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The problem of phosphorus discharge is related to environmental protection and food security. Struvite crystallization is a useful technology for phosphate recovery from wastewater. In the research, struvite crystallization process with CO2 degasification continuous U-shape reactor (CUSR) was application for phosphate recovery from animal manure wastewater. The result indicated PO4 3--P recovery ratio could achieve 47-53% without magnesium addition when CUSR hydraulic retention time controlled at 60 min. With extra magnesium addition, PO4 3--P recovery ratio could significant achieve 80-86% at magnesium addition amount 57.5 mg/dm3. PHREEQC modeling predictions trend of struvite crystallization was close to CUSR experimental results. The modeling calculation can provide a theoretical guide for operational parameters design. For seeding technology, high phosphate recovery efficiency was obtained and preformed struvite was the most effective seeding material. Surface characterization analysis demonstrated the dominant composition of chemical solids was struvite. Water extraction analysis indicated chemical solids recovery from animal manure wastewater could release PO4 3--P slowly and be available as slow-release fertilizer.

The problem of nutrient pollution from piggy wastewater has been considered as a serious problem. Enhancing struvite crystallization process is an efficient technology for ammonium recovery. In our study, the optimal reaction conditions of pH, Mg2+: NH4+: PO43- molar ratio, mixing reaction time, and different kinds of chemicals combinations for ammonium recovery were examined. The conclusions were drawn as following. The optimal pH for ammonium recovery was 9.0. The optimal Mg2+: NH4+: PO43- molar ratio for ammonium recovery was 1.3:1:1. The optimal mixing reaction time for ammonium recovery was 10 min. The chemicals combination of MgCl2 + Na2HPO4 was the most efficient for ammonium recovery. Scanning electron microscopy analysis indicated the unshaped struvite crystal was coarse and its size was irregular.

a b s t r a c t How to ensure both food security and sustainable development is one of the largest challenges in the 21st century. Over 10% of the world's population is still chronically malnourished today. Our environ- ment has been severely degraded by agricultural systems in many parts of the world. Precious agricultural resources are not efficiently utilized, but regrettably wasted in large quantities. Precision agriculture has the potential to improve crop yield, resource use efficiency and at the same time, protect the environment. However, current precision agricultural research has mainly focused on improving resource use efficien- cies, without much impact on yield. Here we developed a preliminary integrated precision rice (Oryza sativa L.) management (PRM) system by combining site-specific nutrient management with alternate drying and wetting irrigation and optimized transplanting density, with the aim to increase both yield and nitrogen (N) use efficiency (NUE). It was compared with a high efficiency system optimizing nutrient and water management (HEM), a high yield system optimizing transplanting density and water man- agement (HYM) and farmer's practice (FP) in an on-farm plot experiment conducted in 2010 and 2011 in Northeast China. It was further evaluated in three on-farm demonstration experiments conducted in 2010. Our results show that this PRM system increased grain yield by 10% and NUE by 51-97% over FP. The on-farm results show that it increased yield by 16% and N agronomic efficiency by 27%. The HEM sys- tem improved NUE by 46-63% over FP, without significantly affecting yield. The HYM system increased yield by 11% and NUE by 19-89% over FP. Compared with HEM system, the PRM system increased grain yield by 10% and NUE by 1-33%. Compared with HYM system, the PRM system achieved similar yield, but increased NUE by 5-27%. It is concluded that the preliminary integrated PRM system can optimize both grain yield and N use efficiency better than either the high efficiency or the high yield management sys- tem. This study demonstrates the potential of precision crop management to simultaneously contribute to food security and sustainable development.

Crop Circle is an active multispectral canopy sensor developed to support precision crop management. The Crop Circle ACS-470 model is user configurable, with a choice of six wavebands covering blue, green, red, red edge and near infrared spectral regions. The objectives of this study were to determine how well nitrogen (N) status of rice ( Oryza sativa L.) can be estimated with the Crop Circle ACS-470 active sensor using green, red edge and near infrared (NIR) bands at key growth stages and identify important vegetation indices for estimating rice N status indicators. Six field experiments involving different N rates and two varieties were conducted in Sanjiang Plain in Heilongjiang Province, China during 2011 and 2012. Crop sensor data and plant samples were also collected from five farmers’ fields to further evaluate the sensor and selected vegetation indices. The results of the study indicated that among 43 different vegetation indices evaluated, modified chlorophyll absorption reflectance index 1 (MCARI1) had consistent correlations with rice aboveground biomass ( R 2 = 0.79) and plant N uptake ( R 2 = 0.83) across growth stages. Four red edge-based indices, red edge soil adjusted vegetation index (RESAVI), modified RESAVI (MRESAVI), red edge difference vegetation index (REDVI) and red edge re-normalized difference vegetation index (RERDVI), performed equally well for estimating N nutrition index (NNI) across growth stages ( R 2 = 0.76). For rice plant N concentration, the highest R 2 was 0.33, and none of the indices performed satisfactorily with validation using farmers’ field data. We conclude that the Crop Circle ACS-470 active canopy sensor allows users the flexibility to select suitable bands and calculate different vegetation indices and has a great potential for in-season non-destructive estimation of rice biomass, plant N uptake and NNI.

Mycorrhizal and non-mycorrhizal maize ( Zea mays L.) plants were grown in two-compartment rhizoboxes, in order to study the effect of mycorrhizal hyphae-mediated acidification on organic P mineralization in the hyphosphere. The soil in the two compartments was supplemented with either KNO 3 or (NH 4 ) 2 SO 4 , and phytin (0 or 75 mg P kg −1 ) was added to the hyphal compartment. P content in the shoots was significantly higher for the NH 4 + treatment than for the NO 3 − treatment, but only in the combined presence of phytin and AM fungal mycelium ( Rhizophagus intraradices ). NH 4 + treatment under these conditions also led to a decrease in hyphosphere pH, enhanced phosphatase activity in the hyphosphere and accelerated mineralization of phytin compared to the NO 3 − treatment. The results show that hyphosphere acidification induced by absorption of NH 4 + by the AM fungal mycelium leads to an increase in phosphatase activity, and consequently enhances mineralization of phytin and improves maize uptake of P from phytin-P.

