TABLE CONTENTS

SESSION SIX – NEMATODES IN FARMING SYSTEMS
CONVENORS: GRAHAM STIRLING & SAAD HAFEZ
Enhanced Soil Carbon: The Key to Improving Soil Health and Suppressing
Nematode Pests
Stirling, G.R. (1) & M.J. Bell (2)
(1) Biological Crop Protection, 3601 Moggill Road, Moggill, Qld. 4070, Australia; (2) Queensland Department
of Primary Industries and Fisheries, Kingaroy, Qld., 4610, Australia
Observations on sugarcane cropping soils in Australia have shown that conserving soil
organic matter through practices such as residue retention and minimum tillage increases soil
C levels (particularly the labile fraction that is oxidised by 33mM potassium permanganate).
This results in an improvement in aggregate stability, rainfall infiltration rates, cation
exchange capacity, amounts of potentially mineralisable N and a reduction in bulk density
and surface crusting: all positively associated with soil and plant health. Suppressive
mechanisms against plant-parasitic nematodes are also enhanced due to increased microbial
activity. Experiments in microplots and the field have shown that Pratylenchus zeae and
Meloidogyne javanica do not multiply as readily in soils that receive continual C inputs from
a mulch layer of plant residue, are not disturbed by tillage, or are amended with high C/N
residues. Numerous suppressive mechanisms are probably operating, but predatory fungi that
obtain N from nematodes in low N environments appear to be involved. Results of
experiments in other cropping systems also confirm the key role of organic matter in
biological suppression of nematodes. In minimum till cereal cropping systems, Pratylenchus
thornei reaches high population densities at depth but does not multiply readily in surface
soils, where C levels are highest due to stubble retention and suppressive mechanisms are
operating. In capsicum cropping systems, where biological activity is limited by low C
inputs, excessive cultivation and reliance on soil fumigation, populations of M. incognita and
the level of damage caused by the nematode can be reduced by a combination of organic
amendments, minimum tillage and mulching with plant residues. Collectively, these results
suggest that the key to improving sustainability and reducing losses from nematode pests is to
introduce practices that reverse the decline in soil C that currently characterizes most
cropping systems.
5 th International Congress of Nematology, 2008 21