Pasquale Campi1a, Alejandra Navarro2, Francesca Modugno3, Marcello Mastrorilli1
1 Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria – Centro Agricoltura Ambiente (CREA-AA), Via C. Ulpiani, 70125 Bari
2 University of Antwerp, Department of Biology, Centre of Excellence PLECO, Campus Drie Eiken, Room C.006b, Universiteitsplein 1, 2610 Wilrijk, Belgium
3 Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria – Centro Politiche e Bioeconomia (CREA-PB), Via Po', 14 00198 Roma
apasquale.campi@crea.gov.it
Abstract
The sustainability of biomass sorghum (Sorghum bicolor L. Moench) in the Mediterranean environments is related to obtain convenient yield levels also under deficit irrigation. Field experiments were conducted in Southern Italy during two growing seasons to determine the biomass production and to estimate the yielded energy from sorghum cultivated under full and deficit irrigation. The data obtained showed that, under full irrigation, biomass sorghum yields more above-ground dry matter and energy than crops growing under deficit irrigation (23.5 vs 14.8 t ha−1 and 443 vs 258 GJ ha−1). Different indices of water use efficiency were calculated
for analyzing the effects of the water regimes on the biomass sorghum productivity.
Keywords: agro-energy crops; higher heating value; water use efficiency. Parole chiave: colture energetiche; potere calorifico; efficienza d’uso dell’acqua. Introduction
Sorghum production is encouraged by policies on non-food crops in the European Union and the global environmental policy of the Kyoto Protocol. Sorghum bicolor (Moench) is a multipurpose C4 crop for food, forage, fiber and fuel production. Sorghum is a suitable option in drought-prone environments (Barbanti et al., 2006) and in low-input cultivation systems thanks to its deep and dense root system (Stone et al., 1996) and to its high photosynthetic efficiency under drought (Zegada-Lizarazu et al., 2012). For this reason, sorghum has been indicated as a sustainable crop for the production of biogas in marginal environments (Amaducci et al., 2016). The productivity of sorghum, in terms of biomass, has been repeatedly emphasized and its energy potential has been deeply examined. In a Mediterranean environment, a recent study (Campi et al, 2016) has shown that biomass sorghum crops can produce 335 GJ ha-1 in full irrigation conditions. However, in semiarid environments, this agronomic option is not consistent with economic and environmental issues and it is important to identify the capacity of this species to adapt to lower water supplies (Vasilakoglou et al, 2011).
This is a crucial point under the Mediterranean climates, where high temperature and solar radiation levels are in favor of the sorghum eco-physiology, but the scarcity of water resources limits its cultivation. Therefore, in order to achieve a better irrigation strategy that optimizes biomass yield, it is necessary to know the response of the crop energy production when irrigation volumes vary. The aim of this paper is to assess the sustainability of the irrigation deficit on the energy yield of biomass sorghum through the analysis of water use efficiency indices (WUE).
Materials and Methods
The field trials were carried out at the experimental farm of the Agriculture and Economic Research Council - Agriculture and Environment Center (CREA - AA), in Rutigliano (Ba, Lat: 40 ° 59 ', long: 17 ° 59', alt: 147 m a.s.l).
The area is characterized by Mediterranean climate with warm and dry summers: a maximum air temperature ranging from 32°C to 43°C, a minimum relative humidity ranging from 15% to 40% and the annual average precipitation was of 560 mm, Data from 1977 to 2011, (Campi et al, 2016)
The soil of the experimental field contains 40% clay and 45% silt, the field capacity and wilting point of the soil are 36% and 22% (in volume) respectively. It is a shallow soil (0.4 to 0.8 m in depth) with moderate amount of available water (66 mm in 0.6 m rhizosphere).
The sorghum hybrid KWS Bulldozer was used. It is characterized by a medium-late vegetative cycle, high size, good tolerance to bending, and high yields in dry and green biomass. Sorghum was sown on June 7th 2013 and May 19th 2014 with a plant density of 18 plants m–2. Agro-techniques aiming at reducing external inputs were adopted (weeding control at the initial stage of the crop and
nitrogen fertilization of 100 kg N ha–1 after 30 days from sowing).
