Comparison of analytical procedures for measuring phosphorus content of animal manures in China

The concentration and components of manure phosphorus (P) are key factors determining potential P bioavailability and runoff. The distribution of P forms in swine, poultry and cattle manures collected from intensive and extensive production systems in several areas of China was investigated with sequential fractionation and a simplified two-step (NaHCO₃-NaOH/EDTA) procedures. The mean total P concentration, determined by the sequential fractionation procedure of intensive swine, poultry and cattle manure, expressed as g·kg⁻¹, was 14.9, 13.4 and 5.8 g·kg⁻¹, respectively, and 4.4 g·kg⁻¹ in extensive cattle manure. In intensive swine, poultry and cattle manure about 73%, 74% and 79% of total P, respectively, was bioavailable (i.e., P extracted by H₂O and NaHCO₃) and 78% in extensive cattle manure. The results indicated the relative environmental risk, from high to low, of swine, poultry and cattle manure. There is considerable regional variation in animal manure P across China, which needs to be considered when developing manure management strategies.     

INTENSIFICATION OF GRASSLAND-BASED DAIRY PRODUCTION AND ITS IMPACTS ON LAND,NITROGEN AND PHOSPHORUS USE EFFICIENCIES

• Monitoring data of>5000 dairy farms collected and examined in uniform manner. • Environmental performances of farms influenced by government regulations. • N and P surpluses at farm level remained about constant with intensity level. • N and P use efficiencies at farm, herd and soil increased with intensity level. • Accounting for externalization of off-farm feed production affects NUE and PUE. • Ammonia emissions per kg milk decreased with the level of intensification. Many grassland-based dairy farms are intensifying production, i.e., produce more milk per ha of land in response to the increasing demand for milk (by about 2% per year) in a globalized market. However, intensive dairy farming has been implicated for its resources use, ammonia and greenhouse gas emissions, and eutrophication impacts. This paper addresses the question of how the intensity of dairy production relates to N and P surpluses and use efficiencies on farms subjected to agri-environmental regulations. Detailed monitoring data were analyzed from 2858 grassland-based dairy farms in The Netherlands for the year 2015. The farms produced on average 925 Mg·yr⁻¹ milk. Milk production per ha ranged from<10 to>30 Mg·ha⁻¹·yr⁻¹. Purchased feed and manure export strongly increased with the level of intensification. Surpluses of N and P at farm level remained constant and ammonia emissions per kg milk decreased with the level of intensification. In conclusion, N and P surpluses did not differ much among dairy farms greatly differing in intensity due to legal N and P application limits and obligatory export of manure surpluses to other farms. Further, N and P use efficiencies also did not differ among dairy farms differing in intensity provided the externalization of feed production was accounted for. This paper provides lessons for proper monitoring and control of N and P cycling in dairy farming.     

Symbiotic performance,shoot biomass and water-use efficiency of three groundnut (Arachis hypogaea L.) genotypes in response to phosphorus supply under field conditions in Ethiopia

Phosphorus is a key nutrient element involved in energy transfer for cellular metabolism, respiration and photosynthesis and its supply at low levels can affect legume nodulation, N₂ fixation, and C assimilation. A two-year field study was conducted in Ethiopia in 2012 and 2013 to evaluate the effects of P supply on growth, symbiotic N₂ nutrition, grain yield and water-use efficiency of three groundnut genotypes. Supplying P to the genotypes significantly increased their shoot biomass, symbiotic performance, grain yield, and C accumulation. There was, however, no effect on shoot δ¹³C values in either year. Compared to the zero-P control, supplying 40 kg·ha⁻¹ P markedly increased shoot biomass by 77% and 66% in 2012 and 2013, respectively. In both years, groundnut grain yields were much higher at 20 and 30 kg·ha⁻¹ P. Phosphorus supply markedly reduced shoot δ¹⁵N values and increased the %Ndfa and amount of N-fixed, indicating the direct involvement of P in promoting N₂ fixation in nodulated groundnut. The three genotypes differed significantly in δ¹⁵N, %Ndfa, N-fixed, grain yield, C concentration, and δ¹³C. The phosphorus × genotype interaction was also significant for shoot DM, N content, N-fixed and soil N uptake.     

