Context: Determining optimum nitrogen (N) management is essential for maintaining rice yield while reducing the environmental risk caused by N loss. The C/N ratio of agricultural inputs plays a critical role in regulating reactive N (Nr) emissions and soil N retention. Objectives: However, critical knowledge gaps persist regarding the optimization of N management (application rates and surplus levels) to simultaneously achieve yield maximization and yield-scaled Nr loss minimization in straw-incorporated, deep-fertilized paddy systems. Methods: We conducted a three-year field experiment in Sanjiang Plain in northeast China with four N application rate treatments (0, 50, 100, and 150 kg N ha-1). Through systematic evaluation N input (straw-N, biological N fixation, atmospheric N deposition,irrigation-derived N), output (grain N removal, NH3 volatilization, N2O emissions, runoff, leaching, and drainage loss), and yield of paddy system. Results: We identified closely aligned thresholds for agronomic (104.5 kg N ha-1 for maximum yield) and environmental (99.5 kg N ha-1 for minimal yield-scaled Nr loss) objectives, corresponding to similar N surpluses (32.9-34.1 kg N ha-1). The system maintains high efficiency with Nr losses of just 2.3-6.5 kg N ha-1 annually, dominated by NH3 volatilization (2.7-4.4 % of applied N). When N application exceeded 100 kg N ha-1, both Nr losses and yield-scaled Nr losses increased sharply, with a critical inflection point at 110 kg N ha-1 corresponding to accelerated N surplus accumulation. Notably, a negative correlation was observed between paddy Nr losses and the C:N ratio of input materials. Conclusions: The recommended 99.5-110 kg N ha-1 application range provides a scientifically validated pathway for sustainable intensification, requiring 30.3-33.6 % N less than conventional systems while maintaining comparable yields through optimized N cycling rather than increased inputs. The synergistic effects of optimization N rates,straw incorporation, and deep fertilization collectively regulate the C:N ratio and Nr losses of paddy systems, thereby mitigating the typical trade-off between productivity and sustainability in intensive rice systems.

Alternate wetting and drying (AWD) irrigation alleviates prolonged flooding-induced soil redox potential decline and methane emissions in rice paddies. AWD typically maintains a 15 cm water table depth. While straw incorporation intensifies soil reduction under prolonged flooding, the optimal intensity of AWD under straw incorporation remains unclear. We conducted a field experiment in northeast China comparing two AWD regimes (AWD15 and AWD20, draining to 15/20 cm depth) with straw incorporation. Soil reductive substance content, root activity, tillering dynamics and yield were systematically monitored. The results demonstrated that compared with AWD15, the AWD20 treatment significantly reduced the content of soil reductive substances, with a 22.6% and 42.7% decrease in soil Fe2+ and Mn2+ content, respectively, and an 80.9% and 82.7% decrease in total reductive matter content and active reductive matter content, respectively, at mid-season drainage. The soil Fe2+ content was negatively correlated with the redox potential of the soil. After rewetting, AWD20 treatment significantly increased soil microbial biomass carbon (MBC) and nitrogen (MBN) content. Compared with the AWD15 treatment, only the number of tillers decreased by 4.8% in the AWD20 treatment, while there was no statistical difference in rice root activity, effective spike number, carbon and nitrogen content of rice, nitrogen fertiliser partial factor productivity (PFP), harvest index, yield and yield stability. The findings suggest that AWD20 holds promise as a sustainable irrigation strategy for straw-incorporated rice systems, contributing to improved plant growth conditions and enhanced field sustainability.

