Constraints in agroforestry
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1. Trees grown together with agricultural crops can decrease crop yields through competition for resources like light, moisture, and nutrients. The tree canopy absorbs most light and tree roots uptake water and nutrients from the topsoil where crop roots also grow. 2. Trees may also act as alternate hosts for pests of agricultural crops, allowing pests to survive between crop harvests. Additionally, trees can attract birds whose damage impacts crop yields. 3. Allelopathic effects of some tree species like eucalyptus may also negatively impact neighboring food crops through the release of chemical inhibitors from tree leaves and litter. This document discusses several constraints that can arise in agroforestry systems from interference between tree and crop components.
Constraints in agroforestry
- 3. CONSTRAINTS Limitations or restrictions in agro forestry systems.
- 4. CONSTRAINTS IN AGROFORESTRY 1. Interference of trees decreases the crop yield. 2. Competition for light -tree canopy absorbs maximum light 3. Competition for moisture- trees with lateral roots (Eucalyptus) & higher water requirement (bamboo) 4. Competition for nutrient – trees with finer roots in top soil. 5. Tree harvest operations – causes damage to arable crops 6. Trees - as alternate host for pests to food crops
- 5. 7. Agroforestry system need more labour inputs, which may cause scarcity at times in other farm activities 8. Longer period required for trees to grow to maturity. Therefore, delay in returns occurs due to longer gestation period for trees 9. Resistance by farmers to displace food crops with trees especially where land is scarce 10. Trees attract the birds – increased damage to food crops. 11. Allelopathic effect by trees (eucalyptus) on food crops
- 6. 1. Interference of trees decreases the crop yield When the trees are grown together with agricultural crops either as intercrop or on bunds, their adverse effects are visible on the agricultural crops. The adverse effects on the growth and yield of agricultural crops are due to the competition for light, moisture and nutrients. The nature and quantum of these adverse effects depend upon I) the age and size of the trees, ii) nature of the tree species iii) nature of the agricultural crops ,iv) availability of water, nutrients , light, etc.
- 7. 2. Competition for Light Many tree crops are inefficient in interception of radient energy in their early years since full canopy formation in trees may take many years. But, when canopy formation takes place, they will absorb more radiant energy. Reduction in crop yield at later stage of tree growth under agro forestry systems has been reported. The shade effect caused by full canopy of a 13 year old untopped Acacia tortilis was considerable. Compared to open field, the total and net radiation beneath the tree canopy were only 24% and 16% respectively. Under limitation of light, there is an inevitable depression in the intersown crop yields. Establishment and growth of Cenchrus ciliaris was poor under 13 year old unlopped Acacia tortilis plantation.
- 8. 3. Competition for moisture The predominant occurrence of lateral roots in the top 30cm soil has been reported in Eucalyptus and it extracted moisture mostly from the upper soil layer. Thus trees do compete with arables in the top 30cm soil profile. In intercropping experiment, depletion of soil moisture was considerable in bamboo.
- 9. 4. Competition for nutrients A higher concentration of the fine tree roots in the soil layer upto 50cm suggests that trees also obtain most of the nutrient requirements from the soil layer upto 50cm. The main function of the roots reaching greater depths appears to be water uptake, particularly during periods of water stress. The proportional abundance of fine roots of agricultural crops, grasses and trees suggests that there is a keen competition for nutrients between the crops and trees when grown in mixture. Some trees are said to be great transpire of moisture particularly Eucalyptus.
- 10. 5. Trees as a alternate hosts to Agricultural crops Some trees act as alternate hosts for insect pests. For instance, the jowar hopper migrates to neem tree after harvest of crop and returns to the crop after completing its life cycle on the woody perennial.
- 11. 6. Damage due to Birds It is generally believed that planting of trees in the farm will attract the birds and thereby enhance the risk of damage for agricultural crops.
- 12. 7. Allelopathy Allelopathy, the direct or indirect effect of one plant upon another through the production of chemical inhibitors that are released in to the environment, should also be recognized as another factor in analyzing mechanisms of plant interactions. Most of the chemical substances involved in allelopathic reactions are secondary compounds. Though the toxic metabolites are distributed in other plant parts also, leaves are the potent source of allelochemicals. Summer materials are more toxic than those of rainy and winter season. Toxins released from plant litter are the primary causes of allelopathy.
- 15. REFERENCES ALDRICH, J.D., 1984. Weed-crop ecology: Principles and practices. Breton Publishers. 215-241 BELL, D.T. & KOEPPE, D.E., 1972. Non-competitive effects of giant foxtail on the growth of corn. Agronomy Journal 64, 321-325. Stamp, Nancy (March 2003), "Out of the quagmire of plant defense hypotheses", The Quarterly Review of Biology 78 (1): 2355, doi:10.1086/367580, PMID12661508. Fraenkel, Gottfried S. (May 1959), "The raison d'Etre of secondary plant substances", Science129 (3361): 1466–1470, doi:10.1126/science.129.3361.1466 PMID 13658975 AGROFORESTRY – PRINCIPLES & PRACTICES – A.P.DWIVEDI www.agroforestry.net