Soil and Land Management

Soil fertility

"Ability of soil to supply essential nutrients in correct amounts for plant growth"

Soil productivity

"Capacity of soil to produce crops under specific management conditions"

Fertile vs productive soil

"Fertile soils may not be productive without water or management"

Liebig's Law of the Minimum

"Plant growth is limited by the most deficient nutrient"

Barrel analogy

"Shortest plank limits capacity

Effect of low fertility

"Slow growth

Common nutrient deficiencies

"Nitrogen

Natural fertility factors

"Parent material

Parent material

"Source of minerals and nutrients"

Climate effect

"Controls weathering and organic matter decomposition"

Organisms role

"Add organic matter and recycle nutrients"

Topography effect

"Influences drainage and erosion"

Time in soil formation

"Allows soil horizons and nutrient pools to develop"

Soil nutrient pools

"Soil solution

Soil solution

"Immediately available nutrients"

Colloids

"Clay and organic matter particles holding nutrients"

Adsorption

"Attachment of ions to soil particles"

Desorption

"Release of ions into soil solution"

Long-term nutrient storage

"Soil minerals and organic matter"

Short-term storage

"Exchangeable nutrients on colloids"

Clay importance

"High surface area and charge for nutrient storage"

2:1 clay

"Two tetrahedral sheets sandwiching one octahedral sheet"

Montmorillonite

"Expanding clay with high nutrient holding capacity"

CEC

"Ability of soil to hold cations like K+

AEC

"Ability to hold anions like phosphate"

Nutrient exchange

"Continuous movement between soil solution and colloids"

Phosphorus storage

"In minerals

Potassium storage

"In clay interlayers and soil solution"

Nitrogen storage

"Mainly in soil organic matter"

Mineralisation

"Organic N converted to NH4+"

Immobilisation

"Microbes convert inorganic N into organic forms"

Soil pH

"Controls nutrient solubility and availability"

Optimal pH range

"Around 6–7 for most crops"

Low pH effects

"Al toxicity and reduced nutrient availability"

High pH effects

"Micronutrient deficiencies"

Redox potential

"Controls nutrient form under wet/dry conditions"

Salinity

"High salt reduces water uptake"

Quantity vs intensity

"Quantity = total nutrient

Mass flow

"Nutrient movement with water"

Diffusion

"Movement from high to low concentration"

Root interception

"Roots physically contact nutrients"

Rhizosphere

"Soil zone influenced by roots"

NZ soils general

"Low fertility and acidic"

Soil improvement in NZ

"Fertiliser

Development phase

"High inputs to build fertility"

Maintenance phase

"Replace nutrients lost"

Nutrient losses

"Leaching

Diminishing returns

"Extra fertiliser gives smaller yield increases"

Economic optimum

"Best profit point"

Maximum yield point

"Higher than economic optimum"

Why not maximise fertiliser

"Costs exceed yield benefits"

Soil testing

"Assess nutrient availability"

Olsen P

"Indicator of plant-available phosphorus"

Soil sampling factors

"Depth

Fertiliser recommendations

"Based on trials and models"

Excess fertiliser impact

"Pollution and inefficiency"

Eutrophication

"Excess nutrients causing algal blooms"

Algal blooms effect

"Reduce oxygen in water"

Dead zones

"Low oxygen aquatic zones"

Nitrogen role

"Component of proteins and DNA"

Atmospheric nitrogen

"Mostly unavailable N2"

N fixation

"Conversion of N2 to NH3"

Biological fixation

"Done by legumes and bacteria"

Clover fixation

"Major N source in NZ pastures"

N fixation suppression

"High soil N reduces fixation"

Atmospheric deposition N

"3–9 kg/ha/year in NZ"

Fertiliser nitrogen

"Major anthropogenic input"

Imported feed nitrogen

"Adds N to system"

N cycle inputs

"Fixation

N cycle outputs

"Leaching

Nitrate leaching

"NO3- lost through drainage"

Leaching timing

"High in winter"

Urine patches

"High local N concentration"

Ammonia volatilisation

"Loss of NH3 gas"

Conditions for volatilisation

"High pH

Denitrification

"NO3- converted to N2 gas"

Denitrification conditions

"Anaerobic

N2O

"Greenhouse gas from soil"

Nitrification

"NH4+ → NO3-"

Nitrification conditions

"Aerobic soil"

N use efficiency

"More production per unit N"

Nitrification inhibitors

"Slow conversion to nitrate"

DCD

"Example inhibitor"

DMPP

"Another nitrification inhibitor"

Plantain effect

"Reduces nitrate leaching"

Cover crops

"Capture excess nitrogen"

Effluent management

"Redistributes nutrients evenly"

Feed management

"Lower N intake reduces excretion"

Phosphorus role

"Energy transfer (ATP)"

P loss issue

"Small losses cause big impacts"

Dissolved phosphorus

"Passes through filter"

Particulate phosphorus

"Attached to soil particles"

P transport pathways

"Overland flow

Overland flow

"Surface runoff transport"

Macropore flow

"Rapid flow through cracks"

P enrichment

"Higher P in eroded sediment"

P fixation

"Binding of P to soil"

High P soils

"Greater dissolved P loss"

P leaching soils

"Sandy

P management

"Reduce inputs and losses"