A.A. Khara and Pranab Chattopadhyay (firstname.lastname@example.org)
Tree-crop compatibility helps determine a successful agroforestry system. Prior to establishing agroforestry farms, it is important to understand the possible effects of the agronomical, physiological and ecological interactions of the selected trees and alley crops, including their implications on the management practices and the socioeconomic acceptability of the whole system.
Several medicinal and aromatic crops were tried as alley and companion crops to 26 different tree species in the new alluvial plains of West Bengal, India. The trees were planted in July 1990 in five rows, with 20 types of trees in each row. Productivity of the system was assessed based on the different management practices (pruning, pollarding, coppicing, etc.) used on the trees and the alley and companion crops.
Some of the alley crops found to be compatible with the different tree species were as follows:
Ricebean (Vigna unguiculata). This leguminous crop provides good forage, effectively controls weeds, serves as a nitrogen-fixing crop, and improves the organic matter content of the soil. Within three years, the highest average forage yield obtained was 5.85 t/ha from the alleys of Dalbergia sissoo, while the lowest average yield obtained was 3.10 t/ha from the alleys of Acacia auriculiformis. The low yield may be due to the allelopathic effect of the leaf litter of A. auriculiformis.
Lady's finger (Abelmoschus esculentus/Hibiscus esculentus). In three years, the highest average fresh fruit yield of Lady's finger obtained was 5.34 t/ha from the alleys of Dalbergia sissoo. A yield of 5.31 t/ha was obtained from the alleys of Eucalyptus citriodora, while the lowest yield obtained was 3.51 t/ha from the alleys of Acacia auriculiformis. Allelochemicals may be the cause of the reduced yield.
Groundnut (Arachis hypogaea). Within two years, an average pod yield of 0.53 t/ha was obtained from the alleys of Gliricidia sepium. The lowest average pod yield of 0.31 t/ha was obtained from the alleys of Acacia auriculiformis and 0.38 t/ha from the alleys of Albizzia lebbeck. Although all the tree species belonged to the family Leguminosae, the different root and canopy architecture influenced the yield of the groundnut.
Yambean (Pachyrrhizus erosus). The maximum yield of yambean obtained was 20.64 t/ha in open field conditions. In the agroforestry system, 17.26 t/ha were harvested from the alleys of Gmelina arborea and 17.10 t/ha from the alleys of Gliricidia sepium. These yields were significantly higher than those harvested from the alleys of Acacia auriculiformis (14.76 t/ha). Since yambean is a partially shade-tolerant crop, reducing the tree canopies will help increase its production, as soon in the case of the elephant foot yam (Khara et al., 2001).
Ginger (Zingiber officinale). Ginger cv. Garubathan was tried under eight different tree species. The highest mean yield of 14.7 t/ha was recorded from ginger planted in the open fields, while 12.3 t/ha and 12.0 t/ha rhizome yields were recorded from the alleys of poplar and swietenia, respectively. The lowest yield of ginger obtained was 3.30 t/ha and 4.7 t/ha from the alleys of casuarina and dalbergia, respectively. The 48.04% reduced yield of ginger in an agroforestry system may be attributed to reduced photosynthetic active radiation (PAR) being received by the alley crops, and the recorded huge moisture intake of casuarina with sesbania grown in the alleys.
Elephant foot yam (Amorphophallus paeoniifolius). Pollarding increased the corm yield of the Elephant foot yam as compared with the unpollarded but branch-pruned tree species (Khara et al., 2001).
Upland taro (Colocasia esculenta). Among the three improved cultivars, CE6 gave the highest yield of 19.29 t/ha from the alleys of Gmelina arborea. However, in open field conditions, the corm yield obtained was 24.24 t/ha. BCC-1 cultivar fared badly in both the open field conditions and in the agroforestry system, although the differences in yield were not that significant. Corm yield obtained in the alleys and in open field conditions of G. arborea was 16.15 t/ha and 15.72 t/ha, respectively.
Turmeric (Curcuma domestica). Under open field conditions, corm yield was recorded at 25.97 t/ha, while the alleys of Dalbergia sissoo, Swietenia mahogani and Terminalia arjuna obtained yields of 21.36 t/ha, 19.89 t/ha and 18.76 t/ha, respectively (Khara et al. 2001). The biomass of the tree species compensated for the loss of yield in the agroforestry system.
Kaempferia galanga. This is an aromatic and medicinal crop which tolerates partial shading and can be effectively integrated into an agroforestry system. Its finger yield of 13.10 t/ha was obtained from open field conditions in a mono cropping system, but did not differ significantly with the yield obtained from the alleys of Dalbergia sissoo. Significant differences were not observed in finger yields when this crop was harvested from the alleys of Gmelina arborea (6.55 t/ha), Terminalia arjuna (6.86 t/ha) and Delonix regia (7.37 t/ha).
