Abstract
High doses of nitrogen (N) fertiliser input on permanent pastures are crucial in terms of N surplus and N losses. Quantitative analyses of the response of plant functional traits (PFT) driving crop growth rate (CGR) under low N input are lacking in frequently defoliated pastures. This study aimed to understand the significance of PFTs for productivity and N uptake in permanent grasslands by measuring dynamics in tiller density (TD), tiller weight (TW), leaf weight ratio (LWR), leaf area index (LAI), specific leaf area (SLA), as well as leaf N content per unit mass (LNCm) and per unit area (LNCa) in perennial ryegrass (Lolium perenne)-dominated pastures, in a simulated rotational grazing approach over two consecutive growing seasons. Annual N application rates were 0, 140 and 280 kg N ha−1. The phenological development of perennial ryegrass was the main driver of CGR, N uptake and most PFTs. The effect of N application rate on PFTs varied during the season. N application rate showed the greatest effect on TD, LAI and, to a lesser extent, on SLA and LNCm. The results of this study highlight the importance of TD and its role in driving CGR and N uptake in frequently defoliated permanent pastures.
Highlights
In temperate regions of Europe, perennial ryegrass (Lolium perenne) is the most common grass species used as forage for milk production, due to its high feeding quality and dry matter (DM) yield potential
This study examined the effect of N application rate on dynamics in plant functional traits (PFT) expression of perennial ryegrass-dominated pastures at sward and plant level, over two entire vegetation periods in a simulated grazing approach
The results of our study highlighted that the phenological development of perennial ryegrass drives the dynamics in crop growth rate (CGR), N uptake and most PFTs during the vegetation period of permanent grasslands
Summary
In temperate regions of Europe, perennial ryegrass (Lolium perenne) is the most common grass species used as forage for milk production, due to its high feeding quality and dry matter (DM) yield potential. Both high nutritive value and DM yield require an adequate availability of nitrogen [1,2,3]. Quantitative knowledge regarding the effects of fertiliser application is important to define sustainable and productive management strategies in grass-based production systems This is crucial to reduce N surpluses, N losses and fulfil legislative requirements, e.g., EU Water Framework Directive [9] and EU Nitrates Directive [10]
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