Greenhouse Gas Fluxes Dataset Effected by Land-use Conversion from Double Rice Cropping to Vegetables in Southern China

Yuan, Y.¹  Dai, X. Q.^2*  Wang, H. M. ²

1. Anhui Provincial Key Laboratory of the Conservation and Exploitation of Biological Resources, College of Life Sciences, Anhui Normal University, Wuhu 241000, China;

2. Qianyanzhou Ecological Research Station, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China

Abstract: The experimental fields are located at the Qianyanzhou Ecological Research Station (26º44′48″N, 115º04′13″E), operated by Institute of Geographic Sciences and Natural Resources Research of Chinese Academy of Sciences. We converted a portion of the area under rice which had been continuously cultivated with rice for approximately 10 years to vegetable production. The treatments included rice with (R-F) and without fertilization (R-NF) and vegetable with (V-F) and without fertilization (V-NF). There were four spatial replicates for each treatment. We also set up a sub-treatment for removing vegetation in each plot (-no plant). The static opaque chambers and gas chromatographs (GCs) were used to determine the fluxes of methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂) in situ for two years. We studied the greenhouse gas fluxes changes at the beginning period of the land-use conversion from double rice cropping to upland vegetables. Besides, the effect of fertilization and the crops on the fluxes of CH₄, N₂O and CO₂ were investigated. This dataset includes: 1) Management information of the paddy and vegetable fields; 2) CH₄ fluxes of each treatment from July 2012 to July 2014; 3) N₂O fluxes of each treatment from July 2012 to July 2014; 4) CO₂ fluxes of each treatment from July 2012 to July 2014; 5) Soil ammonium and nitrate nitrogen content of 0-20 cm of paddy and vegetable fields; 6) Soil pH of 0-10, 10-20 cm of paddy and vegetable fields; 7) Daily air temperature and precipitation of the experimental area; 8) The water depth of paddy fields. The data set is archived at .xls format with the compressed data size of 286 KB. The analysis papers based on this dataset were published at PLoS ONE ( 2016) and Chinese Journal of Applied Ecology (2015).

Keywords: Land-use conversion; CH₄; N₂O; CO₂; China

1 Introduction

Carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) are the most important greenhouse gases^[1]. Agricultural lands accounts for 52% and 84% of global anthropogenic CH₄ and N₂O emissions and may also act as a sink or source for CO₂^[2]. Rice and vegetables are major crops grown in southern China. Because of the different growing conditions (standing water in rice vs. aerobic condition in vegetables), greenhouse gas (GHG) emissions can be different between the two cropping systems^[3–5]. In standing water or anaerobic condition, CH₄ is emitted under rice primarily through aerenchyma, diffusion, and ebullition^[6]. Nitrous oxide is emitted through denitrification in water-logged condition under rice^[7] and the emissions can be pronounced when flooded fields are drained or N fertilized^[8]. Studies indicate that CH₄ emissions can be higher and N₂O emissions lower under rice than other crops^[4,9]. Nishimura et al.^[3,4] found that the cumulative CH₄ fluxes were 2 to 14 g C m^–2 yr^–1 under lowland rice and ranged from -0.02 to -0.07 g C m^–2 yr^–1 under upland rice and the double cropping of soybean and wheat. They found that cumulative N₂O emissions increased 4.0 to 5.3 times by changing the land-use from lowland rice to upland crops^[3].

The static opaque chambers and gas chromatographs (GCs) were used to determine the fluxes of CH₄, N₂O and CO₂ in situ for two years. We studied the greenhouse gas fluxes changes at the beginning period of the land-use conversion from double rice cropping to upland vegetables. Besides, the effect of fertilization and the crops on the fluxes of CH₄, N₂O and CO₂ were investigated.

2 Metadata of Dataset

The metadata of land-use conversion from double rice cropping to vegetables affects greenhouse gas fluxes in southern China dataset is summarized in Table 1. It includes the dataset full name, short name, authors, year of the dataset, temporal resolution, spatial resolution, data format, data size, data files, data publisher, and data sharing policy, etc^[10].

Table 1  Metadata summary of the Land-use conversion from double rice cropping to vegetables affects greenhouse gas fluxes in southern China

3 Methods

3.1 Study Area

In July 2012, we converted a portion of the area under rice to vegetable production by draining water from the field while leaving the remaining land under rice. The double-rice system, which is comprised of early rice (transplanted in April and harvested in late July) and late rice (transplanted in late July and harvested in November), was adopted as usual with a fallow in the winter. The converted vegetable areas were planted with three kinds of vegetables a year in turn. Each cropping system had two fertilization levels, e.g., conventional fertilization and no fertilization. Thus, the experiment included four treatments in a split plot arrangement in randomized complete block design with four replications. Land use (or crop type) was the main plot and fertilization was the split-plot treatment. The treatments included vegetable with (V-F) and without fertilization (V-NF) and rice with (R-F) and without fertilization (R-NF). Each plot had an area of 120 m² (10 m × 12 m). A sub treatment without vegetation (2 m × 2 m) was set up in each plot and had the same agricultural operations as normal treatments. Compound fertilizer (N??P₂O₅??K₂O = 15%??15%??15%) and urea were applied at a rate of 358 kg N ha^–1 per year to the fertilized plots according to the local typical agricultural management. Conventional tillage was carried out at the beginning of each growing season. Management information of the rice and vegetable fields were shown in Table 2.

