© Springer International Publishing AG 2016 99
M. Farooq, K.H.M. Siddique (eds.), Innovations in Dryland Agriculture,
DOI 10.1007/978-3-319-47928-6_4
Weed Management in Dryland Cropping
Systems
Michael Walsh
1 Introduction
Approximately 40 % of the world’s total land area is generally described as regions
in which crop production is constrained by low annual rainfall (<500 mm) (ACIAR
2002 ; FAO 2000 ; Oram 1980 ). FAO defines drylands as areas with a growing period
of 1–179 days (FAO 2000 ). The United Nations Convention to Combat Desertification
(UNCCD 2015 ) defines drylands as areas where the ratio of precipitation to poten-
tial evapotranspiration ranges from 0.05 to 0.65. Regardless of the definition, crop
production within these regions is primarily restricted by rainfall. Although rainfall
is the primary constraint to cropping in dryland areas soil fertility, land degradation,
poor resources and subsistence farming limit crop production to 4 % of the world’s
dryland regions (Koohafkan and Stewart 2012 ).
Dryland production regions in Mediterranean type climates of hot dry summers
and coil moist winter-spring growing seasons are characterised by cereal dominated
cropping systems (Fig. 1 ). Across these regions consistently the dominating influ-
ence on crop production is climate, specifically rainfall amount and frequency.
Dryland crop production is practised in a moisture limiting environment and weed
control practice must fit within the context of soil water conservation. The increas-
ing need to conserve soil moisture along with improving soil structure and nutrient
retention continues to drive the widespread adoption of conservation cropping prac-
tices based on residue retention and restricted cultivation (FAO 2015 ; Kassam et al.
2012 ; Llewellyn et al. 2012 ). The adoption of these systems has been facilitated by
the availability of highly effective in-crop selective herbicides.
Frequently soils of dryland cropping regions are unproductive and do not support
the full crop production potential thereby creating the opportunity for weed invasion
M. Walsh (*)
Plant Breeding Institute, University of Sydney, Narrabri, NSW 2390, Australia
e-mail: [email protected]