Ammonium nitrogen pollution is a key factor related to water eutrophication. In our works, biochar adsorption for ammonium nitrogen removal from wastewater has been investigated. Transmission Electron Microscope with energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier Transform Infrared spectroscopy was performed to characterize the prepared biochar. The optimal solution pH, and coexisting ions effect for ammonium nitrogen removal from wastewater was examined. Surface characterization demonstrated the obtained biochar was coarse, unshaped, irregular, and contained a great deal of carbon. With an increase in solution pH, biochar adsorption amount of ammonium nitrogen was decrease. With an increase in coexisting ions concentration, biochar adsorption amount of ammonium nitrogen was decrease.

Biochar is environmental friendly materials that can be used for environmental protection. In the research, the application of biochar for phosphate adsorption and recovery from wastewater was examined. The material surface characterization analysis, include Transmission Electron Microscope with energy dispersive X-ray spectroscopy and Fourier Transform Infrared spectroscopy, was performed to characterize the prepared biochar. The application analysis, include optimal solution pH and interfering ions effect, was performed for phosphate adsorption and recovery from wastewater. The research conclusions were drawn as follow: (1) material surface characterization demonstrated the prepared biochar was coarse, unshaped, irregular, and contained a great deal of carbon; (2) application analysis indicated biochar adsorption amount for phosphate was decrease with an increase in solution pH, and biochar adsorption amount for phosphate was also decrease with an increase in interfering ions concentration.

The great achievement of the development of intensive in agriculture in China can be partly attributed to substantial increases in mineral-nutrient application. However, whereas farmers tend to apply high levels of nitrogen (N) and phosphorus (P) application of potassium (K) has been neglected. A greater understanding of the relationship between maize (Zea mays L.) grain yield and K-application rate is thus required to provide an improved rationale for K fertilization for farmers in the various agro-ecological regions of China. In this study, a total of 2765 farmers' survey data and 3124 on-farm experiments across major maize agro-ecological regions in China were collected and evaluated for farmers' K-management status and to determine grain-yield response to K application. Nationally, the average K-application rate on farms was 26 kg K ha–1 and varied from 0 to 158 kg K ha–1, with a coefficient of variation of 107%, but the applied K-fertilizer rates were not related to grain yield. Maize grain yields at recommended K rates increased by 14.0%, 14.7%, 19.4%, and 4.3% in Northeast China, North China Plain, Southwest China, and Northwest China, respectively, compared to zero K fertilization (K0). Increased yield due to K fertilization (IYmax, difference between maximum yield across all treatments and K0-treatment yield for each experiment) averaged 1.4 t ha–1 but varied widely in different agro-ecological regions. Soil extractable K (NH4OAc-K) and intercounty variation resulted in large variation in IYmax in agro-ecological regions, as did other factors, such as use of particular maize hybrids, soil types, or years in different regions.

The challenges facing agriculture in China are probably more severe than ever before. We have developed an integrated technology system in which the focus is on achieving both high crop productivity and high resource use efficiency (“double high” technology system) to ensure food security and environmental sustainability. The components comprise (1) significantly increased grain-yield through high-yield crop management, i.e. an optimal cropping system design and management well adapted to climate conditions; (2) greatly increased nutrient-use efficiency through root/rhizosphere management to optimize the nutrient supply intensity and composition in the root zone to maximize root/rhizosphere efficiency; (3) improved soil quality to ensure long-term food security by managing soil organic matter and eliminating soil physical, chemical and biological constrains and (4) enhanced agricultural sustainability through resource and environment management by increasing resource use efficiency, reducing nutrient losses and greenhouse gas emissions and minimizing negative ecological footprints. In our work in major agricultural regions of China, this system has been successfully tested and demonstrated through well-organized farmer associations, enterprises with improved products and government extension networks. The new “double high” concept has the potential to become an effective agricultural development path to ensure food security and improve environmental quality, especially in China and other rapidly developing economies where agricultural intensification must achieve and must be transformed from low-efficiency systems to achieving high yields with high resource use efficiency.

Root and rhizosphere research has been conducted for many decades, but the underlying strategy of root/rhizosphere processes and management in intensive cropping systems remain largely to be determined. Improved grain production to meet the food demand of an increasing population has been highly dependent on chemical fertilizer input based on the traditionally assumed notion of 'high input, high output', which results in overuse of fertilizers but ignores the biological potential of roots or rhizosphere for efficient mobilization and acquisition of soil nutrients. Root exploration in soil nutrient resources and root-induced rhizosphere processes plays an important role in controlling nutrient transformation, efficient nutrient acquisition and use, and thus crop productivity. The efficiency of root/rhizosphere in terms of improved nutrient mobilization, acquisition, and use can be fully exploited by: (1) manipulating root growth (i.e. root development and size, root system architecture, and distribution); (2) regulating rhizosphere processes (i.e. rhizosphere acidification, organic anion and acid phosphatase exudation, localized application of nutrients, rhizosphere interactions, and use of efficient crop genotypes); and (3) optimizing root zone management to synchronize root growth and soil nutrient supply with demand of nutrients in cropping systems. Experiments have shown that root/rhizosphere management is an effective approach to increase both nutrient use efficiency and crop productivity for sustainable crop production. The objectives of this paper are to summarize the principles of root/rhizosphere management and provide an overview of some successful case studies on how to exploit the biological potential of root system and rhizosphere processes to improve crop productivity and nutrient use efficiency.

Since phosphorus, a non-renewable and non-substitutable resource, has become the principal contributor and limiting factor to water eutrophication, achieving phosphorus removal and recovery from wastewater is pretty essential. Even though struvite crystallization process has been widely used for phosphate (P) recovery in wastewater treatment, its application is hampered by difficulties controlling small particle size and crystal growth. This study was conducted to control the settleability of struvite by calculating and predicting the struvite-settling percentage (Ps), which is always affected by the initial concentration of P (CP), solution pH (pH), reaction time (t), reaction temperature (T), agitation rate (Ar) and inlet flow velocity (vf) of the fluidized bed reactor. The results showed that the settleability of struvite could be enhanced by increasing T and decreasing pH, Ar, or vf and would perform worse with overlong t or excessive CP. The dynamic variation process of the solution supersaturated index (SI) combined with the phase equilibrium theory and Ostwald ripening mechanism explained the above results sufficiently. The logistic model was chosen to predict the Ps under multi-factors, but the accuracy needs to be improved.

