Simulic
English

Farming practices and soil – Green Revolution, erosion and sustainable farming

GeographySoils, Biosphere & EnvironmentAges 15–16

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Use with my class

A field on a hillside is farmed for 30 years. Choose the slope and rainfall, a permanent field or slash-and-burn shifting cultivation with a fallow, the tillage (ploughing, reduced tillage, no-till), the Green Revolution inputs (high-yielding varieties, nitrogen fertiliser, irrigation) and soil conservation (contour ploughing, terraces, windbreaks, cover crops). Each year the model works out the yield, soil lost to erosion, runoff, soil organic matter, topsoil depth and nitrate leached. A second screen compares a monoculture with a polyculture and a permaculture garden (compost, mulch, rainwater tank) next to a pasture with an adjustable stocking rate over 10 seasons.

Lesson: Agriculture and the environment: the Green Revolution, soil erosion and conservation, shifting cultivation, sustainable farming and grazing

What it shows

Farming changes the soil it depends on. In this hillside field, water erosion follows the Revised Universal Soil Loss Equation A = R·K·LS·C·P and wind erosion rises in dry years. Yield depends on the crop variety, nitrogen, water, topsoil depth and organic matter, and organic matter rises with crop residues but falls with ploughing and erosion. Green Revolution inputs raise yields; conservation practices keep the soil in place. The tolerable soil loss is taken as 11 t/ha a year. All numbers are illustrative estimates, not forecasts for a real place.

How to use

On Hillside field, set Slope and Rainfall, choose Farming system, Tillage and Fertiliser, tick High-yielding variety, Irrigation or the conservation boxes, then press Run or +1 year. Switch the Graph between Yield, Soil loss, Organic matter, Runoff and Topsoil; the dashed line is the previous run. On Garden and pasture, pick a Planting design, Compost, Mulch, Rainwater tank and a Stocking rate. Try the three tasks.

Parameters you can change

  • Screen Hillside field over 30 years, Garden and pasture
  • Farming system Permanent field, Shifting cultivation (slash-and-burn, fallow)
  • Fallow period (shifting cultivation) 1–25 years
  • Slope of the field 2–35 %
  • Mean annual rainfall 300–2500 mm/year
  • Tillage Ploughing, Reduced tillage, No-till (direct seeding)
  • High-yielding variety
  • Nitrogen fertiliser 0–250 kg N/ha/year
  • Irrigation
  • Contour ploughing
  • Terraces
  • Windbreak
  • Cover crop between seasons
  • Planting design of the garden Maize monoculture, Maize–bean–squash polyculture, Permaculture food forest
  • Compost
  • Straw mulch
  • Rainwater tank
  • Stocking rate 0–4 LU/ha

Questions to explore

  1. Why do high-yielding varieties raise the yield a lot only when fertiliser and enough water are added?
  2. On a 20% slope, how much do contour ploughing, terraces and no-till each cut the soil loss?
  3. Why does slash-and-burn farming stay sustainable only when the fallow is long enough?

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