Long-term use of a single tillage method degrades soil texture and organic matter, reducing productivity. Therefore, improving soil organic matter and optimizing tillage are vital for sustainable productivity on the North China Plain. The study focused on two factors: tillage method and biochar application. The tillage methods included subsoiling (ST) and conventional rotary tillage (RT), while the biochar application rates were 0 t/hm(2) (B0), 4.5 t/hm(2) (B1), and 9.0 t/hm(2) (B2), with biochar applied before wheat sowing. According to the results, biochar significantly reduced N2O emissions by 19.6 %-29.5 % over the wheat-maize rotation. Compared to rotary tillage, subsoiling enhanced soil total nitrogen, organic matter (SOM) in the 0-20 cm layer by 9.0 %. Biochar significantly increased SOM, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) in the top 20 cm, with greater effects under subsoiling; in the STB2 treatment, increases were 15.5 %, 17.1 %, and 17.1 %, respectively. Biochar also increased soil pH and reduced bulk density, with stronger effects at higher rates. Although biochar exerted no significant effect on the non-water-stable aggregates stability, it did considerably increase the fraction of >5 mm non-water-stable aggregates and stability. The improvement in aggregate stability was only observed in the surface soil after the second crop, where biochar increased the mean weight diameter, geometric mean diameter and water-stable aggregates, while reducing soil erodibility factor (K-factor) and percentage of soil aggregate destruction. Improvements in deeper layers were minimal. Comprehensive evaluation indicated that subsoiling plus 4.5 t/hm(2) biochar showed better nutrient and aggregate stability improvement than 9.0 t/hm(2) biochar with rotary tillage. In summary, subsoiling with 4.5 t/hm(2) biochar enhances soil quality and reduces greenhouse gas emissions, with cumulative benefits over time.

Application of organic amendments and N fertilizer can affect C and N sequestration, however, the degree to which diverse organic amendments and optimal N fertilization for matching demand for high crop productivity contributes to soil organic matter (SOM) of Cambisol in the North China Plain is not fully known. The objective was to evaluate the combined effects of annual maize straw-derived organic amendments (straw, manure, compost, biogas residue, or biochar) and in-season mineral N fertilizer amendment on soil organic carbon (SOC) and total N (TN) accumulation and thermal stability in bulk soils and physically isolated soil aggregate fractions in a long -term field experiment on the North China Plain. Application of organic amendments either alone or with N increased the proportion of macroaggregates (+62 to 137 %), aggregate mean weight diameter (+50 to 106 %), SOC (+38 to 206 %) and TN (+13 to 52 %) contents in bulk soil. The organic amendments and N fertilizer additions also increased SOC and TN contents in each of the isolated fractions: macroaggregates (+119 to 851 % for SOC, +109 to 237 % for TN) and microaggregates (+42 to 192 % for SOC and +30 to 145 % for TN), total fine particulate organic matter (T fPOM, +143 to 891 % for T fPOM-SOC, +129 to 549 % for T fPOM-TN) and total silt + clay within aggregates (53-139 % for SOC and 20-106 % for TN). Biochar resulted in the largest increase in SOC contents and improved soil aggregation without N fertilization, but fertilization greatly decreased these responses. The majority of the accumulated C and N occurred in the total silt + clay fractions, making up 50-90 % of total SOC and 79-96 % of total TN. Total fine POM and total silt + clay within aggregates contributed to 40-78 % and 10-56 % of SOC, 28-60 % and 37-71 % of TN increase between soil with and without organic amendments. Our results suggested that C and N retained in T fPOM and silt + clay fractions within aggregates were important mechanisms for C and N stabilization. Substitution of annual above-ground litter with biochar with or without mineral N fertilizer was the most effective way for SOM build up and stabilization under a wheat/maize system in the North China Plain, while manure, compost and biogas residue resulted in little to no increases of SOM in bulk soils and physically isolated aggregate fractions compared to straw amendment. Besides the effects of each amendment type on SOC, the different recovery rates of the various amendments, which determines the total quantity of each amendment that can be produced, should be taken into consideration in decisions about maize residue management at the regional scale in the North China Plain.

