Atmospheric CO2 Enrichment and Reactive Nitrogen Inputs Interactively Stimulate Soil Cation Losses and Acidification.

Reactive N inputs (Nr) may alleviate N-limitation of plant growth and are assumed to help sustain plant responses to the rising atmospheric CO2 (eCO2). However, Nr and eCO2 may elicit a cascade reaction that alters soil chemistry and nutrient availability, shifting the limiting factors of plant growth, particularly in acidic tropical and subtropical croplands with low organic matter and low nutrient cations. Yet, few have so far examined the interactive effects of Nr and eCO2 on the dynamics of soil cation nutrients and soil acidity. We investigated the cation dynamics in the plant-soil system with exposure to eCO2 and different N sources in a subtropical, acidic agricultural soil. eCO2 and Nr, alone and interactively, increased Ca2+ and Mg2+ in soil solutions or leachates in aerobic agroecosystems. eCO2 significantly reduced soil pH, and NH4+-N inputs amplified this effect, suggesting that eCO2-induced plant preference of NH4+-N and plant growth may facilitate soil acidification. This is, to our knowledge, the first direct demonstration of eCO2 enhancement of soil acidity, although other studies have previously shown that eCO2 can increase cation release into soil solutions. Together, these findings provide new insights into the dynamics of cation nutrients and soil acidity under future climatic scenarios, highlighting the urgency for more studies on plant-soil responses to climate change in acidic tropical and subtropical ecosystems.

Rice-duck co-culture for reducing negative impacts of biogas slurry application in rice production systems.

Nitrogen (N) and phosphorus (P) losses are a potential limitation for the direct application of biogas slurry as a substitute for chemical fertilizer in irrigated rice production systems. The hypothesis was tested that a rice-duck co-culture promotes the rice N and P use efficiencies, reducing the losses of these nutrient elements through run-offs and enabling the use of biogas slurry as a substitute for chemical fertilizers. A field split-plot experiment was carried out to test the hypothesis. Our results showed that the direct application of biogas slurry was harmful for rice production. Compared with rice monoculture under chemical fertilization, biogas slurry application reduced N and P accumulation in grains, P use efficiency, and grain yield by 3.6%, 7.8%, 12.7%, and 14.8%, respectively, but increased the total N and P concentrations in the surface water 1.4- and 2.7-fold, respectively, on average on the eleventh day after fertilization. However, rice-duck co-culture compensated for the negative effects of biogas slurry on rice production. Under the biogas slurry application and in line with our hypothesis, the rice-duck co-culture significantly increased N and P accumulation and use efficiencies, as well as grain yield to levels similar to those acquired with chemical fertilization treatments. Meanwhile, total N and P concentrations were significantly lower for rice-duck co-culture than those of rice monoculture under biogas slurry application. Our results suggest that rice-duck co-culture can maintain rice yield and reduce the risks of N and P loss to local environments when utilizing biogas slurry as a substitute for chemical fertilizers.

Effects of ditch-buried straw return on water percolation, nitrogen leaching and crop yields in a rice-wheat rotation system.

BACKGROUND: Crop residue management and nitrogen loss are two important environmental problems in the rice-wheat rotation system in China. This study investigated the effects of burial of straw on water percolation, nitrogen loss by leaching, crop growth and yield. Greenhouse mesocosm experiments were conducted over the course of three simulated cropping seasons in a rice1-wheat-rice2 rotation. RESULTS: Greater amounts of straw resulted in more water percolation, irrespective of crop season. Burial at 20 and 35 cm significantly reduced, but burial at 50 cm increased nitrogen leaching. Straw at 500 kg ha(-1) reduced, but at 1000 kg ha(-1) and at 1500 kg ha(-1) straw increased nitrogen leaching in three consecutive crop rotations. In addition, straw at 500 kg ha(-1) buried at 35 cm significantly increased yield and its components for both crops. CONCLUSIONS: This study suggests that N losses via leaching from the rice-wheat rotation may be reduced by the burial of the appropriate amount of straw at the appropriate depth. Greater amounts of buried straw, however, may promote nitrogen leaching and negatively affect crop growth and yields. Complementary field experiments must be performed to make specific agronomic recommendations.

Greenhouse gas emissions from cotton field under different irrigation methods and fertilization regimes in arid northwestern China.

