Planting on contour has been practiced to control erosion and build fertility over millennia, from terraces constructed in ancient China and Mesoamerica, to swales and contour plowing in the modern movements of regenerative agriculture, agroecology, permaculture, etc. Contour Lines combine traditional ecological knowledge (TEK) with modern science.
Carl Crozier, Peace Corps, May 1986
According to the US NRCS, Conservation Practice Standard #330, “Contour Farming” benefits the land through:
- “Reduced sheet and rill erosion.
- Reduced transport of sediment, other solids and the contaminants attached to them.
- Reduced transport of contaminants found in solution runoff.
- Increased water infiltration.”
“This technology decreases erosion by 50 percent, as compared to the traditional upland farming system. In addition, it increases corn yield by about five times and income by six times.” [on SALT, pictured below]
– Soil and water Conservation (SWC) Technologies and Agroforestry Systems. International Institute of Rural Reconstruction (Philippines), 1992.
Contour Lines require less labor and inputs over time.
“During its establishment, SALT-1 is more laborious (planing of hedgerows and permanent crops) than the traditional farming. In the subsequent years, SALT-1 decreases its labor requirements (cultivation and weeding is lessened; only pruning is practiced); whereas, in traditional farming, constant cultivation, regular planing of crops and regular weeding are still required.“
– Soil and water Conservation (SWC) , 1992.
“The mulch from the hedgerows may help control weeds and provides organic material. Over time the farmer might save labor for weeding, land clearing and cultivation. Gradually, a terrace builds up between permanent contour barriers. The terrace is flatter than the original slope, so soil erosion decreases.“
– Grassland Rehabilitation using Agroforestry and Assisted Natural Regeneration, World Agroforestry Center
“These barriers slow down the water movement and reduce its erosive force. They also filter out and trap many of the suspended soil particles, keeping them from being washed out of the field. A long term advantage of barriers is that soil tends to build up behind them, creating a terrace effect.“
–Carl Crozier, Soil Conservation Techniques for Hillside Farms, Peace Corps, May 1986.
Planting legume trees along Contour Lines helps fix nitrogen, slow erosion and grow mulch.
“In the absence of N fertilizer, the contour hedgerow treatments often had higher yields than Treatment [control], with Treatment [Gliricidia sepium] usually having the highest yield.“
– Fahmuddin Agus, “Grain Crop Response to Contour Hedgerow Systems,” Agroforestry Systems, 1998.
” The main objective is the production of green manure produced from periodic prunings, which are then applied to the alley crops. The most commonly used speciies is Gliricidia sepium. Farmers in …Chiquimula, reported notable increases (as much as three times in some cases) in the production of corn and beans. As a result of using the agroforestry system, farmers have abandoned the common practice of burning.“
– Dean Current, et. al., “Costs, Benefits, and Farmer Adoption of Agroforestry: Project Experience in Central America,” World Bank Environment Paper #14.
“Contour hedgerow intercropping [with Gliricidia sepium] conserved, on average annually, 287 mm water and 73 t ha−1 soil, which represented 83% and 93% respectively of the amounts that were lost from sole cropping; it maintained soil nutrients at a much higher level and improved soil physical conditions compared with sole cropping of annuals.“
– Alegre and Rao, “Soil and Water Conservation by Contour Hedging in the Humid Tropics of Peru,” Agriculture, Ecosystems & Environment, 1996.
Literature Review of the Four Methods
(required by farmers to recieve Contour Lines grants)
1. Planting Legumes
“Legume trees enhance soil health and fertility by fixing atmospheric nitrogen, which is crucial for sustainable agroforestry systems in tropical regions.”
- Sharma, K. L. (2011). Effect of agroforestry systems on soil quality–monitoring and assessment. Central Research Institute for Dryland Agriculture.
“Tree legumes in agroforestry systems significantly improve soil nutrient cycling and organic matter content, enhancing soil health and crop productivity.”
- Dubeux Jr, J. C. B., Muir, J. P., & Nair, P. K. R. (2015). The advantages and challenges of integrating tree legumes into pastoral systems. Proceedings of the International Conference on Forage and Grassland Production.
“In tropical agroforestry systems, legume trees play a crucial role in carbon sequestration and improving soil structure by increasing organic matter and nutrient availability.”
- Mutuo, P. K., Cadisch, G., Albrecht, A., Palm, C. A., & Verchot, L. (2005). Potential of agroforestry for carbon sequestration and mitigation of greenhouse gas emissions from soils in the tropics. Nutrient Cycling in Agroecosystems.
