Understanding the legacy effect of previous forage crop and tillage management on soil biology, after conversion to an arable crop rotation

Abstract

The soil ecosystem provides a habitat for numerous and diverse fauna which hold a pivotal role driving decomposition and nutrient cycling. However, changing land use or management can alter population dynamics, changing soil biology within the system. The implementation of different field management can improve soil fertility, whilst natural variations in plant species growth and root system may create changes to soil structure and properties. All plant species create a legacy effect within the soil to some extent; changing the environment either physically or through remaining plant residues. An experiment investigated the hypothesis that previous forage cropping and tillage management would alter the diversity and abundance of soil fauna, after changing from a stable soil environment for three years to an annual arable crop rotation to complete a five-year rotation cycle. Four replicate plots (crop 1) of either perennial ryegrass (Lolium perenne), red clover (Trifolium pratense), white clover (Trifolium repens) or chicory (Cichorium intybus) were grown in a randomised block design (2009-2013) as the first crop, before conversion to an arable crop rotation. Spring wheat (Triticum aestivum) was established in 2013, either by conventional ploughing (CP) or direct drilling (DD); and winter barley (Hordeum vulgare) established using the same methodology the following autumn 2013 and harvested in 2014. Soil fauna abundance was sampled each year after the cereal crop was harvested, and included microfauna (nematodes), mesofauna (mites) and macrofauna (earthworms). Nematodes were found in greatest abundance in the previously ryegrass treatments, with greater numbers of bacterial feeders and herbivores (in 2013). Mesostigmata and oribatid mites had larger abundances in the ryegrass treatments, although Prostigmata were found in numbers five times higher after red clover in DD plots (in 2013); earthworms were found in significantly greater numbers in the previously white clover plots, across both cereal crops. These legacy effects began to diminish by the end of the second cereal crop in the rotation (in 2014). Tillage management also affected abundance, although these were fauna dependent, with earthworm numbers being detrimentally affected by ploughing whilst nematode abundances increased with ploughing. The combination of legacy and tillage elucidated interactions with the different groupsof fauna, for example, epigeic earthworms, wireworms, and prostigmatid mites showed changes in abundance dependent on the combined effect of forage and tillage. Overall, legacy effects were found across three organism scales, highlighting the impact agricultural cultivations have across the whole soil food web.