Drip irrigation is broadly extended in order to save water in the arid cotton production region of China. Biochar is thought to be a useful soil amendment to reduce greenhouse gas (GHG) emissions. Here, a field study was conducted to compare the emissions of nitrous oxide (N2O) and methane (CH4) under different irrigation methods (drip irrigation (D) and furrow irrigation (F)) and fertilization regimes (conventional fertilization (C) and conventional fertilization + biochar (B)) during the cotton growth season. The accumulated N2O emissions were significantly lower with FB, DC, and DB than with FC by 28.8%, 36.1%, and 37.6%, while accumulated CH4 uptake was 264.5%, 226.7%, and 154.2% higher with DC, DB, and FC than that with FB, respectively. Irrigation methods showed a significant effect on total global warming potential (GWP) and yield-scaled GWP (P < 0.01). DC and DB showed higher cotton yield, water use efficiency (WUE), and lower yield-scaled GWP, as compared with FC and FB. This suggests that in northwestern China mulched-drip irrigation should be a better approach to increase cotton yield with depressed GHG. In addition, biochar addition increased CH4 emissions while it decreased N2O emissions.

Meta-analysis of interactions between arbuscular mycorrhizal fungi and biotic stressors of plants.

Naturally, simultaneous interactions occurred among plants, herbivores, and soil biota, that is, arbuscular mycorrhizal fungi (AMF), nematodes, and fungal pathogens. These multiple interactions play fundamental roles in driving process, structure, and functioning of ecosystems. In this study, we conducted a meta-analysis with 144 papers to investigate the interactions between AMF and plant biotic stressors and their effects on plant growth performance. We found that AMF enhanced plant tolerance to herbivores, nematodes, and fungal pathogens. We also found reciprocal inhibition between AMF and nematodes as well as fungal pathogens, but unidirectional inhibition for AMF on herbivores. Negative effects of AMF on biotic stressors of plants depended on herbivore feeding sites and actioning modes of fungal pathogens. More performance was reduced in root-feeding than in shoot-feeding herbivores and in rotting- than in wilt-fungal pathogens. However, no difference was found for AMF negative effects between migratory and sedentary nematodes. In return, nematodes and fungal pathogens generated more reduction of root colonization in Non-Glomeraceae than in Glomeraceae. Our results suggested that AMF positive effects on plants might be indirectly mediated by competitive inhibition with biotic stressors of plants. These positive and negative interactions make potential contributions to maintaining ecosystem stability and functioning.

[Short-term effects of different tillage modes combined with straw-returning on the soil labile organic carbon components in a farmland with rice-wheat double cropping].

A two-year (2009-2011) field experiment was conducted to study the effects of different tillage modes, straw-returning, and their interactions on the soil total organic carbon (TOC) and labile organic carbon (LOC) components (easily oxidizable organic carbon (EOC), water-soluble organic carbon (WSOC), and microbial biomass carbon (MBC)) at the soil depths of 0-7, 7-14, and 14-21 cm in a farmland with rice-wheat double cropping. In all treatments of straw-returning, the TOC and LOC contents in each soil layer were significantly higher than those without straw-returning. Under plowing tillage, the MBC content in 0-7 cm soil layer was significantly higher than that under rotary tillage, but the EOC content was in adverse. Rotary tillage made the TOC content in 7 - 14 cm soil layer being significantly higher, as compared with plowing tillage. The TOC, WSOC, and MBC contents in 14-21 cm soil layer under plowing tillage were significantly higher than those under rotary tillage. Plowing tillage combined with rice and wheat straws-returning made the soil TOC content being higher than the other treatments.

Spatial distribution and controlling factors of heavy metals contents in paddy soil and crop grains of rice-wheat cropping system along highway in East China.