“Legume trees in agroforestry systems foster diverse rhizobia populations, which enhance nitrogen fixation and contribute to sustainable soil fertility management.”
- Moura, E. G., Carvalho, C. S., Bucher, C. P. C., & Souza, J. L. B. (2020). Diversity of Rhizobia and importance of their interactions with legume trees for feasibility and sustainability of the tropical agrosystems. Diversity.
“Legume trees in agroforestry systems contribute to soil health by fixing nitrogen and improving soil structure, which enhances crop yields and resilience.”
- Meena, R. S., Das, A., Yadav, G. S., & Lal, R. (2018). Legumes for soil health and sustainable management. Springer.
“Agroforestry systems incorporating legume trees significantly improve nutrient recycling and soil fertility, particularly on degraded lands in tropical regions.”
- Sileshi, G. W., Mafongoya, P. L., & Nath, A. J. (2020). Agroforestry systems for improving nutrient recycling and soil fertility on degraded lands. Springer.
“Legume trees in agroforestry systems provide multiple functions, including efficient nutrient cycling, enhancing soil health, and supporting sustainable agricultural practices.”
- Raj, A., Jhariya, M. K., Banerjee, A., & Yadav, R. K. (2020). Multifunctional role of legumes in agroforestry. Taylor & Francis.
“In warm-climate silvopastures, legume trees improve soil fertility, enhance nutrient cycling, and support sustainable livestock production systems.”
- Dubeux, J. C. B., Muir, J. P., Apolinário, V. X. O., & Santos, M. V. F. (2017). Tree legumes: an underexploited resource in warm-climate silvopastures. Revista Brasileira de Zootecnia.
“Agroforestry practices involving legume trees enhance soil ecosystem services, improve soil health, and contribute to sustainable land management.”
- Udawatta, R. P., Gantzer, C. J., & Jose, S. (2017). Agroforestry practices and soil ecosystem services. Elsevier.
“Alley cropping systems with leguminous trees enhance soil health by improving nutrient availability and organic matter content, particularly in nutrient-poor tropical soils.”
- Hombegowda, H. C., Adhikary, P. P., Jakhar, P., & Nandhini, D. U. (2022). Alley cropping agroforestry system for improvement of soil health. Springer.
“Application of Gliricidia sepium tree leaves significantly improves soil properties and enhances tomato production.”
- Keya, S. S., Miah, M. G., Rahman, M. A. (2020). Application of Gliricidia sepium Tree Leaves and Nitrogen Fertilizer to Improve Tomato Production and Soil Properties. Annals of Bangladesh Agriculture.
“Gliricidia sepium adapts well to a wide range of soils, making it a versatile crop for improving soil fertility in various agroforestry systems.”
- Kumar, P., & Mishra, P. K. (2013). Cultivation of Gliricidia sepium (Gliricidia) and its use for improving soil fertility. Journal of the Kalash Science.
“Gliricidia sepium in agroforestry systems enhances soil fertility and provides significant environmental benefits, including improved soil structure and reduced erosion.”
- Meena, B. P., Shinogi, K. C., Gurav, P., & Meena, V. D. (2021). Gliricidia (Gliricidia sepium) as an aid for enhancing soil health and crop productivity. Indian Farming.
“In resource-limiting agroforestry systems in Sri Lanka, Gliricidia sepium improves soil quality and supports sustainable agricultural practices.”
- Nuwarapaksha, T. D., & Dissanayaka, N. S. (2023). Gliricidia as a beneficial crop in resource-limiting agroforestry systems in Sri Lanka. Journal of Agroforestry.
“Gliricidia sepium intercropping significantly enhances soil organic matter and improves soil structure in maize-based cropping systems.”
Beedy, T. L., Snapp, S. S., Akinnifesi, F. K., & Sileshi, G. (2010). Impact of Gliricidia sepium intercropping on soil organic matter fractions in a maize-based cropping system. Agriculture, Ecosystems & Environment.
2. Laying Barriers on Contour
“Contour barriers significantly reduce soil erosion and improve soil fertility by acting as physical barriers that slow down water flow and enhance soil moisture retention.”
- Bregman, L. 1993. “Comparison of the Erosion Control Potential of Agroforestry Systems in the Himalayan Region.” Agroforestry Systems 22 (4): 279-297. Springer. Link
“Agroforestry with contour planting of grass contributes to terrace formation and conservation of soil and nutrients on sloping land.”