A number of studies of waste-activated sludge (WAS) pretreatments, aimed at releasing phosphorus (P) from WAS and increasing the amount of P that can be recovered, have been performed. Here, a microwave-assisted digestion and NaOH treatment (MWs & NaOH) coupled crystallizing struvite, to promote the solubilization, transformation, and recovery of P from WAS, is proposed. Microwaves (MWs) can cause cavities to form in WAS, weakening the bonds between extracellular polymeric substances and the solid phase. Irradiating with MWs significantly increased the efficiency at which P was dissolved (i.e. transferred from the solid to the liquid phase) and the efficiency at which organic P was hydrolyzed and transformed into inorganic P when the NaOH treatment was performed. The P solubilization and transformation characteristic achieved in different treatments was examined by scanning electron microscopy and three-dimensional excitation emission matrix analysis. The MWs & NaOH method released 34.20–43.73% of total P from WAS, and 23.48–32.07% of the total P was recovered by crystallizing struvite at pH 9.5 and Mg:P ratio of 1.5:1. It would cost about USD 85–103 per ton of dry WAS to treat WAS using the MWs & NaOH method.

Over the past five decades, Chinese grain production has increased 4-fold, from 110 Mt in 1961 to 557 Mt in 2014, with less than 9% of the world's arable land feeding 22% of the world's population, indicating a substantial contribution to global food security. However, compared with developed economies, such as the USA and the European Union, more than half of the increased crop production in China can be attributed to a rapid increase in the consumption of chemicals, particularly fertilizers. Excessive fertilization has caused low nutrient use efficiency and high environmental costs in grain production. We analysed the key requirements underpinning increased sustainability of crop production in China, as follows: (i) enhance nutrient use efficiency and reduce nutrient losses by fertilizing roots not soil to maximize root/rhizosphere efficiency with innovative root zone nutrient management; (ii) improve crop productivity and resource use efficiency by matching the best agronomic management practices with crop improvement; and (iii) promote technology transfer of the root zone nutrient management to achieve the target of high yields and high efficiency with low environmental risks on a broad scale. Coordinating grain production and environmental protection by increasing the sustainability of nutrient use will be a key step in achieving sustainable crop production in Chinese agriculture.

There is an urgent requirement for selecting appropriate technologies to solve food safety problems due to soil contamination. In this study, the hyperaccumulator Noccaea caerulescens and a high Cd accumulator pakchoi cultivar (Brassica rapa L. spp. Chinenesis cv.) were grown in a moderately Cd-contaminated soil with three planting systems (monocrop, inter-crop, and crop-rotation) and three growing durations (25, 50, and 75 days) to study the role of rhizosphere interaction of both species on the uptake of Cd. The Cd accumulations in the shoot of pakchoi were significantly reduced in the inter-crop treatment, also the decreased percentage increased with rhizosphere interaction between the two species. In the inter-crop systems of 75 days, the Cd concentration and amount in the shoot of pakchoi represented 54% and 83% reduction, respectively, while the total depletion of Cd decreased by approximate 19%. Although the Cd concentration and amount in the shoot of pakchoi were significantly reduced by 52% and 44%, respectively, in the crop-rotation treatment, the decreased percentage were markedly lower than in the inter-crop treatment. Therefore, the rhizosphere interaction of hyperaccumulator with non-hyperaccumulator may reduce the risk of vegetable contamination during making full use of or remediating the contaminated soil.

In recent years, agricultural growth in China has accelerated remarkably, but most of this growth has been driven by increased yield per unit area rather than by expansion of the cultivated area. Looking towards 2030, to meet the demand for grain and to feed a growing population on the available arable land, it is suggested that annual crop production should be increased to around 580 Mt and that yield should increase by at least 2% annually. Crop production will become more difficult with climate change, resource scarcity (e.g. land, water, energy, and nutrients) and environmental degradation (e.g. declining soil quality, increased greenhouse gas emissions, and surface water eutrophication). To pursue the fastest and most practical route to improved yield, the near-term strategy is application and extension of existing agricultural technologies. This would lead to substantial improvement in crop and soil management practices, which are currently suboptimal. Two pivotal components are required if we are to follow new trajectories. First, the disciplines of soil management and agronomy need to be given increased emphasis in research and teaching, as part of a grand food security challenge. Second, continued genetic improvement in crop varieties will be vital. However, our view is that the biggest gains from improved technology will come most immediately from combinations of improved crops and improved agronomical practices. The objectives of this paper are to summarize the historical trend of crop production in China and to examine the main constraints to the further increase of crop productivity. The paper provides a perspective on the challenge faced by science and technology in agriculture which must be met both in terms of increased crop productivity but also in increased resource use efficiency and the protection of environmental quality.

Aim To investigate broad-scale patterns of plant leaf ash content and their possible causes in China. Location Mainland China and Hainan island, with the geographic ranges for the data used from 18.7 degrees N to 49.2 degrees N and 76.0 degrees E to 128.3 degrees E. Methods By analysing a data set of 2022 leaf samples, involving 704 species of terrestrial plants. Results Leaf ash content increases with increasing latitude at an average rate of 2.7 mg ash g(-1) dry weight per degree latitude from south to north of China. Plant functional group shows a more powerful influence on the spatial variation in leaf ash than soil pH and climate. Fast-growing species or those with leaves with a short life span have higher leaf ash than slow-growing species or those with a long leaf life span. Plants from alkaline soils have higher leaf ash than those from acid soils (39.5 mg g(-1) increase in leaf ash content per unit increase of pH). Increasing precipitation significantly reduces leaf ash (with a mean rate of 4.8 mg g(-1) for every 100 mm rainfall), whereas the effect of temperature appears to be nonlinear. Main conclusions This study shows a significant latitudinal trend in leaf ash content in China. This geographic pattern is possibly shaped by the floral, edaphic and climatic factors that control the biogeochemical cycling of plant minerals. The results suggest that leaf ash content is a useful biogeographic indicator that can be used to explore the complex interactions between plants and the environment.

The role of root hairs in Cd acquisition from soil was investigated in three pot experiments using a root hairless mutant (bald root barley, brb) and its wild-type (WT) cultivar of barley (Hordeum vulgare). brb had significantly lower concentrations and lower total amounts of Cd in shoots than WT. The Cd uptake efficiency based on total root length was 8-45% lower in brb than in WT. The difference between brb and WT increased with increasing extractable Cd in soil under the experimental conditions used. Additions of phosphate to soil decreased Cd extractability. Both soil and foliar additions of phosphate decreased root length, and root hair formation in WT. These effects resulted in decreased Cd uptake with increasing P supply. Cd uptake in WT correlated significantly with root length, root hair length and density, and soil extractable Cd. Root hairs contribute significantly to Cd uptake by barley.

