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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. [ABSTRACT FROM AUTHOR]

China’s economy has made great strides since 1949, and especially since China initiated economic reforms and the open-door policy in the 1980’s. The growth in agricultural production has been one of the main national accomplishments. By 1999 China was feeding 22 % of the global human population with only 9 % of the world’s arable land and per capita food availability reached the levels of developed countries. The use of fertilizers has played a crucial role, accounting for about 50 % of the yield increase. However, rapid economic growth has led to unprecedented resource exhaustion and environmental degradation. China’s ‘grain security’ will face multiple pressures stemming from resource limitation, environmental pollution and population growth. The Chinese government regards agriculture as the primary field of development of the national economy in the 21st century. The optimal agricultural developmental path for China is to improve the ratio of resource utilization and to protect the environment while guaranteeing the grain supply. This paper summarizes the trends in crop production and crop yields, fertilizer use and soil quality in China, and presents the approach of integrated nutrient management (INM) for improving crop productivity with efficient resource utilization and environmental protection. In the INM approach, the strategy is to emphasize the integrated use of nutrients from fertilizers, wastes and soil and environmental sources; managing nutrients according to different nutrients’ specific characteristics; and integrated nutrient management with sound soil management practices and other farming techniques. These new nutrient management systems can, on average, reduce N fertilizer inputs by 26%, save P fertilizer inputs by 20%, raise grain yields by 8%, and reduce N loss by 47 % compared to conventional agricultural practice.

Global agriculture is facing unprecedented challenges and risks. Rates of yield growth have slowed since the 1980s (ref. 4), and even stagnated in many areas (5-7). Meanwhile, agriculture incurs substantial [...], Agriculture faces great challenges to ensure global food security by increasing yields while reducing environmental costs (1,2). Here we address this challenge by conducting a total of 153 site-year field experiments covering the main agro-ecological areas for rice, wheat and maize production in China. A set of integrated soil-crop system management practices based on a modern understanding of crop ecophysiology and soil biogeochemistry increases average yields for rice, wheat and maize from 7.2 million grams per hectare (Mg [ha.sup.-1]), 7.2 Mg [ha.sup.-1] and 10.5 Mg [ha.sup.-1] to 8.5 Mg [ha.sup.-1], 8.9 Mg [ha.sup.-1] and 14.2 Mg [ha.sup.-1], respectively, without any increase in nitrogen fertilizer. Model simulation and life-cycle assessment (3) show that reactive nitrogen losses and greenhouse gas emissions are reduced substantially by integrated soil-crop system management. If farmers in China could achieve average grain yields equivalent to 80% of this treatment by 2030, over the same planting area as in 2012, total production of rice, wheat and maize in China would be more than enough to meet the demand for direct human consumption and a substantially increased demand for animal feed, while decreasing the environmental costs of intensive agriculture.

Author(s): Zhenling Cui [1]; Hongyan Zhang [1]; Xinping Chen [1]; Chaochun Zhang [1]; Wenqi Ma [2]; Chengdong Huang [1]; Weifeng Zhang [1]; Guohua Mi [1]; Yuxin Miao [1]; Xiaolin Li [...]

We investigated the effects of land use conversion from cereal grain fields (GF) to greenhouse vegetable fields (VF) on total soil organic C (SOC) and total N (TN) and the labile soil organic matter pools dissolved organic C (DOC), permanganatc-oxidizable C (POC), dissolved organic N (DON), mineral N, and microbial biomass C (MBC) in the top 30 cm of the soil profile. The soil samples were collected in 20 sets of paired soils (greenhouse vegetable vs. wheat [Triticum aestivum L.]-maize [Zea mays L.] rotation fields) in northeast China. Compared with those in GF, the SOC and TN concentrations in VF increased by 28 and 58%, respectively,. The accumulation rate of TN vs. SOC, however, led to a significant decrease in soil C/N ratio in VF compared with GF systems. The greatest difference in C/N ratios between GF and VF was observed in the large macroaggregates (>2000 [micro]m). Conversion to VF led to increased DOC, POC, and DON concentrations and an increase in the percentage of SOC as DOC and POC. The pH, MBC, and percentage of SOC as MBC, however, were lower in the VF than GF systems. Furthermore, a significant positive relationship was found between pH and MBC in the VF systems, while MBC was positively related to total SOC and POC in the GF systems. In conclusion, the results show tradeoffs between increasing SOC sequestration when agricultural land is converted from wheat-maize to vegetable systems and decreased C/N ratios and soil acidification. Improvements in soil and crop management for vegetable production systems in China, particularly the avoidance of excess N fertilizer and manure applications, are recommended. doi: 10.2136/sssaj2009.0222