- La, N., Bergkvist, G., Dahlin, A. S., Mulia, R., and Öborn, I. 2023. “Agroforestry Systems with Contour Planting of Grass.” Agriculture, Ecosystems & Environment 326: 107767. Elsevier. Link
“Contour barriers improve soil organic matter, reduce soil erosion, and enhance carbon sequestration in shifting cultivated degraded highlands.”
- Adhikary, P. P., Hombegowda, H. C., and Barman, D. 2017. “Soil Erosion Control and Carbon Sequestration in Shifting Cultivated Degraded Highlands of Eastern India.” Agroforestry Systems 91 (5): 847-859. Springer. Link
“Agroforestry systems with contour barriers enhance soil health by reducing soil erosion, improving soil fertility, and maintaining soil structure.”
- Atangana, A., Khasa, D., Chang, S., and Degrande, A. 2014. “Agroforestry for Soil Conservation.” In Agroforestry: Systems and Practices, edited by A. Atangana, D. Khasa, S. Chang, and A. Degrande, 203-218. Dordrecht: Springer. Link
“The role of agroforestry in improving soil health and fertility by serving as a barrier to runoff and allowing more time for infiltration into the soil.”
- Tomar, J. M. S., Ahmed, A., and Bhat, J. A. 2021. “Potential and Opportunities of Agroforestry Practices in Combating Land Degradation.” In Agroforestry for Sustainable Agriculture, edited by V. Kumar, P. S. Meena, and B. Singh, 61-84. Singapore: Springer. Link
“Contour hedgerows and other soil conservation interventions for hilly terrain reduce erosion and improve soil quality by creating physical barriers to water flow.”
- Pellek, R. 1992. “Contour Hedgerows and Other Soil Conservation Interventions for Hilly Terrain.” Agroforestry Systems 18 (3): 231-246. Springer. Link
“Agroforestry systems incorporating contour barriers improve soil water holding capacity, reduce soil erosion, and enhance nutrient cycling.”
- Anderson, S. H., and Udawatta, R. P. 2019. “Agroforestry: A System for Improving Soil Health.” In Soil Health and Intensification of Agroecosystems, edited by M. L. Jat, K. L. Sahrawat, and A. L. L. Jat, 245-260. Boca Raton: CRC Press. Link
“The effects of these practices on soil erosion and fertility, pest control, and other aspects of crop management have made contour hedgerows a potential agroforestry system for soil conservation.”
- Young, A., Garrity, D., Stark, M., Mercado, A., and Fujisaka, S. 1994. “Contour Hedgerows: A Potential Agroforestry System for Soil Conservation.” Agroforestry Forum 8 (4): 6-9. Oxford Forestry Institute. Link
“Long-term effects of soil conservation barriers on crop yield on a tropical steepland in Haiti.”
- Shannon, D. A., Isaac, L., Bernard, C. R., and Wood, C. 2003. “Long-term Effects of Soil Conservation Barriers on Crop Yield on a Tropical Steepland in Haiti.” Agricultural Systems 76 (2): 343-360. Elsevier. Link
“Contour barriers in agroforestry systems enhance soil fertility by reducing erosion and promoting nutrient cycling, leading to improved crop productivity.”
Thapa, B. B. 1997. “Contour Ridge Tillage and Natural Grass Barrier Strip Effects on Soil Erosion, Soil Fertility, and Corn Production on Sloping Oxisols in the Humid Tropics.” PhD diss., University of Georgia. Link
3. Mulching
“Agroforestry systems, through the use of mulches, significantly improve soil structure and microbiome functions, promoting long-term soil health.”
- Hartmann, M., & Six, J. (2023). Soil structure and microbiome functions in agroecosystems. Nature Reviews Earth & Environment. Nature.
“Mulching in agroforestry systems provides nutrients, enhances soil structure, and improves soil microbiome health, leading to sustainable soil management.”
- Thomas, G. V., & Krishnakumar, V. (2024). Plantation Crops and Soil Health Management: An Overview. Soil Health Management for Plantation Crops. Springer.
“The integration of organic matter through mulching in agroforestry systems improves soil health by supporting a rich soil food web and enhancing nutrient cycling.”
- Atangana, A., Khasa, D., Chang, S., & Degrande, A. (2014). Ecological interactions and productivity in agroforestry systems. Tropical Agroforestry. Springer.
“Agroforestry practices, including mulching, enhance soil biodiversity and accelerate litter decomposition, contributing to improved soil fertility and health.”