Field experiments were conducted to evaluate the effects of improved crop management (OPT) for irrigated rice (Oryza sativa L.) on grain yield and N recovery efficiency in southwestern China. In the OPT treatment, rice seedlings were transplanted in a triangular spatial pattern and the N fertilizer was split, based on the difference between the estimated total N requirement and the soil and environmental N supply. Fine-tuning of application rates was achieved using leaf greenness measurements. The performance of OPT was tested in two adjacent fields in which the crops preceding rice were wheat (Triticum aestivum L.; R w ) and rapeseed (Brassica napus var. napus; R o ). The OPT and traditional farming practice (TRA) treatments both gave higher average grain yields than zero-N controls (CK). Rice yields were considerably smaller in R W than R o under CK. Compared with TRA, OPT led to significantly higher aboveground N uptake, biomass accumulation, and grain yield in R w . Over the 2 yr of the study, average rice grain yields under OPT increased by 19 and 22% compared with TRA and 30 farmers' fields, respectively. The OPT treatment performed better than TRA in 15 N recovery efficiency. Compared with TRA, OPT led to increased 15 N fertilizer recovery efficiency from 19% in TRA to 42% in OPT, and decreased loss from 68% in TRA to 39% in OPT. In conclusion, OPT practice is a feasible means to attain increased yield with efficient N use. This study provides guidance for farmers using rice-based cropping systems, especially in southwestern China.

Nitrous oxide (N 2 O) emissions from a typical greenhouse vegetable system in Northern China were measured from February 2004 to January 2006 using a close chamber method. Four nitrogen management levels (NN, MN, CN, and SN) were used. N 2 O emissions occurred intermittently in the growing season, strongly correlating with N fertilization and irrigation. No peak emissions were observed after fertilization in the late Autumn season due to low soil temperature. 57–94% of the seasonal N 2 O emissions came from the initial growth stage, corresponding to the rewetting process in the soil. The annual N 2 O emissions ranged from 2.6 to 8.8 kg N ha −1 yr −1 , accounting for 0.27–0.30% of the annual nitrogen input. Compared with conventional N management, site-specific N management reduced N fertilization rate by 69% in 2004 and by 76% in 2005, and consequently reduced N 2 O emissions by 51% in 2004 and 27% in 2005, respectively.

The effect of N form (NO3− versus NH4+) on growth and uptake of Cd and Zn by the hyperaccumulator Thlaspi caerulescens (Ganges ecotype) was investigated in hydroponic and rhizobox experiments. In the hydroponic experiments, NO3− or NH4+ was supplied to plants with the pH of the nutrient solution being unbuffered or buffered at around 6.0. A moderately contaminated soil was used in the rhizobox experiment with or without additions of NO3−, NH4+ or NH4+ + DCD (dicyanodiamide, a nitrification inhibitor). A higher biomass was obtained when N was supplied as NO3− in both experiments, indicating that T. caerulescens prefers NO3− over NH4+. In the hydroponic experiments, supplying NO3− resulted in a doubling of Cd concentration in the shoots compared with the NH4+ treatment, regardless whether solution pH was buffered or not. The form of N also had a noticeable effect on root Zn concentrations. In the rhizosphere box experiment, rhizosphere pH was markedly influenced by the N treatment. The acidification in the NH4+ and NH4+ + DCD treatments increased the concentrations of extractable Cd and Zn, both of which showed a considerable depletion in the rhizosphere. However, total uptake of Cd and Zn were highest in the NO3− treatment, despite the fact that concentrations of extractable Cd and Zn in the rhizosphere were the lowest in this treatment. The results showed that supplying N as NO3− promoted growth and phytoextraction of Cd and Zn by T. caerulescens compared with NH4+.

Nutrient and water management is crucially important in shallow-rooted vegetable production systems characterized by high input and high environmental risk. A 2-year field experiment on greenhouse cucumber double-cropping systems examined the effects of root zone nitrogen management and planting of sweet corn as a catch crop in the summer fallow period on cucumber yield and soil Nmin dynamics compared to conventional practices. Cucumber fruit yields were not significantly affected by root zone N management and catch crop planting despite a decrease in N fertilizer application of 53% compared to conventional N management. Soil Nmin content to a depth of 0.9 m decreased markedly and root zone (0–0.3 m) soil Nmin content was maintained at about 200 kg N ha−1. Root zone N management efficiently and directly reduced apparent N losses by 44% and 45% in 2005 and 2006, respectively. Sweet corn, the summer catch crop, depleted Nmin residue in the soil profile of 1.8 m at harvest of winter–spring season cucumber by 304–333 kg N ha−1, which contributed 19–22% reduction in N loss. Compared to conventional N management, N loss was reduced by 56% under root zone N management and catch crop planting.

Cadmium accumulation among 12 cultivars of radish (Raphanus sativus) and 10 cultivars of carrot (Daucus carota var. sativa) was studied in a Cd-contaminated soil. The Cd concentration in the edible parts of radish and carrot ranged from 0.04 to 0.14 and 0.14 to 0.19 mg kg(-1) fresh weight, respectively. All the tested carrot cultivars and 33% of the tested radish cultivars exceeded the Chinese allowable limit for Cd. The study showed a greater scope for selecting radish cultivars than for carrot to avoid the excess of the Cd limit when grown on lightly contaminated soils.

Nitrogen (N) supply is the most important factor affecting yield and quality of flue-cured tobacco (FCT). A field experiment and an in situ incubation method were used to study the effects of soil N mineralization in the later stages of growth on yield and nicotine content of FCT in Fenggang and Jinsha, Guizhou Province. The yield and market value of FCT at Fenggang were much lower than those at Jinsha. However, the nicotine content of middle and upper leaves was much higher at Fenggang than at Jinsha when the same rate of fertilizer N was applied, which might be due to a higher N supply capacity at the Fenggang site. At later stages of growth (7–16 weeks after transplanting), the soil net N mineralization at Fenggang (56 kg N ha−1) was almost double that at Jinsha (30 kg N ha−1). While soil NH4-N and NO3-N were almost exhausted by the plants or leached 5 weeks after transplanting, the N taken up at the later growth stages at Fenggang were mainly derived from soil N mineralization, which contributed to a high nicotine content in the upper leaves. The order of soil N contribution to N buildup in different leaves was: upper leaves > middle leaves > lower leaves. Thus, soil N mineralization at late growth stages was an important factor affecting N accumulation and therefore the nicotine content in the upper leaves.

