J Soils Sediments (2009) 9:511–514 DOI 10.1007/s11368-009-0134-5
SOILS, SEC 2 & GLOBAL CHANGE, ENVIRON RISK ASSESS, SUSTAINABLE LAND USE & SHORT COMMUNICATION
Winter mulch increases soil CO2 efflux under Phyllostachys praecox stands Peikun Jiang & Hailong Wang & Jiasen Wu & Qiufang Xu & Guomo Zhou
Received: 1 June 2009 / Revised: 19 August 2009 / Accepted: 19 August 2009 / Published online: 25 September 2009 # Springer-Verlag 2009
Abstract Purpose The bamboo species Phyllostachys praecox has been planted in large areas of southern China for the production of edible bamboo shoots. In recent years, high rates of fertilizer application and heavy winter mulch have been employed to achieve an earlier harvest of the shoots and a better economic return. Little is known about the potential impact of these intensive management practices on the receiving environment. Therefore, a field experiment was conducted to quantify the effect of winter mulch on soil CO2 efflux, which contributes to greenhouse gas emissions. Materials and methods The field study was established in 6-year-old P. praecox stands for the period between December 2006 and February 2007 in Lin’an County, Zhejiang Province, China. The treatments included a 200mm mulch with rice straw and rice husks, and a control without mulch. Soil CO2 efflux rates and soil temperature changes were measured monthly and comparisons were made between the treatments. Results and discussion Soil CO2 efflux rates in the mulch treatment were 10.98 and 4.27 µmol m−2 s−1 in December 2006 and January 2007, respectively, which was eight times greater than soil CO2 efflux rates measured in the nonmulch control treatment in the corresponding months. The Responsible editor: Chengrong Chen P. Jiang : H. Wang : J. Wu : Q. Xu : G. Zhou (*) School of Environmental Science and Technology, Zhejiang Forestry University, North Circular Road #88, Lin’an, Hangzhou 311300, Zhejiang, China e-mail:
[email protected] H. Wang Scion, Private Bag 3020, Rotorua, New Zealand
significantly higher temperature and increased dissolved organic carbon in the mulch treatment were considered to have contributed to the enhanced soil CO2 emission. Conclusions Heavy winter mulch in a P. praecox plantation can greatly enhance soil respiration rates due to increases in both soil temperature and readily mineralizable labile organic matter. The increased CO2 emissions from soil respiration under winter mulch treatments can potentially reduce the greenhouse gas emission mitigation function of the bamboo forest plantations. It is recommended that new management practices be developed to alleviate the impacts of winter mulch on the environment. Keywords Bamboo . CO2 emission . Greenhouse gas . Intensive management . Mulching . Soil moisture . Soil respiration . Soil temperature
1 Introduction Carbon dynamics in the soil play the most important role in the carbon cycle of terrestrial ecosystems (Raich and Schlesinger 1992; Deng et al. 2009; Xu et al. 2009). However, there are relatively few studies on the effect of forest soil respiration on the carbon cycle (Schinel 1995). Most historical soil respiration studies have been conducted during crop-growing seasons, and soil CO2 efflux during winter was assumed to be negligible (Fahnestock et al. 1998). More recently, it has been revealed that respiration in winter could account for up to 30% of annual soil CO2 emissions (Jones 1999; Wang et al. 2007a). Some studies have shown that forest soil CO2 efflux may be affected by temperature, moisture, and management practices such as fertilizer application and harvesting (Pypker and Fredeen 2002; Samuelson et al. 2004). There is little published
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2 Materials and methods 2.1 Experimental site description The experimental site was located in Tai-hu-yuan Town, Lin’an County (30°18′ N, 119°34′ E), Zhejiang Province, China. This area experiences a typical central-subtropical climate. The average annual precipitation is 1,629 mm. The annual average temperature is 16.4°C, with the maximum and minimum temperatures being 41.7 and −13.3°C, respectively. Annual sunshine hours average at around 1,847 h and the number of frost-free days is 239. The experimental area is 65 m above sea level, and the soils were classified as Ferrosols. The experimental site was selected from P. praecox stands with a uniform original fertility.
