NUTRIENT CONTENT AND UPTAKE BY MISCANTHUS PLANTS

Magdalena Borzęcka-Walker
Department of Agrometeorology and Applied Informatics, Institute of Soil Science and Plant Cultivation – Puławy State Research Institute

ABSTRACT

The aim of the work was to determine the nutrient content in Miscanthus and the value of nutrient uptake from the soil under different environmental conditions. The research was carried out in 2004-2006 in the eastern part of Poland at two experimental stations. The three-year average yield of Miscanthus oscillated between 15 and 17 t·ha^-1·yr^-1. Nitrogen content in shoots varied between 0.22 and 1.23%, whereas the phosphorus content in shoots was between 0.01 and 0.08%, and potassium content in shoots was from 0.16 to 1.11%. The differences depended on the localisation and year. Nitrogen uptake by the plant was between 49 and 216 kg·ha^-1, whereas the phosphorus uptake oscillated between 3 and 28 kg·ha^-1, and potassium uptake was from 37 to 275 kg·ha^-1. The differences depended on the localisation and year.

Key words: Miscanthus, nitrogen, nutrient uptake, phosphorus, potassium.

INTRODUCTION

The key factor in the production of renewable energy in Poland is going to be bio crops. An important biomass element for energy production is the amount and quality of yield. One of the potential plants for Polish conditions can be Miscanthus, which is a perennial C-4 plant originating from East Asia. It is an environmentally benign plant that can be grown at a very low level of fertiliser input, especially nitrogen [15]. Biomass quality is influenced by fertilization, in particular with nitrogen, and an increase in the N dose causes an increase in the N content in the plant [10,12,15].

Miscanthus is often harvested in late winter or early spring, when the biomass reaches a low moisture content, which eliminates additional costs of biomass drying. In winter however, the crop loses a considerable part of its mass, which could be retrieved with an early harvest before the cold season [7]. Moreover, during spring harvest, the content of nutrients in plants decreases in comparison with autumn harvest [13].

Miscanthus is a plant that has a relatively high-level of nitrogen use efficiency; therefore, fertilization with its content may be low [5]. Danalatos et al. [6] found that nitrogen fertilization had no effect on plant height. Taking into account the amount of yield and its quality, as well as the impact on the environment, Himken et al. [10] found that the optimum dose of nitrogen should be 70-100 kg·ha^-1. Miscanthus plants responded to a 0-50 kg N·ha^-1 dose of nitrogen and produced a good yield. At doses exceeding 110 kg N·ha^-1, the growth and development of plants is inhibited [6,16]. Himken et al. [10] recommend the use of other components at the dose levels of 5–10 kg P·ha^-1, 60-100 kg K·ha^-1, and 10–20 kg Mg·ha^-1. Low demand for fertilizer is also involved in the movement of nutrients to the rhizomes at the end of growing season. The aim of the work was to determine the nutrient content in Miscanthus and the value of nutrient uptake from the soil under different environmental conditions.

MATERIAL AND METHODS

The plant material used for the research originated from field experiments conducted in 2004–2006 with five genotypes of Miscanthus. The field experiment was established in 2003 at two Experimental Stations of the Institute of Soil Science and Plant Cultivation State Research Institute (IUNG-PIB). The experimental fields were located at the Experimental Stations Osiny and Grabów. The experimental Station in Osiny is located about 10 km away from Puławy, in Lublin Voivodeship (51°28' N and 22°03' E) on heavy black soil (complex 8 – cereal-fodder strong). The Experimental Station in Grabów is located about 30 km away from Puławy, in Masovian Voivodeship (51°21' and N 21°39' E) on medium-heavy soil (complex 4 – very good rye). Five genotypes of Miscanthus were planted: (Miscanthus x giganteus (M.gig), M. sinensis 'Gofal' (M.7), M. sinensis 'Silver Feather' (M.40), M. sinensis (M.105), and M. sacchariflorus x M. sinensis (M.115).

