Soils Workshop 2008

Soil Fertility Session

13th August 2008

John Standley

Soil Carbon

• Labile carbon – oxidised with dilute potassium permanganate; the fraction changing most rapidly

• Organic carbon – oxidised by potassium dichromate in sulphuric acid; about 70% of total carbon

• Total carbon – converted to carbon dioxide at high temperature; may include carbonate

Organic carbon in soils

• Comparisons - surface and subsoil

• Different soils

• Uncleared land or by trees

• Under pasture or lawn

• In cultivated paddocks or gardens

• Bare soil

• See S-O3, S-O4

Soil pH and liming

• Some soils may be too acid for some plants

• Adjust pH by adding lime. Does gypsum have the same effect?

• Compare the three soils without and with the addition of lime

• Experiment with different rates• See S-O6

Fertilisers and pH

• Compare ammonium sulphate, ammonium nitrate, potassium nitrate and urea

• Check the effect of urea on the three soils

• Experiment with your soils

• See N-O6

Urea changes

• Expect urea to be converted ammonium to make soils more alkaline

• Expect ammonium to be converted to nitrate

• Check what has happened with the three soils

• Beware of units – measuring N (14) or NO3 (62) ppm?

Fertiliser experiments

• Grow various plants with various fertilisers and record what happens

• Compare rates and plot growth response curve

• Maybe in conjunction with maths teacher run a replicated trial, fertiliser rates replicated three or four times to separate treatment and environmental effects

Nutrient removal

• Consider removal by various crops

• Consider fertiliser analyses and how much needs to be applied

• Consider manures

• See N-O5

Manure composition

• An example

• Cattle manure from feedlots

• Nitrogen 2%

• Phosphorus 0.8%

• Potassium 2.3%

• Compare with inorganic fertilisers and calculate how much will be required

Deficiency symptoms

• What does the plant tell us?

Mycorrhizae

• Have a look

• Experiment with linseed in pots

• Soil “as is”, sterilised , with and without inoculum added

• Also with and without P fertiliser

• Could consider zinc too

• See O-O6

Nodulation

• Examine the roots of grasses and legumes

• Grow soybeans with and without rhizobial inoculum

• Examine nodules

• With and without N fertiliser

• See O-O7