Sown Diversity Effects on the C and N Cycle and Interactions with Fertilization

A better understanding of the role of plant composition and N cycle on agroecosystems is necessary, as these will be affected by future developments in agriculture intensification. To explore the effect of plant diversity on yield and carbon (C) and nitrogen (N) balances in forage mixtures, identifying potential co-benefits between functions. We analyzed results from a field experiment where plants of three forage species (a grass, a legume, and a non-legume forb) were cultivated in monocultures and mixtures. Three years after sward establishment, dry matter yield, together with δ¹⁵N, δ¹³C, and C and N content in plant and soil material were measured. In addition, we analyzed a second scenario to investigate the effect of fertigation with pig slurry (δ¹⁵N = +8.4‰) on the C and N balances of forage species. Results support the hypothesis that C and N allocation is affected by plant diversity. Plant composition affected N source (% N derived from air, % N derived from soil, and % N transferred in mixtures). In addition, sown diversity increased yield and modulated C and N balances. The δ¹⁵N of samples was affected by both plant composition and fertigation. These results are consistent with previous work showing strong plant composition effects on N-balances, and the potential role that legumes play in enhancing nitrogen sources (derived from the atmosphere) into forage mixture systems. This study contributes to the prediction of suitable sown plant community composition and N management for the optimum agriculture with increased productivity and at the same time reduced environmental impact.