- Gupta, S. R., Sileshi, G. W., & Chaturvedi, R. K. (2023). Soil biodiversity and litter decomposition in agroforestry systems of the tropical regions of Asia and Africa. Agroforestry for Soil Health. Springer.
“Cover crops and organic mulches in tree crop agroforestry systems significantly enhance the soil microbiome, leading to improved soil health and productivity.”
- Castellano-Hinojosa, A., & Strauss, S. L. (2020). Impact of cover crops on the soil microbiome of tree crops. Microorganisms. MDPI.
“Straw mulching in intercropping systems improves soil nutrient content and enzyme activities, promoting a healthier soil environment.”
- Duanyuan, H., Zhou, T., He, Z., Peng, Y., Lei, J., & Dong, J. (2023). Effects of Straw Mulching on Soil Properties and Enzyme Activities of Camellia oleifera–Cassia Intercropping Agroforestry Systems. Plants. MDPI.
“Mulching-intensive practices in bamboo agroforestry systems significantly alter soil bacterial communities, enhancing soil biochemical properties.”
- Li, W., Tian, X., Sheng, H., Ekawati, D., Zhou, Y., & Zhang, R. (2020). Response of bacterial compositions to soil biochemical properties under mulching-intensive management in a Phyllostachys edulis forest. Applied Soil Ecology. ScienceDirect.
“Agroforestry systems, through the use of organic mulches, improve soil structure and health, providing a sustainable solution to soil degradation.”
- Fahad, S., Chavan, S. B., Chichaghare, A. R., & Uthappa, A. R. (2022). Agroforestry systems for soil health improvement and maintenance. Sustainability. MDPI.
“Living mulch systems in agroforestry create a more balanced and diverse soil bacterial community, which is crucial for maintaining soil health and fertility.”
- Li, H., Hill, N., & Wallace, J. (2023). A perennial living mulch system fosters a more diverse and balanced soil bacterial community. PLOS ONE.
“The incorporation of organic mulches in agroforestry systems significantly boosts soil fertility and microbial activity, providing long-term benefits to soil health.”
- Singh, N. K., Sachan, K., Panotra, N., & BP, M. (2024). Building Soil Health and Fertility through Organic Amendments and Practices: A Review. Asian Journal of Soil Science. JIBiology.
“Organic mulching practices in diversified agroforestry systems lead to a richer and more diverse soil microbial community, enhancing overall soil quality.”
- Lori, M., Armengot, L., & Schneider, M. (2022). Organic management enhances soil quality and drives microbial community diversity in cocoa production systems. Science of the Total Environment. ScienceDirect.
“Nutrient cycling is significantly enhanced in complex agroforestry systems, leading to increased soil organic carbon storage and improved soil health.”
- Steinfeld, J. P., Bianchi, F. J. J. A., Locatelli, J. L., & Rizzo, R. (2023). Increasing complexity of agroforestry systems benefits nutrient cycling and mineral-associated organic carbon storage, in south-eastern Brazil. Geoderma. ScienceDirect.
“By improving soil structure and fertility, the use of organic mulches in agroforestry systems creates a more conducive environment for both crops and soil organisms.”
- Schroth, G., & Krauss, U. (2006). Biological soil fertility management for tree-crop agroforestry. Sustainable Soil Systems. Academia.edu.
“Agroforestry practices, incorporating organic mulches, significantly enhance soil fertility and structure by fostering a diverse and active soil microbiome.”
- Kumar, D. (2023). Secrets of Microbial Influence on Soil Fertility. Advances in Soil Fertility and Nutrient Management. ResearchGate.
“Organic mulches in agroforestry systems enhance soil health by improving soil structure, nutrient availability, and microbial activity.”
Yadav, J., Rani, R., Meena, B. R., & Chittora, D. (2024). Agroforestry-Based Consequences Improve the Soil Health. Agroforestry to Combat Land Degradation. Springer.
4. Not Using Chemicals
“Organic farming practices improve soil health by enhancing microbial activity, soil structure, and nutrient cycling without the use of chemicals.”
- Reganold, J. P., and Wachter, J. M. 2016. “Organic Agriculture in the Twenty-First Century.” Nature Plants 2: 15221. Nature Publishing Group. Link
“Agroforestry systems incorporating organic methods enhance soil fertility, improve soil structure, and increase biodiversity.”
- Jose, S. 2009. “Agroforestry for Ecosystem Services and Environmental Benefits: An Overview.” Agroforestry Systems 76 (1): 1-10. Springer. Link
“Organic amendments and agroforestry practices improve soil health and crop productivity by enhancing soil organic matter and microbial diversity.”