There is consensus concerning the heavy metal pollution from traffic emission on roadside agricultural land. However, few efforts have been paid on examining the contamination characteristics of heavy metals in roadside paddy-upland rotation field, and especially in combination with detailed quantitative analysis. In this study, we investigated the concentrations of heavy metals (Pb, Cd, Cr and Zn) in soil and crop grains of the rice-wheat cropping system along a major highway in East China in 2008 and analyzed the spatial distribution characteristics of heavy metals and their influencing factors with GIS and Classification and Regression Trees (CART). Significantly elevated levels of heavy metals in soil, rice and wheat grains indicated the heavy metals contamination of traffic emission in roadside rice-wheat rotation field. The contamination levels of Cd, Cr and Zn in wheat grain were higher than rice grain, while that of Pb showed an opposite trend. Obvious dissimilarities in the spatial distributions of heavy metals contents were found between in the soil, rice and wheat grains, indicating that the heavy metals contents in the roadside crop grains were not only determined by the concentrations of heavy metals in the paddy soil. Results of CART analysis showed that the spatial variation of the heavy metals contents in crop grains was mainly affected by the soil organic matter or soil pH, followed by the distance from highway and wind direction. Our findings have important implications for the environmental assessment and crop planning for food security along the highway.

[Effects of different fertilization modes on paddy field topsoil organic carbon content and carbon sequestration duration in South China].

Based on the organic carbon data of 222 topsoil samples taken from 38 paddy field experiment sites in South China, calculations were made on the relative annual change of topsoil organic carbon content (RAC) and carbon sequestration duration in the paddy fields in South China under five fertilization modes (inorganic nitrogen fertilization, N; inorganic nitrogen and phosphorus fertilization, NP; inorganic nitrogen, phosphorus, and potassium fertilization, NPK; organic fertilization, O; and inorganic plus organic fertilization, OF). The RAC under the fertilizations was 0-0.4 g x kg(-1) x a(-1), with an increment of 0.20 and 0.26 g x kg(-1) x a(-1) in double and triple cropping systems, respectively. The RAC was higher in treatments O and OF than in treatments N, NP, and NPK, being the highest (0.32 g x kg(-1) x a(-1)) in treatment OF. The topsoil organic carbon accumulation rate decreased with increasing time, and the carbon sequestration duration in treatments N, NP, NPK, O, and OF was about 22, 28, 38, 57, and 54 years, respectively. Inorganic plus organic fertilization was the most effective practice for soil carbon sequestration in the paddy fields in South China.

[Effects of nitrogen fertilization and root separation on the plant growth and grain yield of maize and its rhizosphere microorganisms].

A field experiment with root separation was conducted to study the effects of root interaction in maize-soybean intercropping system on the plant growth and grain yield of maize and its rhizosphere microorganisms under different nitrogen fertilization levels (0.1, 0.3, 0.5, and 0.7 g x kg(-1)). Root interaction and nitrogen fertilization had positive effects on the plant height, leaf length and width, and leaf chlorophyll content of maize. Less difference was observed in the root dry mass of maize at maturing stage between the treatments root separation and no root separation. However, as compared with root separation, no root separation under the nitrogen fertilization levels 0.1, 0.3, 0.5, and 0.7 g x kg(-1) increased the biomass per maize plant by 8.8%, 6.3%, 3.6%, and 0.7%, and the economic yield per maize plant by 17.7%, 10.0%, 8.2%, and 0.9%, respectively. No root separation increased the quantity of rhizosphere fungi and azotobacteria significantly, as compared with root separation. With increasing nitrogen fertilization level, the quantity of rhizosphere bacteria, fungi, and actinomycetes presented an increasing trend, while that of rhizosphere azotobacteria decreased after an initial increase. The root-shoot ratio of maize at maturing stage was significantly negatively correlated with the quantity of rhizosphere bacteria, fungi, and actinomycetes, but less correlated with the quantity of rhizosphere azotobacteria. It was suggested that the root interaction in maize-soybean intercropping system could improve the plant growth of maize and increase the maize yield and rhizosphere microbial quantity, but the effect would be decreased with increasing nitrogen fertilization level.

[Eco-fitness of county-level agricultural leading industry structure: assessment and development prediction].

Based on the 'three critical points' theory of eco-fitness, and by using dynamic weighting and fitting methods, an assessment system for the eco-fitness of county-level agricultural leading industry structure was constructed, and, taking Zhangqiu of Shandong Province, East China as a case, the eco-fitness of county-level agricultural leading industry structure was assessed and predicted. Due to the limited agro-ecological resources, the comprehensive eco-fitness index of four kinds of agricultural leading industry in Zhangqiu presented an upward trend from 2005 to 2010, but a downward trend from 2011 to 2015. The eco-fitness indices of oil crops and fruits would be negative in 2015. The applied research in Zhangqiu confirmed the validity of the assessment system constructed for the eco-fitness of county-level agriculture leading industry structure and the rationality of the prediction model.

