Carbon Balance Of Plastic Greenhouse Ecosystems In China

Farming is believed to be the primary cause of soil carbon loss, and this has led to discussion concerning ways in which to reduce CO2 emissions from anthropogenic exploitation and ways to sequester carbon within agroecosystems. Conservation tillage is a practice that has been adopted in agriculture in recent decades as has reduced tillage, no-till, and straw return practices to increase the potential of soil carbon sequestration while simultaneously decreasing carbon emissions associated with agricultural practices such as fertilizer input and fossil fuels typically used on farms. With relatively low agricultural inputs and consequent low crop production, these optimizing agricultural practices can act as small carbon sinks. Few studies have been carried out to show whether other types of intensified cultivation practices that incorporate large amounts of agricultural inputs to achieve high levels of production could also act as carbon sinks. Plastic greenhouse vegetable cultivation (PGVC) has played a vital role in increasing incomes of smallholder farmers. A dramatic expansion in PGVC usage has taken place in the last several decades. However, carbon sequestration potential after conversion from conventional open field vegetable cultivation (CVC) to PGVC has been poorly quantified with regards to carbon emissions that will occur due to the intensification in agricultural practices.A full carbon cycle analysis approach was used in this study to estimate the net carbon flux from PGVC systems. The study sample sites included 23 provinces,4 municipalities,5 autonomous regions throughout China. Besides the carbon balance, we also analyzed the ecosystems services of PGVC systems. The results shows as follow: 1. PGVC systems in China act as an carbon sink relative to atmosphere with the value 0.58±0.27 Mg C ha-1 yr-1 and the carbon absorption capacity is 2.5 times more than that of CVC systems (0.23±0.23 Mg C ha-1 yr-1). TheΔnet carbon flux (e.g. the difference of net carbon flux between PGVC systems and CVC systems) varies with the difference regions and the northern PGVC regions always higher than southern regions. This indicated that PGVC systems is suitable to performance is northern China.2.Following the conversion from CVC systems to PGVC systems the average increment of SOC (0-20 cm) achieved 41%. The region with arid, semi-arid and semi-moisture climate has the higher SOC content than that of moisture region. The cultivation style significantly affects the SOC content on the surface (0-20 cm) soil layer. Similar to the conventional cropland systems, SOC in PGVC system would accumulate slightly during the first 10 years; and the accumulation rate would sharply increase with the following 5 years; the SOC would decline for the following 5 years and then achieve the new steady state in year 20.3. The NPP of PGVC systems in China is 1.7 times more than that of CVC systems (PGVC systems:8.87±0.46 Mg C ha-1 yr-1; CVC systems:5.36±0.66 Mg C ha-1 yr-1). This difference is attributed to the variation of agricultural practices is different systems.4. Carbon sequestration in PGVC systems is 3.10±0.28 Mg C ha-1 which 2 times higher than that of CVC systems (1.33±0.34 Mg C ha-1 yr-1).5. The carbon density (0-100 cm) of PGVC systems is about 122.99 Mg C ha-1 and is 1.2 higher than that of CVC systems. In PGVC systems, the soil carbon occupied 93% of the total carbon density. While the carbon storage of PGVC systems is much lower than that of CVC systems for the total area of PGVC systems far below the CVC area. 6. The conversion form CVC systems to PGVC systems, the carbon emission associated with agricultural practices of the new systems is far more than that of CVC systems. While the difference of carbon emission between the two systems varies with the different regions, which indicated that the cultivation style affect the carbon emission volume directly.7. PGVC could produce more fresh vegetables, more regulating services (e.g., net carbon fixation, soil retention, water saving), as well as more environmental impacts (e.g., soil salinization, N2O emissions, plastic wastes, etc), compared to CVC. Overall, PGVC has higher net environmental benefits than CVC. PGVC is a win-win cultivation method that can not only provide more economic benefits for farmers but is also environmental friendly.8. Based on the carbon fixed campacity of PGVC, if converted 50% of total China vegetable cultivation area to PGVC, the carbon storage of vegetable cultivation system would increased by 3.2 Tg C (1 Tg= 1012 g); and if 100% converted, the carbon storage would achieve 7.4 Tg C which can offset 1.8% carbon emission from fosil fuel consumption (1,500 Tg C).