EVALUATING QUINOA LODGING RISK AND YIELD UNDER DIFFERENT IRRIGATION THRESHOLDS,NITROGEN RATES AND PLANTING DENSITIES IN NORTH-WESTERN CHINA

● A moderate irrigation threshold of −25 kPa gave the greatest actual yield. ● Nitrogen rates of 80−160 kg·ha⁻¹ reduced lodging risk without yield decrease. ● Planting density of 30 plants·m⁻² provided both high yield and lodging resistance. ● A lower-stem lodging index was best for prediction of quinoa lodging risk. Lodging is a major yield-limiting factor of quinoa production. In 2018 and 2019, the orthogonal field experiments were conducted to investigate the responses of quinoa lodging risk and yield to irrigation threshold (soil matric potential of −15, −25 and −55 kPa), nitrogen rate (80, 160 and 240 kg·ha⁻¹) and planting density (20, 30 and 40 plants m⁻²). Results showed that high irrigation thresholds and nitrogen rates significantly (P < 0.05) increased plant height and fresh weight per plant, and high planting densities reduced stem diameter and strength, all of those led to significantly ( P < 0.05) high lodging risks. The −15 and −55 kPa treatments gave the lowest actual yield ( P < 0.05) in 2018 and 2019, respectively. Higher lodging rate with a nitrogen rate of 240 kg·ha⁻¹ resulted in a lower actual yield than 80 and 160 kg·ha⁻¹ in both years. Planting density of 30 plants m⁻² gave a significantly (P < 0.05) greater estimated yield than 20 plants m⁻² and had a lower lodging rate than 40 plants m⁻², resulting in the maximum actual yield among planting densities. In conclusion, a moderate irrigation threshold of −25 kPa, a nitrogen rate of 80−160 kg·ha⁻¹ and an intermediate planting density of 30 plants m⁻² were determined to be best for quinoa cultivation in North-western China. In addition, the lower-stem lodging index (quarter plant height) could evaluate lodging risk more accurately than middle-stem (half plant height) or upper-stem (three quarters plant height) lodging indexes.     

NEW ZEALAND DAIRY FARM SYSTEMS AND KEY ENVIRONMENTAL EFFECTS

• NZ dairy farming systems are based on year-round grazing of perennial pasture (ryegrass/white clover). • Milk production per hectare has increased by about 29% with increased use of externally-sourced feeds over the last two decades. • Externally-sourced feeds with a low protein concentration can potentially reduce N₂O emissions and N leaching per unit of production. • Systems analysis is important for evaluating mitigations to minimize trade-offs between environmental impacts. This paper provides an overview of the range of dairy pasture grazing systems used in New Zealand (NZ), the changes with increased inputs over time and associated key environmental effects including nitrogen (N) leaching and greenhouse gas (GHG) emissions. NZ dairy farming systems are based on year-round grazing and seasonal milk production on perennial ryegrass/clover pasture where cows are rotationally grazed in paddocks. There was an increase in stocking rate on NZ dairy farms from 2.62 cows ha⁻¹ in 2000/2001 to 2.84 cows ha⁻¹ in 2015/2016. During the same period annual milk solids production increased from 315 to 378 kg·yr⁻¹ per cow. This performance has coincided with an increase in N fertilizer use (by ~ 30%) and a twofold increase in externally-sourced feeds. Externally-sourced feeds with a low protein concentration (e.g., maize silage) can increase the efficiency of N utilization and potentially reduce N losses per unit of production. Off-paddock facilities (such as standoff or feed pads) are often used to restrict grazing during very wet winter conditions. A systems analysis of contrasting dairy farms in Waikato (largest NZ dairying region) indicates that the increased input would result in an increase in per-cow milk production but little change in efficiency of milk production from a total land use perspective. This analysis also shows that the increased inputs caused an 11% decrease in N footprint (i.e., N emissions per unit of milk production) and a 2% increase in C footprint (i.e., greenhouse gas (GHG) emissions per unit of milk production).     

