Ecosystem services of the soil food web after long-term application of agricultural management practices

The structure of soil nematode assemblages was assessed in field plots in the San Joaquin Valley of California which have 16-year management system histories. Attributes of the ecosystem functions of the assemblages were determined in laboratory studies. The four agricultural management systems were no tillage (minimum tillage) with cover crops in the intervals between economic crops, standard tillage with cover crops, minimum tillage without cover crops and standard tillage without cover crops. The economic crops were sorghum and garbanzo beans. A soil column system was used in laboratory studies to evaluate the nitrogen mineralization ecosystem service associated with nematode assemblages in soils from the four management systems compared to that in defaunated soil. In an additional comparison, defaunated soil was amended with mineral fertilizer solution for comparison with the mineralization service of the soil fauna. Management systems using cover crops, which created a continuity of both photosynthetic production and roots in the soil, strongly enhanced the nematode assemblages in the field soil. Management systems with cover crops had greater total abundance, measured as numbers, biomass and metabolic footprints, of nematodes, and also of the functional guilds of nematodes considered important in soil fertility and as prey for predators. Leachates from soil columns with intact nematode assemblages had greater total mineral nitrogen and supported greater plant growth than those from defaunated columns. Soil carbon levels in field plots were strongly affected by the management systems. The biomass and diversity-weighted footprint of bacterivore and microbivore (bacterivores plus fungivores) nematodes, in turn, were correlated with levels of soil carbon.