Hai-Lin Zhang

Challenges and adaptations of farming to climate change in the North China Plain

Climate change has been a concern of policy makers, scientists, and farmers due to its complex nature and far-reaching impacts. It is the right time to analyze the impacts of climate change and potential adaptations, and identify future strategies for sustainable development. This study assessed changes in climatic factors (e.g., temperature and precipitation) at three typical sites (i.e., Luancheng, Feixiang, and Huanghua) in the North China Plain (NCP), and analyzed adaptations of farming practices. Results indicated that the mean annual temperature followed a significant increasing trend during 1981–2011, with 0.57, 0.47, and 0.44xa0°C decade−1 for Luancheng, Huanghua, and Feixiang, respectively. A significant increase of 0.67, 0.53, and 0.38xa0°C decade−1 was observed for the winter-wheat (Triticum aestivum L.) season for Luancheng, Huanghua, and Feixiang, respectively (Pu2009<u20090.05), but no significant change for the summer-corn (Zea mays L.) season for thexa0three sites. The annual accumulated temperature (≥10xa0°C) increased significantly during 1981–2011 (Pu2009<u20090.01), with 17.60, 10.49, and 14.09xa0°Cxa0yr−1 for Luancheng, Huanghua, and Feixiang, respectively. There was no significant increase of mean annual precipitation, which had large inter-annual fluctuations among thexa0three sites. In addition, significant challenges lie ahead for the NCP due to climate change, e.g., increasing food grain demand, water shortages, high inputs, high carbon (C) emissions, and decreasing profits. Trade-offs between crop production, water resource conservation, and intensive agricultural inputs will inhibit sustainable agricultural development in the NCP. Farming practices have been adapted to the climate change in the NCP, e.g. late seeding for the winter-wheat, tillage conversion, and water saving irrigation. Therefore, innovative technologies, such as climate-smart agriculture, will play important roles in balancing food security and resources use, enhancing water use efficiency, reducing C emissions in the NCP. Coordinated efforts from the government, scientists, and farmers are also necessary, in response to climate change.

Methane and nitrous oxide emissions under no-till farming in China: a meta-analysis.

No-till (NT) practices are among promising options toward adaptation and mitigation of climate change. However, the mitigation effectiveness of NT depends not only on its carbon sequestration potential but also on soil-derived CH4 and N2O emissions. A meta-analysis was conducted, using a dataset involving 136 comparisons from 39 studies in China, to identify site-specific factors which influence CH4 emission, CH4 uptake, and N2O emission under NT. Comparative treatments involved NT without residue retention (NT0), NT with residue retention (NTR), compared to plow tillage (PT) with residue removed (PT0). Overall, NT0 significantly decreased CH4 emission by ~30% (P < 0.05) compared to PT0 with an average emission 218.8 kg ha(-1) for rice paddies. However, the increase in N2O emission could partly offset the benefits of the decrease in CH4 emission under NT compared to PT0. NTR significantly enhanced N2O emission by 82.1%, 25.5%, and 20.8% (P < 0.05) compared to PT0 for rice paddies, acid soils, and the first 5 years of the experiments, respectively. The results from categorical meta-analysis indicated that the higher N2O emission could be mitigated by adopting NT within alkaline soils, for long-term duration, and with less N fertilization input when compared to PT0. In addition, the natural log (lnR) of response ratio of CH4 and N2O emissions under NT correlated positively (enhancing emission) with climate factors (temperature and precipitation) and negatively (reducing emission) with experimental duration, suggesting that avoiding excess soil wetness and using NT for a long term could enhance the benefits of NT. Therefore, a thorough understanding of the conditions favoring greenhouse gas(es) reductions is essential to achieving climate change mitigation and advancing food security in China.

Emissions of CH4 and N2O under different tillage systems from double-cropped paddy fields in Southern China.

