Soil fauna groups respond differentially to changes in crop rotation cycles in rice production systems

Abstract

Permanently flooded rice cropping is increasingly converted to rotation systems including upland crops, managed with adaptive nitrogen fertilizer application schemes for the sake of both saving water and optimizing nutrient application. Such changes alter the diversity and composition of the edaphic fauna, with a critical impact on soil functioning. We conducted a survey at 12 plots in Central Luzon (Philippines) over four cropping seasons to quantify the response of soil nematodes, enchytraeids, and microarthropods (collembolans and mites) to different crop rotations. We additionally assessed the impact of three different N-fertilizer input levels. A marked shift from enchytraeids to microarthropods (i.e. from semi-aquatic to terrestrial taxa) occurred in crop rotations involving upland crops. Microarthropod abundance increased faster in permanently non-flooded rotation system than in rotation schemes including temporal flooding. Mites and most springtail taxa proved to be very vulnerable to crop-associated flooding. Enchytraeids, in contrast, responded positively. Bacterivorous and fungivorous nematodes were affected to a much greater degree by the level of nitrogen input than by crop rotation. N fertilizer application thus significantly altered the trophic composition only of the soil micro-food web. According to our results we propose that the establishment of a genuine terrestrial soil food web after cropping scheme conversion in the conditions of volcanic soils in Central Luzon island may potentially be driven by two processes: The first is associated with the seasonally disrupted increase of microarthropod abundance driven by individuals invading from associated habitats through the top of the bunds, accompanied by an extinction of the semi-aquatic mesofauna, and second, the recovery of microarthropods that are able to survive submerged conditions in low numbers. The marked effect of N fertilizer application on the microfauna indicates that fertilizer management may significantly impact the conversion process by altering the microbial base of the soil food web.