Organic and mineral fertilization increase crop productivity, but their combined effects on soil quality index (SQI) and ecosystem multifunctionality (EMF, defined as the capacity of soils to simultaneously provide multiple functions and services) are not clear. We conducted a 13-year field trial in North China Plain to examine how five maize-derived organic fertilizers (straw, manure, compost, biogas residue, and biochar) at equal C input rate (3.2 t C ha-1), with or without nitrogen (N) fertilization influenced topsoil (0-15 cm) physico-chemical properties, activities of enzymes responsible for carbon (C), N, and phosphorus (P) cycling, as well as SQI and soil EMF. Organic fertilizers with or without N increased SQI by 51-187 % and EMF by 31-351 % through the enhancement of soil physical (mean weight diameter of soil aggregates) and chemical properties (C, N, and P contents) as well as C, N, and P acquisition enzyme activities, albeit the biochar effects were of minor importance. N application increased EMF compared to soil without N. Soil quality increased with EMF. Random forest analysis revealed that microbial biomass C and N, available P, permanganate oxidizable C, dissolved organic C and N, mean weight diameter of aggregates, hot water extractable C, and electrical conductivity were the main contributions to soil EMF. We conclude that application of maize-derived organic fertilizers, especially compost and straw, with optimal N fertilization is a plausible strategy to increase SQI and EMF under a wheat/maize system.

Anthropogenic activities have raised nitrogen (N) input worldwide with profound implications for soil carbon (C) cycling in ecosystems. The specific impacts of N input on soil organic matter (SOM) pools differing in microbial availability remain debatable. For the first time, we used a much-improved approach by effectively combining the 13C natural abundance in SOM with 21 years of C3-C4 vegetation conversion and long-term incubation. This allows to distinguish the impact of N input on SOM pools with various turnover times. We found that N input reduced the mineralization of all SOM pools, with labile pools having greater sensitivity to N than stable ones. The suppression in SOM mineralization was notably higher in the very labile pool (18%-52%) than the labile and stable (11%-47%) and the very stable pool (3%-21%) compared to that in the unfertilized control soil. The very labile C pool made a strong contribution (up to 60%) to total CO2 release and also contributed to 74%-96% of suppressed CO2 with N input. This suppression of SOM mineralization by N was initially attributed to the decreased microbial biomass and soil functions. Over the long-term, the shift in bacterial community toward Proteobacteria and reduction in functional genes for labile C degradation were the primary drivers. In conclusion, the higher the availability of the SOM pools, the stronger the suppression of their mineralization by N input. Labile SOM pools are highly sensitive to N availability and may hold a greater potential for C sequestration under N input at global scale.

The straw incorporation in paddy fields exacerbates the reductive toxicity caused by flooding during the rice tillering stage in cold regions. Mid-drainage can alleviate reductive toxicity, while nitrogen fertilizer (NF) application can enhance the drought resistance of rice. However, there is still a lack of convincing evidence about the types of reductive toxicity and appropriate draining thresholds with straw incorporation. A field experiment was conducted in northeast China to investigate the reductive toxicity of paddy fields caused by flooding and straw incorporation. Primarily, the study aimed to investigate the reduction of toxicity caused by straw incorporation. Additionally, the investigation verified the role of varying NF (0, 50, 100, 150 kg N ha-1) in conjunction with mid-season drainage (-15 cm) to mitigate soil reductive toxicity while preserving root activity. Before mid-season drainage, the contents of soil total amount of reductive matter, active reductive matter, Fe2+, and Mn2+ were 5.1-5.9 cmol kg-1, 3.2-3.9 cmol kg-1, 399.4-410.1 mg kg-1 and 290.3-340.1 mg kg-1, respectively. Mid-season drainage of 15 cm depth decreased the total amount of reductive matter, active reductive matter and Fe2+ content by 51.8%, 56.0% and 29.6%, respectively. However, upon rewetting, the content of reductive substances reverted to pre-drainage levels. Drainage led to a reduction in soil organic acid content by 56.6-78.8% and an increase in rice root activity by 160-290%. While increased NF application correlated with higher rice root activity, a significant yield increase was only observed within the range of 0-100 kg ha-1. In summary, an alternate wetting and drying threshold of -15 cm in combination with 100 kg ha-1 of NF rate significantly increased root activity and reduced reductive toxicity of the tillage layer without decreased rice yield. The reductive substance content rebounded to the pre-drainage level after reflooding in the subsequent growth stage. Therefore, to minimize the reductive toxicity and methane emission caused by straw incorporation, rice fields can be drained to a depth of 15 cm during mid-season drainage. Additionally, the fields should be drained several times in the following growth stage.