Two irrigation treatments (IRR and STR) per seasons were imposed according a complete randomized experimental design and three repetitions (each block 400 m2 in surface). IRR restored 100% of the water lost through evapotranspiration (ET) calculated according to the FAO56 approach (Allen et al, 1998). For IRR were provided 304 mm in 2013 and 241 mm in 2014 of irrigation water. The deficit irrigation in STR was scheduled differently in the two seasons: in 2013 by restoring 50% of the water lost through ET (seasonal irrigation volume: 125 mm); in 2014 by supplying 100% of the ET until the stem elongation stage (51 days after sowing), subsequently sorghum was grown under rainfed conditions (seasonal irrigation volume: 147 mm).
During two seasons, at regular intervals (every 7–10 days), dry biomass was measured. At the end of the sorghum cycle (on second week of September) all plants from 20 m2 plots were harvested and aboveground biomass determined.
The higher heating value (HHV; MJ kg−1) of sorghum was measured using a bomb calorimeter (LECO Corp., MI, USA) end the energy yield per hectare was calculated (GJ ha-1, HHV x Kg ha-1).
Results and Discussion
Under full water supply (IRR), biomass production (25.5 t ha-1 of dry matter) in both seasons (Table 1) is consistent with literature (Gherbin et al., 1996; Mastrorilli et al 2011, Campi et al, 2016) for the Mediterranean environment. As evidenced by the statistical analysis (significance of interaction between irrigation treatments and season of growth), season influences production, due to weather conditions. The gap of 8 t ha-1 of dry biomass between the IRR treatments is due to the difference in rain during the two
growing seasons (262 mm in 2014 and 72 in 2013).
STR treatment significantly reduces dry biomass production by 58% compared with IRR treatment (Tab. 1).
Fig. 1: Effect of irrigation treatments (IRR and STR) on growth of sorghum during 2013(a) and 2014 (b) seasons. Fig. 1: Effetto dei trattamenti irrigui (IRR e STR) sull’accrescimento del sorgo durante due stagioni (2013 e 2014)
Sorghum growth (Fig. 1) is affected by irrigation treatment. The differences between IRR and STR occur 50 days after sowing in 2013 and 100 days after sowing in 2014. Despite the suspension of irrigations from the 51st day after sowing, in 2014 the exceptional
amount of rain in July (124 mm) reduces the effect of the deficit irrigation.
The best performance in energy yielding is achieved by full irrigation (IRR), with the highest values in 2014. HHV measures agree with those reported by Fernando et al. (2010) and Campi et al., (2016), in the case of optimal irrigation. Effects of water stress on HHW are not reported literature and the observations here shown underline that the irrigation regime does not affect significantly HHV values (Tab. 1).
Tab. 1: Effects of growing season (S), irrigation treatment (I) and their interaction (SxI) on biomass (bWUE) and energy (eWUE) water use efficiency. *** = significance at 0.001; ns = absence of significance. Different letters in the columns indicate significant differences between treatments (Duncan’s test, P < 0.05).
Tab.1: Effetti della annata (S), dell'irrigazione (I) e della interazione (SxI) sull’efficienza d'uso dell'acqua in biomassa (bWUE) e energia (eWUE). *** = significatività a 0.001 e ns = assenza di significatività. Lettere diverse nelle colonne indicano differenze significative tra i trattamenti (test di Duncan, P <0.05).
Biomass (t ha-1) HHV (MJ kg-1) Energy yield (GJ ha-1) bWUE (kg m-3) eWUE (MJ m-3) Season (S) 2013 16.1 b 17.5 a 282 b 7.5 b 131 b 2014 24.1 a 17.3 a 417 a 12.4 a 215 a Irrig. (I) IRR 25.5 a 17.4 a 443 a 9.3 b 162 b STR 14.8 b 17.5 a 258 b 10.8 a 190 a P1 S *** ns *** *** *** I *** ns *** *** *** SxI *** ns *** *** ***
The conversion index of irrigation water into biomass (bWUE, kg of dry matter per m-3 of irrigated water) is a criterion for analyzing
the effectiveness of the irrigation regime and it is a requisite in modeling the agro-energy crops in the Mediterranean environment. On the contrary, the conversion index of irrigation water into bioenergy (eWUE, MJ m-3) represents a general criterion for assessing
the economic value of the irrigation supplied to the biomass crops. For the sorghum, biomass (bWUE) and energy (eWUE) water use efficiencies are significantly higher for deficit irrigation (STR) and during the rainy season (Tab. 1).
