Response of giant reed (Arundo donax L.) to nitrogen fertilization and soil water availability in semi-arid Mediterranean environment

Highlights

• Giant reed was evaluated under three levels of soil water availability and nitrogen fertilization.

• Biomass DM yield was greater at the highest inputs, reducing at intermediate levels.

• WUE was significantly higher in the most stressed irrigation treatment.

• NUE was significantly higher in the intermediate levels of both inputs.

• Giant reed was able to uptake water at 160–180 cm soil depth when irrigation was applied.

Abstract

The aim of the present work was to evaluate the effect of soil water availability and nitrogen fertilization on yield, water use efficiency and agronomic nitrogen use efficiency of giant reed (Arundo donax L.) over four-year field experiment.

After the year of establishment, three levels for each factor were studied in the following three years: I₀ (irrigation only during the year of establishment), I₁ (50% ETm restitution) and I₂ (100% ETm restitution); N₀ (0 kg N ha⁻¹), N₁ (60 kg N ha⁻¹) and N₂ (120 kg N ha⁻¹).

Irrigation and nitrogen effects resulted significant for stem height and leaf area index (LAI) before senescence, while no differences were observed for stem density and LAI at harvest.

Aboveground biomass dry matter (DM) yield increased following the year of establishment in all irrigation and N fertilization treatments. It was always the highest in I₂N₂ (18.3, 28.8 and 28.9 t DM ha⁻¹ at second, third and fourth year growing season, respectively). The lowest values were observed in I₀N₀ (11.0, 13.4 and 12.9 t DM ha⁻¹, respectively).

Water use efficiency (WUE) was significantly higher in the most stressed irrigation treatment (I₀), decreasing in the intermediate (I₁) and further in the highest irrigation treatment (I₂). N fertilization lead to greater values of WUE in all irrigation treatment.

The effect of N fertilization on agronomic nitrogen use efficiency (NUE) was significant only at the first and second growing season.

Giant reed was able to uptake water at 160–180 cm soil depth when irrigation was applied, while up to 140–160 cm under water stress condition.

Giant reed appeared to be particularly suited to semi-arid Mediterranean environments, showing high yields even in absence of agro-input supply.

Introduction

Global and regional simulation climate models for Mediterranean area give a collective picture of a substantial drying and warming, especially in the warm season with precipitation reduction of −25% to −30% and warming exceeding 4–5 °C (Giorgi and Lionello, 2008). The Mediterranean climate is indeed characterized by hot and dry summers and water shortage is the main constraint limiting yield of major crops (Araus et al., 2002).

Out of the potential consumers of the available water resources is agriculture with about 69%. In the Mediterranean region this percentage rises up to 75% (Rana and Katerji, 2000). Despite the huge amount of water used for irrigation, only 13–30% of all water resources are used for transpiration by crops, reducing to 5% in arid and semi-arid environments in rainfed crops (Wallace, 2000).

Nitrogen requirement is a significant issue in intensive agriculture and greatly affects the energetic balance of crops (Boehmel et al., 2006). Furthermore, losses following nitrogen fertilization have environmental impacts both on the local level (e.g. NO₃ leaching) and on the global level (e.g. N₂O gaseous emissions) (Strullu et al., 2011).

Hence, reduced nitrogen fertilizer by means of low input cropping systems could directly mitigate greenhouse gas emissions (GHG). Perennials are considered the leading energy crops due to environmental benefits as compared to annual species (Fernando et al., 2010, Rettenmaier et al., 2010). GHG emissions mitigation by means of perennial energy crops can be expected either directly, through reduced field emissions of CO₂ and N₂O due to lower soil disturbance and fertilizers input, or indirectly by increasing levels of soil C sequestration and offsetting of fossil fuel emissions (Adler et al., 2007).

Thus, it is strategically important for the introduction of perennial energy crops in Mediterranean areas to develop plants (i) with increased yield potential, (ii) better adapted to present and future environmental constraints and (iii) able to grow well in water deficit conditions and with reduced input supply.

The cultivation of energy crops in arable lands, however, has raised a number of concerns in regards to land use change, either direct (DLUC) or indirect lands use change (ILUC). While DLUC are more easily assessed locally (i.e., introduction of a new cropping system at a site where it has not taken place before), ILUC (i.e., use of agricultural land that displaces food production and causes natural land elsewhere in the world to be cultivated for food instead) need to be considered at a global scale (Van Stappen et al., 2011, Shortall, 2013).

Hence, energy crops should be grown on the so-called marginal lands (e.g. agronomic, economic or social reasons of marginality) to ensure biomass production without encroaching agricultural lands, forest lands, highly biodiverse grassland or lands with high carbon stocks (Shortall, 2013).

At present, most of species cultivated for bioenergy are commonly bred in and for more temperate climates (e.g. Miscanthus and switchgrass). Consequently their introduction in Mediterranean areas, under rainfed and sub-optimal soil water conditions, poses severe limitations for the fully exploitation of their potential production.

Species characterized by high water use efficiency and low nitrogen requirement, hence well adapted to use natural resources of a specific environment, could enclose several solutions.

In this regard, giant reed (Arundo donax L.) can be considered one of the most promising dedicated species for Southern Europe. This perennial, rhizomatous, grass can be used for many non-food uses, such as cellulose pulp, paper (Shatalov and Pereira, 2006), second generation bioethanol (Scordia et al., 2011, Scordia et al., 2012, Scordia et al., 2013), giving high yields with reduced input supply (Christou et al., 2001, Cosentino et al., 2006, Mantineo et al., 2009).

According to its fast growth rate and ease of vegetative propagation, giant reed is considered as invasive species in the warm-temperate regions with winter floods that widely disperse this plant (Lambert et al., 2010, Copani et al., 2013). However, contrary to its invasive characteristics, as in the USA, giant reed has received social consensus by Mediterranean farmers, who have learned to live and deal with this species a long time ago due to its multiple usage. Indeed, giant reed is naturalized in the Mediterranean basin, it grows spontaneously and abundantly all over Mediterranean and warm-temperate areas of the world (Perdue, 1958, Rossa et al., 1998, Tucker, 1990, Angelini et al., 2005). In addition, thanks to a highly developed canopy and a deep root system, it covers the whole ground in the years following the establishment preventing the risk of soil erosion (Ranney and Mann, 1994, Kort et al., 1998, Sharma et al., 1998).

Although giant reed is considered as a drought tolerant species, reduced soil water availability coupled with low level input studies have not been reported to date.

To this end, a four-year field trial was carried out with the aim to evaluate the influence of soil water availability and nitrogen fertilization on productivity, water use efficiency and agronomic nitrogen use efficiency of giant reed in semi-arid Mediterranean area.