Despite broad information on greenhouse gas (GHG) emissions from the soil surface, only few studies have examined the depth related GHG concentration and production within the soil. We coupled chamber surface GHG flux measurements with analysis of subsurface GHG concentrations at five depths (0, 10, 30, 50 and 70 cm) using silicon tubes in a grassland and cropland soils in a semi-arid agro-pastoral ecotone over a full year. Grassland and cropland soils behaved as net CO2 and N2O sources, but sinks of CH4. CO2 and N2O concentrations increased but CH4 decreased with soil depth. Subsurface GHG fluxes calculated using Fick's law decreased with depth. The modeled GHG and measured surface fluxes agreed much better for CO2 than N2O or CH4. Spring-thaw and rainfall events triggered N2O pulses, CH4 uptake peaks and CH4 concentration drops. Annual emissions or uptake based on chamber method were 4820-7580 kg C ha-1 yr- 1, 2.4-1.5 kg C ha-1 yr- 1, and 0.13-0.14 kg N ha-1 yr- 1 for CO2, CH4, and N2O across the grassland and cropland, respectively. Modeled annual accumulation of GHG fluxes dropped with depth, whereas the topsoil (0-20 cm) contributed about 65% for CO2, 68% for N2O and 72% for CH4 of the total profile. The vertical distribution of GHG fluxes reflected those of soil organic carbon and root biomass. The grassland had higher annual CO2 flux but lower CH4 uptake than the cropland. Annual N2O fluxes were similar between the two ecosystems.

Livestock sheds are local and regional hotspots of greenhouse gases (GHG) emissions, but only very few studies analyse the intensities of GHG emissions from this source. The objective of this study was to quantify annual CH 4 , CO 2 and N 2 O emissions from inside and outside of sheepfolds and summer cattle sheds in a typical agro‐pastoral ecotone using static chamber technique. Both sheepfolds and cattle shed functioned as huge net sources of CH 4 and N 2 O at annual scale. Animal presence increased CH 4 , CO 2 and N 2 O effluxes for up to 1100 times compared to the animal sheds without animals. N 2 O emissions boosted for 160%–280% during and after rainfall and spring‐thaw events. The CH 4 and CO 2 fluxes increased exponentially with faeces temperature for the outside sheepfold and summer cattle shed. The annual GHG emissions from both sheepfolds and summer cattle shed were 56 t CO 2 equivalents ha −1 , of which N 2 O contributed to 94%. Sheepfold dominated the total GHG emissions from animal sheds and accounted for 83% of the annual GHG flux. Annual emission on a per animal basis was 15, 0.2 and 28 kg CO 2 eq year −1 sheep −1 and 26, 10 and 140 kg CO 2 eq year −1 cattle −1 for N 2 O, CH 4 and CO 2 , respectively. The annual N 2 O emissions from animal sheds were 70–250 times larger than nearby grassland soils, which were also net sink for atmospheric CH 4 . Concluding, animal sheds are very intensive local hotspots of GHG emissions, which should be considered at the local and regional scales.