The sizes of the individual experimental plots ranged from 200 to 700 m². Miscanthus was planted in the number of 14.705 plants per hectare, 1.5 plants per m² at intervals of 0.85 m between the plants and 0.85 m between the rows. The establishment of the overwintering rate was < 2–6%. Fertilization of the tested plants with NPK-fertiliser and ammonium nitrate was carried out in doses given in Table 1. Fertilization was applied each year in early spring. In June 2005, due to high weed infestation, herbicide was applied (Chwastox Turbo 2.5 dm³·ha^-1).

Biomass samples were collected during the autumn harvest. The samples, after weighing the fresh matter of shoots, were dried at 80ºC for three days. The chemical analyses of the content of macroelements in the biomass were carried out in the main Chemical Laboratory of IUNG – PIB. The collected biomass was analysed towards the content of N, P using a flow spectrophotometer, and K using a flame spectrophotometer. The results of the chemical analysis were used to calculate N, P, and K uptake. Harvest took place in October and February by removing the whole plants from the field.

All the data were subject to statistical treatment involving standard deviation (SD), mean (M), standard error of the mean (m), and coefficient of variation (CV).

Weather conditions during the years of experiment varied (Table 2). Year 2004 was characterized by shortages precipitation from April to July, while 2005 – in August and October. In the third year of the experiment unsuitable weather conditions were observed, including late spring ground-frost and long summer drought. Precipitation in June and July was very low, approximately 25% of the long-term average.

RESULTS AND DISCUSSION

The dry matter yield of Miscanthus genotypes was significantly different at an average of 10–19 t·ha^-1 (Table 3) in Osiny, while in Grabów it measured from 14 to 21 t·ha^-1. The yield from the first year of the experiment was low; this could result from the fact that it was the second year of cultivation when the plant was still not mature enough to obtain an economic yield [3]. In the second year of the experiment, the yield increased considerably and was close to the presupposed simulated yields for Miscanthus cultivations (17.7–21.8 t·ha^-1) located on very good soils of Eastern Europe [8]. It can be assumed that limited water conditions in 2005 did not influence the experimental Miscanthus yield but there was an influence from weather conditions in 2006. The average three-year moisture content at harvest in autumn ranged from 33.5 to 52.2%. Moisture content for biomass should be under 25%, which is why it is advisable to harvest in late winter or early spring [13].

Miscanthus, cultivated for the production of solid fuels, had to reach national or international standards. According to the Austrian (Önorm M 7135), German (DIN 51731), and Swedish standards (SS 18 71 20 1-group) for wood pallets, nitrogen content should be below 0.3% of dry mater. High nitrogen content increases the emissions of NOx, HCN, and N₂O (Hahn, 2004). Nitrogen content in the harvested biomass fell within the range of 0.22 to 1.23% (Table 4) on heavy black soil and from 0.34 to 0.94% (Table 5) on medium heavy black soil, depending on the genotype and cultivation year. The highest three-year average content of N was measured for M.40 and M.105, and the lowest for M.gig and M.7, for both localisations. The highest genotype average N content was measured in 2006 for both localisations (Table 5). In the studies of Beale and Long [1], they obtained a nitrogen content of about 0.5%. Xiong et al. [17] and confirmed findings from the earlier studies that delaying harvest improves the quality of biomass due to the lower content of many minerals.

Phosphorus content in the harvested biomass fell within the range of 0.01 to 0.07% (Table 4) on heavy black soil, and 0.01 to 0.08% (Table 5) on medium heavy black soil, depending on the genotype and cultivation year. The highest three-year average content of P was measured for M.40 and M.105 in both localisations and the lowest for M.gig grown on heavy black soil and M.7 grown on medium heavy soil. The standards of wood pellets did not take into account the P content in their dry matter. Phosphorus in biomass is responsible for the increase in the melting temperature of ash, causing contamination retention and affecting the possibility of ash usage [9]. Lewandowski et al. [15] presented a content obtained in Germany between 0.04 and 0.11%. In this study, the phosphorus content was lower in comparison with other studies, despite the fact that the dose of this component was higher than the uptake.

