Soils and cropping systems

Soils and cropping systems

1. Soil : types

   • Peat Soils
     • Characteristics
       • Acidic (pH 2)
       • Highly productive and fertile however:
         • Oxidative
         • Wind erosion
     • Can cause a formation of = DRUMMY LAYER
       • 5–15cm thick are formed at the peat/subsoil interface
       • Formed due to fluctuating iron and aluminium water table deposits
     • Cropping
       • Use of fertilisers is only needed for P concentration but little to no N
       • Intensive vegetable production
   • Clay Soils
     • Cropping
       • Root crops difficult to harvest (esp. when wet) and may cause soil structural damage
       • Autumn rather than spring sown (as the ground is wet in spring).
     • Friable range
       • Narrow friable range : hard when dry, plastic when wet
       • higher organic matter content will have a larger friable range
     • Characteristics
       • Self structuring and surface tilth, means clays will break into clumps which make them workable
       • High potential yields
       • Artificial drainage required
   • Soil texture
     • Many different texture of soil
     • Purpose
       • Drainage
       • Water holding capacity
       • Working properties
       • Suitability of crops
       • Soil structure
   • Sandland
     • Characteristics
       • Free working, easy to sow, easy to harvest
       • Low organic matter levels
       • Water limiting (2.5 - 4cm water per 30cm soil
       • Intensive vegetable production
     • Cropping
       • Leaching can occur
       • Blowing sand: loss of topsoil and even seeds/seedlings
       • Dry soils can lead to herbicide activity alternatively it is easy to apply too much herbicide
   • Silt sand
     • Characteristics
       • Low OM (organic matter) and phosphate
       • High water holding capacity
       • Structurally unstable
     • Cropping
       • Potatoes

2. Soil Categories

   • Primary types
     • Sands
     • Loamy sands
     • Sandy Loams
     • Sandy silt Loams
     • Loams
   • Subcategories
     • Fine : more than two-thirds of the sand fraction is between 0.06 -0.02mm (approximate).
     • Medium: less than to-thirds of the sand is between 0.06 – 0.02mm and less than one third is larger than 0.06 mm.
     • Course: more than one third of the sand fraction is larger than 0.6mmm

3. Rotations

   • Purpose
     • Maintain/increase soil fertility/structure
     • Weed control
     • Pest control
     • Disease control
     • Diversity of cropping
   • Designed to improve/maintain soil properties

4. Organic matter

   • Increases water holding capacity of sands
   • Makes clays more friable (easily crumbles)
     • friable range of a soil is the range of moisture contents at which a soil can be cultivated effectively, without damaging soil structure
   • Decline in Organic Matter (OM) causes:
     • loss of structural strength
     • water cannot penetrate
   • How to increase OM in soil
     • Leaving the soil for a period of time with no cultivation will restore the organic matter in the soil (fallow)
   • How to preserve OM in soil
     • Agroforestry
     • Conservation of agriculture

5. Tropical Soil

   • Possibility of containing fertile soil but dependant on:
     • parent material
     • temperature and humidity that dictates the rapid decrease of OM
     • level and intensity of rainfall (risk of leaching and loss of structure)
   • Mainly poor land as it does not contain efficient variables (hot, humid, poor geological area)