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. [ABSTRACT FROM AUTHOR]

Meeting the future food security challenge without further sacrificing environmental integrity requires transformative changes in managing the key biophysical determinants of increasing agronomic productivity and reducing the environmental footprint. Here, we focus on Chinese rice production and quantitatively address this concern by conducting 403 on-farm trials across diverse rice farming systems. Inherent soil productivity, management practices and rice farming type resulted in confounded and interactive effects on yield, yield gaps and greenhouse gas (GHG) emissions (N2O, CH4 and CO2-equivalent) with both trade-offs and compensating effects. Advances in nitrogen, water and crop management (Best Management Practices—BMPs) helped closing existing yield gaps and resulted in a substantial reduction in CO2-equivalent emission of rice farming despite a tradeoff of increase N2O emission. However, inherent soil properties limited rice yields to a larger extent than previously known. Cultivating inherently better soil also led to lower GHG intensity (GHG emissions per unit yield). Neither adopting BMPs only nor improving soils with low or moderate productivity alone can adequately address the challenge of substantially increasing rice production while reducing the environmental footprint. A combination of both represents the most efficient strategy to harness the combined-benefits of enhanced production and mitigating climate change. Extrapolating from our farm data, this strategy could increase rice production in China by 18%, which would meet the demand for direct human consumption of rice by 2030. It would also reduce fertilizer nitrogen consumption by 22% and decrease CO2-equivalent emissions during the rice growing period by 7% compared with current farming practice continues. Benefits vary by rice-based cropping systems. Single rice systems have the largest food provision benefits due to its wider yield gap and total cultivated area, whereas double-rice system (especially late rice) contributes primarily to reducing GHG emissions. The study therefore provides farm-based evidence for feasible, practical approaches towards achieving realistic food security and environmental quality targets at a national scale. [ABSTRACT FROM AUTHOR]

Abstract: A 3-year field experiment examined the effects of non-flooded mulching cultivation and traditional flooding and four fertilizer N application rates (0, 75, 150 and 225kgha-1 for rice and 0, 60,120, and 180kgNha-1 for wheat) on grain yield, N uptake, residual soil Nmin and the net N balance in a rice–wheat rotation on Chengdu flood plain, southwest China. There were significant grain yield responses to N fertilizer. Nitrogen applications of >150kgha-1 for rice and >120kgha-1 for wheat gave no increase in crop yield but increased crop N uptake and N balance surplus in both water regimes. Average rice grain yield increased by 14% with plastic film mulching and decreased by 16% with wheat straw mulching at lower N inputs compared with traditional flooding. Rice grain yields under SM were comparable to those under PM and TF at higher N inputs. Plastic film mulching of preceding rice did not affect the yield of succeeding wheat but straw mulching had a residual effect on succeeding wheat. As a result, there was 17–18% higher wheat yield under N0 in SM than those in PM and TF. Combined rice and wheat grain yields under plastic mulching was similar to that of flooding and higher than that of straw mulching across N treatments. Soil mineral N (top 60cm) after the rice harvest ranged from 50 to 65kgha-1 and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil Nmin ranged from 66 to 88kgNha-1 and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621kgha-1), but low N inputs resulted in a negative balance (-85 to -360kgha-1). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79kgha-1) as mulching materials. There was not clear trend found in net N balance between PM and TF. Results from this study indicate non-flooded mulching cultivation may be utilized as an alternative option for saving water, using efficiently straw and maintaining or improving crop yield in rice–wheat rotation systems. There is the need to evaluate the long-term environmental risks of non-flooded mulching cultivation and improve system productivity (especially with straw mulching) by integrated resource management. [Copyright &y& Elsevier]

