Effect of irrigation and nitrogen fertilization on biomass yield and efficiency of energy use in crop production of Miscanthus
Introduction
Several plant species have been investigated for their potential as biomass crops. As biomass conversion techniques have been advanced, interest has focused on the cultivation of Miscanthus species, which have potential for high yields of biomass in European conditions with yields of 25 to 35 t ha−1 year−1 once the crop has been established (Schwarz, 1993; van der Werf et al., 1993; Hotz, 1996; Himken et al., 1997; Venendaal et al., 1997).
Miscanthus is a C4 rhizomatous perennial grass originating from Asia. In temperate climates, its growth is limited by low temperature. In Europe it begins growth in April and continues until halted by frost in November. In winter the above-ground parts are killed by frost. Regrowth occurs from crowns in spring. Nutrients and carbohydrates stored in rhizomes during fall are mobilized to shoots in late April/early May, supporting rapid growth. The plant has an extensive root system that responds quickly to a rapid demand for nutrients during spring growth, thus reducing the risk of nitrate leaching (Himken et al., 1997).
Nursery plants are planted in spring and the crop can be harvested annually for up to 15 years after establishment (Schwarz et al., 1994). Although maximum above-ground dry matter yield is attained in late summer, harvest can be delayed until February/March when the crop has its highest dry matter concentration (Petrini et al., 1996; Himken et al., 1997). This is important for net energy production, as energy requirements for drying of the plant material prior to combustion is less for standing dead material than for green material. At harvest, shoots are mechanically cut near ground level.
The C4 photosynthetic pathway contributes to high water-use efficiency and to a low nitrogen content of the biomass. Long (1983)and Beale and Long (1997)calculated a requirement of 450 mm water and 92 kg N ha−1 for a crop producing an above-ground harvest of 15 t ha−1 dry matter. It has been reported that the effect of N fertilization on biomass yield is not high: Schwarz et al. (1994), reported an increase of only 1.1 t ha−1 in biomass dry weight (from 20.6 to 21.7 t ha−1) with an increase in N level from 0 to 180 kg ha−1 in a 3-year-old crop. Himken et al. (1997)calculated an annual removal of N from the field (equivalent to the fertilizer demand of an established Miscanthus crop) around 50 to 70 kg N ha−1 in a 4-year-old crop. Christian et al. (1997)found, in 1-year-old plants, that of the 117 kg ha−1 N taken up by the crop, only 23 kg ha−1 (38%) was derived from the fertilizer.
Long-term experience on Miscanthus is still lacking, especially about how to establish a good crop, about its nutritional demands and how yield will vary in the course of an estimated 10–20 years of usage.
The objective of this research was to determine the effects of irrigation and nitrogen fertilizer on yield and nitrogen content of Miscanthus sinensis cv. Giganteus. In addition, the use of energy resources was analyzed to determine the energy cost of management techniques and the energy balance of the crop.
Section snippets
Crop culture
A field study was conducted at Pisa (43°40′N, 10°19′E) in Italy from 1992 to 1995. Soil physical and chemical properties were 34% sand, 21% silt, 45% clay, pH 7.2, 2.15% organic matter (Walkley-Black method), 0.12% nitrogen (Kjeldahl method), 33 μg g−1 available P (Olsen method), and 22 μg g−1 available K (Dirks Scheffer method). During the trial period, no water table was observed within the top 1.2 m of soil.
Age of crop at harvest was 1, 2, 3 or 4 years. Treatments were crop age, irrigation, and
Results
Precipitation during the 1992 growing season was 69 mm greater than the 110-year-average (330 mm), while those in 1993, 1994 and 1995 were lower by 199, 129 and 144 mm respectively (Table 1). The amounts of water distributed by irrigation were about the same in all years, ranging from 219 to 250 mm.
Conclusions
After an establishing period of about 1 year, the cultivation of Mscanthus resulted in a dry matter production of over 37 t ha−1 year−1 during the next 4 years when the crop was well irrigated and fertilized. In the absence of N fertilization, irrigation did not modify biomass yield, the effect of irrigation increased with the increase in N level. The effect can be estimated as +3.7 t ha−1 with 100 kg N ha−1 and +9.8 t ha−1 with 200 kg N ha−1. Increase in nitrogen level also increased N concentration of
Acknowledgements
This research was supported by the Italian Ministry of Food Agriculture and Forestry Resources, Project PRisCa. The work is to be attributed to all four authors in equal parts.
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