Lecture 4 Flashcards
contour plowing
follows contour of land to minimise soil degradation
agro-forestry (trees on edge of crop lands) use of trees
to recycle nutrients and water deep in soils - below the rooting depth of annuals crops
problems from focussing on growing just a small diversity (or one) species of crop
= global food security threat
- outbreak of pest / disease
- the irish potato famine 1845 - 1849
- over 1,500,500 dies of starvations
increasing the diversity of crops may:
- reduce pest & disease pressures,
- increase nutrient-use efficient
- reduce risks of large-scale crop failures
- improve soil quality
- may improve food security especially in relation to increasing threats from CC and pests and diseases resistance to chemical control
soil provides plants with
- support
- nutrients
- water
- oxygen requirement of roots (except wetland plants)
- protection of underground buds from temp. extremes
soil can be hostile environment:
- pathogens
- root grazers
- toxins
- too much or too little water
- inadequate aeration
soil: a 3-phase system
- solid (mineral, organic)
- liquid (free water, structural/unavailble water)
- gas (air): (enriched in CO2, depleted in O2)
approximately half go the volume of soil is
pore space containing water/ air
most UK soils now have less than _% organic matter
2%
-provides most of energy to plants
soil air is _____ from atmosphere and varies with
distinct and varies with depth
-e.g. CO2, CH4 increases as you go down , O2 decreases
why are soils tilled?
- prepare a fine loose soil layer for seedlings to establish
- bury weeds, crop residues and pathogens
- release nutrients
- reduce surface & subsurface compaction
-ISSUE: Long term effects of tillages on soil sustainability and soil erosion
types of tillage
- different types mean different times the soil is driven over, disturbed and left bare
- conventional
- minimum tillage
- zero tillage
conventional tillage:
1) inversion tillage
2/3) disking /power harrow
3/4) seed (Drill)
minimum tillage:
1) shallow disc cultivation
2) drill (And chemical weed kill)
- leaves behind partial crop residue
- depended on herbicide
zero tillage (direct drill):
1) slot drill (and chemical weed kill)
- almost complete cover by crop residue
- depended on herbicide
- tractor tyres = wide, low pressure to reduce compactor
power harrow:
breaks down big clumps to smaller
-if soil dry, loss of substance to wind
consequence of machinery driving on fields
- compact soils leads to compact traffic pan under ‘plow’ layer soil
- effects root penetration
uptake of lesser tillage in canada?
rapid uptake, helps reduce soil erosion
uptake of lesser tillage in north america?
adopted minimum tillage and no-tillage but erosion rates remain unsustainable
uptake of lesser tillage in UK?
lagging behind, 60% conventional, 32% reduced, 8% zero
reduced tillage potential savings of __% energy use per
26%
less fuel required!!
conventional tillage causes loss of
- organic matter
- nutrients
- water storage
- increases soil erosion
- earthworn populations
- interrupts fungal interactions
soil properties: Texture
based on particle size distribution of mineral fragments in soil
- Gravel >2mm
- coarse sand 0.2-2mm
- fine sand 0.02-0.2mm
- silt 0.002-0.02mm
- clay <0.002mm
Sand soil = drain quick, store little water good aeration
clay = oposite
loam soil = mixture –> good for most plants
soil texture changes
very stable, only changes slowly due to weathering
