CAPÍTULO V Los Resultados
5.6. Comprobación de Hipótesis
5.6.1 Comprobación de Hipótesis Específicas
As mentioned earlier in the introductions to case studies, CHI has been introduced in Sri Lanka to cropping systems where considerable soil erosion and loss of fertility have already taken place. It is an imperative need that crop production is sustained in these lands. In the case of tea plantations, sustainable tea production is vital to the entire economy and a considerable fraction of the population that is dependent on the tea industry. In the case of lands where seasonal annual crops are grown, a large number of subsistence farmer families depend on sustained crop production for their livelihood. A synopsis of results of all three case studies show that CHI as a means of ensuring sustainable crop production in these lands presents the growers with a ‘‘double-edged sword.’’
0
0 2 4 6 8 10 12 14 16
200 400 600 800 1000 1200 1400
Row number Pod yield (gm−2)
Tithonia Control Gliricidia Vetiveria
FIGURE 7.22 Variation of cowpea yield across transects between contour hedgerows of different tree and grass species under mulched conditions in the subhumid zone of Sri Lanka. Row numbers start from the upslope side.
TABLE 7.25
Biomass of Prunings Produced during an 80 Day Cropping Season by Contour Hedgerows of Different Tree and Grass Species in the Subhumid Zone of Sri Lanka
Fresh Weight (Mg ha1) Dry Weight (Mg ha1)
Gliricidia sepium 27.92 7.05
Tithonia diversifolia 68.79 20.12
Vetiveria zizanioides 6.97 2.59
LSD0.05 2.43 1.1
CV (%) 11.60 7.66
A Case Study on the Potential of Contour Hedgerow Intercropping 151
If used improperly (e.g., too closely spaced hedgerows, export of hedgerow prunings from the system without using it as mulch, too infrequent pruning of hedgerows, etc.), it could result in accelerated decreases of crop yields because of excessive resource competition. On the other hand, if properly practiced, CHI has demonstrated, in these case studies, its capability of regenerating soil fertility on a longer time scale and sustaining crop yields in these highly fragile and degraded lands.
Results of these studies leaves us in no doubt that almost all species used in contour hedgerows, whether tree, shrub, or grass, compete with the crop for essential growth resources. However, results also show that it is possible to select species with lower resource competition. They also demon-strate that it is possible to maximize the positive effects of contour hedgerows to an extent that the negative effects of competition are outweighed. First, properly established and maintained contour hedgerows reduce soil erosion and surface runoff significantly and thereby slow down the whole process that leads tofinal land degradation. Second, by adding hedgerow prunings as mulch, the processes of regenerating soil fertility are set in motion. Evidence that this rebuilding process has started was shown in the present studies, with observations of reduced soil BD, increased SOM and CEC, and increased nutrient recycling. However, it should be realized that regeneration of soil fertility, which has been lost over a period of several decades, through CHI is a very slow process.
During these intervening years, the system has to be managed with patience and adequate care with proper maintenance of hedgerows,filling of any gaps that occur due to tree death, application of hedgerow prunings as mulch to the crop, and minimum disturbance of soil during crop establish-ment. During this period of rebuilding soil fertility, yield reductions due to competition could be minimized by practices such as trenching and judicious application of inorganic fertilizer. As shown in the case of tea, cost of fertilizer can be reduced by taking into account the nutrients provided by hedgerow prunings.
These studies also demonstrated the possibility that grass hedges could exert less competition than tree or shrub hedges and thereby provide higher yields in the associated crop. However, the capacity of grass hedges for long-term regeneration of soil fertility have to be studied before deciding whether to replace tree hedges with grass hedges. Perhaps, grass hedges could be recommended for lands that are only slightly degraded or have been rehabilitated for a considerable period with tree hedges.
In addition to the agronomic aspects, socio-economic aspects of CHI have to be given due attention to ensure its continued adoption by farmers in these fragile ecosystems. Demonstration plots, extension, and training programs coupled with moderate incentive packages and close monitoring of progress during the period of regenerating soil fertility are of crucial importance in this regard.
ACKNOWLEDGMENTS
Research data presented in this chapter are from projects funded by the International Foundation of Science, Sweden (Case Studies 2 and 3) and the National Science Foundation, Sri Lanka (Case Study 1).
REFERENCES
Agus, F., D.K. Cassel and D.P. Garrity. 1997. Soil-water and soil physical properties under contour hedgerow systems on sloping oxisols. Soil and Tillage Research 40:185–199.
Anonymous. 1975. Soil Taxonomy: A Basic System of Soil Classification. Washington, DC: United States Department of Agriculture.