Interactions between soil quality and climate change may influence the capacity of croplands to produce sufficient food. Here, we address this issue by using a new dataset of soil, climate and associated yield observations for 12,115 site-years representing 90% of total cereal production in China. Across crops and environmental conditions, we show that high-quality soils reduced the sensitivity of crop yield to climate variability leading to both higher mean crop yield (10.3 ± 6.7%) and higher yield stability (decreasing variability by 15.6 ± 14.4%). High-quality soils improve the outcome for yields under climate change by 1.7% (0.5–4.0%), compared to low-quality soils. Climate-driven yield change could result in reductions of national cereal production of 11.4 Mt annually under representative concentration pathway RCP 8.5 by 2080–2099. While this production reduction was exacerbated by 14% due to soil degradation, it can be reduced by 21% through soil improvement. This study emphasizes the vital role of soil quality in agriculture under climate change. Food demand is increasing, while climate change is impacting the magnitude and stability of crop yields. High-quality soils are able to buffer the negative impacts of climate change and lead to smaller yield reduction and higher yield stability, indicating a potential adaptation strategy.

Crop rotation of flooded rice with an upland crop like maize on previous continuous paddy soils is an emerging cropping system in South China. A four-year experiment was conducted at a research area in Hunan province, having a long history of double paddy-rice cropping throughout the year. Maize was introduced as an upland crop in rotation with paddy rice, thus providing two parallel cropping systems i.e., the previous flooded rice-rice (R-R) and the new maize-rice rotation (M-R) systems. We used three treatments in both cropping systems; namely, farmer's practice (without external C input) as a control, straw addition, and biochar addition. The straw and biochar were added to soil in late rice season on an equal C input basis (3000 kg C ha(-1)yr(-1)). In the R-R plots, rice straw was added while in M-R plots maize straw was added during late rice field preparation. Our results show that there were no changes in soil organic carbon (SOC) concentration when R-R was replaced by M-R rotation. Straw addition had no effect on SOC but improved late rice yield. Biochar addition significantly increased SOC and late rice yield in both cropping systems. Moreover, biochar addition resulted in a more significant accumulation of SOC (9% higher) in M-R than R-R. Among soil aggregates, only the 0.25-2mm fraction had a significantly higher SOC concentration with biochar relative to the control and straw return; and this increase was significantly more pronounced under M-R (28% higher) than R-R cropping system. In general, a significantly higher proportion of small macro-aggregates (0.25-2 mm) were found under M-R, while smaller aggregates (0.05-0.25 and< 0.05 mm) were more abundant under R-R. delta C-13 analyses from M-R plots reveal that the quantity of maize-derived C was marginally higher in the straw treatment than control, but this was not reflected in any significant impact on total SOC of the bulk soil or of aggregates. In conclusion, no detectable changes in SOC were observed over four years experimental period following shift from R-R to M-R cropping system. M-R system with biochar addition led to higher productivity and environmental benefits.

Biochar (BC) application to low fertility soils is a promising approach to increase crop yield, improve soil quality, and mitigate climate change simultaneously. Only few studies evaluated the combined effects of BC and nitrogen (N) fertilization rates on crop productivity and N losses under field conditions. The objectives were to investigate combined effects of BC (2 rates) and N (5 rates) fertilization on crop productivity and N losses in a long-term field experiment started in 2008 in a winter wheat/summer maize rotation system in the North China Plain. Linear-plateau models best described the responses of wheat and maize yields to N rates. N2O fluxes, NH3 volatilization, and soil mineral N contents increased exponentially with N fertilization rates. Despite the effect of BC on wheat or maize yields was negligible, BC retains of mineral N at 240 kg N ha-1 yr-1. BC application increased NH3 volatilization by 31% in wheat season and 26% in maize season because of pH increase. BC reduced N2O emissions by 8-23% in the wheat season and by 24% at lower N rates (≤60 kg ha-1) in the maize season, due to BC induced complete denitrification to N2. BC stimulated N2O emissions by 18-26% compared to soils without BC in maize season at N rates higher than 60 kg ha-1. The combination of increased mineral N retention and C availability with BC addition increased nitrification and/or denitrification rates, leading to increased N2O emissions. For the wheat/maize rotation system, BC application decreased N2O emissions at lower N rates (≤120 kg ha-1 yr-1) but had no effects at higher N rates.

