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.
Preparing Gliricidia sepium stakes to install living contour lines. 
Staking contour lines with Gliricidia Sepium, for erosion control, mulch production and nitrogen fixation.
“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.