This paper aims at investigating the electrical tree characteristics of isotactic polypropylene (iPP)/syndiotactic polypropylene (sPP) blends for thermoplastic cable insulation. PP blended samples with sPP contents of 0, 5, 15, 30, and 45 wt% are prepared, and electrical treeing experiments are implemented under alternating current (AC) voltage at 50, 70, and 90 °C. Experimental results show that with the incorporation of sPP increasing to 15 wt%, the inception time of electrical tree increases by 8.2%. The addition of sPP by 15% distinguishes an excellent performance in inhibiting electrical treeing, which benefits from the ability to promote the fractal dimension and lateral growth of branches. Further increase in sPP loading has a negative effect on the electrical treeing resistance of blended insulation. It is proved by DSC and POM that the addition of sPP promotes the heterogeneous crystallization the of PP matrix, resulting in an increasing density of interfacial regions between crystalline regions, which contains charge carrier traps. Charges injected from an electrode into a polymer are captured by deep traps at the interfacial regions, thus inhibiting the propagation of electrical tree. It is concluded that the modification of crystalline morphology by 15 wt% sPP addition has a great advantage in electrical treeing resistance for PP-based cable insulation. [ABSTRACT FROM AUTHOR]

This work focuses on the coupling effect of molecular chain displacement and trap characteristics on direct current (DC) breakdown properties of high density/low density polyethylene (HDPE/LDPE) blend insulation. Frequency domain spectroscopy (FDS) and isothermal discharge current (IDC) are used to characterize the dielectric relaxation and trap characteristics of HDPE/LDPE blends. A DC breakdown model is proposed to reveal the mechanisms of the molecular chain displacement and carrier trap on the DC breakdown strength. The dielectric relaxation α and δ present segmental motions and thermal ion polarization behaviours of HDPE/LDPE blends, respectively. α dielectric relaxation strength (Δεα) increases as the amount of HDPE increases from 0 to 5 wt%, and then declines with a further increase of HDPE content to 20 wt%. According to the velocity equation, the increase of Δεα will increase the molecular chain displacement, resulting in a larger free volume, which will provide electrons with larger free path λ to form hot electrons. A positive correlation exists between the activation energy of the dielectric relaxation process δ and trap density, and the increase of δ dielectric relaxation strength (Δεδ) will adversely affect the breakdown strength of the specimen. HDPE/LDPE blends with 15 wt% HDPE content have lower Δεα and lowest Δεδ, which decreases the mean free path λ of molecular chain and thermal ion polarization. At the same time, it has the highest deep trap density, thus increasing the probability of hot electrons being captured and improving the DC breakdown strength. It is concluded the breakdown of the dielectric is synergistically affected by the molecular chain displacement and carrier trap. [ABSTRACT FROM AUTHOR]

Objective:China’s food production has increased 6-fold during the past half-century, thanks to increased yields resulting from the management intensification, accomplished through greater inputs of fertilizer, water, new crop strains, and other Green Revolution’s technologies. Yet, changes in underlying quality of soils and their effects on yield increase remain to be determined. Here, we provide a first attempt to quantify historical changes in inherent soil productivity and their contributions to the increase in yield. Methods:The assessment was conducted based on data-set derived from 7410 on-farm trials, 8 long-term experiments and an inventory of soil organic matter concentrations of arable land. Results:Results show that even without organic and inorganic fertilizer addition crop yield from on-farm trials conducted in the 2000s was significantly higher compared with those in the 1980s — the increase ranged from 0.73 to 1.76 Mg/ha for China’s major irrigated cereal-based cropping systems. The increase in on-farm yield in control plot since 1980s was due primarily to the enhancement of soil-related factors, and reflected inherent soil productivity improvement. The latter led to higher and stable yield with adoption of improved management practices, and contributed 43% to the increase in yield for wheat and 22% for maize in the north China, and, 31%, 35% and 22% for early and late rice in south China and for single rice crop in the Yangtze River Basin since 1980. Conclusions:Thus, without an improvement in inherent soil productivity, the ‘Agricultural Miracle in China’ would not have happened. A comprehensive strategy of inherent soil productivity improvement in China, accomplished through combining engineering-based measures with biological-approaches, may be an important lesson for the developing world. We propose that advancing food security in 21st century for both China and other parts of world will depend on continuously improving inherent soil productivity. [ABSTRACT FROM AUTHOR]