Understanding greenhouse gases (GHG) emissions is becoming increasingly important with the climate change. Most previous studies have focused on the assessment of soil organic carbon (SOC) sequestration potential and GHG emissions from agriculture. However, specific experiments assessing tillage impacts on GHG emission from double-cropped paddy fields in Southern China are relatively scarce. Therefore, the objective of this study was to assess the effects of tillage systems on methane (CH4) and nitrous oxide (N2O) emission in a double rice (Oryza sativa L.) cropping system. The experiment was established in 2005 in Hunan Province, China. Three tillage treatments were laid out in a randomized complete block design: conventional tillage (CT), rotary tillage (RT) and no-till (NT). Fluxes of CH4 from different tillage treatments followed a similar trend during the two years, with a single peak emission for the early rice season and a double peak emission for the late rice season. Compared with other treatments, NT significantly reduced CH4 emission among the rice growing seasons (P<0.05). However, much higher variations in N2O emission were observed across the rice growing seasons due to the vulnerability of N2O to external influences. The amount of CH4 emission in paddy fields was much higher relative to N2O emission. Conversion of CT to NT significantly reduced the cumulative CH4 emission for both rice seasons compared with other treatments (P<0.05). The mean value of global warming potentials (GWPs) of CH4 and N2O emissions over 100 years was in the order of NT<RT<CT, which indicated NT was significantly lower than both CT and RT (P<0.05). This suggests that adoption of NT would be beneficial for GHG mitigation and could be a good option for carbon-smart agriculture in double rice cropped regions.

Opportunities and Challenges of Soil Carbon Sequestration by Conservation Agriculture in China

Abstract Conservation agriculture (CA), an emerging technology for sustainable agriculture, has been practiced in China for more than 30 years and is increasingly being adopted on cropland. CA system has four components: (i) no-till (NT), (ii) residue mulch, (iii) complex/diverse cropping system, and (iv) integrated nutrient management. Conservation tillage (CT, main technology of CA) methods, relevant to a range of cropping systems, are practiced on 6.67xa0million hectare (Mha) in China. With growing concerns about global warming, soil organic carbon (SOC) sequestration is an important strategy to offset anthropogenic emissions. This chapter collates and synthesizes available research literature on SOC sequestration under different tillage systems in China. Specific focus is on the SOC dynamics, SOC stock, rate of SOC sequestration, and soil quality under different tillage systems in diverse agroeco regions. The research on CT effects on SOC sequestration has been conducted in China for more than 20 years since the 1990s. The review of the literature indicates that NT can increase SOC concentration in the surface layer under dryland farming and rice ( Oryza sativa L.) paddy soils. The average rate of increase of SOC (gxa0kg −xa01 year −xa01 ) in 0–20xa0cm depth under NT systems is 0.60–3.74, 0.14–4.15, 0.50–5.94, and 8.81–17.95 for the Northeast, North, Northwest, and paddy fields of Southern China, respectively. However, most research results indicate that SOC under NT is concentrated more in the surface soil (8.6–31.3xa0gxa0kg −xa01 in NT vs. 5.3–26.8xa0gxa0kg −xa01 in plow tillage (PT)) and is relatively less in the subsoil (6.9–17.6xa0gxa0kg −xa01 in NT vs. 10.2–24.5xa0gxa0kg −xa01 in PT). Residue management is the key factor in SOC sequestration, which also influences SOC dynamics. Cropping system and rotation also affect SOC sequestration. Further, NT can improve soil quality by enhancing and stabilizing aggregation. Because of relatively short duration, soil processes under CA management are not clearly understood and are confounded by the diverse cropping systems. There is a need to study pedospheric processes affecting SOC sequestration and soil quality under long-term use of CA in diverse cropping systems and complex agroeco regions of China. Potential and limitations of CA, and research priorities in China are discussed.

Assessment of carbon sustainability under different tillage systems in a double rice cropping system in Southern China

PurposeAdoption of the carbon (C)-friendly and cleaner technology is an effective solution to offset some of the anthropogenic emissions. Conservation tillage is widely considered as an important sustainable technology and for the development of conservation agriculture (CA). Thus, the objective of this study was to assess the C sustainability of different tillage systems in a double rice (Oryza sativa L.) cropping system in southern China.MethodsThe experiment was established with no-till (NT), rotary tillage (RT), and conventional tillage (CT) treatments since 2005. Emission of greenhouse gasses (GHG), C footprint (CF), and ecosystem service through C sequestration in different tillage systems were compared.Result and discussionEmission of GHG from agricultural inputs (Mg CO2-eqxa0ha−1xa0year−1) ranged from 1.81 to 1.97 for the early rice, 1.82 to 1.98 for the late rice, and 3.63 to 3.95 for the whole growing season, respectively. The CF (kg CO2-eqxa0kg−1 of rice year−1) in the whole growing seasons were 1.27, 1.85, and 1.40 [excluding soil organic carbon (SOC) storage] and 0.54, 1.20, and 0.72 (including SOC storage) for NT, RT, and CT, respectively. The value of ecosystem services on C sequestration for the whole growing seasons ranged from ¥3,353 to 4,948xa0ha−1xa0year−1 and followed the order of NT > CT > RT. The C sustainability under NT was better than that under RT for the late, but reversed for the early rice. However, NT system had better C sustainability for the whole cropping system compared with CT.ConclusionsTherefore, NT is a preferred technology to reduce GHG emissions, increase ecosystem service functions of C sequestration, and improve C sustainability in a double rice cropping region of Southern China.