A field experiment and farm survey were conducted to test nitrogen (N) inputs, 15N-labelled fertilizer balance and mineral N dynamics of a rice–wheat rotation in southwest China. Total N input in one rice–wheat cycle averaged about 448 kg N ha−1, of which inorganic fertilizer accounted for 63% of the total. The effects of good N management strategies on N cycling were clear: an optimized N treatment with a 27% reduction in total N fertilizer input over the rotation decreased apparent N loss by 52% and increased production (sum of grain yield of rice and wheat) compared with farmers’ traditional practice. In the 15N-labelled fertilizer experiment, an optimized N treatment led to significantly lower 15N losses than farmers’ traditional practice; N loss mainly occurred in the rice growing season, which accounted for 82% and 67% of the total loss from the rotation in farmers’ fields and the optimized N treatment, respectively. After the wheat harvest, accumulated soil mineral N ranged from 42 to 115 kg ha−1 in farmers’ fields, of which the extractable soil NO3 −–N accounted for 63%. However, flooding soil for rice production significantly reduced accumulated mineral N after the wheat harvest: in the 15N experiment, farmers’ practice led to considerable accumulation of mineral N after the wheat harvest (125 kg ha−1), of which 69% was subsequently lost after 13 days of flooding. Results from this study indicate the importance of N management in the wheat-growing season, which affects N dynamics and N losses significantly in the following rice season. Integrated N management should be adopted for rice–wheat rotations in order to achieve a better N recovery efficiency and lower N loss.

Strategy I peanut plants are frequently subjected to iron deficiency when growing in calcareous soils, which contain high concentrations of bicarbonate. In calcareous soils under field conditions, it has been noted that chlorosis increases in severity after excessive rainfall or irrigation, but the chlorosis symptoms of peanuts are alleviated after waterlogged soils dry. A pot experiment was conducted simulating the chlorosis symptom observed in the field when peanut plants are exposed to fluctuating soil water content induced from rainfall or irrigation. We investigated the bicarbonate fluctuations resulting from adjustable soil water content (SWC) that could lead to bicarbonate-induced iron chlorosis of peanuts growing in calcareous soil. The experiments included three treatments of SWC (50% of water holding capacity (WHC), 80% of WHC, and 100% of WHC) under two levels of CaCO 3 concentrations (at 8.67% and 18.67%.) The results showed that the iron nutrition of peanuts could be regulated by different SWC at both CaCO 3 levels. Our observations indicate that iron deficiency chlorosis symptoms in peanuts grown in high soil water content were more severe, compared to those of peanuts in lower soil water content. A shift from high soil water content to lower soil water content could improve or eliminate the iron deficiency chlorosis symptom of peanuts. The HCO 3 − concentration in the peanut rhizosphere increased with increasing SWC and CaCO 3 content and it correlated with the level of soil water content. We suggest that variations in the soil water content could induce HCO 3 − concentration variation in the rhizosphere of peanuts. Consequently, the high HCO 3 − concentration, which is induced by a high water content in calcareous soil and a high CaCO 3 level, could inhibit the physiological response to iron deficiency of peanuts, resulting in iron deficiency chlorosis. The study indicates that a reasonable agricultural practice of irrigation and drainage should be considered to improve and prevent iron deficiency chlorosis of strategy I plants in calcareous soil.

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.

Arabidopsis halleri is a well-known zinc (Zn) hyperaccumulator, but its status as a cadmium (Cd) hyperaccumulator is less certain. Here, we investigated whether A. halleri can hyperaccumulate Cd and whether Cd is transported via the Zn pathway. Growth and Cd and Zn uptake were determined in hydroponic experiments with different Cd and Zn concentrations. Short-term uptake and root-to-shoot transport were measured with radioactive Cd-109 and Zn-65 labelling. A. halleri accumulated > 1000 mg Cd kg(-1) in shoot dry weight at external Cd concentrations >= 5 mu m>, but the short-term uptake rate of Cd-109 was much lower than that of Zn-65. Zinc inhibited short-term Cd-109 uptake kinetics and root-to-shoot translocation, as well as long-term Cd accumulation in shoots. Uptake of Cd-109 and Zn-65 were up-regulated, respectively, by low iron (Fe) or Zn status. A. halleri was much less tolerant to Cd than to Zn. We conclude that A. halleri is able to hyperaccumulate Cd partly, at least, through the Zn pathway, but the mechanisms responsible for cellular Zn tolerance cannot detoxify Cd effectively.

In a greenhouse experiment with tomato, the N fertilizer reduction potential, tomato yield, N use and environmental implications were examined, in a comparison of site-specific N management with conventional N fertilization during three successive growing seasons from Feb. 2004 to Jun. 2005 in Shouguang, a typical greenhouse vegetable production region in Shandong province, Northern China. Fertilizer N recommendation with site-specific management was based on the difference between N target value and soil initial nitrate-N content (0–0.3 m) with pre-sidedress soil nitrate testing (PSNT) and nitrate-N applied from irrigated water. The same basal dressing of 8, 11 and 8 t ha−1 of chicken manure (supplying 260, 360 and 316 kg N ha−1 in the first, second, and the third growing season, respectively) was broadcasted with conventional N, site-specific N and N from manure three treatments. The N target value with site-specific management was 300 kg N ha−1 in the first season, and then modified to 200 kg N ha−1 in the second and third seasons. In comparison with the fertilizer N applied rate with conventional N management (870, 720 and 630 kg N ha−1 in the three seasons, respectively), site-specific management reduced N fertilizer by 62, 78 and 80% without significant influences on tomato yield. The fruit yield of tomato with only basal dressing manure treatment was significantly decreased in the second season, compared with conventional N management. The nitrate content in 0–0.9 m soil depth with site-specific management was much lower than that with conventional N management in all three seasons. The 53–83% of emitted nitrous oxide (N2O) was measured from transplanting to the first sidedressing in the three seasons, strongly related to drying–wetting soil process. As a result, the cumulative emission with site-specific management was only reduced by 38% than that with conventional N management throughout three seasons. Considering N release from mineralization and irrigation water, site-specific N management could efficiently control N application in intensive irrigated-vegetable production region. Thus, it is valuable to obtaining vegetable crops with high yield and economic return while alleviating the risk of environmental pollution. But it is necessary to optimize irrigation regime to minimize N loss through nitrate leaching and N2O emission.