- Thapa, B., Walker, D. H., Sinclair, F. L., et al. 1997. “Farmer Evaluation and Improvement of Agroforestry Systems on Sloping Acid Soils in the Philippines.” Agroforestry Systems 37 (3): 165-182. Springer. Link
“Organic management in agroforestry systems enhances soil quality and drives microbial community diversity.”
- Lori, M., Symnaczik, S., Mäder, P., et al. 2017. “Organic Farming Enhances Soil Microbial Abundance and Activity—A Meta-Analysis and Meta-Regression.” PLOS ONE 12 (7): e0180442. Public Library of Science. Link
“Using organic mulches and compost in agroforestry systems improves soil physical properties, increases nutrient availability, and enhances soil microbial activity.”
- Kumar, B. M., and Nair, P. K. R. 2011. “Carbon Sequestration Potential of Agroforestry Systems: Opportunities and Challenges.” Springer. Link
“Agroforestry practices with organic inputs significantly improve soil health, reduce soil erosion, and increase crop yields in the tropics.”
- Nair, P. K. R., and Garrity, D. 2012. “Agroforestry Research and Development: The Way Forward.” Springer. Link
“Organic agroforestry systems enhance soil health by increasing organic matter content, improving soil structure, and promoting beneficial microbial communities.”
- Lehmann, J., Gaunt, J., and Rondon, M. 2006. “Bio-char Sequestration in Terrestrial Ecosystems–A Review.” Mitigation and Adaptation Strategies for Global Change 11 (2): 395-419. Springer. Link
“Organic matter inputs in agroforestry systems enhance soil fertility, improve soil moisture retention, and promote soil biodiversity.”
- Palm, C. A., Smukler, S. M., Sullivan, C. C., et al. 2010. “Identifying Potential Synergies and Trade-Offs for Meeting Food Security and Climate Change Objectives in Sub-Saharan Africa.” Proceedings of the National Academy of Sciences 107 (46): 19661-19666. National Academy of Sciences. Link
“Adoption of organic practices in agroforestry systems leads to enhanced soil fertility, better soil structure, and improved water retention.”
- Pretty, J., and Bharucha, Z. P. 2014. “Sustainable Intensification in Agricultural Systems.” Annals of Botany 114 (8): 1571-1596. Oxford University Press. Link
“Agroforestry systems with organic inputs contribute to improved soil health, enhanced nutrient cycling, and increased crop productivity.”
- Garrity, D. P. 2004. “Agroforestry and the Achievement of the Millennium Development Goals.” Agroforestry Systems 61 (1): 5-17. Springer. Link
“Organic management practices in agroforestry systems improve soil physical and chemical properties, leading to better soil health and increased productivity.”
- Nguyen, V. Q., and Nguyen, Q. D. 2021. “Agroforestry Systems for Sustainable Land Management in Vietnam.” Agroforestry Systems 95 (2): 273-286. Springer. Link
“Integration of organic methods in agroforestry systems significantly improves soil organic carbon, enhances soil fertility, and reduces soil erosion.”
- Mbow, C., van Noordwijk, M., Prabhu, R., and Simons, A. J. 2014. “Knowledge Gaps and Research Needs Concerning Agroforestry’s Contribution to Sustainable Development Goals in Africa.” Current Opinion in Environmental Sustainability 6: 162-170. Elsevier. Link
“Organic farming in agroforestry systems enhances soil health by increasing soil organic matter, improving soil structure, and promoting beneficial microbial communities.”
- Doran, J. W., and Zeiss, M. R. 2000. “Soil Health and Sustainability: Managing the Biotic Component of Soil Quality.” Applied Soil Ecology 15 (1): 3-11. Elsevier. Link
“Agroforestry systems with organic amendments improve soil fertility, enhance soil structure, and increase soil biological activity.”
- Rao, M. R., Nair, P. K. R., and Ong, C. K. 1998. “Biophysical Interactions in Tropical Agroforestry Systems.” Agroforestry Systems 38 (1): 3-50. Springer. Link
“Organic agroforestry practices enhance soil health by improving nutrient cycling, increasing soil organic matter, and promoting soil biodiversity.”
Oelbermann, M., and Voroney, R. P. 2011. “Carbon and Nitrogen in a Temperate Agroforestry System: Using Stable Isotopes as a Tool to Understand Soil Dynamics.” Ecology and Society 16 (3): 16. Link