Nr. Hulugalle et J. Cooper, EFFECT OF CROP-ROTATION AND RESIDUE MANAGEMENT ON PROPERTIES OF CRACKING CLAY SOILS UNDER IRRIGATED COTTON-BASED FARMING SYSTEMS OF NEW-SOUTH-WALES, Land degradation & rehabilitation, 5(1), 1994, pp. 1-11
The effects of planting cereal or leguminous crops in rotation with ir
rigated cotton (Gossypium hirsutum L.) on the properties of cracking d
ay (swelling) soils in the Macquarie and Namoi Valleys of New South Wa
les, Australia were evaluated during the summer of 1992-3. The observa
tions were made on commercial farmers' fields. The soil properties eva
luated were the particle size distribution, the dispersion index, the
plastic limit, the percentage of coarse (particle diameter 212-2000 mu
m) and fine (particle diameter 53-212 mum) particulate soil organic ma
tter, soil respiration rate, soil reactivity, soil aggregate density,
pH, nitrate-N and exchangeable Ca, Mg, K and Na. In general, the plant
ing of rotation crops decreased the dispersion index, plastic limit an
d soil aggregate density, and increased the amount of coarse particula
te organic matter. Planting rotation crops also resulted in significan
tly higher clay and lower silt contents in the Macquarie Valley, and s
ignificantly higher soil respiration in the Namoi Valley. Soil pH, nit
rate-N and exchangeable cation concentrations were not significantly a
ffected by planting rotation crops in the Macquarie Valley, whereas ex
changeable Na was increased in the Namoi Valley. The retention of crop
residues in situ, compared with burning crop residues, decreased the
dispersion index, plastic limit and aggregate density, and increased t
he amount of coarse particulate soil organic matter at all measured de
pths of the Macquarie Valley. The retention of crop residues in the Na
moi Valley decreased the plastic limit and dispersion index only in th
e 0-50 mm depth range, whereas burning crop residues increased exchang
eable K at all depths. In general, planting rotation crops and the ret
ention of crop residues had greater beneficial effects on the soil phy
sical properties in the Macquarie Valley than in the Namoi Valley, and
in the topsoil compared with the subsoil. These differences are attri
buted to a shorter rotation interval in the Namoi Valley, smaller amou
nts of coarse particulate soil organic matter in the subsoil, and diff
ering soil types in the two valleys. In the Namoi Valley the coarse or
ganic matter produced by leguminous crops appeared to be more effectiv
e in promoting structural stability than that from non-leguminous crop
s, although no such difference was observed in the Macquarie Valley.