Source attributions of heavy metals in rice plant along highway in Eastern China.

Air and soil pollution from traffic has been considered as a critical issue to crop production and food safety, however, few efforts have been paid on distinguish the source origin of traffic-related contaminants in rice plant along highway. Therefore, we investigated metals (Pb, Cd, Cr, Zn and Cu) concentrations and stable Pb isotope ratios in rice plants exposed and unexposed to highway traffic pollution in Eastern China in 2008. Significant differences in metals concentrations between the exposed and unexposed plants existed in leaf for Pb, Cd and Zn, in stem only for Zn, and in grain for Pb and Cd. About 46% of Pb and 41% of Cd in the grain were attributed to the foliar uptake from atmosphere, and there were no obvious contribution of atmosphere to the accumulations of Cr, Zn and Cu in grain. Except for Zn, all of the heavy metals in stem were attributed to the root uptake from soil, although significant accumulations of Pb and Cd from atmosphere existed in leaf. This indicated that different processes existed in the subsequent translocation of foliar-absorbed heavy metals between rice organs. The distinct separation of stable Pb isotope ratios among rice grain, leaf, stem, soil and vehicle exhaust further provided evidences on the different pathways of heavy metal accumulation in rice plant. These results suggested that further more attentions should be paid to the atmospheric deposition of heavy metals from traffic emission when plan crop layout for food safety along highway.

[Effects of domestic wastewater slow infiltration on the growth of poplar 'Zhonglin 2001' plantation].

A slow infiltration experiment with different hydraulic loads (0, 3, 6, 9, 12, and 15 cm per week) of domestic wastewater was conducted in a 'Zhonglin 2001' poplar plantation to study the effects of the wastewater slow infiltration on the growth of the plantation. Comparing with the control (0 cm), the other five treatments increased the soil organic matter, total N, total P, total K, and Na+ contents in the plantation averagely by 1.940 g x kg(-1), 0.115 g x kg(-1), 0.029 g x kg(-1), 1.454 g x kg(-1) and 0.030 g x kg(-1), respectively. At lower hydraulic loads (3-12 cm per week), the poplar biomass growth and the N, P and Na+ contents in different poplar organs averagely increased by 17.583 t x hm(-2) x a(-1), 3.086 g x kg(-1), 0.645 g x kg(-1), and 0.121 g x kg(-1), with the maximum (36.252 t x hm(-2) x a(-1), 13.162 g x kg(-1), 5.137 g x kg(-1), and 0.361 g x kg(-1), respectively) at hydraulic loads 6-12 cm per week. The further increase of the hydraulic load decreased the poplar biomass growth and the N, P and Na+ contents in different poplar organs. The K content in different poplar organs decreased with increasing hydraulic load. Treating with domestic wastewater increased the leaf length, decreased the leaf asymmetry, and delayed leaf-falling. At high hydraulic load (15 cm per week), the higher soil Na+ and water contents would threat the poplar growth. The proper domestic wastewater hydraulic loads for the growth of poplar 'Zhonglin 2001' plantation would be 3-12 cm per week.

[Identification of the prior regions for agricultural and rural pollution control in Changshu].

The characteristics such as wide area, dispersion and randomness of agricultural and rural pollution make it difficult to seize the key to pollution control in rural areas. On the scale of township, using inventory analysis, accounting for emissions and emission intensity of the chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) in Changshu, Jiangsu Province, which exists in a total of 4 classes and 6 kinds of agricultural and rural sources such as farmland cultivation (chemical fertilizer application and crop straw abandoned), animal breeding, aquaculture, rural life (domestic sewage and human waste, solid waste), using cluster analysis, identify the prior regions and the prior pollution sources for agricultural and rural pollution control by the sensitivity evaluation, and make agricultural and rural pollution control and management measures more focused. It shows that: in 2007, COD, TN and TP emissions of agricultural and rural pollution sources were 5496.07, 4161.03, and 647.54 t x a(-1), and the emission intensity of COD, TN and TP was 48.84, 36.98, and 5.75 kg x hm(-2). The main pollution source of COD was rural life and aquaculture, and the contribution rate was more than 75%; the main pollution source of TN and TP was agricultural cultivation and aquaculture, and the contribution rate was more than 80%. The sensitivity evaluation identified that the town of Guli and Shajiabang were the prior regions for agricultural and rural pollution control in Changshu; farmland cultivation and aquaculture were the prior pollution sources in the two areas.