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 225 kg ha−1 for rice and 0, 60,120, and 180 kg N ha−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 >150 kg ha−1 for rice and >120 kg ha−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 60 cm) after the rice harvest ranged from 50 to 65 kg ha−1 and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil Nmin ranged from 66 to 88 kg N ha−1 and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621 kg ha−1), but low N inputs resulted in a negative balance (−85 to −360 kg ha−1). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79 kg ha−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.

The nutrient management of phosphorus (P) contained in swine wastewater is an important challenge to enhance P use efficiency. In the present study, assessment of P recovery from swine wastewater in Beijing was performed. P amounts of swine wastewater increased from 11,687 tons in 1980 to 16,237 tons in 2014. Without treatment of swine wastewater, P concentration will reach a maximum 1.20 mg/L. The maximum P recovery was 99.36% under the condition of crystallization coupled BPR (biological phosphorus removal) when the operating conditions were 60.6 mg/L for Cp (initial P concentration (mg/L)), 1.2 for Mg/P (magnesium-to-P molar ratio), 9.7 for pH of crystallization process, and 8.0 for pH, 1.6 h for anaerobic stage time, 15 days for sludge retention time of BPR. The P concentration for water quality was 0.03 mg/L to meet the water regulation standard. Under this situation, if the target P concentration were set as Grade II and III, pig breeding numbers reached 42.07 and 95.90 million heads. Construction investments for the crystallization, BRP, and coupled methods are 411 (104 Yuan, 604,307 USD), 301 (104 Yuan, 442,580 USD), and 551 (104 Yuan, 810,170 USD), respectively. The running costs are 15.205 (104 Yuan/year, 22,360 USD/year), 28.907 (104 Yuan/year, 42,500 USD/year) and 44.112 (104 Yuan/year, 64,860 USD/year). To manage non-point pollution, swine wastewater treatment facilities should be used and pig breeding numbers should be managed within reasonable ranges.

Iron plaque on root surfaces greatly influenced selenium uptake and played different roles in selenite and selenate uptake. Iron plaque commonly forms on rice root surfaces under flooded conditions, but little is known about the relationship between iron plaque and selenium (Se) accumulation. Here, we investigate the effects of iron plaque on Se uptake by and translocation within rice (Oryza sativa) seedlings, and the kinetics of selenite and selenate influx into rice roots (with or without iron plaque) were determined in short-term (30 min) experiments. Rice seedlings were planted in nutrient solutions containing different levels of ferrous ion for 3 days and then transplanted into nutrient solutions with selenite or selenate. Se concentrations in iron plaque were positively associated with the amounts of iron plaque in both selenite and selenate treatments and iron plaque had a higher affinity for selenite than selenate. Results showed that iron plaque on root surfaces greatly influenced Se uptake and played different roles in selenite and selenate uptake. The selenite and selenate uptake kinetics results demonstrated that the presence of iron plaque enhanced selenite uptake, but decreased selenate uptake. In addition, root-Se concentrations increased with the increasing amounts of iron plaque, but Se translocation from roots to shoots was reduced with the increasing amounts of iron plaque in the +selenite treatment. Iron plaque significantly influenced selenite uptake and might act as a pool to selenite accumulation in rice plants. However, iron plaque had no significant effect on selenate uptake or even as a barrier to selenate uptake.

Levels of cadmium (Cd), arsenic (As), mercury (Hg), lead (Pb), iron (Fe), and zinc (Zn) were investigated in 285 samples of 9 species of edible fungi (Lentinus edodes, Auricularia auricula, Pleurotus ostreatus, Tremella fuciformis, Flammulina velutipes, Agrocybe chaxinggu, Armillaria mellea, Agaricus bisporus, and Pholiota nameko), which were collected from markets in Beijing, China. In addition, edible fungi and culture substrates were collected from 7 cultivation bases to examine the role of the substrate in trace metal accumulation. Trace metal concentrations were determined on a dry weight basis. Data showed that all the edible fungi contained trace metals, the levels of which varied among species, and there were significant positive correlations between trace metal (Cd, Pb, and As) concentrations in mushrooms and their substrates. The concentrations of Cd, As, Hg, Pb, Fe, and Zn in the tested fungi ranged from 0.005 to 13.8 mg/kg, nd to 1.62 mg/kg, nd to 0.506 mg/kg, 0.011 to 22.1 mg/kg, 46.3 to 2514 mg/kg, and 14.6 to 289 mg/kg, respectively. In general, concentrations of Cd, As, Hg, Pb, Fe, and Zn were relatively high in L. edodes, whereas Tremella fuciformis and P. nameko had relatively low levels of trace metals. Furthermore, the estimated weekly intake of trace metals was calculated and compared with the WHO/FAO provisional tolerable weekly intake. The estimated weekly intake of Cd, As, Hg, Pb, Fe, and Zn from consuming edible fungi was lower than the provisional tolerable weekly intake.This paper reports information about trace metal concentrations in edible fungi collected from Beijing, China. This paper provides useful information for consumers and regulators about levels of trace metals in edible fungi.

Previous studies have shown that a combination of coal fly ash (10% w/w) and lime (1% w/w) amendment was effective in stabilizing biosolids (ACS) by killing the pathogens and reducing heavy metal availability, and the product contained a high B content. It was, therefore, the aim of the present study to evaluate the suitability of the ACS as a B fertilizer for a degraded acid soil with B deficiency in South China. An acid and B deficient loamy soil was amended with the ACS at application rates of 6.4, 12.7, 25.5, 63.7 and 127.4 mg ha−1, which were then compared to the same soil receiving an equivalent B fertilizer application rates of 0.9, 1.4, 2.2, 4.5 and 8.4 kg ha−1, respectively. Soil hot water soluble B content and pH increased significantly with an increase in the amendment rate of the ACS mixture. Soil amended with the ACS mixture had a significantly higher dry weight yield for both cucumber and corn than the control and its counterparts of soil with B fertilizer. The highest yield was obtained in ...

