Soil quality and ecosystem multifunctionality after 13-year of organic and nitrogen fertilization.

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

Optimal nitrogen rate strategy for sustainable rice production in China.

Avoiding excessive agricultural nitrogen (N) use without compromising yields has long been a priority for both research and government policy in China1,2. Although numerous rice-related strategies have been proposed3-5, few studies have assessed their impacts on national food self-sufficiency and environmental sustainability and fewer still have considered economic risks faced by millions of smallholders. Here we established an optimal N rate strategy based on maximizing either economic (ON) or ecological (EON) performance using new subregion-specific models. Using an extensive on-farm dataset, we then assessed the risk of yield losses among smallholder farmers and the challenges of implementing the optimal N rate strategy. We find that meeting national rice production targets in 2030 is possible while concurrently reducing nationwide N consumption by 10% (6-16%) and 27% (22-32%), mitigating reactive N (Nr) losses by 7% (3-13%) and 24% (19-28%) and increasing N-use efficiency by 30% (3-57%) and 36% (8-64%) for ON and EON, respectively. This study identifies and targets subregions with disproportionate environmental impacts and proposes N rate strategies to limit national Nr pollution below proposed environmental thresholds, without compromising soil N stocks or economic benefits for smallholders. Thereafter, the preferable N strategy is allocated to each region based on the trade-off between economic risk and environmental benefit. To facilitate the adoption of the annually revised subregional N rate strategy, several recommendations were provided, including a monitoring network, fertilization quotas and smallholder subsidies.

Effect of sPP Content on Electrical Tree Growth Characteristics in PP-Blended Cable Insulation.

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.

Coupling Effect of Molecular Chain Displacement and Carrier Trap Characteristics on DC Breakdown of HDPE/LDPE Blend Insulation.

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.

Biochar effects on crop yields and nitrogen loss depending on fertilization.

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

Pursuing sustainable productivity with millions of smallholder farmers.

Sustainably feeding a growing population is a grand challenge, and one that is particularly difficult in regions that are dominated by smallholder farming. Despite local successes, mobilizing vast smallholder communities with science- and evidence-based management practices to simultaneously address production and pollution problems has been infeasible. Here we report the outcome of concerted efforts in engaging millions of Chinese smallholder farmers to adopt enhanced management practices for greater yield and environmental performance. First, we conducted field trials across China's major agroecological zones to develop locally applicable recommendations using a comprehensive decision-support program. Engaging farmers to adopt those recommendations involved the collaboration of a core network of 1,152 researchers with numerous extension agents and agribusiness personnel. From 2005 to 2015, about 20.9 million farmers in 452 counties adopted enhanced management practices in fields with a total of 37.7 million cumulative hectares over the years. Average yields (maize, rice and wheat) increased by 10.8-11.5%, generating a net grain output of 33 million tonnes (Mt). At the same time, application of nitrogen decreased by 14.7-18.1%, saving 1.2 Mt of nitrogen fertilizers. The increased grain output and decreased nitrogen fertilizer use were equivalent to US$12.2 billion. Estimated reactive nitrogen losses averaged 4.5-4.7 kg nitrogen per Megagram (Mg) with the intervention compared to 6.0-6.4 kg nitrogen per Mg without. Greenhouse gas emissions were 328 kg, 812 kg and 434 kg CO2 equivalent per Mg of maize, rice and wheat produced, respectively, compared to 422 kg, 941 kg and 549 kg CO2 equivalent per Mg without the intervention. On the basis of a large-scale survey (8.6 million farmer participants) and scenario analyses, we further demonstrate the potential impacts of implementing the enhanced management practices on China's food security and sustainability outlook.

Exploiting Co-Benefits of Increased Rice Production and Reduced Greenhouse Gas Emission through Optimized Crop and Soil Management.

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.

Producing more grain with lower environmental costs.

Agriculture faces great challenges to ensure global food security by increasing yields while reducing environmental costs. 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(-1)), 7.2 Mg ha(-1) and 10.5 Mg ha(-1) to 8.5 Mg ha(-1), 8.9 Mg ha(-1) and 14.2 Mg ha(-1), respectively, without any increase in nitrogen fertilizer. Model simulation and life-cycle assessment 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.

Plant-based assessment of inherent soil productivity and contributions to China's cereal crop yield increase since 1980.

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.

Improving crop productivity and resource use efficiency to ensure food security and environmental quality in China.

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.

Integrated soil-crop system management: reducing environmental risk while increasing crop productivity and improving nutrient use efficiency in China.

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.

[Nitrogen status diagnosis of rice by using a digital camera].

