Soil fauna increase nitrogen loss in tilled soil with legume but reduce nitrogen loss in non-tilled soil without legume

We conducted a factorial microcosm experiment to determine whether the effects of soil fauna on N dynamics differ in tilled vs. non-tilled soil with and without a legume. Soil monoliths were taken from two neighboring fields that had been continually tilled or non-tilled for the past 15 years; the soil was defaunated, and meso- and macrofauna were added back to half the monoliths. In addition, half of the monoliths were planted with a legume (Lotus corniculatus), and the other half were maintained without vegetation. Nitrogen losses by leaching from soil were periodically determined. After 3 months, the plants were harvested, and the soil and plants in each treatment were analyzed for, plant biomass, microbial respiration and biomass, PLFA. Fauna significantly increased N loss only in the tilled soil with legume and significantly decreased N loss in the non-tilled soil without legume. When fauna were absent, legume biomass was higher in the non-tilled soil than in the tilled soil, but when fauna were present, legume biomass did not differ between tilled and non-tilled soil. Our results show that non-tilled soil with fauna conserves soil N and enhances the efficient use of N by plants.