3.2 Measurement of the greenhouse gas fluxes

A static chamber was used to simultaneously measure CH₄, CO₂ and N₂O fluxes^[12]. The chamber was comprised of two parts: a cylindrical steel anchor and a cover (Figure 1). The internal diameter of the anchor was 50 cm. The anchor was inserted into the soil to a depth of 15 cm for rice and 10 cm for vegetables. The bottom part of the anchor inserted into the soil contained holes for water and nutrient exchange between inside and outside of the anchor. The groove on the upper

part of the anchor was equipped with a sealing strip to ensure that gas does not leak from the joint of the anchor and the cover box when gas samples were collected. The anchor was kept in place throughout the entire study period, except during tillage and planting. The cover had heights of 40 cm (used for vegetables) and 70 cm (used for rice) and internal diameter was 50 cm. Before starting the experiment measurements of greenhouse gas fluxes in the bare soil from the chambers with two different heights showed that the height had no significant effect on gas fluxes. A tin foil reflective coating was used to cover the chamber to minimize solar heating and fluctuations in the headspace temperature. Five seedlings of rice or three seedlings of vegetables were planted inside the anchor. The planting density inside the chamber was similar to that of the crop planted outside.

Five gas samples were collected from each chamber using 100 mL plastic syringes at 10-min interval twice each week between 8:00 AM and 12:00 PM throughout the growing season. Immediately after tillage, fertilization, irrigation or drainage, however, samples were collected daily for one week. The gas samples were analyzed using a gas chromatograph (GC System, 7890A, Agilent Technologies) equipped with an electron capture detector (ECD) and a flame ionization detector (FID). CH₄, N₂O and CO₂ fluxes were calculated from linear or nonlinear changes in the gas concentrations over time^[13–14]. The lowest accepted correlation coefficient (r) value for the regression of CH₄, N₂O and CO₂ evolutions was 0.87. When the absolute value of r from the nonlinear model minus that from the linear model was equal to or less than 0.000,2, the fluxes from the linear model were adopted and vice versa.

Figure 1  Design of the static chamber used for measuring greenhouse gas fluxes^[15]

4 Results and Validation

4.1 Data Composition

We obtained the following data from July 2012 to July 2014.

1) Management information of the paddy and vegetable fields.

2) CH₄ fluxes of each treatment from July 2012 to July 2014.

3) N₂O fluxes of each treatment from July 2012 to July 2014.

4) CO₂ fluxes of each treatment from July 2012 to July 2014.

5) Soil ammonium and nitrate nitrogen content of 0-20 cm of paddy and vegetable fields.

6) Soil pH of 0-10, 10-20 cm of paddy and vegetable fields.

7) Daily air temperature and precipitation of the experimental area.

8) The water depth of paddy fields.

4.2 Data Products

The results indicate that land-use conversion from rice to vegetables significantly reduced CH₄ fluxes and significantly increased N₂O fluxes. The conversion had inconsistent effects on CO₂ fluxes across seasons (Figure 2, Table 3, 4, 5). The total global warming impact of the three greenhouse gases was significantly increased after the land-use conversion from paddy to vegetables. Fertilization had no significant effect on CH₄ fluxes, while significantly increased N₂O and CO₂ fluxes and had an interaction with land-use types. The changes of CH₄, N₂O and CO₂ fluxes with the land-use conversion from paddy to vegetable fields were caused by the changes of soil properties and the changes of crop types together. The authors partially elaborated on the results in “Effects of Land-Use Conversion from Double Rice Cropping to Vegetables on Methane

Figure 2  Seasonal variations of CH₄ fluxes and the water depth of paddy fields. The data shown are means of the four replicates for individual treatments

Table 3  Cumulative emissions of CH₄ in the observing period and each growing season (kg C ha^–1)

Note: Different letters within the same column represent significant differences among treatments.

and Nitrous Oxide Fluxes in Southern China”^[15] and “Effects of land-use conversion from double rice cropping to vegetables on methane and carbon dioxide fluxes in southern China”^[16].

Table 4  Cumulative emissions of N₂O in the observing period and each growing season (kg C ha^–1)

Note: Different letters within the same column represent significant differences among treatments.

Table 5  Cumulative emissions of CO₂ by ecosystem respiration in the observing period and each growing season (kg C ha^–1)

Note: Different letters within the same column represent significant differences among treatments.

5 Discussion and Conclusion

Previous studies about greenhouse gas emissions from paddy and vegetable fields were only comparison between rice paddy fields and vegetable fields that have been planted for several years, ignoring the differences in the initial conditions of the plots^[17]. And most of the studies did not consider the effect of transition time^[18]. In this research, we converted part of the paddy which had been continuously cultivated with rice to vegetable production to ensure that the initial conditions were the same between the two land-use types. Both the changes of soil properties and the changes of crop types have effect on greenhouse gas emissions. However, most of the previous studies did not differentiate their influence. In the present study, sub treatments without vegetation were set up to differentiate the effect of soil properties and crop types on greenhouse gas fluxes.

Author Contributions

Dai, X. Q. and Wang, H. M. designed the algorithms of dataset; Dai, X. Q. and Yuan, Y. contributed to the data processing and analysis; Yuan, Y. wrote the data paper.

Acknowledgements

We thank Li, B., Xie, Y., Liu, C. H. for their substantial assistance in the field measurements.

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