In the present research, a field experiment with different N application rate was conducted to study the possibility of using visible band color analysis methods to monitor the N status of rice canopy. The Correlations of visible spectrum band color intensity between rice canopy image acquired from a digital camera and conventional nitrogen status diagnosis parameters of leaf SPAD chlorophyll meter readings, total N content, upland biomass and N uptake were studied. The results showed that the red color intensity (R), green color intensity (G) and normalized redness intensity (NRI) have significant inverse linear correlations with the conventional N diagnosis parameters of SPAD readings, total N content, upland biomass and total N uptake. The correlation coefficient values (r) were from -0.561 to -0.714 for red band (R), from -0.452 to -0.505 for green band (G), and from -0.541 to 0.817 for normalized redness intensity (NRI). But the normalized greenness intensity (NGI) showed a significant positive correlation with conventional N parameters and the correlation coefficient values (r) were from 0.505 to 0.559. Compared with SPAD readings, the normalized redness intensity (NRI), with a high r value of 0.541-0.780 with conventional N parameters, could better express the N status of rice. The digital image color analysis method showed the potential of being used in rice N status diagnosis in the future.

Evidence of decreasing mineral density in wheat grain over the last 160 years.

Wheat is an important source of minerals such as iron, zinc, copper and magnesium in the UK diet. The dietary intake of these nutrients has fallen in recent years because of a combination of reduced energy requirements associated with sedentary lifestyles and changes in dietary patterns associated with lower micronutrient density in the diet. Recent publications using data from food composition tables indicate a downward trend in the mineral content of foods and it has been suggested that intensive farming practices may result in soil depletion of minerals. The aim of our study was to evaluate changes in the mineral concentration of wheat using a robust approach to establish whether trends are due to plant factors (e.g. cultivar, yield) or changes in soil nutrient concentration. The mineral concentration of archived wheat grain and soil samples from the Broadbalk Wheat Experiment (established in 1843 at Rothamsted, UK) was determined and trends over time examined in relation to cultivar, yield, and harvest index. The concentrations of zinc, iron, copper and magnesium remained stable between 1845 and the mid 1960s, but since then have decreased significantly, which coincided with the introduction of semi-dwarf, high-yielding cultivars. In comparison, the concentrations in soil have either increased or remained stable. Similarly decreasing trends were observed in different treatments receiving no fertilizers, inorganic fertilizers or organic manure. Multiple regression analysis showed that both increasing yield and harvest index were highly significant factors that explained the downward trend in grain mineral concentration.

[Nutrient management strategy of paddy rice-upland crop rotation system].

Paddy rice-upland crop rotation system is a major cropping system in China, and practiced widely along the Yangtze River basin. A unique feature of this system is the annual conversion of soil from aerobic to anaerobic and then back to aerobic condition, which can result in the changes of soil physical, chemical, and biological prosperities among seasons, making a special agroecosystem. The major challenges faced by this system include declining or stagnating productivity, increasing shortage of irrigation water, improper management of nutrients, low efficiency of resource utilization, and environmental pollution. Based on an overview of the characteristics and problems of paddy rice-upland crop rotation system, this paper put forward a strategy of practicing integrated nutrient management to solve the contradictions between nutrient input, crop production and environmental risk. The key points of this strategy included nutrient management from the whole rotation system perspective, integrated use of nutrients from various sources (chemical fertilizers, organic fertilizers, and nutrients from the environment), synchronization of nutrient supply and crop nutrient demand, application of different management technologies based on the characteristics of different nutrient resources, and integration of nutrient management with other cropping system technologies like water saving and high-yielding cultivation, etc.

Historical changes in the concentrations of selenium in soil and wheat grain from the Broadbalk experiment over the last 160 years.

Selenium (Se) intake has decreased substantially in the UK population since 1970s. To investigate whether Se concentration in wheat grain has changed as a result of yield improvement or environmental changes, we analyzed archived wheat grain from the Broadbalk Wheat Experiment at Rothamsted, England, which has been run continuously for over 160 years. Wheat grain and soil samples were selected from plots receiving different fertilizer or manure treatments. Grain Se concentration varied from 11 to 236 ng g(-1), with a mean and median of 44 and 32 ng g(-1), respectively. Grain samples from the unfertilized control plot had significantly higher concentrations of Se than those from fertilized or manured plots; the latter received various amounts of S and also had higher grain yield. No significant trends in grain Se concentrations were detected in the fertilized or manured plots, in spite of a dramatic increase in grain yield since the introduction of modern short-straw cultivars in the mid 1960s. In the control plot, grain samples had higher Se concentrations in the periods before 1920 or after 1970 than those during 1920-1970. This temporal pattern mirrored that of SO(2) emissions and atmospheric S deposition. Soil Se concentrations showed an increasing trend in all plots over 160 years. The results show that the Se concentration of wheat grain from the Broadbalk experiment was influenced by S inputs from fertilizers and atmospheric deposition, and that improving grain yield through plant breeding has not resulted in a significant decrease in grain Se concentration in the fertilized plots.