Anonymous. 1990. Crop Recommendations Technoguide. Peradeniya, Sri Lanka: Department of Agriculture.
Bene, J.G., H.W. Beall and A. Côté. 1977. Trees, Food and People—Land Management in the Tropics. Ottawa:
IDRC.
Cannell, M.G.R., M. van Noordwijk and C.K. Ong. 1996. The central agroforestry hypothesis: the trees must acquire resources that the crop would not otherwise acquire. Agroforestry Systems 34:27–31.
152 Ecological Basis of Agroforestry
Corlett, J.E., C.R. Black, C.K. Ong and J.L. Monteith. 1992. Above- and below-ground interactions in a Leucaena=millet alley cropping system. II. Light interception and dry matter production. Agricultural and Forest Meteorology 60:73–91.
Craswell, E.T., A. Sajjapongse, D.B.J. Howlett and A.J. Dowling. 1997. Agroforestry in the management of sloping lands in Asia and the Pacific. Agroforestry Systems 38:121–137.
Dassanayake, A.R. and L.S.K. Hettiarachchi. 1999. Soils of the Up Country wet zone. In Soils of the Wet Zone of Sri Lanka: Morphology, Characterization and Classification, ed. R.B. Mapa, S. Somasiri and S. Nagarajah, 122–137. Peradeniya, Sri Lanka: Soil Science Society of Sri Lanka.
De Costa, W.A.J.M. and A.G. Chandrapala. 2000. Environmental interactions between different tree species and mung bean (Vigna radiata (L.) Wilczek) in hedgerow intercropping systems in Sri Lanka. Journal of Agronomy and Crop Science 184:145–152.
De Costa, W.A.J.M. and A.M.L.K. Atapattu. 2001. Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka. Agroforestry Systems 51:201–211.
De Costa, W.A.J.M. and P. Surenthran. 2005. Tree–crop interactions in hedgerow intercropping with different tree species and tea in Sri Lanka: 1. Production and resource competition. Agroforestry Systems 63:199–209.
De Costa, W.A.J.M., P. Surenthran and K.B. Attanayake. 2005. Tree–crop interactions in hedgerow intercrop-ping with different tree species and tea in Sri Lanka: 2. Soil and plant nutrients. Agroforestry Systems 63:211–218.
Eswaran, H., S.M. Virmani and L.D. Spivey Jr. 1993. Sustainable agriculture in developing countries:
constraints, challenges and choices. In Technologies for Sustainable Agriculture in the Tropics, ed.
J. Ragland and R. Lal, 7–24. ASA Special Publication 56. Madison, WI: American Society of Agronomy.
Fernandes, E.C.M., C.B. Davey and L.A. Nelson. 1993. Alley cropping on an acid soil in the upper Amazon:
Mulch, fertilizer and hedgerow root pruning effects. In Technologies for Sustainable Agriculture in the Tropics, ed. J. Ragland and R. Lal, 77–96. ASA Special Publication 56. Madison, WI: American Society of Agronomy.
Garrity, D.P. 1996. Tree–soil–crop interactions on slopes. In Tree–Crop Interactions: A Physiological Approach, ed. C.K. Ong and P. Huxley, 299–318. Wallingford, UK: CAB International.
Gillespie, A.R., D.M. Knudson and F. Geilfus. 1993. The structure of four homegardens in the Peten, Guatemala. Agroforestry Systems 24:157–170.
Govindarajan, M., M.R. Rao, M.N. Mathuva and P.K.R. Nair. 1996. Soil-water and root dynamics under hedgerow intercropping in semiarid Kenya. Agronomy Journal 88:513–520.
Hulugalle, N.R. and B.T. Kang. 1990. Effect of hedgerow species in alley cropping systems on surface soil physical properties of an Oxic Paleustalf in south-western Nigeria. Journal of Agricultural Science (Cambridge) 114:301–307.
Hulugalle, N.R. and J.N. Ndi. 1994. Changes in soil properties of a newly-cleared Ultisol due to establishment of hedgerow species in alley cropping systems. Journal of Agricultural Science (Cambridge) 122:435–443.
Huxley, P.A. 1996. Biological factors affecting form and function in woody-non-woody plant mixtures. In Tree–Crop Interactions: A Physiological Approach, ed. C.K. Ong and P. Huxley, 235–298. Wallingford, UK: CAB International.
Huxley, P.A. 1999. Tropical Agroforestry. Oxford, UK: Blackwell Science.