Climate warming and anthropogenic nitrogen (N) loads are two major global change components interactively affecting carbon cycling. However, the effects of N forms and amounts on temperature sensitivity (Q10) of soil organic matter (SOM) mineralization remain incomplete. With this goal, soil was sampled after 23 years of mineral and (or) organic N fertilization, and then incubated for one year at 10, 20, and 30°C. For the first time, we compared four approaches (Equal time, Equal C, 1‐C pool, and 2‐C pool model) to evaluate the Q10 of SOM mineralization. All approaches showed that the Q10 decreased by more than one third with N fertilization compared to unfertilized control at low temperatures. The '1‐C pool model' was not adequate for Q10 estimation with various C availability. The Q10 estimated by '2‐C pool model' was strongly depended on incubation duration. The 'Equal C' approach was more powerful for separating SOM pools and it revealed the decreased Q10 of the recalcitrant pool at high N rates. The impact of N fertilization on Q10 was more evident at high N than at low N. Notably, the Q10 decreased more by mineral N compared to organic fertilizers (~60% vs. ~40% decreased in Q10) at 10–20oC. The added benefit of N fertilization in protecting SOM under climate warming was demonstrated by decreased Q10. Such one‐third reduction of temperature sensitivity by N fertilization is large enough to be considered in predictions of global SOM stocks under warming and anthropogenic N loads.

Soil organic matter (SOM) concentration and enzyme activity are important biochemical indicators of soil health for assessing the sustainability of agricultural management practices. However, little is known about the long-term effects of tillage and crop residue management on SOM and enzyme activities in soil particle-size fractions on the Loess Plateau of Northern China. The objective of this study was to investigate the effects of 11 years of combined tillage and crop residue management treatments on soil organic carbon (SOC), total nitrogen (TN) concentrations and enzyme activities in bulk soil and particle-size fractions from a rainfed wheat (Triticum aestivum. L.) monoculture system in this region. We hypothesized that reduced tillage and increased residue retention would increase SOC, TN and enzyme activities in both bulk soil and particle-size fractions, and that enzyme activity would serve as a more sensitive indicator of soil health in response to management. Compared with conventional tillage and residue removal (CTRR), reduced tillage and stubble mulch residue retention (RTSM) increased bulk soil activities of most enzymes (sulfatase +68%, invertase +62%, beta-glucosidase +58%, dehydrogenase +46%). These increases were greater than the relative increases in total SOC (34%) and TN (33%) concentrations, supporting our hypothesis of a stronger response in microbial activity to management than total element stocks. The RTSM treatment also increased SOC and TN concentrations, as well as beta-glucosidase, acid phosphatase and urease activities in all particle-size fractions (2000-250, 250-53, 53-2 and < 2 mu m) compared with the CTRR treatment. Both beta-glucosidase and acid phosphatase showed a general decrease from coarse-to fine-sized fractions, and resembled the distribution of SOC and TN concentrations in particle-size fractions. Conversely, urease activity was greater in sand and clay fractions, which was decoupled from SOC and TN distributions. Our results indicate that biological indicators of soil health were more sensitive than C and N stocks to cumulative long-term changes in tillage and residue management.