Yield gap (Yg) analysis is useful to map the scope for sustainable intensification of agriculture, but explaining and quantifying the underlying causes of yield gaps remains a considerable challenge. The objective of this study was to decompose maize yield gaps under different nitrogen (N) application rates and soil quality conditions across irrigated and rainfed cropping systems in China. A comprehensive database consisting of 5228 on-farm trials located in three major maize production regions of China was used for this purpose. The on-farm trials contained detailed information for four different treatments: fertilizer omission (control), optimal N rate (optimal N), 50% of optimal N rate (low N) and 150% of optimal N rate (high N). These were combined with biophysical and yield potential data from the Global Yield Gap Atlas (http://yieldgap.org). An analytical framework integrating stochastic frontier analysis and principles of production ecology was applied to decompose the overall maize yield gap into components of efficiency (and respective management and soil quality effects, Yg-M and Yg-S), resource (Yg-R), and technology Yg (Yg-T). The potential yield (Yp) of irrigated maize averaged 14.5 Mg/ha in Northeast China (NE) and 11.9 Mg/ha for North China Plain (NCP), and the water-limited potential yield (Yw) of rainfed maize averaged 12.0 Mg/ha in NE and 10.5 Mg/ha in Southwest China (SW), respectively. Maize yield gaps were highly variable across N treatments and cropping systems and ranged between 27–56% of Yp or Yw. Larger absolute yield gaps were observed in irrigated cropping systems in NE (4.8–8.1 Mg/ha) than in NCP (3.8–6.1 Mg/ha) and in rainfed cropping systems in NE (3.6–6.7 Mg/ha) and SW (2.8–5.9 Mg/ha). The components of the yield gap differed in size across cropping systems and N treatments. Yg-T was fairly small and consistent across N treatments ranging between 7.0% and 12.0% of Yp for irrigated maize and only ca. 2.0% of Yw for rainfed maize in NE. Yg-R was strongly associated with the N treatment explaining between 16.0–26.0% of Yp (or Yw) for control and low N treatments and being close to negligible for the optimal and high N treatments. Yg-M due to inefficient crop management accounted for 6.0–14.0% of Yp (or Yw) across cropping systems and N treatments, which is equivalent to 0.7–1.8 Mg/ha. The Yg-S explained the largest proportion of the total yield gap, especially in trials with low and medium soil quality levels, accounting for 11.0–24.0% of Yp or Yw (1.3–3.1 Mg/ha). The Yg-S was linked to partly manageable soil properties, such as low soil organic matter contents and low available P and/or K. This study is one of the first to incorporate the effects of soil quality in yield gap analysis and provides a basis to target management practices that can improve soil quality and N use efficiency while narrowing maize yield gaps in China. [ABSTRACT FROM AUTHOR]