Huxley, P.A., A. Pinney, E. Akunda and P. Muraya. 1994. A tree=crop interface orientation experiment with a Grevillea robusta hedgerow and maize. Agroforestry Systems 26:23–45.
Ikerra, S.T., J.A. Maghembe, P.C. Smithson and R.J. Buresh. 1999. Soil nitrogen dynamics and relationships with maize yields in a Gliricidia–maize intercrop in Malawi. Plant and Soil 211:155–164.
Jacob, V.J. and W.S. Alles. 1987. Kandyan gardens of Sri Lanka. Agroforestry Systems 5:123–137.
Jensen, M. 1993. Productivity and nutrient cycling of a Javanese homegarden. Agroforestry Systems 24:187–201.
Jose, S., A.R. Gillespie, J.R. Seifert, D.B. Mengel and P.E. Pope. 2000. Defining competition vectors in a temperate alley cropping system in the midwestern USA: 3. Competition for nitrogen and litter decom-position dynamics. Agroforestry Systems 48:61–77.
Kang, B.T., L. Reynolds and A.N. Atta-Krah. 1990. Alley farming. Advances in Agronomy 43:315–359.
A Case Study on the Potential of Contour Hedgerow Intercropping 153
Kang, B.T., F.E. Caveness, G. Tian and G.O. Kolawole. 1999. Long-term alley cropping with four hedgerow species on an Alfisol in southwestern Nigeria—effect on crop performance, soil chemical properties and nematode population. Nutrient Cycling in Agroecosystems 54:145–155.
Kumar, B.M. and P.K.R. Nair. 2004. The enigma of tropical homegardens. Agroforestry Systems 61–62:135–152.
Lehmann, J., G. Gebauer and W. Zech. 2002. Nitrogen cycling assessment in a hedgerow intercropping system using15N enrichment. Nutrient Cycling in Agroecosystems 62:1–9.
Livesley, S.J., P.J. Gregory and R.J. Buresh. 2002. Competition in tree row agroforestry systems. 2. Distribu-tion, dynamics and uptake of soil inorganic N. Plant and Soil 247:177–187.
Mapa, R.B. and H.P.M. Gunasena. 1995. Effects of alley cropping on soil aggregate stability of a tropical alfisol. Agroforestry Systems 32:237–245.
McIntyre, B.D., S.J. Riha and C.K. Ong. 1997. Competition for water in a hedge-intercrop system. Field Crops Research 52:151–160.
Mohotti, A.J., M.D. Dennett and D.W. Lawlor. 2000. Electron transport as a limitation to photosynthesis of tea (Camellia sinensis (L.) O. Kuntz.) in comparison with Sunflower (Helianthus annus L.) with special reference to irradiance. Tropical Agricultural Research 12:1–10.
Nair, P.K.R. 1990. Classification of agroforestry systems. In Agroforestry: Classification and Management, ed.
K.G. MacDicken and N.T. Vergara, 31–57. Chichester, UK: Wiley.
Nair, P.K.R. 1993. An Introduction to Agroforestry. Dordrecht, the Netherlands: Kluwer Academic Press.
Nair, P.K.R. and C. Sreedharan. 1986. Agroforestry farming systems: the homesteads of Kerala, Southern India. Agroforestry Systems 4:339–363.
Nye, P.H. and D.J. Greenland. 1960. The Soil under Shifting Cultivation. Technical Communication 51.
Harpenden, UK: Commonwealth Bureau of Soils.
Oades, J.M. 1984. Soil organic matter and structural stability: Mechanisms and implications for management.
Plant and Soil 76:319–337.
Ong, C.K. 1996. A framework for quantifying the various effects of tree–crop interactions. In Tree–Crop Interactions: A Physiological Approach, ed. C.K. Ong and P. Huxley, 1–23. Wallingford, UK: CAB International.
Ong, C.K., J.E. Corlett, R.P. Singh and C.R. Black. 1991. Above and below ground interactions in agroforestry systems. Forest Ecology and Management 45:45–57.
Palm, C.A. 1995. Contribution of agroforestry trees to nutrient requirements of intercropped plants. Agrofor-estry Systems 30:105–124.
Palm, C.A., M.J. Swift and P.L. Woomer. 1996. Soil biological dynamics in slash-and-burn agriculture.
Agriculture, Ecosystems and Environment 58:61–74.
Panabokke, C.R. 1996. Soils and Agro-ecological Environments of Sri Lanka. Colombo, Sri Lanka: Natural Resources, Energy and Science Authority of Sri Lanka.
Ranasinghe, D.M.S.H.K. and S.M. Newman. 1993. Agroforestry research and practice in Sri Lanka. Agrofor-estry Systems 22:119–130.
