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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. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: Increasing evidences have shown that dissolved organic components are responsible for the significant C and N exports from terrestrial ecosystems to the surrounding aquatic ecosystems and very sensitive to CO2 enrichment. However, there is still a lack of direct evidence about CO2-led effects on these components at the ecosystem scale, especially in wetlands. We, therefore, simultaneously investigated the contents of dissolved organic carbon (DOC) and dissolved nitrogen (DN) in the surface water and soil layer in a paddy field under FACE facility in Eastern China. Elevated CO2 significantly increased the contents of DOC and DN in the surface water by 18.0% and 14.3% on average. Elevated CO2 also increased DOC content in the soil, but decreased DN content. The contents of DOC and DN in the soil–water interface of 0–1cm soil layer were on average 22.4% and 47.5% higher than in the 5–15cm soil layer. Besides, significant higher DOC and DN contents existed in the soil porewater than in the surface water. Due to multiple drainage regime and rainstorm-induced runoffs in rice cropping regions, CO2-led DOC and DN increments in the surface water may increase C and N exports from paddies to the surrounding aquatic ecosystems under future climate patterns. [Copyright &y& Elsevier]

Reactive N inputs (Nr) may alleviate N-limitation of plant growth and are assumed to help sustain plant responses to the rising atmospheric CO 2 (eCO 2 ). However, Nr and eCO 2 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 eCO 2 on the dynamics of soil cation nutrients and soil acidity. We investigated the cation dynamics in the plant-soil system with exposure to eCO 2 and different N sources in a subtropical, acidic agricultural soil. eCO 2 and Nr, alone and interactively, increased Ca 2+ and Mg 2+ in soil solutions or leachates in aerobic agroecosystems. eCO 2 significantly reduced soil pH, and NH 4 + -N inputs amplified this effect, suggesting that eCO 2 -induced plant preference of NH 4 + -N and plant growth may facilitate soil acidification. This is, to our knowledge, the first direct demonstration of eCO 2 enhancement of soil acidity, although other studies have previously shown that eCO 2 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.

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.

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.

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.

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.

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.