Outline presentation Discussion on last session PPC – concept and use in Agroforestry Optimal crop combination Tree crop interactions conclude

Production Possibility Curve A production possibility curve is the local of the combinations of forest and agricultural products that can be obtained with a given amount of resources. Such curves are also called iso-cost curves, production transformation curve or production possibility frontier.

Production Possibility Curves (PPC) The product relations in Agro-forestry can be explained with PPCs which also help to determine the optimal combination for profit maximisation in Agro-forestry.

Product relations in Agro- forestry Three types of relationships in Agro- forestry explain the trees and agriculture crop intercropping as follows: Complementary Supplementary Competitive

Complementary 1. Complementary is a synergistic or symbiotic type of relationship between the two crops and intercropping results in increased production for both of the crops. e.g., wind break/ shelter belt – synergistic e.g., bee keeping (apiculture) in horticulture farm, Cardamom - Alnus nepalensis.

Supplementary 2. Supplementary is a type of relationship where the intercropping results into increased of production for one crop while the production of another crop remains unchanged. For example if agriculture and tree crops are intercropped, production of agriculture crop increases while the tree crops remains unchanged or vice versa. Taungya gives good example of supplementary relationship.

Competitive 3. Competitive is the relationship where the production of agriculture crop decreases with increased tree crops e.g.,Tea with Albezzia yielded less than with other shade trees (Willey, 1975).

Production Possibility Curves

Optimal crop production Yield of tree crop Yield of agriculture crop YaYa YtYt

Optimal crop production The optimal crop combination from financial point of view depends on production relationship and price ratio of forest products to agricultural crops. The combination is the point where PPC is tangent to the price line. If the price ratio changes the optimal combination also changes. PPC convex to origin results in either agriculture or forestry. A PPC concave to origin is favourable for agroforestry. Specialisation might occur if price line is either steep or flat, and in such cases agroforestry is only practiced if strong complementary or supplementary relations exist.

Tree crop interactions Agroforestry systems PositiveNegative 1. Perennial crop with trees ComplementaryCompetitive- water/nutrients/shade 2. Trees intercropped - agriculture crops ComplementaryCompetitive- water/nutrients/shade 3. Alley plantingComplementaryCompetitive- water/nutrients/shade 4. Contour plantingIncreased production through soil protection and organic matter contribution. Competitive - water/nutrients/shade

5. Wind break Increased production through protection from winds crop production helps to cover cost of plantation establishment. Competitive- space/water/nutrients. 6. Taungya Crop production helps to cover cost of plantation establishment. Shade and competition eliminate crop production in 3-4 years. 7. Woodlot Isolate trees from crops, avoiding potential negative tree-crop interaction Competition for crop production area, poor matching of species to site and poor management can increase soil erosion

Tree-crop interaction continued 8. Home garden Generally does not compete for crop production area. There is no tree-crop interface, little interaction. Source: Current et al., 1995.

Optimum crop production depend both on production relationship and price ratio of forest crop to the agriculture crop. Optimum crop production is the point in PPC that is tangent to the price line. In the optimum point the value of marginal product also called the marginal value product of the resource in forestry is equal to that of the agriculture.

PPC concave to the origin will promote agro-forestry if both crops have value but PPC convex to the origin promotes specialisation or monoculture. But even if PPC is concave specialisation or monoculture will prevail if the price line is very steep or flat. Hence if the price line changes, optimal combination of tree and agriculture crops also changes

Agro-forestry tools Land Equivalent Ratio (LER) m LER = Σ yi/yii (a) i=1 yi – yield from the intercropped area yii- yield from sole cropping. In formula (a) If LER >or <1, then the yield in intercropping exceeds or is smaller than that of the sole cropping, rejecting or accepting intercropping.

However LER has weakness due to localised measures of biological productivity. It is because the effects of total plant density and the density of one plant on the other are compounded (Trenbath, 1976 as cited by Ranganathan et al., 1991). In order to overcome the weakness of LER, Ranganathan (1991) proposed Yield Advantage Index (YAI).

Thought of the day Leuceana is planted on field boundaries and seldom interspersed with field crops. (Leuceana with sorghum/pigeon pea – hedgerow intercropping is economically inferior than sole planting (ICRISAT experiments) gives convex curve. The finding was in consistence with intercropping practices in that region)

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