A potential solution for food security in Kenya: implications of the Quzhou model in China

Poor soil fertility due to low nutrient inputs is a major factor limiting grain production in Kenya. Increasing soil fertility for crop productivity in China has implications for food security in Kenya. The purpose of this study was therefore to investigate the historical patterns of grain production, nutrient inputs, soil fertility and policies in Quzhou, a typical agricultural county on the North China Plain, and to compare grain production in Quzhou County and Kenya to identify a potential approach for increasing grain production in Kenya. Grain yields in Quzhou increased from 1 to 3 t·ha⁻¹ between 1961 and 1987 by increasing manure application accompanied by small amounts of chemical fertilizer after soil desalinization. There was a further increase from 3 to 5 t·ha⁻¹ up to 1996 which can be mainly attributed to chemical fertilizer use and policy support. Hence, a beneficial cycle between soil fertility and plant growth in Quzhou grain production was developed and strengthened. In contrast, there was only a slight increase in grain yields in Kenya over this period, resulting from low soil fertility with limited external nutrient inputs, a consequence of poor socioeconomic development. It is suggested that grain yields in Kenya would likely be boosted by the development of a self-reinforcing cycling between soil fertility and plant growth with manure and chemical fertilizer use if supported by policy and socioeconomic development.     

A comparison of the biological activities of ethyl acetate fractions from the stems and leaves of Penthorum chinense Pursh

Penthorum chinense Pursh (PCP) is a popular traditional medicinal plant in China, widely used for the treatment of a variety of liver diseases. Although it has been long recognized that the main active elements of PCP are contained in ethyl acetate fraction (EAF), little is known so far in terms of the relative effectiveness of EAF derived from the stems versus leaves of this plant. In the current study, we prepared EAF by reflux extraction and sequential extraction from the stems (SEAF) and leaves (LEAF) of PCP and tested their hepatoprotective efficacies. The extract rates and flavonoid contents of LEAF were higher than those of SEAF. EAFs (>50 μg·mL⁻¹) prevented lipid accumulation in cells and protected against lipotoxicity injury when the concentration exceeded 25 μg·mL⁻¹. More than 95% free radicals released by 2,2-diphenyl-1-picrylhydrazyl (DPPH) were eliminated by 25 μg·mL⁻¹ SEAF and 50 μg·mL⁻¹ LEAF, respectively. Further, EAFs (25 μg·mL⁻¹) also showed protective antioxidant effects, with the activity of LEAF being significantly higher than that of SEAF. EAFs (10 mg·mL⁻¹) also showed similar unspecific bacteriostatic activity. In comparison with SEAF, LEAF contained more flavonoids and had a higher anti-oxidation capability and for these reasons we suggest it should be better for clinical use.     

EFFECTS OF SUBSTITUTION OF MINERAL NITROGEN WITH ORGANIC AMENDMENTS ON NITROGEN LOSS FROM SLOPING CROPLAND OF PURPLE SOIL

● Interflow acts as the dominant pathway for N loss loadings. ● The purple soil region is a hot spot of nitrate leaching in China. ● Mineral N substitution with organic amendments can be recommended as optimal practices for cropland N management. Nitrogen loss from purple soil can lead to large negative impacts to the environment considering the wide distribution of this soil type in the upper reaches of the Yangtze River. Therefore, nitrogen loss patterns from sloping cropland of purple soil in the Sichuan Basin with the following fertilization regimes were studied in a wheat-maize rotation system: 100% organic fertilizer (OM), using pig manure to replace 30% of mineral N (OMNPK) and crop residue to replace 15% of the mineral N (CRNPK) plus standard mineral fertilization (NPK) and no fertilizer control. The cumulative hydrological N loss could be as high as 45 kg·ha⁻¹ N. The interflow accounted for up to 90% of the total N loss followed by sediment and overland flow losses. The high N loss via interflow found in this study highlighting that sloping cropland of purple soil may be one of the hot spots of N leaching. Compared to the NPK regime, organic substitution regimes (i.e., OM, OMNPK and CRNPK) decreased total hydrological N loss loadings by 30% to 68%. In addition, they can maintain annual crop yields and decrease yield-scaled total hydrological N losses by 18% to 71%. In conclusion, long-term substitution of mineral N with organic amendments can maintain high crop productivity and reduce environmental N loss loadings, and thereby recommended as good N management practices to minimize the risk of agricultural non-point source pollution in the purple soil region of China.     

