Agriculture Reference
In-Depth Information
and Plane 2000). Other recent developments in hand weeding technology include self-pro-
pelled and tractor-drawn platforms on which people lie while moving along crop rows and
weed by hand (Leinonen and Närkki 2000, Bishop et al. 2002).
Mulches
Mulches can be used economically in many organic horticultural crops including annual herbs
and vegetables as well as perennial vine and tree crops. In addition to suppressing weeds, organic
mulches have other benefits such as conserving soil and moisture, reducing soil temperature
f fluctuations, adding organic matter and nutrients to the soil and preventing soil from splashing
onto crop leaves (Patriquin 1988, Teasdale and Mohler 1993, Whitten 1999). Materials used as
organic mulches include compost and manures, crop residues (ash, grass, hay, in situ residues,
starch, straw), tree products (bark, sawdust and woodchips), fibre products (fabric, jute, coconut
fibre, wool), and paper products (pellets, sheets, rolls, chopped, shredded).
Synthetic mulches are allowed for limited use in organic production (IFOAM 2002) and offer
many of the benefits of organic mulches but are considered less sustainable owing to the non-
renewable source materials, energy required in manufacture, single usage limitation and long-
term disposal requirements (Olsen and Grounder 2001). Woven plastic material, such as weed
matting, is permitted for restricted, short-term use only. Shade cloth (Sutton 1998) and weed
matting (Monks et al . 1997) have been used in conventional vegetable production, and weed
matting has been tested in organic peach ( Prunus persica ) orchards (Zimmerman 2002), but few
examples were identified in the literature about the use of these synthetic mulches for organic
herb and vegetable growing (Birkeland and Døving 2000, Radics and Székelyné Bognár 2002).
Several problems have been reported with the use of mulches for weed control including
acquiring enough material, transporting and handling and laying large amounts of often
bulky material, cost of materials, introducing weed seeds, applying an inadequate depth and
interfering with crop growth harvesting (Henderson and Bishop 2000). The negative effects of
mulches on crop yield are related to several mechanisms including nutrient immobilisation
(especially N), phytotoxin release, poor weed control, increased pests levels and modified soil
aeration, moisture and temperature (Teasdale 1998, Leary and Defrank 2000).
With regard to mulch handling and application, the lack of efficient equipment for laying
organic mulches is a serious constraint to wider usage (Olsen and Gounder 2001, Schäfer et al .
2001). Strategies for reducing the costs of laying mulch include the use of novel materials such
as f lowable, pelletised mulches (Smith et al . 1997), spray-on mulch (Russo 1992) or paper rolls
that could be applied in a similar way to polythene mulch (Runham et al . 2000). In situ mulches
such as cover crops grown on site and terminated (mechanically or through senescence) prior
to planting a vegetable crop, offer the benefit of reducing mulch handling costs, although
skilled management is required to grow effective weed-suppressing mulches while optimising
growth of the subsequent cash crop (Abdul-Baki and Teasdale 1997, Creamer and Dabney
2002, Ngouajio et al . 2003). Ngouajio and Mennan (2005) report that fresh rye ( Secale cereale )
residue can interfere with planting seedlings and that, despite good weed suppression by hairy
vetch ( Vicia villosa ), subsequent cucumber yields were unacceptably low.
Grazing
Organic agriculture has traditionally relied on the integration of livestock and cropping phases
for various functions including weed control, crop protection and fertility management (Köpke
and Geier 1999). More recently, the international organic movement is now heavily dominated,
in terms of the land area certified, by extensive grazing systems, principally in Australia and
Argentina (Willer and Yussefi 2005). Globally, a diverse range of animals are used to control
weeds on organic farms including poultry, goats, cattle and pigs. The animals may be used for
Search WWH ::




Custom Search