PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Non-living agents (contd)
CLIMATE CHANGE, SALINITY.
CLIMATE
CHANGE
‘global warming’
‘greenhouse
effect’
Although the term ‘climate change’ can refer to any variation in climate or atmospheric
conditions which has taken place over millions of years, in recent times, the term is taken
to mean changes in climate that are the direct result of human activity.
The most important greenhouse gases are water vapour, carbon dioxide, methane and
ozone. Increases in these gases over recent decades are considered to be due to human
activity, eg transportation, agriculture, etc. The effect on sea levels, water and food
supplies, pests, weeds, social conflict and the migration of peoples is being researched.
Dept. of Climate Change www.climatechange.gov.au/
Left: Sun and Earth Under Normal Conditions The greenhouse effect is a natural process -
redistributed around the globe through atmospheric and oceanic circulation patterns (winds, ocean
currents, etc). Energy is then radiated back from the earth into the atmosphere as long-wave radiation.
Over time long and short wave radiation should balance. Right: Increasing energy radiated back to
earth. Greenhouse gases absorb some of the energy radiated back into the atmosphere as long wave
radiation. Increasing concentrations of these gases mean that more is absorbed and less released into
space - radiation is trapped in the atmosphere and reflected back to earth causing a heating of the
www.ecn.ac.uk)
SALINITY
Do not confuse
salinity with
acid soils or
sodicity:
Sodicity refers to soil
containing levels of
sodium that affects its
physical properties,
when they become wet,
clay particles lose their
tendency to stick
together, become
unstable, erode and
impermeable to water
and roots
Acid soils are a
condition in which the
surface soil pH has
declined to less than
pH 5.5 as a result of
human activity, such as
agriculture (page 395
Fig. 228)
Saline soils are defined as those in which the concentration of soluble salts in soil
and water is sufficient to restrict plant growth, increase soil erosion and salt pollution of
rivers, water supplies, irrigation systems, damage roads, fences and buildings.
Department of Agriculture, Fisheries & Forestry www.daff.gov.au/
Primary or natural salinity has developed in former marine areas or on rocks which
contained trapped marine salts that break down to form soils.
Secondary or induced salinity occurs when surplus water percolates into the water
table making it rise. Naturally occurring salts found in the soil and rock are dissolved
and brought to the surface, coming into contact with vegetation.
– Irrigation salinity results from poor irrigation practices. More water is applied than can be
used by the crop, excess water causes water to rise bringing the salts into contact with plants.
– Dryland salinity is typically caused by extensive clearing of vegetation (mainly trees) for
agricultural and grazing land.
CSIRO Land & Water www.clw.csiro.au/issues/salinity/
Effects on soils and plants. Soils crust on the surface, soil clays swell and fine soil
particles disperse. Salt in soil reduces the availability of water to plants and at high
enough concentrations can kill plants, it may also result in toxicity of certain ions
namely sodium and calcium, nutritional imbalances and deficiencies, and favour some
diseases, eg Phytophthora root rot of some tomato cultivars. Salt-affected sites are
complex and are influenced by interaction between soil, water, plant species and climate.
Salt may occur in the soil/media, fertilizer or irrigation water. Some forms of fertilizers are
more prone to result in salinity problems, eg potassium as potassium chloride (potassium as
potassium sulphate less likely)
Plants continually remove water from soil via evapo-transpiration. Left: Trees have deeper and more
extensive roots systems and extract more water from the ground than do grasses and shallow-rooted crops.
Right: When trees are removed and replaced with shallow-rooted grasses and crops, surplus water
percolates into the water table causing it to rise bringing dissolved salts with it (adapted from Wakefield 1994).
394 Non-parasitic pests and diseases