SUSTAINABLE NITROGEN MANAGEMENT INDEX: DEFINITION,GLOBAL ASSESSMENT AND POTENTIAL IMPROVEMENTS

● A composite N management index is proposed to measure agriculture sustainability. ● Nitrogen management has been moving towards sustainability targets globally. ● The improvement was achieved mainly by yield increase, while Nitrogen Use Efficiency (NUE) stagnated. ● No country achieved both yield and NUE targets and spatial variation is large. ● Region-specific yield targets can be used to supplement the standard Sustainable Nitrogen Management Index (SNMI). To represent the sustainability of nitrogen management in the Sustainable Development Goals indicator framework, this paper proposes a sustainable nitrogen management index (SNMI). This index combines the performance in N crop yield and N use efficiency (NUE), thereby accounting for the need for both food production and environmental protection. Applying SNMI to countries around the world, the results showed improvement in the overall sustainability of crop N management over the past four decades, but this improvement has been mainly achieved by crop yield increase, while global NUE has improved only slightly. SNMI values vary largely among countries, and this variation has increased since the 1970s, implying different levels of success, even failure, in improving N management for countries around the world. In the standard SNMI assessment, the reference NUE was defined as 1.0 (considered an ideal NUE) and the reference yield was defined as 90 kg·ha⁻¹·yr⁻¹ N (considering a globally averaged yield target for meeting food demand in 2050). A sensitivity test that replaced the reference NUE of 1.0 with more realistic NUE targets of 0.8 or 0.9 showed overall reduction in SNMI values (i.e., improved performance), but little change in the ranking among countries. In another test that replaced the universal reference yield with region-specific attainable yield, SNMI values declined (i.e., improved performance) for most countries in Africa and West Asia, whereas they increased for many countries in Europe and South America. The index can be improved by further investigation of approaches for setting region-specific yield targets and high-quality data on crop yield potentials. Overall, SNMI offers promise for a simple and transparent approach to assess progress of countries toward sustainable N management with a single indicator.     

EXPLORING THE RECYCLING OF MANURE FROM URBAN LIVESTOCK FARMS: A CASE STUDY IN ETHIOPIA

• Livestock manure was the main organic waste in urban and peri-urban areas.• Manure production will increase by a factor of 3–10 between 2015–2050.• Only 13%–38% of excreted N by livestock will be recycled in croplands.• Intensification of urban livestock production greatly increased N surpluses.• Reducing population growth and increasing livestock productivity needed.Urban population growth is driving the expansion of urban and peri-urban agriculture (UPA) in developing countries. UPA is providing nutritious food to residents but the manures produced by UPA livestock farms and other wastes are not properly recycled. This paper explores the effects of four scenarios: (1) a reference scenario (business as usual), (2) increased urbanization, (3) UPA intensification, and (4) improved technology, on food-protein self-sufficiency, manure nitrogen (N) recycling and balances for four different zones in a small city (Jimma) in Ethiopia during the period 2015-2050. An N mass flow model with data from farm surveys, field experiments and literature was used. A field experiment was conducted and N use efficiency and N fertilizer replacement values differed among the five types of composts derived from urban livestock manures and kitchen wastes. The N use efficiency and N fertilizer replacement values were used in the N mass flow model.Livestock manures were the main organic wastes in urban areas, although only 20 to 40% of animal-sourced food consumed was produced in UPA, and only 14 to 19% of protein intake by residents was animal-based. Scenarios indicate that manure production in UPA will increase 3 to 10 times between 2015 and 2050, depending on urbanization and UPA intensification. Only 13 to 38% of manure N will be recycled in croplands. Farm-gate N balances of UPA livestock farms will increase to>1 t·ha⁻¹ in 2050. Doubling livestock productivity and feed protein conversion to animal-sourced food will roughly halve manure N production.Costs of waste recycling were high and indicate the need for government incentives. Results of these senarios are wake-up calls for all stakeholders and indicate alternative pathways.     