Stratification and Storage of Soil Organic Carbon and Nitrogen as Affected by Tillage Practices in the North China Plain

Tillage practices can redistribute the soil profiles, and thus affects soil organic carbon (SOC), and its storage. The stratification ratio (SR) can be an indicator of soil quality. This study was conducted to determine tillage effects on the profile distribution of certain soil properties in winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) systems in the North China Plain (NCP). Three tillage treatments, including no till (NT), rotary tillage (RT), and plow tillage (PT), were established in 2001 in Luancheng County, Hebei Province. The concentration, storage, and SR of SOC and soil total nitrogen (TN) were assessed in both the wheat and maize seasons. Compared with RT and PT, the mean SRs for all depth ratios of SOC under NT increased by 7.85% and 30.61% during the maize season, and by 14.67% and 30.91% during the wheat season, respectively. The SR of TN for 0–5:30–50 cm increased by 140%, 161%, and 161% in the maize season, and 266%, 154%, and 122% in the wheat season compared to the SR for 0–5:5–10 cm under NT, RT and PT, respectively. The data indicated that SOC and TN were both concentrated in the surface-soil layers (0–10 cm) under NT but were distributed relatively evenly through the soil profile under PT. Meanwhile, the storage of SOC and TN was higher under NT for the surface soil (0–10 cm) but was higher under PT for the deeper soil (30–50 cm). Furthermore, the storage of SOC and TN was significantly related to SR of SOC and TN along the whole soil profile (P<0.0001). Therefore, SR could be used to explain and indicate the changes in the storage of SOC and TN. Further, NT stratifies SOC and TN, enhances the topsoil SOC storage, and helps to improve SOC sequestration and soil quality.

Soil carbon storage and stratification under different tillage/residue-management practices in double rice cropping system

Abstract The importance of soil organic carbon (SOC) sequestration in agricultural soils as climate-change-mitigating strategy has become an area of focus by the scientific community in relation to soil management. This study was conducted to determine the temporal effect of different tillage systems and residue management on distribution, storage and stratification of SOC, and the yield of rice under double rice (Oryza sativa L.) cropping system in the southern China. A tillage experiment was conducted in the southern China during 2005–2011, including plow tillage with residue removed (PT0), plow tillage with residue retention (PT), rotary tillage with residue retention (RT), and no-till with residue retention on the surface (NT). The soil samples were obtained at the harvesting of late rice in October of 2005, 2007 and 2011. Multiple-year residue return application significantly increased rice yields for the two rice-cropping systems; yields of early and late rice were higher under RT than those under other tillage systems in both years in 2011. Compared with PT0, SOC stocks were increased in soil under NT at 0–5, 5–10, 10–20, and 20–30 cm depths by 33.8, 4.1, 6.6, and 53.3%, respectively, in 2011. SOC stocks under RT were higher than these under other tillage treatments at 0–30 cm depth. SOC stocks in soil under PT were higher than those under PT0 in the 0–5 and 20–30 cm soil layers. Therefore, crop residues played an important role in SOC management, and improvement of soil quality. In the 0–20 cm layer, the stratification ratio (SR) of SOC followed the order NT>RT>PT>PT0; when the 0–30 cm layer was considered, NT also had the highest SR of SOC, but the SR of SOC under PT was higher than that under RT with a multiple-year tillage practice. Therefore, the notion that conservation tillage lead to higher SOC stocks and soil quality than plowed systems requires cautious scrutiny. Nevertheless, some benefits associated with RT system present a greater potential for its adoption in view of the multiple-year environmental sustainability under double rice cropping system in the southern China.