cultivation management practice, i.e., mulch or non-mulch control treatment. Each treatment received high rates of fertilizer application. Annual rates of urea, compound fertilizer, and organic manure were 1.5, 1.5, and 90 t ha−1, respectively. The fertilizers were applied three times a year, with 35%, 30%, and 35% of planned total annual rate being applied in May, September, and December, respectively. Prior to the last annual fertilizer application in early December, the soil was watered until the top 0–0.2 m reached saturation. The winter mulch treatment was applied following fertilizer application in December. A layer of rice straw (50 mm deep) was placed on the soil surface then covered with a 150 mm layer of rice husks. The control area received the same fertilizer and water treatments but no mulch. 2.3 Measurements Ten paired measurement points, including five from the mulch treatment and five from the control treatment, were randomly selected for measurement of soil respiration as CO2 efflux. Each measurement point covered 0.008 m2. Soil seclusion cups for determination of soil CO2 efflux were placed on the soil under the bamboo stands 24 h before measurement to allow sufficient time for recovery from the disturbance. Determination of soil CO2 efflux was conducted at 10:00 on a fine day at the end of each month between December 2006 and February 2007. The time and frequency of soil CO2 efflux measurements were adapted from Wang et al. (2007b). In addition, monitoring of the diurnal change of soil temperature and volumetric water content was conducted on January 30, 2007 when the monthly measurement took place. Soil CO2 efflux was measured using two LI-6400 Portable Photosynthesis Systems and 6400-9 Soil CO2 Flux Chambers (LI-COR, USA). A thermocouple sensor was installed and attached to each respiration chamber for soil temperature measure20
Air temperature Control soil temperature
15 Temperature (oC)
information on the relationships between mulch and forest soil respiration. There is approximately 14 million ha of bamboo forests globally (Wang et al. 2008). A significant proportion of these forests is located in southern China, where 56 species have been recommended for production of edible shoots, 58 species for timber production, and 18 species for pulp and paper production (Li and Kobayashi 2004; Xu et al. 2008). Phyllostachys praecox is one of the more favored species used for producing edible bamboo shoots, and has been planted in large areas of China, with 60,000 ha planted in Zhejiang Province alone (Jiang et al. 2006). To achieve an earlier harvest of the edible shoots (and consequently attract a higher market value), intensive cultivation practices are carried out. This involves applying a thick layer of mulch (0.15–0.25 m) made from farm organic residues, which contributes to elevated soil temperatures and helps maintain soil moisture. This practice has been applied extensively to P. praecox plantations throughout China since the 1990s (Fang et al. 1994; Jiang et al. 2006). It has been reported that mulch treatments could significantly increase topsoil (0–0.1 m) temperatures, which helps early emergence of bamboo shoots (Cao et al. 1995). In a greenhouse study, Hu et al. (1994) found that respiration rates of underground stems and roots of bamboo plants increased with soil temperature. However, there is no published information on the effect of mulch on soil CO2 efflux under field conditions. Therefore, the objective of this study was to evaluate the effect of winter mulch on soil CO2 emissions under P. praecox stands.
J Soils Sediments (2009) 9:511–514
Mulched Mulch soilsoil temperature temperature
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2.2 Fertilizer application and mulch treatment The P. praecox stands in this study were established in 2000. Within the stands, two areas of approximately 2 ha each were selected and subjected to one of two types of
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Fig. 1 Effect of mulch treatment on soil temperature under the P. praecox stands at various times on January 30, 2007. Air temperature is also shown for comparison
Respiration rate (µmol CO2 m-2 s-1)
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Control
measurement times over the 24-h period (Fig. 2). Changes in soil CO2 efflux rate in the mulch treatment during this period ranged from 3.04 to 4.55 µmol CO2 m−2 s−1 with a 13.4% coefficient of variation, whereas daily changes in soil CO2 efflux in the control treatment ranged from 0.52 to 1.02 µmol CO2 m−2 s−1 with a 21.6% coefficient of variation. The peak soil CO2 efflux in the mulch treatment occurred 2 h later than that in the control treatment (see Fig. 2). Monthly measurements showed that soil temperatures in the mulch treatment were significantly (P
