Michael Beare, Denis Curtin, Glyn Francis, Trish Fraser, Richard Gillespie, and Tina Harrison-Kirk. Institute of Crop & Food Research, Private Bag 4704, Christchurch, 8020, New Zealand
Management of soil organic matter (SOM) may be important to sustaining long-term arable cropping following improvements under pasture in New Zealand mixed-cropping rotations. The establishment of crops with different tillage (conventional [CT], minimum [MT] and no-tillage [NT]) and cover crop management practices were investigated for their effects on SOM dynamics, soil structure and soil water storage. After five years of continuous cropping, organic C loss ranged from 5 to 12 Mg C/ha and was greatest under CT, intermediate under MT and lowest under NT. Loss of C from an uncultivated chemical fallow treatment was high, indicating that continuous inputs of plant matter are important to maintaining SOM. Particulate C represented the largest fraction (12-21%) of total soil C. Surface soil aggregate stability (MWD) decreased from 2.0 mm under grass pasture to about 1.1, 1.5 and 1.7 mm after 5 years of cropping under CT, MT, and NT, respectively, in line with organic C losses. Surface soil (0-20 cm) under no-tillage maintained an average of 15 and 6 mm more water than CT and MT treatments, respectively, during the summer irrigation period. Good to average crops of barley, wheat and peas were achieved with little or no differences between tillage systems.
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