A comprehensive synthesis of 32 long-term experiments in China is performed by comparing yields and SOM contents and their time by nutrient management responses (TNMR) to determine whether and to what extent combined application of organics amendments and fertilizers (organics + fertilizers) can increase productivity and soil organic matter (SOM) content and enhance the sustainability of diverse cropping systems. TNMR is defined as percentage changes over time in yields and SOM contents in external nutrient input treatments relative to initial and control plots and represents the net effects of nutrient management strategies on yields and SOM contents. Organics + fertilizers significantly increased yields over three crops (wheat, maize and rice) on average by 29% relative to sole organics and 8% to fertilizer only. Higher TNMR values in yields were found with organics + fertilizers in the sequence wheat (53%) > maize (40%) > rice (8%). Significant and positive time trends in TNMR of organics + fertilizers in wheat and maize yield may imply enhanced sustainability of cropping systems. Addition of organics (alone or combined with fertilizers) increased SOM contents and their TNMR over fertilizers applied alone. However, benefits varied between organics and organics + fertilizers by land use type. The latter led to higher SOM contents than (for dry land) and similar to the former (for dry-flooded and flooded systems). 2.3 and 1.4 times higher TNMR of organics + fertilizers in SOM content in dry land than dry-flooded and flooded systems implies that dry land was more responsive in SOM content increase upon adoption of organics + fertilizers than the latter. Overall, despite variation in the quantitative magnitude in crop or land use type, compared with application of organics or fertilizers only, a combination of both represents the most effective way to produce more food, build up SOM and enhance sustainability, especially in dry land cropping systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] The HEM system optimizing nutrient and irrigation increased NUE over farmer's practice by 46–63%, without affecting rice yield. [•] The HYM system optimizing transplanting density and irrigation increased yield by 11% and NUE by 19–89% over farmer's practice. [•] The PRM system optimizing transplanting density, nutrient and irrigation increased yield by 10% and NUE by 51–97% over farmer's practice. [•] Integrated precision crop management has the potential to contribute to both food security and sustainable development. [Copyright &y& Elsevier]

Abstract: The Loess Plateau in northwest China is one of the most eroded landscapes in the world, and it is urgent that alternative practices be evaluated to control soil erosion. Our objective was to determine how three different tillage practices for monoculture of winter wheat (Triticum aestivum L.) affected soil organic carbon (SOC) and N content after 11 years. Conventional tillage with residue removal (CT), shallow tillage with residue cover (ST), and no-tillage with residue cover (NT) were investigated. Carbon and N in various aggregate-size classes and various labile organic C fractions in the 0–15- and 15–30-cm soil layers were evaluated. The ST and NT treatments had 14.2 and 13.7% higher SOC stocks and 14.1 and 3.7% higher total N (Nt) stocks than CT in the upper 15cm, respectively. Labile C fractions: particulate organic C (POC), permanganate oxidizable C (KMnO4-C), hot-water extractable C (HWC), microbial biomass C (MBC) and dissolved organic C (DOC) were all significantly higher in NT and ST than in CT in the upper 15cm. KMnO4-C, POC and HWC were the most sensitive fractions to tillage changes. The portion of 0.25–2mm aggregates, mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates from ST and NT treatments were larger than from CT at both 0–15- and 15–30-cm soil depths. The ST and NT treatments had significantly higher SOC and Nt in the 0.25–2mm fraction at both depths and significantly higher Nt content in the upper 15cm. Positive significant correlations were observed between SOC, labile organic C fractions, MWD, GMD, and macroaggregate (0.25–2mm) C within the upper 15cm. We conclude that both variants of conservation tillage (NT and ST) increase SOC stock in the rainfed farming areas of northern China and are therefore more sustainable practices than those currently being used. [Copyright &y& Elsevier]

During the past 47 yr (1961-2007), Chinese cereal production has increased by 3.2-fold, successfully feeding 22% of the global human population with only 9% of the world's arable land, but at high environmental cost and resource consumption. Worse, crop production has been stagnant since 1996 while the population and demand for food continue to rise. New advances for sustainability of agriculture and ecosystem services will be needed during the coming 50 yr to reduce environmental risk while increasing crop productivity and improving nutrient use efficiency. Here, we advocate and develop integrated soil-crop system management (ISSM). In this approach, the key points are (i) to take all possible soil quality improvement measures into consideration, (ii) to integrate the utilization of various nutrient resources and match nutrient supply to crop requirements, and (iii) to integrate soil and nutrient management with high-yielding cultivation systems. Recent field experiments have shed light on how ISSM can lead to significant increases in crop yields while increasing nutrient use efficiency and reducing environmental risk., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)