Potassium content in the harvested biomass fell within the range of 0.60 to 1.11% (Table 4) on heavy black soil, and 0.16 to 0.94% (Table 5) on medium heavy black soil, depending on the genotype and cultivation year. Hight three-year average content of K was measured for M.7 and M.105 for both localisations and the lowest for M.gig grown on heavy medium black soil and M.7 grown on medium heavy soil. M.115 genotype was characterised by the highest average content of K. K content in the dry matter was not taken into account in the standards for wood pellets. Potassium content in biomass is very important because its high amount can increase the corrosion effect in heating systems and reduces the melting temperature of ash [9]. For optimum plant growth, potassium content should amount to 1–5% of dry matter (Collura et al. [4] after: Marschner 1993). The content of potassium in the studies by Jørgensen et al. [13] was from 0.77 to 2.17 for the autumn harvest. Lewandowski et al. [15] presented a summary of potassium content determined by several authors for some locations in Europe. The lowest content was observed in Denmark (0.31–0.48), while the highest in Germany (0.52–1.28). Potassium combined with chlorine produces a gas in a form of KCl, and the emission of this gas has a strong influence on the corrosion of heating systems. Therefore, potassium content should be as low as possible [14].

Nitrogen uptake calculated for 2004 was the highest for M.105 on medium heavy soil and the lowest for M.gig grown on heavy black soil (Table 6). Nitrogen uptake calculated for 2005 was the highest for M.115 in both localisations, whereas in 2006, a higher uptake was characteristic for M. gig genotype on heavy black soil and M.40 grown on medium-heavy soil. Much higher average results were calculated for 2006 (173 kg N·ha^-1) in comparison to 2005 (92 kg N·ha^-l). Average nitrogen uptake for the total plant during the study period was 132 kg N·ha^-l. Average uptake for all locations was very similar. Jones and Walsh [11] determine it to be between 111 and 177 kg N·ha^-l. Himken et al. [10] presented the uptake at a level of 130 kg N·ha^-l in the second year of the research.

Phosphorus uptake calculated for 2004 was the highest for M.105 on medium heavy soil and the lowest for M. gig on heavy black soil. Average uptake of P for total plants in the studies was 12 kg P·ha^-l (Table 7). P uptake on medium heavy soil (14 kg P·ha^-l) was much higher than on heavy black soil (9 kg P·ha^-l). Moreover, in 2006, P uptake (12 kg P·ha^-l) was twice higher than in 2005 (7 kg P·ha^-l). The lowest P uptake was observed in M. gig genotype. The studies of Jones and Walsh [11] found the phosphorus uptake of 11 and 19 kg P·ha^-l. Himken et al. [10] measured it to be 4–5 kg P·ha^-l.

The highest amount of nutrient uptake by plants M7 was calculated for potassium as 275 kg K·ha^-l on medium heavy soil in 2005 (Table 7), while the lowest K uptake was measured for M.40 grown on medium heavy soil. The average uptake of potassium by total plants in the studies was 153 kg K·ha^-l. There was a difference in K uptake between the localisations. Jones and Walsh [11] in their study calculated potassium uptake to be 107 and 223 kg K·ha^-l in two successive years of cultivation. Himken et al. [11] determined it at a level of 117 and 162 kg K·ha^-l. They also indicated that the highest uptake of potassium occurs during intensive plant growth in June.

CONCLUSIONS

1. The three-year-long mean for nitrogen and potassium content was higher in Miscanthus plants grown on heavy black soil than in the ones grown on medium heavy soil.

2. The highest N content in Miscanthus biomass, together with the lowest yield, was measured in 2006 due to the occurrence of drought.

3. The three-year-long average of nutrient uptake by Miscanthus genotypes was higher on medium heavy soil compared with black heavy soil.

4. Miscanthus biomass was characterised by good chemical composition. Nutrient content depended on the genotype, cultivation year, and experiment localisation.

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Accepted for print: 4.08.2010

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