Characterization of grain cadmium concentration in indica hybrid rice

As a consequence of contamination of soil with heavy metals, cadmium accumulation in grain is of great concern worldwide, but especially in southern China. It is important to evaluate the Cd accumulation potential of grain before or when examining and approving new cultivars. An evaluation method and criteria for verifying Cd accumulation potential in rice are proposed, and the Cd accumulation potential of 56 mid-season indica hybrids collected from the provincial cultivar trials in 2016 were investigated. Genotype, environment and their interactions strongly affected the variation in grain Cd accumulation. Two hybrids were identified as slightly Cd accumulating. Hybrids with slight Cd accumulation potential would be suitable for safe grain production on polluted land (total Cd under 2.0 mg·kg⁻¹) in Hunan Province (China) and should be considered for new cultivar evaluation and approval. This evaluation method and criterion could be applied for certifying Cd accumulation potential of rice cultivars.     

Polyaniline–polypyrrole nanocomposites using a green and porous wood as support for supercapacitors

Wood is an ideal type of support material whose porous structure and surface functional groups are beneficial for deposition of various guest substances for different applications. In this paper, wood is employed as a porous support, combined with two kinds of conductive polymers (i.e., polyaniline (PANI) and polypyrrole (PPy)) using an easy and fast liquid polymerization method. Scanning electron microscope observations indicate that the PANI–PPy complex consists of nanoparticles with a size of ~20 nm. The interactions between oxygen-containing groups of the wood and the nitrogen composition of PANI–PPy were verified by Fourier transform infrared spectroscopy. The self-supported PANI–PPy/wood composite is capable of acting as a free-standing supercapacitor electrode, which delivers a high gravimetric specific capacitance of 360 F·g⁻¹ at 0.2 A·g⁻¹.     

GROUNDWATER DEPLETION IN THE NORTH CHINA PLAIN: THE AGROHYDROLOGICAL PERSPECTIVE

Agricultural production in the North China Plain with rainfall of less than 500 mm·yr⁻¹ has been steadily increasing over the past 40 years, with the groundwater levels decreasing at a rate of over 1 m·yr⁻¹. In this paper, it is demonstrated theoretically that the water level in the aquifer can be expressed as a function of agricultural production and the sum of water added as rainfall and imported from outside the basin. Therefore, the most effective measures to halt groundwater depletion are importing water, decreasing cropping intensity and growing less thirsty crops. Irrigation improvements, mulching and agronomic measures that could increase the yield per unit area have less of an impact on solving the declining groundwater levels.     

A novel aldo-keto reductase gene, IbAKR, from sweet potato confers higher tolerance to cadmium stress in tobacco

High concentrations of Cd can inhibit growth and reduce the activity of the photosynthetic apparatus in plants. In several plant species, aldo-keto reductases (AKRs) have been shown to enhance tolerance to various abiotic stresses by scavenging cytotoxic aldehydes; however, few AKRs have been reported to enhance Cd stress tolerance. In this study, the gene IbAKR was isolated from sweet potato. The relative expression levels of IbAKR increased significantly (approximately 3-fold) after exposure to 200 mmol·L⁻¹ CdCl₂ or 10 mmol·L⁻¹ H₂O₂. A subcellular localization assay showed that IbAKR is predominantly located in the nucleus and cytoplasm. IbAKR-overexpressing tobacco plants showed higher tolerance to Cd stress than wild-type (WT). Transgenic lines showed a significant ability to scavenge malondialdehyde (MDA) and methylglyoxal (MG). In addition, proline content and superoxide dismutase activity were significantly higher and H₂O₂ levels were significantly lower in the transgenic plants than in the WT. Quantitative real-time PCR analysis showed that the reactive oxygen species (ROS) scavenging genes encoding guaiacol peroxidase (GPX), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR) and peroxidase (POD) were significantly upregulated in transgenic plants compared to WT under Cd stress. These findings suggest that overexpressing IbAKR enhances tolerance to Cd stress via the scavenging of cytotoxic aldehydes and the activation of the ROS scavenging system.     

