Nr. Hulugalle et al., EFFECT OF LONG-FALLOW ON SOIL QUALITY AND COTTON LINT YIELD IN AN IRRIGATED, SELF-MULCHING, GREY VERTOSOL IN THE CENTRAL-WEST OF NEW-SOUTH-WALES, Australian Journal of Soil Research, 36(4), 1998, pp. 621-639
Reduced crop growth rates ('long-fallow disorder') can be a feature of
long-fallow; cotton (cotton, alternating with a bare fallow, is sown
every other year). This is usually attributed to decreased development
of arbuscular mycorrhiza (AM), although associated soil physical, che
mical, and biological properties are very rarely reported. A study was
conducted from 1993 to 1997 in a grey, self-mulching Vertosol in the
central-west of New South Wales to characterise soil properties under
long-fallow cotton with a view to identifying soil factors other than
AM that could contribute to cotton growth rate reductions. Soil qualit
y indicators monitored were compaction (bulk density and air-filled po
rosity), strength (cone resistance), plastic limit, exchangeable catio
ns, nitrate-N, pH, organic C, development of AM, and incidence of cott
on root diseases. In comparison with continuous cotton, long-fallow co
tton had lower soil strength, and lower plastic limit. Exchangeable Ca
and Mg Ir ere higher with continuous cotton only in 1994. Higher nitr
ate-N was also observed with long-fallow during the first fallow phase
of the experiment. Long-fallow did not have any significant effect on
soil organic carbon. However, a net decline in soil organic C and exc
hangeable Mg occurred with both treatments. During the cotton phase, s
ubsoil nitrate-N and incidence of black root rot were lower with long-
fallow cotton. Uptake of nitrogen by continuous cotton may have been r
educed by greater severity of black root rot. Vegetative and reproduct
ive growth, water extraction, and cotton lint yields in long-fallow co
tton plots were higher than those in continuous cotton plots. AM devel
opment was similar with continuous cotton and long-fallow cotton. Comp
ared with long-fallow cotton, the lower lint yield in continuous cotto
n was thought to be due to the interactive effects of declining nutrie
nt availability, higher soil strength, and greater severity of black r
oot rot causing decreases in nutrient and water uptake.