Soil nutrient levels define herbage yield but not root biomass in a multispecies grass-legume ley

Wen-Feng Cong,Bent T Christensen,Jørgen Eriksen

doi:10.1016/j.agee.2019.02.014

Wen-Feng Cong, Bent T Christensen + Show 1 more

Open Access

https://doi.org/10.1016/j.agee.2019.02.014

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Abstract

The response of above- and below-ground biomass to soil nutrient availability is crucial for estimating belowground carbon input and predicting changes in soil carbon storage. However, the response is far from clear at plant community level, especially for grassland systems. Using a long-term field experiment initiated 123 years ago with varying soil nutrient levels (deficient, sub-optimal, optimal and over-optimal) established by use of two nutrient sources (animal manure or mineral fertiliser), we examined the effects of soil nutrient level and source on herbage yield and composition, root biomass and root-to-shoot (R/S) ratio of an unfertilised multispecies grass-legume ley. Increased nutrient levels enhanced herbage yield, but did not affect root biomass. The R/S ratio decreased from deficient to sub-optimal level, but remained constant from optimal to over-optimal level. Nutrient source did not influence herbage yield, root biomass or R/S ratio, but the legume proportion increased in soils previously receiving mineral fertiliser. The R/S ratio decreased with herbage yield, but did not vary with herbage composition. We conclude that soil nutrient level and herbage yield rather than nutrient source and herbage composition determine biomass allocation between aboveground and belowground in temperate grassland leys.

Highlights

The increase in atmospheric CO2 concentration and global food demand has stimulated interest in sequestering carbon (C) in the world’s croplands to mitigate climate change and improve soil quality (IPCC, 2014; Lal, 2004)
This study aims to explore the effects of soil nutrient availability on above- and below-ground biomass allocation of multispecies production grasslands using a 120-year-old Askov Long-Term Experiment (AskovLTE)
The 1⁄2 animal manure (AM) and 1⁄2 NPK treatments tended to increase soil C concentration compared to the unfertilised treatment, but differences were not statistically significant

Summary

Introduction

The increase in atmospheric CO2 concentration and global food demand has stimulated interest in sequestering carbon (C) in the world’s croplands to mitigate climate change and improve soil quality (IPCC, 2014; Lal, 2004) Simulation models, such as RothC (Coleman et al, 1997) and C-TOOL (Taghizadeh-Toosi et al, 2014), are often employed to evaluate soil C sequestration of various land uses and to derive management practices with soil C sequestration potentials. Bolinder et al, 2007), without considering the impact of environmental factors such as nutrient availability (Poorter et al, 2012) This allometric approach has been questioned in recent studies showing that a fixed root-to-shoot (R/S) ratio may over-estimate belowground C input at higher nitrogen (N) fertiliser levels (Taghizadeh-Toosi et al, 2016) and lead to large uncertainty in estimating plant C inputs to soils (Keel et al, 2017). It remains unclear to which extent changes in species composition compensate for changes in biomass allocation in multispecies grassland subject to nutrient stress

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