It was also observed that the distance from the tree rows helped increase the yield, except from the alleys of Albizzia lebbeck. The highest finger yield of 11.84 t/ha was obtained when harvested from a distance of 2.5 m, while yields of 10.99 t/ha were obtained from a distance of 2.5 m and 10.16 t/ha was obtained from a distance of 1.5 m from the Populus deltoides rows. The highest average yield of 10.12 t/ha was obtained from the alleys of Swietenia mahogani and 9.64 t/ha from the alleys of Populus deltoides.
Coffee (Coffea canephora). Coffee is in great demand in this part of India. But despite limited supply, efforts are not being made to explore its possible integration into the agroforestry system. Research revealed that coffee under Eucalyptus citriodora and Albizzia lebbeck yielded 3 936 kg/ha per year and 3 509 kg/ha per year, respectively. But Chukrasia tabularis inhibited the growth and fruit-bearing capacity of coffee.
Among the associated crops found to be compatible with the different tree species were the following:
Black pepper (Piper nigrum). The trees in the agroforestry system, which were pruned but not pollarded, were utilized as support for the growth of black pepper. The highest fresh weight of berries was recorded with Gmelina arborea at 2 903.33 g/vine, but the lowest fresh weight was obtained with Albizzia lebbeck at 1 521.67 g/vine. Although black pepper is a leguminous plant, root interference may be the reason for the low fresh weight of berries.
Dioscorea (Dioscorea alata). This is considered a poor man's crop as it has medicinal uses and grows even in very harsh climates. Findings showed that dioscorea with Gliricida sepium recorded a corm yield of 18 t/ha even without irrigation. However, the growth and pruning of G. sepium was hampered due to the prolific growth of the vines. The lowest yield of dioscorea at 7.25 t/ha was obtained from the alleys of Delonix regia. Research also revealed compatibility of dioscorea with Terminalia arjuna and Delonix regia.
Vanilla (Vanilla planifolia). Vanilla is one of the most lucrative aromatic spice crops. Findings showed that vanilla grows well and is productive when integrated with softwood tree species like Albizzia lebbeck. When integrated with Eucalyptus citriodora and Populus deltoides, vanilla's growth and production were found superior than when integrated with Dalbergia sissoo, Casuarina equisetifolia and Gmelina arborea. When vanilla reached the height of the tree, and manual pollination could be carried out, the vines were trained on the bamboo-roof: This enabled vanilla to extract food and water from the tree and grow well even with minimum management. The highest yield of the fresh beans was recorded from the associated trees Eucalyptus citriodora, Populus deltoides and Albizzia lebbeck. These trees not only provide important products, but also facilitate the growth of the alley and companion crops.
Careful selection of trees, alley and companion crops and management practices such as pollarding and coppicing are important considerations to verify tree-crop compatibility for the success of agroforestry systems. Pruning branches and roots, pollarding and coppicing at the appropriate time were found to increase the productivity of the alley crops.
Aggressive vines like black pepper and dioscorea need to be regularly pruned to facilitate tree growth.
Findings showed that the leaf structure of casuarinas allowed effective infiltration of sunlight and provided better PAR to promote the growth of the alley crops, except that of ginger. The fast-growing tree, Chukrasia tabularis, was found to inhibit the growth of coffee as it competed with moisture intake. Pruning of branches before and after the rainy season was found to help provide more PAR to the crops grown in both seasons.
Crops that were found to be suitable in agroforestry systems were tuber crops and vines like Vanilla planifolia, Piper longum, Piper nigrum and Dioscorea alata.
The yield of majority of the crops was found to be lower in the agroforestry system (Khara et al., 2004) than those in the monocropping system in open field conditions. Nevertheless, the income obtained from the trees, the generation of fodder, fuelwood, timber, fruits, medicines, dye and other products in the agroforestry system not only provided diversified products but also increased income. In agroforestry, farmers have the choice of trees and crops that can be combined to obtain optimum yield and maximize benefits in a sustainable manner. (The authors can be contacted at Bidhan Chandra Krishi Viswavidyalaya, W.B., India).
References: Khara, A.; P. Chattopadhyay; B. Bandyopadhyaya; Srikanta Das and H. Sen (2001). Ecofriendly farming in the plains of W. B. - a decade study. Proc. National Symp. On Biodiversity vis-à-vis Research exploitation: an introspection 152 pp; 23-24 April, 2001; Port Blair, India.
Khara, A.; B. Bandyopadhyaya; P. Chattopadhyay; Srikanta Das and Saon Bandyopadhyay (2004). Proc. 1st World Congress on Agroforestry, Orlando, USA. 27 June to 2nd July, 2004.