Data from the literature clearly showed that bWUE in sorghum grown in the Mediterranean area can vary remarkably from 5.84 to 22.81 kg m−3, even with similar water amounts of irrigation (Mastrorilli et al., 2011; Palumbo et al., 2014). This can be mainly
explained by the genotype and the rainfall trend during the sorghum growing season. The bWUE values calculated in 2014 are significantly higher due to the greater amount of precipitation. The eWUE values reported by Campi et al. (2016) are lower (105 MJ m-3) than those calculated after the observations collected in this field trial. In the seasons 2013 and 2014 the higher eWUE value is
Conclusions
This study confirms that irrigation is the main agro-technique affecting the biomass yield in the Mediterranean environments. However, the agro-meteorological trend does influence yields, both under full or deficit irrigation regime (up to 50% more dry matter in the rainy summer).
The original results reported in this work concern the application of controlled stress irrigation on dedicated energy crops in the Mediterranean area. In general, sorghum biomass production is reduced by water stress and, as a consequence, also the production of energy per unit of cultivated area tends to decrease. Sorghum crops under deficit irrigation can produce appreciable biomass yields (15 t ha-1 of above-ground dry matter) with high efficiency in converting irrigation water in biomass (bWUE = 11 kg m-3). Reducing
by the 50% the supplied irrigation water amount (273 mm in IRR and 136 mm in STR) the loss of energy yielded per hectare is less than proportional. Calculated eWUE shows that under deficit regime, sorghum improves the efficiency of transforming irrigation water into energy by 17% if compared to the eWUE calculated for the full irrigation. This experimental evidence allows to retain that full irrigation regime for the biomass sorghum crops should be reconsidered for attaining a sustainable goal in the water management.
References
Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration. Guide-lines for computing crop water requirements. FAO Irrigation and Drainage Paper No. 56.
Amaducci S., Colauzzi M., Battini F., FracassoA., Perego A., 2016. Effect of irrigation and nitrogen fertilization on the production ofbiogas from maize and sorghum in a water limited environment. Europ. J. Agronomy 76, 54–65.
Barbanti, L., Grandi, S., Vecchi, A., Venturi, G., 2006. Sweet and fibre sorghum (Sorghum bicolor (L.) Moench), energy crops in the frame of environmental protection from excessive nitrogen loads. Eur. J. Agron. 25, 30–39.
Campi P., Navarro A., Palumbo A.D., Modugno F., Vitti C., Mastrorilli M., 2016. Energy of biomass sorghum irrigated with reclaimed wastewaters. Europ. J. Agronomy 76, 176–185
Gherbin, P., Perniola, M., Tarantino, E., 1996. Sweet and paper sorghum yield as influenced by water use in southern Italy. In: Proceedings of the First European Seminar on Sorghum for Energy and Industry, INRA, Toulouse, France, 1–3April, pp. 222–227.
Mastrorilli, M., Campi, P., Palumbo, A.D., Navarro, A., Modugno, F., Turci, V., 2011.Water use efficiency of sorghum cultivated for energy in Mediterranean environments. In: Proceedings of the 19th European Biomass Conference and Exhibition, Berlin, Germany, 6–10 June, pp. 565–568.
Palumbo, A.D., Vonella, A.V., Garofalo, P., D’Andrea, L., Rinaldi, M., 2014. Response of a two-year sugar beet-sweet sorghum rotation to an agronomic management approach diversified by soil tillage and nitrogen fertilization. Ital. J. Agron. 9 (3), 109–114.
Stone, L.R., Schlegel, A.J., Gwin Jr., R.E., Khan, A.H., 1996. Response of corn grain sorghum, and sunflower to irrigation in the High Plains of Kansas. Agric. Water Manage. 30, 251–259.
Vasilakoglou, I., Dhima, K., Karagiannidis, N., Gatsis, T., 2011. Sweet sorghum productivity for biofuels under increate soil salinity and reduced irrigation. Field Crops Res. 120, 38–46.
Zegada-Lizarazu, W., Zatta, A., Monti, A., 2012. Water uptake efficiency and above-and belowground biomass development of sweet sorghum and maize under different water regimes. Plant Soil 351, 56–60.
Acknowledgements
This work was supported by the Italian Ministry of Agriculture (MiPAAF) under the AGROENER project (D.D. n. 26329, 1 april 2016) - http://agroener.crea.gov.it/