Rao, M.R., M.M. Sharma and C.K. Ong. 1990. A study of the potential of hedgerow intercropping in semi-arid India using a two-way systematic design. Agroforestry Systems 11:243–258.
Rao, M.R., C.K. Ong, P. Pathak and M.M. Sharma. 1991. Productivity of annual cropping agroforestry systems on a shallow Alfisol in semi-arid India. Agroforestry Systems 15:51–63.
Rao, M.R., P.K.R. Nair and C. Ong. 1998. Biophysical interactions in tropical agroforestry systems. Agrofor-estry Systems 38:3–50.
Ray, H.C. (ed). 1959. History of Ceylon. Colombo: Ceylon University Press.
Robinson, D.M. and S.J. McKean. 1992. Shifting Cultivation and Alternatives. An Annotated Bibliography, 1972–1989. Wallingford, UK: CAB International.
Ruhigwa, B.A., M.P. Gichuru, B. Mambani and N.M. Tariah. 1992. Root distribution of Acioa barteri, Alchornea cordifolia, Cassia siamea and Gmelina arborea in an acid Ultisol. Agroforestry Systems 19:67–78.
Samsuzzaman, S., D.P. Garrity and R.U. Quintana. 1999. Soil property changes in contour hedgerow systems on sloping land in the Philippines. Agroforestry Systems 46:251–272.
Sanchez, P.A. 1995. Science in agroforestry. Agroforestry Systems 30:5–55.
Singh, R.P., C.K. Ong and N. Saharan. 1989. Above and below ground competitions in alley cropping in semi-arid India. Agroforestry Systems 9:259–274.
154 Ecological Basis of Agroforestry
Sivapalan, P., S. Kulasegaram and A. Kathiravetpillai. 1986. Handbook on Tea. Talawakelle, Sri Lanka: Tea Research Institute of Sri Lanka.
Spaargaren, O.C. 1994. World Reference Base for Soil Resources. Wageningen, the Netherlands:
ISSS=ISRIC=FAO.
Szott, L.T., C.A. Palm and P.A. Sanchez. 1991. Agroforestry in acid soils of the humid tropics. Advances in Agronomy 45:275–301.
Teubig, P. 1996. Observation of the root systems of Gliricidia sepium, Calliandra calothyrsus, Desmodium ransonii, Cassia spectabilis and Flemingia congesta used in the Sloping Agriculture Land Technology (SALT) in the Up-Country of Sri Lanka. Unpublished report submitted to the Upper Mahaweli Water-shed Management Project, Sri Lanka.
Vandenbeldt, R.J. 1990. Agroforestry in the semi-arid tropics. In Agroforestry: Classification and Manage-ment, ed. K.G. MacDicken and N.T. Vergara, 150–194. Chichester, UK: Wiley.
van Noordwijk, M. and P. Purnomosidhi. 1995. Root architecture in relation to tree–soil–crop interactions and shoot pruning in agroforestry. Agroforestry Systems 30:161–173.
van Noordwijk, M., G. Lawson, A. Soumare, J.J.R. Groot and K. Hairiah. 1996. Root distribution of trees and crops: competition and=or complementarity. In Tree–Crop Interactions: A Physiological Approach, ed.
C.K. Ong and P. Huxley, 319–364. Wallingford, UK: CAB International.
Weischet, W. and C.N. Caviedes. 1993. The Persisting Ecological Constraints of Tropical Agriculture.
Harlow, UK: Longman.
Wieder, R. and G. Lang. 1982. A critique of the analytical methods used in examining decomposition data obtained from litter bags. Ecology 63:1636–1642.
Wiersum, K.F. 1991. Soil erosion and conservation in agroforestry systems. In Biophysical Research for Asian Agroforestry, ed. M.E. Avery, M.G.R. Cannell and C. Ong, 209–230. New Delhi:
Winrock=Oxford & IBH.
Woomer, P.L., A. Martin, A. Albrecht, D.V.S. Resck and H.W. Scharpenseel. 1994. The importance and management of soil organic matter in the tropics. In The Biological Management of Tropical Soil Fertility, ed. P.L. Woomer and M.J. Swift, 47–80. Chichester, UK: Wiley-Sayce=TSBF.
Yamoah, C.F., A.A. Agboola, G.F. Wilson and K. Mulongoy. 1986. Soil properties as affected by the use of leguminous shrubs for alley cropping with maize. Agriculture, Ecosystems and Environment 18:167–177.
A Case Study on the Potential of Contour Hedgerow Intercropping 155