Comparing nematode and earthworm communities under combinations of conventional and conservation vegetable production practices

Although reduced tillage, organic inputs and diverse cropping rotations are often promoted as practices that facilitate greater abundance and diversity of soil biota, rarely have these management systems been examined in concert to investigate their individual and cumulative long-term effects on soil invertebrates. This study investigated two key functional groups of soil invertebrates, nematodes and earthworms, after 10 years in a field experiment investigating three types of agricultural management practices. Agricultural management treatments were tillage (moldboard plow vs. strip tillage), inputs (synthetic fertilizers, pesticides and fumigation vs. inputs approved for organic production) and crop rotation (continuous tomatoes (Solanum lycopersicum L.) vs. diverse vegetable rotation). The experiment was established in western NC (United States) on a fine-sandy loam (FAO: Acrisol). Nematode sampling and earthworm extractions were performed in spring and fall of 2004. The rotation effect on nematode and earthworm populations was generally non-significant. Averaged over sampling dates and other treatments, total nematode counts for synthetic input treatments were 59% of organic input treatments; likewise, plow treatments were 52% of strip till treatments. The strip till organic treatment combination (strip tillage with organic inputs) resulted in over four times as many nematodes as the plow synthetic treatment combination (moldboard plow with synthetic inputs). These data demonstrate that while nematode abundance responds sensitively to tillage and input practices individually, combinations of treatments displayed consistently greater nematode abundance when organic inputs and strip tillage were applied together. Long-term strip tillage increased earthworm populations 31-fold compared to plowed treatments. Organic inputs resulted in more earthworms than synthetic inputs in spring, but not fall. Strip tillage increased earthworm populations far more effectively than organic inputs. Even so, earthworms also displayed the positive combination effect of strip tillage and organic inputs; on average, 24 earthworms m−2 were extracted from strip till organic treatments vs. 15 from strip till synthetic and just one from plow organic treatments. We conclude that the data support our hypothesis; there is a positive combination effect resulting in greater nematode and earthworm abundance when strip tillage and organic inputs are used together in agricultural production systems. These results confirm the long-term benefits of conservation practices observed in agricultural ecosystems and we suggest that the principle of compounded benefits from combinations of conservation practices extend to all managed ecosystems. We recommend that agricultural researchers consider both tillage and agricultural inputs when interpreting or predicting soil biological responses to agricultural management decisions.