Understanding the legacy effect of previous crop rotations on soil biology:Extended abstract

The importance of crop history in relation to soil processes and soil community structure and function was investigated. Legacy effects have been studied for plant invasions and environmental fluctuation, but here the focus was on the importance of previous forage crop during rotation. Soil communities are extremely important, complex and diverse, driving nutrient cycling and decomposition. Maintaining a healthy soil food web is known to increase agricultural productivity (DuPont et al., 2009), monitoring how the individual invertebrate orders are affected by legacy effects will provide an indication of the impact of agricultural practice. The effect of perturbation or environmental change and the consequences on biodiversity dynamics and function may differ depending on plant type within an ecosystem. An experiment was set up to test the hypothesis that previous forage cropping and establishment method would alter the soil ecosystem leading to changes in the food web, during crop rotation. Studies normally focus on the first cereal crop after a forage rotation (Kirkegaard & Ryan, 2014), whereas here we want to focus on the impact of different forage crops on the second cereal crop in rotation. Plots were grown containing pure swards of chicory (Cichorium intybus), red or white clover (Trifolium pratense, T. repens) or perennial ryegrass (Lolium perenne) for three years before becoming part of a crop rotation. Four replicate plots of each of the forages were established (12 m × 7.5 m) in 2009 (crop 1) in a randomised block design; these were split (12 m × 3.75 m) in spring 2013 and winter wheat established either by ploughing, or by direct drilling; with wheat harvested autumn 2013 (crop 2). Winter barley (cv. Pearl) was established using the same methodology and plan as for the previous wheat establishment (crop 3). It was hypothesised that legacy effects of the original crop (crop 1) pure forage swards would affect the diversity and abundance of soil faunal population to a varying extent dependent on original forage type, even though both crop 2 and 3 were the same across all plots. It was also hypothesised that direct drilling would disturb the soil food web less than ploughing. The findings presented here are the assessment of the soil faunal populations after barley harvest (crop 3, autumn 2014); the soil fauna sampled included microfauna, mesofauna, and macrofauna. Overall, our preliminary findings show that for a number of soil faunal groups across the three scales of sampling, there was a trend for the original previous forage to affect the current soil food web, even though the ecosystem has now been standardised between the different plots and two years and crops had elapsed. There was also a significant effect over all soil faunal populations when assessing the difference in cultivation method – plough versus direct drill particularly for earthworm numbers (Fig. 1A,B). Our findings have begun to show the linkage between soil biodiversity and the legacy effects of agriculture on the whole ecosystem and show the influence one crop type can have within a rotation. The legacy effects varied between faunal groups, some diminishing with time elapsed whilst other groups maintained the differences created by the original forage treatment. The legacy effects seen here after two crops and years in a rotation have important implications in relation to the impact of crop sequence choices within agriculture.