the role of compost in soil

Introducing by

2006-2007

Introduction

Composting organic wastes is

an environmentally sound

means

of recycling raw organic

materials into valuable soil

amendments with many

uses .

Why use compost?

• Composting is a method of stabilizing organic wastes by the action of microorganism

• Increasing soil organic matter 30t/ha compost provides ~ 6 t/ha of organic matter = long-term benefits for soil structure, fertility and water holding

• Slow release nutrients 30 t/ha compost is worth ~ £90/ha

• Increasing soil microbial population

• Stabilizing soil pH (fertilizers acidify soil) Better crop establishment & yields

The composting process

The basic process is very simple:•Collection of suitably balanced feedstock

materials

•Shredding

•Composting

•Maturation

•Screening

•Application of finished product

Distributed by: Information Packaging Centre Alberta Agriculture, Food and Rural Development 7000 - 113 Street, Edmonton, Alberta Canada T6H 5T6

Material flow for the conventional composting process.

How does composting work?

Types of composting

-Farmyard manure (FYM)

-Poultry Manure

-Cattle slurry

-Town refuse

-Sewage sludge

Characteristics of compostGeneral properties of green waste compost

pH8.6

Electrical conductivity (dS cm-1)0.773

Dry matter(%) 59

Density (kg L-1)0.5

Organic matter(%) 19

Characteristics of compost

Nutrient contents

Contamination with heavy metals (mg/kg dry weight)

Contamination with heavy metals (mg/kg dry weight)

Contamination with heavy metals (mg/kg dry weight)

HM loading rates(kg metal/ha/year when compost applied at

35t/ha/yr)

Contamination with inert fragments(% by weight)

The effects of compostapplication

Greater diversity ofsoil organisms

Improved soil structureand water retention

Supply of plantnutrients

Suppression of plantpathogens

Effects on soil chemistry

• The nitrogen in compost is very stable and is only released slowly – there is therefore little risk of it being leached

• Compost is a good source of potassium (in a readily available form)

• Compost is a reasonably good source of phosphorous

• Trace elements are also retuned to the soil

Copper addition when organic materials are spread (g/ha/yr)

Zinc addition when organic materials are spread (g/ha/yr)

Organic matter additions (250 kg/ha N)

Effect of organic matter inputs on topsoil available water capacity (AWC)

Compost can help conserve soil moisture

Moisture at 10 cm

Effect of organic matter inputs on topsoil microbial biomass-

An example of the effects on crop yields

Yie

ld (

per

cen

t o

f co

ntr

ol)

Potatoes Onions Cabbages Carrots

Effect of organic matter inputs on topsoil microbial biomass

Effect of total nitrogen inputs on topsoil PMN (potentially mineralisableN)

Effects on soil structure

• Organic matter additions improve soil structure on both heavy and light land.

• This has beneficial effects on water holding capacity, drainage, erosion and root penetration.

• Cultivations are made easier.

Effects on soil biology

• Biological activity is stimulated by the addition of nutrients and by the improvement to soil structure

• Some evidence suggests that there can be inhibition of plant diseases

Maximum supply of soil microelements and heavy metals content

ElementUnited Land (mg/kg) United Kingdom (Kg/h)

Zn1000560

Cu400280

Ni10070

Cd1050

Pb2501000

Hg22

Cr-1000

Maximum limit for soil microelements and heavy metals content due to supply compost

(mg/kg soil)

ElementLand

UnitedEngland

European United

Germany

Zn150300300300

Cu50135140100

Ni50757550

Cd2333

Pb100300300100

Hg144.52

Cr150--100

ConclusionsComposting can be an effective way of

managing organic wastes.

On-farm composting is a useful technique for dealing with farm generated wastes – bringing in material from elsewhere can be a good business in itself.

Application of compost adds to the organic matter in the soil

Compost is a good source of available P and K.

The nitrogen it contains is in a stable state and relatively unavailable in the short term.