Applying a salinity response function and zoning saline land for three field crops： a case study in the Hetao Irrigation District, Inner Mongolia, China

Abstract Salinity is one of the major abiotic factors affecting the growth and productivity of crops in Hetao Irrigation District, China. In this study, the salinity tolerances of three local crops, wheat ( Triticum aestinum L.), maize ( Zea mays L.) and sunflower ( Helianthus annuus L.), growing in 76 farm fields are evaluated with modified discount function. Salinity ecological zones appropriate for these local crops are characterized and a case study is presented for crop salinity ecological zoning. The results show that the yield reductions of wheat, maize and sunflower when grown in saline soils are attributed primarily to a reduction in spikelet number, 1 000-grain weight and seed number per head, respectively. Sunflower is the most tolerant crop among the three which had a salinity tolerance index (ST-index) of 12.24, followed by spring maize and spring wheat with ST-Indices of 9.00 and 7.43, respectively. According to the crop salinity tolerance results, the arable land in the Heping Village of this district was subdivided into four salinity ecological zones: the most suitable, suitable, sub-suitable and unsuitable zones. The area proportion of the most suitable zone for wheat, maize and sunflower within the Heping Village was 27.5, 46.5 and 77.5%, respectively. Most of the most suitable zone occurred in the western part of the village. The results of this study provide the scientific basis for optimizing the local major crop distribution and improving cultural practices management in Hetao Irrigation District.

Effects of nitrogen application rates on net annual global warming potential and greenhouse gas intensity in double-rice cropping systems of the Southern China

The net global warming potential (NGWP) and net greenhouse gas intensity (NGHGI) of double-rice cropping systems are not well documented. We measured the NGWP and NGHGI including soil organic carbon (SOC) change and indirect emissions (IE) from double-crop rice fields with fertilizing systems in Southern China. These experiments with three different nitrogen (N) application rates since 2012 are as follows: 165xa0kgNxa0ha−1 for early rice and 225xa0kgNxa0ha−1 for late rice (N1), which was the local N application rates as the control; 135xa0kgNxa0ha−1 for early rice and 180xa0kgNxa0ha−1 for late rice (N2, 20xa0% reduction); and 105xa0kgNxa0ha−1 for early rice and 135xa0kgNxa0ha−1 for late rice (N3, 40xa0% reduction). Results showed that yields increased with the increase of N application rate, but without significant difference between N1 and N2 plots. Annual SOC sequestration rate under N1 was estimated to be 1.15xa0MgCxa0ha−1xa0year−1, which was higher than those under other fertilizing systems. Higher N application tended to increase CH4 emissions during the flooded rice season and significantly increased N2O emissions from drained soils during the nonrice season, ranking as N1xa0>xa0N2xa0>xa0N3 with significant difference (Pxa0<xa00.05). Two-year average IE has a huge contribution to GHG emissions mainly coming from the higher N inputs in the double-rice cropping system. Reducing N fertilizer usage can effectively decrease the NGWP and NGHGI in the double-rice cropping system, with the lowest NGHGI obtained in the N2 plot (0.99xa0kg CO2-eqxa0kg−1 yield year−1). The results suggested that agricultural economic viability and GHG mitigation can be simultaneously achieved by properly reducing N fertilizer application in double-rice cropping systems.

Management-induced greenhouse gases emission mitigation in global rice production

Mitigating greenhouse gases (GHGs) emissions from rice paddy (Oryza sativa L.) and balancing the trade-offs between reducing emission and sustaining food security have raised global concerns. A global meta-analysis of rice experimental data was conducted to assess changes in emissions of GHGs (CH4 and N2O) and global warming potential (GWP) in response to improvements through 12 field management practices. The results indicated that changes in GWP were mainly attributed to CH4 emission even though N2O emission was significantly affected by conversion of field management practices. Specifically, GWP per unit rice plant area (area-scaled) was significantly increased by 20.1%, 66.2%, and 84.5% with nitrogen (N) fertilizer input, manuring, and residue retention (Pu202f<u202f0.05), along with significant increments in area-scaled CH4 emission under the above management practices by 8.9%, 60.4%, and 91.8%, respectively (Pu202f<u202f0.05). Due to the significant increase in rice yield, a decreasing trend for GWP per unit rice yield (yield-scaled) was observed with N fertilizer input. In addition, CH4 and GWP decreased significantly at both area- and yield-scale under non-flooding irrigation but with a reduction in rice yield by 3.3% (Pu202f<u202f0.05). Improvement in rice variety significantly enhanced crop yield by 15.3% while reducing area-scaled GWP by 27.7% (Pu202f<u202f0.05). Furthermore, other management practices, such as application of herbicides, biochar, and amendments (non-fertilizer materials) reduced yield-scaled GWP while increasing rice yield. Thus, changes in field management practices have the potential to balance the trade-offs between high yield and low emission of GHGs. However, in-depth studies are needed to determine the interactions between field management practices and site-specific soil/climate conditions.