• Trees permit the penetration of light into the ground and promote better crop, pasture growth and yield.
• Tree species can withstand pruning operation if it posses dense canopy.
• Tree species should have high survival rate and easy establishment
• Trees species should have high survival percentage,
• Leave little or no gaps after transplanting.
• Hardy tree species are easy to establish.
• They have less mortality percentage because they can tolerate transplanting shocks easily.
• Trees should have the ability to regenerate lateral roots within a short period of time after transplanting.
• Tree species should have fast growing habit and easy management
• Tree species for agroforestry system should be essentially fast growing,
• Rapid growth, especially in the early years,
• Tree should have short rotation (the period between planting and final harvesting)
• Fast growing species such as Poplar, Casuriana, Leucaena leucocephala etc. are important species which provide lot of opportunities to be planted in AFS
• Tree species should have wider adaptability
• A tree species selected for agroforestry combinations must have a wider adaptability.
• Tree species should have high palatability as a fodder
• Most of the Indian farmers rear livestock separately and cut and carry method of fodder production is quite prevalent.
• Therefore, in agroforestry, farmer must select those tree species which are palatable to livestock and had a high digestibility.
• Tree species should have shelter conferring and soil stabilization attributes
• Some tree species, because of their inherent growth habit and adaptability, are especially helpful in providing protection for soils, crops and livestock. Poplars (Populus spp.), Willows (Salix spp.), Casurina equisetifolia, etc. for example, have been extensively used in soil erosion control because of their extensive root system and ability to grow in water-logged soils.
• Tree species should have capability to withstand management practices
• Many agroforestry systems demand extensive pruning and lopping of the trees in order to maximize production. In such cases, the trees must be able to withstand such treatment without drastically restricting growth rate.
• Tree species should have nutrient cycling and nitrogen fixation attributes
• Within an agroforestry system, trees can play an important role in recycling nutrients, leached down through the soil profile and minerals released from weathering parent material such as rocks and sediments.
• These nutrients are used in the growth and development of the tree, many returning to the top-soil in form of dead leaves, twigs, flowers and seeds which slowly decompose on the surface, or are eaten by animals.
• Although all trees play some role in maintaining the nutrient status of the soil through recycling.
• Deciduous trees drop most of their leaves in autumn leaving a thick mat of leaves on the ground, whereas most evergreen species maintain some level of litter fall throughout the year.
• Another important factor is the ability of many tree species to convert atmospheric nitrogen into organic nitrogen for their own use through complex symbiotic relationship between Rhizobium bacteria and their fine roots.
• The bacteria form nodules on the roots which can convert nitrogen gas, as it is in the atmosphere, into usable nitrogen for the plant.
• Most leguminous trees and some non-leguminous ones, such as Acacia, Leucaena and Prosopis as well as Casuarina spp. fix the atmospheric nitrogen.
• The litter of these nitrogen fixing trees is generally high in nitrogen, thus increasing the nitrogen status of the soil.

The following are a few tree species which help in fixing atmospheric nitrogen through their roots:

Table 8.1 Nitrogen fixing tree species

1.	Acacia albida	21.	Bauhinia variegata
2.	Acacia auriculiformis	22.	Butea monosperma
3.	Acacia catechu	23.	Cassia fistula
4.	Acacia aneura	24.	Cassia siamea
5.	Acacia dealbata	25.	Casuarina equisetifolia
6.	Acacia decurrens	26.	Dalbergia latifolia
7.	Acacia farnesiana	27.	Dalbergia sissoo
8.	Acacia implexa	28.	Delonix regia
9.	Acacia leucophloea	29.	Gliricidia sepium
10.	Acacia mearnsii	30.	Hardwickia binata
11.	Acacia melanoxylon	31.	Leucaena leucocephala
12.	Acacia mollissima	32.	Moringa oleifera
13.	Acacia nilotica	33.	Oogeinia oojeinensis
14.	Acacia planifrons	34.	Parkinsonia aculeata
15.	Acacia senegal	35.	Peltophorum ferrugineum
16.	Albizia chinensis	36.	Pithecellobium dulce
17.	Albizia lebbek	37.	Prosopis alba
18.	Albizia procera	38.	Prosopis chilensis
19.	Alnus nepalensis	39.	Prosopis cineraria
20.	Alnus nitida	40.	Robinia pseudoacacia
41.	Samanea saman	44.	Sesbania bispinosa
42.	Saraca indica	45.	Sesbania grandiflora
43.	Sesbania aegyptica	46.	Tamarindus indica

• Tree species should have thin bark
• Species selected for agroforestry combinations should not shed its bark regularly but it should retain for longer period as bark shedding creates unhygienic conditions for under-ground crop.
• Tree species should be free from chemical exudations
• The species selected for agroforestry combination must be free from allelo-chemicals as these allelo-chemicals affect the growth of under-ground crops.
• Tree species should have easily decomposable leaves
• The suitable tree species for agroforestry will be that one in which fallen leaves decompose with fast rate.
• The leaves of most of the legume tree species are small in size, decompose quickly and easily, and add a large quantity of organic matter and nutrients to the soil.
• Tree species having broad leaves such as teak, mango and banyan should not be preferred for agroforestry system.
• They contain more fibre matter and also require longer time for decomposition. Further, broad leaves when fall on the tender crop plants, block their photosynthetic activities.
• Tree species should have their multiple uses
• The selected tree species should have multiple uses.
• The tree should yield more than one of the main produce like fuelwood, leaf fodder, edible fruit, edible flower and fibre.
• Tree species should have high yield potential
• High yield potential is the most important criterion of selection of tree species for agroforestry systems as the main aim is to obtain overall more output per unit area. Care should be taken before collection of seeds and seedlings that they are being procured from reliable source.

CHARACTERISTICS OF AGRICULTURAL CROPS FOR AGROFORESTRY

a) Agricultural crops should be short duration and quick growing.
b) They should be at least partially tolerant to shade.
c) Most of them should belong to Leguminosae family.
d) They should respond well to high density tree planting.
e) They should bear some adverse conditions, like water stress and/or excess of watering;
f) Crops should return adequate organic matter to soil through their fallen leaves, root system, stumps, etc.
g) Crops should appropriately be fitted in intensive or multiple cropping system.