C hina is now successfully feeding 22% of the global population with only 9% of the world's arable land, and per capita food availability has now reached the levels of developed countries. Increasing the amounts of inputs (e.g., fertilizers and water) has played a crucial role in agricultural intensification. However, the total consumption of chemical fertilizers in China exceeded 53.15 Mt (52.31 M tn) in 2007, nearly 35% of the total global consumption. Fertilizer applications are often not based on real-time nutrient requirements of the crop and/or site-specific knowledge of soil nutrient status. This has led to low resource efficiency, declining annual growth rates in crop yields and damage to the environment. It is therefore a matter of some urgency to develop nutrient management technology to meet increasing crop yields with enhanced nutrient efficiencies and sustaining the environment. With the support of the Chinese Ministry of Agriculture and the National Natural Science Foundation of China, we have carried out a large-scale project since 2003 that features integrated nutrient management (INM) systems. A total of 1,517 experiments have been conducted covering 12 cropping systems at 123 sites in 20 provinces to test the principles of INM. ### INTEGRATED NUTRIENT MANAGEMENT In an …

A greenhouse pot experiment was conducted to investigate the boron (B) release capacity of coal fly ash and sewage sludge mixtures, and the accumulation of B in Agropyron elongatum after two consecutive growing seasons. Sludge was amended with fly ash at application rates of 0, 5, 10, 35, and 50% (w/w), and each mixture was then mixed with a loamy soil at either 1:1 or 1:5 (v/v). Both water soluble B (WS-B) and hot water soluble B (HWS-B) increased with increasing fly ash amendment rate. Shoot B concentrations also increased significantly according to the rate of ash amendment. The ash-sludge mixture improved plant growth with the highest total dry weight yield at 10% ash amendment rate. Boron toxicity symptoms in leaf tips were observed at 35% and 50% ash amendment rate at both soil mixing ratios. Hot water soluble B and WS-B decreased significantly after consecutive cropping of Agropyron especially at low ratio of mixure with soil i.e., 1:5 (v/v). However, soil available B contents at ≥ 35% ash application rate and 1:1 (v/v) soil mixing ratio were still excessive for normal plant growth, suggesting that deleterious effects on plant growth would be experienced in later seasons owing to the high amounts of residual B.

GreenSeeker active crop canopy sensor has been widely reported in literature for in-season nitrogen (N) management. An N fertilization optimization algorithm has been developed to use this sensor for topdressing N recommendation. An important component of this algorithm is to use crop sensor to estimate yield potential before topdressing N application. In addition to GreenSeeker, another commercial crop sensor, Crop Circle ACS - 470, has been recently developed with 6 possible spectral band choices (blue, green, two red bands, red edge and NIR). Little research has been conducted to compare these two sensors for estimating rice yield potential. The objective of this research was to determine how much improvements the Crop Circle ACS 470 would achieve for estimating rice yield potential at stem elongation stage, as compared with GreenSeeker sensor. Four N rate experiments were conducted in Jiansanjiang, Heilongjiang Province, in Northeast China in 2008 and 2009. The FieldSpec 3 hyperspectral canopy sensor was used to collect canopy reflectance, which was used to simulate spectral bands of GreenSeeker and Crop Circle sensors. The results indicated that in-season estimate of yield (INSEY) calculated with GreenSeeker NDVI and RVI could explain 42% and 62% of yield potential variability. The INSEY calculated with nine vegetation indices using simulated Crop Circle spectral bands performed better than GreenSeeker indices, with R2 being 0.64-0.75. INSEY (MTCARI) had the best performance, explaining 75% of the yield potential variability, followed by INSEY (MCARI1) (R2=0.73). The preliminary result indicated that Crop Circle ACS 470 sensor could explain 13% more variability in rice yield potential at stem elongation stage. More studies are needed to more systematically evaluate all possible vegetation indices that can be calculated with Crop Circle spectral bands for estimating rice yield potential at different growth stages.

Axiom ranking plays an important role in ontology repairing. There has been a number of criteria that can be used in axiom ranking, but there still lacks a framework for combining multiple criteria to rank axioms. To provide such a framework, this paper proposes an analytic hierarchy process (AHP) based approach. It expresses existing criteria in a hierarchy and derives weights of criteria from pairwise comparison matrices. All axioms are then ranked by a weighted sum model on all criteria. Since the AHP based approach does not work when a pairwise comparison matrix is insufficiently consistent, a method is proposed to adjust the matrix. The method expresses the adjustment problem as an optimization problem solvable by level-wise search. To make the proposed method more practical, an approximation of it is also proposed. Experimental results show that the proposed method is feasible for small pairwise comparison matrices but is hard to scale to large ones, while the approximate method scales well to large pairwise comparison matrices.

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.

Here, we report on a two-years field experiment aimed at the quantification of the emissions of nitrous oxide (N2O) and methane (CH4) from the dominant wheat maize double cropping system in North China Plain. The experiment had 6 different fertilization strategies, including a control treatment, recommended fertilization, with and without straw and manure applications, and nitrification inhibitor and slow release urea. Application of N fertilizer slightly decreased CH4 uptake by soil. Direct N2O emissions derived from recommended urea application was 0.39% of the annual urea-N input. Both straw and manure had relatively low N2O emissions factors. Slow release urea had a relatively high emission factor. Addition of nitrification inhibitor reduced N2O emission by 55%. We conclude that use of nitrification inhibitors is a promising strategy for N2O mitigation for the intensive wheat maize double cropping systems. (C) 2013 Elsevier Ltd. All rights reserved.

China consumes more than 1/3 of global N fertilizers for rice with less than 1/5 of the world rice planting area. As a consequence, N efficiency is low and nitrate pollution risk is high. Developing efficient N management strategies and technologies for rice are therefore needed. Here, we developed an active canopy sensor-based precision N management strategy for rice in Northeast China. Four site-years of field N rate experiments were conducted in 2008 and 2009 in Sanjiang Plain, Heilongjiang, China. The GreenSeeker active sensor was used to collect rice canopy reflectance data at different growth stages. Three on-farm experiments were conducted in 2011 to evaluate the performance of the developed strategy. The results show that the crop sensor can be used to calculate rice yield potential without additional topdressing N application at stem elongation or booting stage. The GreenSeeker-based precision N management strategy has a regional optimum N rate of 90–110 kg N ha−1 as initial total amount and 45 and 20 % as basal and tillering N application. It uses the crop sensor to estimate the topdressing N rate at stem elongation stage. GreenSeeker-based precision management and chlorophyll meter-based site-specific N management increased the partial factor productivity of farmers by 48 and 65 %, respectively, without significant change in grain yield. The crop sensor-based N management strategy can therefore improve N use efficiency of rice. It is more suitable for practical on-farm applications, and will contribute to the sustainable development of rice farming.

