Soil fauna in rainfed paddy field ecoystems: their role in organic matter decomposition and nitrogen mineralization (Volume 3) (English shop)

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The increase in food crop production, such as rice, to compensate for population growth in
Indonesia should be sustainable in order to maintain environmental quality and conserve natural
resources for future generations. In this study, the biological enhancement of soil organism
populations and their ecological services, such as organic matter decomposition and nitrogen
mineralization has been studied in a rainfed paddy field ecosystem in Pati, Indonesia. The
cropping system used by local farmers is (1) two rice seasons, consisting of dry-seeded rice,
planted at the beginning of the rainy season and transplanted rice, planted at the end of the rainy
season, and (2) a short fallow (dry phase) during the dry season.
In the rice seasons, the soil fauna abundance, biomass and diversity, and the role of soil
fauna in litter decomposition and nitrogen mineralization were evaluated in treatment plots with
two different bund distances (4m and 8m) and crops cultivated on the bund (control, cassava
and mungbean). The short bund distance (4m) would facilitate the movement of the soil fauna
from the field (during the flooding) to the bunds, and cultivation of crops on the bunds would
increase the soil surface cover thus protecting the soil fauna on the bund from direct sunshine.
This was, therefore, expected to enhance the soil fauna population and its ecological services.
The soil fauna population was studied using the Berlese funnel extractor method, and litter
decomposition using three different mesh-sized (coarse, medium and fine) litterbags. Nitrogen
mineralization was studied using undisturbed soil confined within PVC tubes containing ion-
exchanged resins.
Generally, abundance, biomass and diversity of soil fauna were lower during the rice
field phases than in the dry phase. The most numerous taxa in the dry phase were Oribatida
(oribatid mites), whereas Sminthuridae (Collembola) dominated during the rice phases. In terms
of biomass, Coleoptera was the most dominant taxon in the dry fallow phase, while their larvae
along with the larvae of Diptera were the most dominant taxa under (flooded) rice phases.
Earthworms sporadically occurred both in the fallow and in the rice seasons, without any
particular pattern. Once they occurred in the soil samples, their biomass could make up for more
than 60% of the total.
Though the soil fauna population was suppressed in the field during the (flooded) rice
seasons, the physical environmental conditions, such as warm air temperature and high soil
moisture may adequately support their activities to play their role in litter decomposition and N-
mineralization. In the rice seasons, the short bund distance (4m) tended to increase soil fauna
abundance, biomass and diversity. This effect was more pronounced when the bund was
cultivated with crops, in which they enhanced macrofauna biomass during the dry-seeded rice.
A combined effect of short bund distance and crop-planted bund was also shown in litter
decomposition and N-mineralization in the field. Mungbean on the bund increased the litter
decomposition, whereas cassava increased N-mineralization, suggesting that both mungbean
and cassava are appropriate for bund crops. Thus, the short-bund distance with crops planted on
the bund seemed to be favorable habitat for soil fauna population, so that they can enhance their
role in soil processes and help in the management of crop residues.