[Effects of long-term continuous cropping of cotton and returning cotton stalk into field on soil biological activities].

The study on the effects of long-term continuous cropping of cotton and returning cotton stalk into field on the quantities of soil microbes and the activities of soil urease, invertase, catalase and diastase showed that the soil biological activities in cotton field were negatively affected by continuous cropping of cotton, but positively affected by the returning of cotton stocks into filed. The obstacle of short-term (5-10 years) continuous cropping was more obvious. After 5 and 10 years continuous cropping and stalk returning, the total quantity of soil microbes was decreased by 36.54% and 25.66%, and the quantities of bacteria and actinomyces were decreased by 61.12% and 70.16%, and 67.91%, 145.89%, respectively, while the quantity of fungi was increased, compared with those after 1 year cropping. The activities of soil urease and invertase after 5 and 10 years continuous cropping and stalk returning were decreased by 0.76% and 2.52%, and 28.12% and 11.44%, respectively, and the soil catalase activity after 5 years continuous cropping and stalk returning was decreased by 9.21%, compared with those after 1 year cropping. Under long-term continuous cropping and stalk returning, soil biological properties improved, and soil biological diversity index increased. Compared with those after 5 years continuous cropping and stalk returning, the quantities of bacteria and actinomyces after 15 and 20 years continuous cropping and stalk returning were increased by 71.52% and 61.03%, and 141.74%, 240.83%, respectively, with the proportion of fungi declined and the activities of urase, catalase and invertase increased. Soil amylase activity after 5, 10, and 20 years continuous cropping and stalk returning was increased by 11.38%, 10.41%, and 31.34%, respectively, compared with those after 1 year cropping.

[Temperature differences of air-rice plant under different irrigated water depths at spiking stage].

With rice cultivars Yangdao 6, Yangjing 9538 and Wuxiangjing 14 as test materials, field experiment was conducted to study the effects of 3 irrigated water depths (0 cm, 2-4 cm, and > 10 cm) on the temperature of different parts of rice plant at spiking stage. The results showed that from 10:30 to 15:00 on sunny days, irrigated water depth on paddy field had significant effects on the temperature of field surface, middle part of rice plant, and rice spike. The higher the water depth on field surface, the lower the temperature of rice plant and rice spike. At the water level > 10 cm, the average temperature differences between air and the rice spike, middle part of rice plant and field surface of these three cultivars were 1.37, 2.98 and 4.12 degrees C higher than those at the water depth of 0 cm, and 0.67, 1.59 and 2.17 degrees C higher than those at the water depth of 2-4 cm, respectively. In addition, the temperature differences were 0.71, 1.39 and 1.95 degrees C higher at the water depth of 2-4 cm than those at the water depth of 0 cm, respectively. Obvious temperature differences of air-rice plant were also observed among the three rice varieties under different irrigated water depths. The analysis of the characteristics of temperature transfer among field surface, middle part of plant and rice spike indicated that the temperature transfer patterns under all test water management regimes accorded with the principles of energy transfer, suggesting that keeping proper water depth on the field surface at rice spiking stage contributed great to the decrease of rice spike temperature and the alleviation of rice heat injury.

[A modified method of ecological footprint and its application].

The Wackernagel's method of ecological footprint assumes that arable lands are cropped only once a year in a country or a region, which does not accord with the conception of ecological footprint referring to the area of productive land. In this paper, the method of cropland footprint was modified by regulating with multi-cropping index, and the ecological footprint calculated with the new method was for the area of cropland but not that of multi-cropping. The ecological economic systems in Binhai and Funing counties of Jiangsu Province from 1995 to 2003 were analyzed by the modified method, and the results showed that when calculated with conventional Wackernagel's method, the ecological footprints of Binhai and Funing were from 1.79 hm2 to 2.22 hm2 and from 1.38 hm2 to 2.81 hm2, and the percentages of cropland ecological footprint in total ecological footprints decreased from 42.65% to 38.81% and from 45.73% to 38.85%, respectively, while calculated with the modified method, the ecological footprints and the percentage of cropland ecological footprint in total ecological footprints were from 1.43 hm2 to 1.88 hm2 and from 1.12 hm2 to 2.43 hm2, and decreased from 28.45% to 22.89% and from 32.94% to 29.42%, respectively. It was indicated that the ecological footprint calculated with the new method was for the area of cropland, which more accorded with the eco-capacity and changed the size and composition of ecological footprints, being able to reflect the use of natural resources more precisely.

