Multispecies swards improve nitrogen use efficiency and reduce nitrogen surplus in agricultural grasslands

Abstract

Aim: Improving nitrogen use efficiency (NUE) is critical for enhancing the sustainability of agricultural grasslands. However, there is limited research assessing NUE of grasslands managed with different nitrogen (N) fertilization inputs. We tested the hypothesis that multispecies swards managed with the combination of chemical and organic fertilizer would perform best with respect to herbage N yield and NUE. Methods: A grassland field experiment was conducted over two years with four sward types: permanent pasture (baseline sward), perennial ryegrass monoculture, 6-species and 12-species swards; and three N fertilizer treatments: chemical, organic and a combination of chemical and organic fertilizer. Perennial ryegrass received 170 kg N/ha/yr while the other swards received 70 kg N/ha/yr. Results: We found significant main effects of sward types and the N fertilizer treatments on herbage N yield and NUE indices. The multispecies swards (i.e., 6- and 12-species) had higher NUE, more negative partial N balance and higher partial factor productivity than perennial ryegrass sward across both years (P < 0.05). The proportion of legumes in the multispecies swards explained 55% of the herbage N yield. All N fertilizer treatments had NUE > 1 and negative partial N balance with the highest value in chemical fertilizer. NUE > 1 and negative partial N balance indicate greater herbage N yield relative to total N input. Conclusion: Multispecies swards consistently outperformed perennial ryegrass across the three NUE indices. This highlights the potential of multispecies swards as a suitable option for improving NUE and minimizing the risk of N surplus without compromising yields.