Quantitative analysis of yield and soil water balance for summer maize on the piedmont of the North China Plain using AquaCrop

The North China Plain (NCP) is a major grain production area in China, but the current winter wheat-summer maize system has resulted in a large water deficit. This water-shortage necessitates the improvement of crop water productivity in the NCP. A crop water model, AquaCrop, was adopted to investigate yield and water productivity (WP) for rain-fed summer maize on the piedmont of the NCP. The data sets to calibrate and validate the model were obtained from a 3-year (2011–2013) field experiment conducted on the Yanshan piedmont of the NCP. The range of root mean square error (RMSE) between the simulated and measured biomass was 0.67–1.25 t·hm⁻², and that of relative error (RE) was 9.4%–15.4%, the coefficient of determination (R²) ranged from 0.992 to 0.994. The RMSE between the simulated and measured soil water storage at depth of 0–100 cm ranged from 4.09 to 4.39 mm; and RE and R² in the range of 1.07%–1.20% and 0.880–0.997, respectively. The WP as measured by crop yield per unit evapotranspiration was 2.50–2.66 kg·m⁻³. The simulated impact of long-term climate (i.e., 1980–2010) and groundwater depth on crop yield and WP revealed that the higher yield and WP could be obtained in dry years in areas with capillary recharge from groundwater, and much lower values elsewhere. The simulation also suggested that supplementary irrigation in areas without capillary groundwater would not result in groundwater over-tapping since the precipitation can meet the water required by both maize and ecosystem, thus a beneficial outcome for both food and ecosystem security can be assured.     

Integrating space and time: a case for phenological context in grazing studies and management

In water-limited landscapes, patterns in primary production are highly variable across space and time. Livestock grazing is a common agricultural practice worldwide and a concern is localized overuse of specific pasture resources that can exacerbate grass losses and soil erosion. On a research ranch in New Mexico with average annual rainfall of 217 mm, we demonstrate with a quantitative approach that annual seasons vary greatly and examine foraging patterns in Angus-Hereford (Bos taurus) cows. We define five seasonal stages based on MODIS NDVI: pre-greenup, greenup, peak green, drydown and dormant, and examine livestock movements in 2008. Daily distance traveled by cows was greater and foraging area expanded during periods with higher precipitation. A regression model including minimum NDVI, rainfall and their interaction explained 81% of the seasonal variation in distance traveled by cows (P<0.01). Cows explored about 81 ha·d⁻¹ while foraging, but tended to explore smaller areas as the pasture became greener (greenup and peak green stages). Cows foraged an average of 9.7 h daily and spent more time foraging with more concentrated search patterns as pastures became greener. Our findings suggest that phenological context can expand the capacity to compare and integrate findings, and facilitate meta-analyses of grazing studies conducted at different locations and times of year.     

Optimum nitrogen fertilization of Calophyllum inophyllum seedlings under greenhouse conditions

A greenhouse pot experiment was conducted to study the effects of nitrogen fertilization on Calophy- llum inophyllum seedlings grown with 0, 50, 100, 150, 200, 300, 400 and 600 mg N per seedling according to exponential functions. Seedling height, root collar diameter, leaf area and total biomass increased with increasing fertilization from 0 to 200 mg N per seedling and decreased with further increase in fertilization from 300 to 600 mg N per seedling. The net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration and transpiration rate of C. inophyllum seedlings showed a unimodal parabolic trend, with peak values of 7.29 mmol·m⁻²·s⁻¹, 0.071 mol·m⁻²·s⁻¹, 220 mmol·mol⁻¹ and 1.34 mmol·m⁻²·s⁻¹, respectively, when the rate of fertilization was 200 mg N per seedling. Photosynthetic gas exchange parameters were significantly different among nitrogen treatments. Based on the critical values of leaf N and P concentration and N/P ratio, the optimum amount of nitrogen of C. inophyllum seedlings was 200–400 mg per seedling for leaf N and P concentration, and 100–400 mg per seedling for N/P ratio. It was concluded that 200–400 mg N per seedling was the most suitable nitrogen range for C. inophyllum seedlings.     