While the concept of sustainability as a goal has become widely accepted, the dominant agricultural paradigm still considers high yield and reduced environmental impact being in conflict with one another. During the past 49 years (1961–2009), the 3.4-fold increase in Chinese agricultural food production can be partly attributed to a 37-fold increase in N fertilization and a 91-fold increase in P fertilization, but the environment costs have been very high. New advances for sustainability of agriculture and ecosystem services will be needed during the coming 50 years to improve nutrient use efficiency (NUE) while increasing crop productivity and reducing environmental risk. Here, we advocate and develop integrated nutrient management (INM) based on more than 20 years of studies. In this INM approach, the key components comprise (1) optimizing nutrient inputs by taking all possible nutrient sources into consideration, (2) matching nutrient supply in root zone with crop requirements spatially and temporally, (3) reducing N losses in intensively managed cropping systems, and (4) taking all possible yield-increasing measures into consideration. Recent large-scale application of INM for cereal, vegetable, and fruit cropping systems has shed light on how INM can lead to significantly improved NUE, while increasing crop yields and reducing environmental risk. The INM has already influenced Chinese agricultural policy and national actions, and resulted in increasing food production with decreased climb of chemical fertilizer consumption at a national scale over recent years. The INM can thus be considered an effective agricultural paradigm to ensure food security and improve environmental quality worldwide, especially in countries with rapidly developing economies.

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.

Crop production in China has been greatly improved by increasing phosphorus (P) fertilizer input, but overuse of P by farmers has caused low use efficiency, increasing environmental risk and accumulation of P in soil. From 1980 to 2007, average 242 kg P ha−1 accumulated in soil, resulting in average soil Olsen P increasing from 7.4 to 24.7 mg kg−1. China is facing huge challenges to improve P use efficiency through optimizing corresponding technology and policies. The problem is exacerbated because people have been shifting their diet from plant-based to animal-enriched foods. This results in higher P load in the food chain and lower P use efficiency. A multidisciplinary approach has been used to improve P management at the field and national level in China. Management strategies based on the soil and on the plant rhizosphere have been developed to increase efficient use of P. A national soil testing and fertilizer recommendation program has been used since 2005 to control build-up and maintenance of P levels. Interactions between root growth and the rhizosphere have been manipulated in intercropping systems and plant genetic traits have been exploited. Phosphorus surplus is highly associated with animal concentrated feed. The P-saving potential by the integrated P management strategies of P flow reaches 1.46 Mt P in 2050 compared to 2005.

Summary • Efficient root-to-shoot translocation is a key trait of the zinc/cadmium hyperaccumulators Thlaspi caerulescens and Thlaspi praecox, but the extent of variation among different accessions and the underlying mechanisms remain unclear. • Root-to-shoot translocation of Cd and Zn and apoplastic bypass flow were determined in 10 accessions of T. caerulescens and one of T. praecox, using radiolabels 109Cd and 65Zn. Two contrasting accessions (Pr and Ga) of T. caerulescens were further characterized for TcHMA4 expression and metal compartmentation in roots. • Root-to-shoot translocation of 109Cd and 65Zn after 1 d exposure varied 4.4 to 5-fold among the 11 accessions, with a significant correlation between the two metals, but no significant correlation with uptake or the apoplastic bypass flow. The F2 progeny from a cross between accessions from Prayon, Belgium (Pr) and Ganges, France (Ga) showed a continuous phenotype pattern and transgression. There was no significant difference in the TcHMA4 expression in roots between Pr and Ga. Compartmentation analysis showed a higher percentage of 109Cd sequestered in the root vacuoles of Ga than Pr, the former being less efficient in translocation than the latter. • Substantial natural variation exists in the root-to-shoot translocation of Cd and Zn, and root vacuolar sequestration may be an important factor related to this variation.

The southern French (Ganges) ecotype of Thlaspi caerulescens J & C Presl is able to hyperaccumulate several thousand mg Cd kg(-1) shoot dry weight without suffering from phytotoxicity. We investigated the effect of Cd on growth and the activity of carbonic anhydrase (CA), a typical Zn-requiring enzyme, of T. caerulescens in soil and hydroponic experiments. In one of the hydroponic experiments, T. caerulescens was compared to the non-accumulator Thlaspi ferganense N. Busch. In the soil experiment, additions of Cd at 5-500 mg kg(-1) soil increased the growth of T. caerulescens significantly. In the hydroponic experiments, exposure to Cd at 1-50 microM for three weeks had no significant effect on the growth of T. caerulescens, but decreased the growth of T. ferganense markedly even at the lowest concentration of Cd (1muM). Cadmium exposure significantly increased the CA activity in T. caerulescens, but decreased it in T. ferganense. The CA activity in T. caerulescens correlated positively with the Cd concentration in the shoots up to 6000 mg kg(-1), even though shoot Zn concentration was decreased by the Cd treatments. For comparison, Cd treatments had no consistent effect on the activity of superoxide dismutase in T. caerulescens. The results suggest that Cd may play a physiological role in the Cd-hyperaccumulating ecotype of T. caerulescens by enhancing the activities of some enzymes such as CA. Further research is needed to establish whether a Cd-requiring CA exists in T. caerulescens.

Species difference in Cd accumulation is important for selection of agronomic technologies aimed at producing low-Cd vegetables. Six vegetable species (Chinese leek, pakchoi, carrot, radish, tomato and cucumber) were grown in pot and field experiments to study the accumulation of Cd under different conditions. In the field trial (Cd 2.55 mg kg(-1)), Cd concentrations in the edible parts ranged from 0.01 to 0.1 mg kg(-1) and were below the permissible limits (0.2 mg kg(-1) for pakchoi and leek; 0.1 mg kg(-1) for carrot and radish; 0.05 mg kg(-1) for cucumber and tomato), but exceeded the limit in pakchoi, Chinese leek, carrot and tomato at a Cd addition level of 2.0 mg kg(-1). Plant Cd concentrations increased linearly with the increasing concentration of Cd added to the soil, with the slope of the regression lines varying by 28-fold among the six species. The bioconcentration factor (BCF) varied substantially, and was much higher in the pot experiment than in the field trial. It is concluded that the vegetable species differed markedly in the Cd accumulation and species performed consistently under different growth conditions.