Introduction

Compatibility means the ability of a plant or crop or animal to exist or to be used together without causing any problems to other component. For making agroforestry system more compatible, we have to select best trees and agriculture crops, and or animals.

Generally, trees grow in close proximity to crops and pastures, which compete for 1) space, 2) light, 3) water and 4) nutrients. Many farmers view shade as a challenging situation for growing plants. Tree shade can be divided into three categories that are light, medium and full shade, which are described below:

Light shade may be described as an area that is partially shaded. It may be shaded for only few hours each day. The sun’s rays may be blocked by tree canopy for several hours at midday or early in the morning etc, but the area is sunny the rest of the day.

Partial or medium shade is present when direct sun rays are blocked from an area for most of the day. Many established landscapes have large areas of partial shade, where sections of the yard are shaded by mature trees for much of the day but receive some direct sun early or late in the day. Bright, north-facing exposures may also be classified as medium shade.

Tea, coffee and cardamom are light to medium shade tolerant crops. In eastern Nepal, cardamom is planted as an under storey with Uttis (Alnus nepalensis) trees. Similarly, Siris (Albezia spp) and Sissoo (Dalbergia sisssoo) trees are planted for providing shade to tea, and Ipil Ipil (Leucaena leucocephala) is the best trees for providing shade to coffee plants. Medicinal plants such as Chiraito (Swertia chirayita) can also be grown successfully under light to medium tree shades.

Full shade– little or no direct sunlight reaches the ground at any time of the day. Dense shade refers to full shade under thick tree canopies or in dense groves of trees.

Some forage (Desmodium- Desmodium intortum and forage peanut – Arachis pinotoi and horticulture crops such as ginger (Zingiber officinale), turmeric (curcuma longa), yam (Dioscorea spp) etc can be grown well under full to medium shade.

Plants growing in the shade must compete with shading trees for space, light, nutrients and water, and tolerate poor air circulation, and therefore, interactions between trees and crops occur both above and below the ground, which will have both beneficial and harmful effects to understory crops.

The beneficial effects are:

• Trees and shrubs grown in agroforestry system help to secure and renew the soil.
• Trees cover and protect under storey crops and soils, and animals from extreme heat and cold, and then slow down the natural forces of soil erosion like wind, water and gravity. They can also control runoff and thereby reducing losses of water, soil material, organic matter and nutrients, and increase infiltration of rain water into the soil.
• Fallen leaves, wooden debris, twigs, flowers and fruit etc help to add organic matter and humus into the soil, which increases microbial activities in the soil that helps to improve productivity of soil and production of under storey crops.
• Legume trees and crops help to improve soil fertility fixing atmospheric nitrogen into the soil or roots that helps to increase production of under storey crops.
  • Subedi et al. (2001) give the following values for the nitrogen fixation capacity of legume fodder and forage species which is 900 kg/ha/year for Desmodium, 40-70 kg/ha/year for Stylo, 52-77 kg/ha/year for White clover, 60-168 kg/ha/year for centro and 63-342 kg/ha/year for Ipil Ipil.

• Trees help to soil nutrient recycling.
  1. Nutrient recycling from the soil is a common agroforestry hypothesis.
  2. Deep-rooting trees can absorb leached nitrate and other nutrients from the subsoil.
  3. This depends on trees and crop species, climate and soil conditions.
  4. Deep nutrient capture by trees increases total nutrient availability in the system.
  5. Fallen leaves, twigs, flowers and fruit, and crop residues etc help to add organic matter and humus into the soil, which also increase microbial activities in the soil.
  6. Soil microorganisms are decomposers that break down organic matter into humus and plant available nutrients and cycle nutrients back to plants, starting the cycle over again.
• There is symbiotic relationship between trees, crops and microorganisms in an agroforestry system.

Symbiosis (from Ancient Greek syn “with” and biosis “living”) is close and often long-term interactions between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens. In 1879, the German mycologist Heinrich Anton de Bary defined it as “the living together of unlike organisms. In agroforestry system, exchange of nutrients among the plants occurs from the activity of appropriate micro-organisms.

Rhizobium (legume species) and frankia (uttis-Alnus nepalensis) have potential roles for nitrogen fixation, plant growth regulation, phosphate solubilization and concerned with nutrient transformation of decaying plant materials.

The most common-and possibly the most important-mutualistic, symbiotic relationship in the plant kingdom is known as mycorrhiza.

1. The word mycorrhiza is derived from the Greek words mykes, meaning “fungus,” and rhiza, meaning “root.”
2. Mycorrhiza is a specialized, symbiotic association between the roots of plants and fungi that occurs in the vast majority of plants-both wild and cultivated.
3. In a mycorrhizal relationship, the fungi assist their host plants by increasing the plants’ ability to capture water and essential elements such as phosphorus, zinc, manganese, and copper from the soil, and transfer them into the plant’s roots.
4. The fungi also provide protection against attack by pathogens and nematodes.
5. In return for these benefits, the fungal partner receives carbohydrates, amino acids, and vitamins essential for its growth directly from the host plant.
6. It has been estimated that mycorrhizal fungi amount to 15 percent of the total weight of the world’s plant roots.

• Trees and shrubs, and crops residues provide feed to animals and animals add organic matter (manure) into the soil. Similarly, animals also help to disperse seeds of different species.
• In the maintenance of soil fertility under agroforestry, the role of roots of trees and crops is at least as important as that of above-ground biomass.
• Animals also assist in reducing fire hazard when they are allowed in grazing. The grasses are grazed and leaf litter mixed with soils, which helps to protect grass land from fire.
• Organic matter added by trees and shrubs, crops and animals help to increase water holding capacity of soil.
• Trees can check the development of soil toxicities, or reduce existing toxicities – both soil acidification and salinization can be checked, and trees can be employed in the reclamation of polluted soils.
• Trees can moderate microclimates. Shelter given by trees improves yields of nearby crops and livestock. Shade in summer can be beneficial for livestock, reducing stress.
• Finally, trees and shrubs grown in agroforestry systems also improve the soil productivity, and production.