TOWARD SUSTAINABLE MAIZE PRODUCTION FOR SMALLHOLDERS THROUGH OPTIMIZED STRATEGIES IN NORTH CHINA

● County-level sustainability assessment of maize production is presented. ● County-level improvement potential exhibits a large spatial heterogeneity. ● Promoting technical innovations can facilitate China’s agricultural transition. Agricultural production by smallholders is crucial for ensuring food provision in China. However, smallholders face a series of challenges on their farms including high-to-excess resource inputs, low use efficiency, as well as negative environmental impacts, which may be unfavorable for sustainable agriculture production. This study developed a county-level sustainability assessment of maize production in Hebei, China, by applying multiple data sources in combination with emergy, carbon footprint, nitrogen footprint and cost-benefit analyses. Scenario analysis was applied to explore the localized implementation strategies to achieve the sustainable farming system. The results show that the average emergy sustainability index (ESI) of maize at 2.31 is relatively low. The average greenhouse gas (GHG) emissions and reactive nitrogen (Nr) losses are 0.15 g·kcal⁻¹ CO₂-eq and 3.75 mg·kcal⁻¹ N, respectively. The average cost and net income are 12,700 and 4340 CNY·ha⁻¹, respectively. These results indicate a great potential to improve the environmental-economic sustainability of the maize production system of smallholders. In addition, the environmental and economic indicators calculated from the maize production show a substantial spatial heterogeneity among counties, indicating a requirement for different optimization strategies to improve the environment-economy sustainability at a finer scale. Based on the multiple scenario analysis, optimal strategies targeting each county are proposed. By adopting the optimal strategies, the average ESI and net income could increase by 32% and 83%, respectively, and the average GHG emissions and Nr losses reduce by 33% and 35%, respectively. These findings provide an important reference for adopting different strategies to achieve environment-economy sustainability for smallholders production systems with diverse landscapes in North China and propose a transition pathway toward achieving agriculture sustainability for smallholders worldwide.     

Three-dimensional numerical simulation of flow in trapezoidal cutthroat flumes based on FLOW-3D

To solve the common problem of flumes flow-measurement accuracy without sacrificing water head, a new type of trapezoidal cutthroat flume to measure the discharge in terminal trapezoidal channels is presented. Using the computational fluid dynamic method, three-dimensional flow fields in trapezoidal cutthroat flumes were simulated using the RNG k-ε three-dimensional turbulence model along with the TruVOF technique. Simulations were performed for 12 working conditions, with discharges up to 0.075 m³·s⁻¹ to determine hydraulic performance. Experimental data for the trapezoidal cutthroat flume in terminal trapezoidal channel were also obtained to validate the simulation results. Velocity distribution of the flume obtained from simulation analyses were compared with observed results based on time-averaged flow field and comparison yielded a solid agreement between results from the two methods, with relative error below 10%. The results indicated that the Froude number and the longitudinal average velocity increased along the convergence section and decreased in the divergent section. In the upper throat, the Froude number was less than 0.5, which meets the water measurement requirement, and the critical flow appeared near the throat section. The maximum water head loss of the trapezoidal cutthroat flume was less than 9% of the total head, compared to the rectangular cutthroat flume, and head loss of trapezoidal cutthroat flume was significantly less. Regression models developed for upstream depth versus discharge under different working conditions were satisfactory, with a relative error of less than 2.06%, which meets the common requirements of flow measurement in irrigation areas. It was concluded that trapezoidal cutthroat flumes can improve flow-measurement accuracy without sacrificing water head.