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
soil structure controls
the passage of water and oxygen into the soil and affects nutrient-holding capacity
- structure can overcome some of the limitations by texture
- -clay -increase creation and drainage
- -sand - improve water and nutrient holding
how does tillage affect structure?
more than half of larger aggregates are lost
- so larger pore spaces are not generated
- less able to hold water
loss of soil organic matter as a result of cultivation has compromised soil functioning:
nutrient and water-holding capacity - limiting crop yields and increasing vulnerabilities to water logging and drought
how does tillage affect pores?
lose larger pores when you till
–results in loss of clays and OM – cycle
7 major factors of ped formation
- colloidal fraction (clay&humus)
- cementing agencies
- expansion and contraction by wetting and drying
- plant roots
- micro-organisms
- micro and meso fauna (earthworms, grazing animals)
- cultivation and drainage
macroaggrogate formation:
- fine roots, especially grasses
- mychorrhizal fungi and other fungi
- earthworms and other soil animals
earthworms: ploughing and harrowing
- ploughing brings them to surface, predation by seagulls
- harrowing chops them up
ploughing on mychorrhizal
breaks them up
once lost? how long does it take to restore macroaggrogates?
-10 years of pasture and still no where near virgin soil values
macroaggregates and soil organic carbon may be restores by
stopping cultivation and use of grass (lets)
loss of organic matter leads to loss of
water storage capacity, soil compaction