Synthesis evaluation with entire-array-polygon method to ecological economic system of Funing County in Jiangsu Province.

Based on the theory of ecological footprint this paper analyzed the ecological economic system in Funing County in the view of demands of economic system to natural resource and supply of ecosystem for natural resources. It was proposed that the concept of ecological deficit (ecological remainder) per ten thousands yuan GDP be used to evaluate development of ecological economic system. With a synthesis appraisement to the ecological economic system using entire-array-polygon method combined with Ulanowicz development ability and with ecological deficit (ecological remainder) per ten thousands yuan GDP, it provides a theoretical base for reconstructing and managing of demonstration eco-region.

[Appropriate parameters for high-yielding cultivation of machine-transplanted rice].

A field experiment with japonica rice variety Wuxiangjing 14 in 2002-2005 showed that the appropriate sowing rate was 150-180 g per tray (1624 cm2), seedling-strengthening agent was more conducive than compound fertilizer in improving the quality of machine-transplanted seedlings, the rational dose of compound fertilizer (N-P2O5-K2O) was 150 g x m(-2), seedlings should be machine-transplanted within 21 days after sowing, densely planting a fewer seedlings in each cluster could improve the individual and population quality of machine-transplanted rice, and applying 315 kg x hm(-2) of N and 6:4 of basal-tillering: heading fertilizer could obtain the highest rice yield. The marked increase of glumous flowers per unit area was the main cause of the increase of machine-transplanted rice yield.

[Diurnal dynamics of microclimate at different succession stages of vegetation communities in inner-river wetland of Zhenjiang City].

To study the diurnal dynamics of microclimate at different succession stages of vegetation communities in the inner-river wetland of Zhenjiang City, three typical communities were chosen, and the light intensity, air temperature, soil temperature, and air relative humidity were measured. The results showed that with the succession of barren land --> Phalaris arundinacea --> Phragmites communis, the diurnal mean values of light intensity, air temperature, and soil temperature decreased from 1204.7 micromol x m(-2) x s(-1) to 141.28 micro.mol x m(-2) x s(-1), 32.2 degrees C to 24.9 degrees C, and 21.83 degrees C to 19.47 degrees C, and their daily variations decreased from 1126 micromol x m(-2) x s(-1) to 265 miromol x m(-2) x s(-1), 12.75 degrees C to 4.8 degrees C, and 4.5 degrees C to 2.1 degrees C, respectively. The air relative humidity increased from 58.95% to 87.3%, while its variation decreased from 29.75% to 5.15%. Habitats were open at early succession stage but more closed at late succession stage, microclimatic conditions developed towards much more cloudy, cold, and moist, and microclimate had a less fluctuation. There were definite correlations among the light intensity, air temperature, soil temperature, and air relative humidity in the vegetation communities, but the correlation coefficients among the test factors were differed at different succession stages.

[Systematic analysis on water ecological adaptability of upland crops in loess hilly zone].

Based on the survey and experimental results, this paper analyzed the time-sequence relationship between crop growth and rainfall distribution, and the potential water use rate, water supply-demand equilibrium and deficit features of different upland crops in the loess hilly zone of south Ningxia. The model of water ecological adaptability index (WEAI) was proposed to evaluate these features of upland crops. The results showed that autumn crops were superior to summer crops in the coupling characteristics between crop growth and rainfall distribution. There were also differences in rainfall potential use rate among crops, the order being: perennial crops > root and stem crops > grain crops; autumn crops > summer crops. The water satiety rate and water ecological adaptability were higher for autumn crops than for summer crops, and higher in rainy years than in dry years. In line with water ecological adaptability index, the 6 main crops could be put in order of millet > potato > panic > flax > pea > spring wheat. The results of this study may provide theoretic basis for drawing up the decision scheme of cropping system in upland regions.