Abstract
The purported benefits of conservation tillage and continuous cropping in
agricultural systems include enhancement of soil ecosystem functions to
improve nutrient availability to crops and soil C storage. Studies relating
soil management to community structure allow the development of
bioindicators and the assessment of the consequences of management practices
on the soil food web. During one year (December 2003-December 2004), we
studied the influence of continuous cropping (CC), intermittent fallow (F),
standard tillage (ST) and no tillage (NT) on the nematode assemblage and the
soil food web in a legume-vegetable rotation system in California. The most
intensive systems included four crops during the study period. Tillage
practices and cropping pattern strongly influenced nematode faunal
composition, and the soil food web, at different soil depths. Management
effects on nematode taxa depended on their position along the
coloniser-persister (cp) scale and on their trophic roles. At the last
sampling date (December 2004), Mesorhabditis and Acrobeloides were
positively associated with NH+4, while Panagrolaimus and Plectus were
negatively correlated with certain phospholipid fatty acids (PLFA).
Microbial-feeders were in general associated with both bacterial and fungal
PLFA, microbial biomass C (MBC) by chloroform fumigation-extraction, total C
and N, NH+4 and NO−3, and were most abundant in the surface soil of the NTCC
treatment. Fungal-feeders were more closely related to PLFA markers of fungi
than to ergosterol, a purported fungal sterol. Discolaimus, Prionchulus,
Mylonchulus and Aporcelaimidae, in contrast, were associated with
intermittent fallow and deeper soil layers. The organisms in the higher
levels of the soil food web did not respond to the continuous input of C in
the soil and a long recovery period may be required for appropriate taxa to
be reintroduced and to increase. At the end of the experiment, each
treatment supported quite different nematode assemblages and soil food
webs.
Incorporation of mineral nitrogen into the soil food web as affected by plant community composition