The semi-arid grasslands in northern China are subjected to accelerating land use change due to population growth and food demand. Considerable uncertainty exists on annual methane (CH4) fluxes of different land uses because most measurements have only been conducted during the growing season. Using static chamber - gas chromatographic technique, we quantified and characterized annual CH4 fluxes (from 2012 to 2015) from four land uses common in an agro-pastoral ecotone of northern China: summer-grazed grassland (SumGrazed), winter-grazed grassland (WinGrazed), ungrazed grassland since 1997 (Ungrazed) and oat cropland (OatCrop). The soil at all land uses functioned exclusively as a sink for atmospheric CH4 through the entire three years. Annual CH4 uptake rates averaged 1.42, 2.36,1.12 and 2.57 kg C ha(-1) yr(-1) for SumGrazed, WinGrazed, Ungrazed and OatCrop, respectively, during 2012-2015. Compared to Ungrazed, OatCrop and WinGrazed increased annual CH4 uptake by 129 and 111%, respectively. Non-growing season (October-April) contributed 28-43% of the annual CH4 uptake at all land uses. Across all four land uses, annual cumulative CH4 uptake decreased with increasing soil water-filled pore space (WFPS) explaining 81% of the variance in annual CH4 uptake. WFPS negatively correlated to CH4 uptake in the growing season (R-2 =0.16-0.35, P < 0.001). CH4 uptake increased with soil temperature through the entire observed period (R-2 = 0.38-0.63, P < 0.001) and the non-growing season (R-2 = 0.51-0.74, P < 0.001). We conclude that grazing has the potential to increase CH4 uptake from the atmosphere and consequently, contribute positively to CH4 related part of C budget. (C) 2017 Elsevier B.V. All rights reserved.

Overgrazing and intensive farming have led to severe land degradation in the past half century in the agro-pastoral ecotone of northern China. Currently, complete and periodical exclusions of grazing are commonly adopted for the restoration of these degraded grasslands. However, little is known about the effects of such land uses on nitrous oxide (N2O) emission in this region. Using static chamber technique, we quantified annual N2O emissions (from May 2012 to September 2013) from four land uses: summergrazed grassland (SG), winter-grazed grassland (WG), ungrazed grassland since 1997 (UG) and oat cropland (0C). N2O emissions occurred mainly after farmyard manure fertilization and during spring thaw periods. Annual N2O fluxes from the SG, WG, UG and OC were 0.19, 0.15, 0.43 and 0.98 kg N ha-1 yr(-1), respectively. The spring-thaw N2O emissions from UG and OC dominated the annual emission and accounted for 70% and 65% of the annual fluxes, respectively. In contrast, the contributions of spring thaw fluxes to total annual N2O emissions for SG and WG were only 32%. N2O fluxes during spring thaw season were positively related to soil NH4+ + NO3- content accounting for 80% of N2O flux variability across all land uses. Land use conversion from the native grassland to cropland increased N2O flux both during growing and spring thaw seasons due to farmyard manure application. Instead, grazing has the potential to decrease annual N2O losses mainly through reducing spring-thaw N2O emissions. (C) 2015 Elsevier B.V. All rights reserved.

Field measurements of net ecosystem CO2 exchange (NEE) with high temporal resolution are essential to construct a meaningful ecosystem C balance. The objectives of this study were to monitor NEE in high temporal resolution in cropland and grassland between middle August and middle November (2006) at Kleinhohenheim, Germany and to evaluate NEE in autumn. A fully automated temperature controlled closed chamber system with an infrared CO2 analyzer was used to measure NEE. The measured NEE varied between the two ecosystems depending on changes in above-ground vegetation and environmental factors. The diurnal NEE pattern of daytime CO2 uptake and night time CO2 release was evident in the grassland, but not in the cropland as the crops were harvested at the beginning of the measurement period. The grassland generally showed higher night time NEE, but lower daytime NEE than the cropland. Night time NEE showed exponential dependence on air and soil temperature, resulting in Q10 of 1.8 and 1.9 (for air temperature), 2.3 and 2.4 (for soil temperature) in the grassland and cropland, respectively. The average daily NEE was 2.77 and 1.86 g CO2-C m−2 day−1 in the cropland and grassland, respectively. Both ecosystems were sources of CO2, during 3 months in autumn, but the grassland emitted less CO2 by 87.9 g CO2-C m−2 than the cropland.