[Effects of organic fertilizer application on crop yield and soil properties in rice-wheat rotation system: A meta-analysis]

To clarify the effects of organic fertilizer application on crop yield and soil properties in rice-wheat rotation system in China, we carried out a meta-analysis to quantitatively evaluate the effects of organic fertilizer types (ordinary organic fertilizer, biochar, and straw), fertilization regimes (organic fertilizer alone, organic fertilizer + partial chemical fertilizer, and organic fertilizer + full amount of chemical fertilizer), and experiment duration (short term, medium term, and long term) on soil properties and the yield of rice and wheat, as well as their responses to soil conditions (acid, neutral, basic). Results showed that the application of organic fertilizer had similar yield-increase effect on rice yield (3.1%) and wheat yield (3.0%) compared to chemical fertilizer application alone. The effect of organic fertilizer application on soil quality was more obvious, significantly reducing soil bulk density by 5.7%, and increasing the concentrations of soil organic matter, total nitrogen, total phosphorus, alkali-hydrolyzable nitrogen, available phosphorus, available potassium, microbial biomass carbon, and microbial biomass nitrogen by 11.7%-38.4%. Among different types of organic fertilizer, the effects of ordinary organic fertilizer and biochar on soil properties improvement were better than straw. Compared to the organic fertilizer application alone, the effects of organic fertilizer combined with chemical fertilizer on crop yield was better, but poorer on soil property improvement. With the increasing duration of organic fertilizer application, crop yield and soil fertility gradually increased. Under the condition of acid soil, the effect of organic fertilizer application on crop yield was the best. The annual yield of rice and wheat showed significant negative correlation with soil bulk density, but a significant positive correlation with the concentrations of soil total nitrogen, available phosphorus, available potassium, and microbial biomass nitrogen.

[Effects of environmental stresses on soil functional stability under different water management measures in a paddy field]

With the increase of global environmental changes and intensive anthropogenic activities, it is important to maintain and improve soil function. Here, we evaluated the effects of environmental stress (i.e., drying, high temperature and the combination of drying and high temperature) on soil functional stability (resistance and resilience) under three kinds of water management mea-sures, which included conventional-flooded cultivation, non-flooded with uncovered cultivation and non-flooded with straw mulching. Results showed that, compared to single environmental stress (drying or high temperature), combined stress led to lower soil fungal biomass, bacterial biomass, basal respiration, and soil functional resistance, and higher contents of dissolved organic carbon (DOC) and NH₄⁺-N after one day treatment of stress. Combined stress significantly decreased soil functional resilience after 56 days treatment of stress. Results from the correlation analysis showed that bacterial and fungal biomass were significantly related to soil resistance and resilience. Different water management measures could regulate the effects of environmental stress on soil functional stability. Non-flooded with straw mulching treatment significantly increased the contents of soil DOC, NH₄⁺-N, fungal biomass and bacterial biomass, resulting in higher soil functional resistance and resilience compared with conventional-flooded cultivation and non-flooded with uncovered cultivation under both single and combined stress. In summary, non-flooded with straw mulching could improve soil functional stability under environmental stress, and it could be a suitable agricultural management for non-continuously flooded rice cultivation under multiple stresses.

[Effects of nitrogen fertilization and straw amendment on soil microbial biomass and soil functions after heat stress]

A 60-day incubation experiment was conducted to study the effects of nitrogen fertilization (N), rice straw amendment (R), and their combination (RN) on the changes of soil microbial biomass and soil functions (basal respiration, substrate-induced respiration, and straw decomposition) after heat stress (40 degrees C for 18 h). Heat stress tended to promote the soil microbial biomass and soil functions, but the effects were weak and transient. Either with or without heating, treatment R and especially RN could greatly stimulate soil microbial biomass, basal respiration, substrate-induced respiration and straw decomposition, as compared to no straw amendment and with nitrogen fertilization alone, but the parameters in treatment N had less change, and even, presented a decreasing trend. It was suggested that straw amendment and its combination with nitrogen fertilization could improve soil functions in natural conditions or after environmental stress.

[Characteristics of soil nematode communities in coastal wetlands with different vegetation types]

An investigation was conducted on the characteristics of soil nematode communities in different vegetation belts (Spartina alterniflora belt, Sa; Suaeda glauca belt, Sg; bare land, B1; Phragmites australis belt, Pa; and wheat land, Wl) of Yancheng Wetland Reserve, Jiangsu Province of East China. A total of 39 genera and 20 families of soil nematodes were identified, and the individuals of dominant genera and common genera occupied more than 90% of the total. The total number of the nematodes differed remarkably with vegetation belts, ranged from 79 to 449 individuals per 100 grams of dry soil. Wheat land had the highest number of soil nematodes, while bare land had the lowest one. The nematode ecological indices responded differently to the vegetation belts. The Shannon index (H) and evenness index (J) decreased in the order of Pa > Sg > Wl > Sa > Bl, and the dominance index (lambda) was in the order of Bl > Sa > Wl > Sg > Pa, suggesting that the diversity and stability of the nematode community in bare land were lower than those in the other vegetation belts, and the nematode community in the bare land tended to be simplified. The maturity index (MI) was higher in uncultivated vegetation belts than in wheat land, suggesting that the wheat land was disturbed obviously. The nematode community structure differed significantly with vegetation belts, and the main contributing species in different vegetation belts also differed. There existed significant correlations between the soil physical and chemical characteristics and the nematode numbers, trophic groups, and ecological indices. Our results demonstrated that the changes of soil nematode community structure could be used as an indicator well reflecting the diversity of vegetation belt habitat, and an important bio-indicator of coastal wetland ecosystem.

[Distribution characteristics of soil organic carbon, nitrogen and phosphorus in densely populated village landscapes of different hilly regions of China]

Based on high spatial resolution remote sensing map (1 m) and sampling with a stratified design on different site types, the effects of fine-scale land use patterns in villages on top soil (0-30 cm) organic carbon (OC), total nitrogen (TN) and total phosphorus (TP) within and across the densely populated hilly landscapes, i. e., Sichuan Hilly Region (SIHR; Jintang County, Sichuan Province), Subtropical Hilly Region (SUHR; Yiyang County, Hunan Province), and Tropical Hilly Region (THR; Dianbai County, Guangdong Province), were investigated. The results showed that soil OC density was decreased in the order of SUHR (2.72 +/- 0.76 kg x m(-2)) > THR (2.65 +/- 0.73 kg x m(-2)) > SIHR (2.15 +/- 0.57 kg x m(-2)), TN density was in the order of SUHR (0.28 +/- 0.06 kg x m(-2)) > SIHR (0.27 +/- 0.06 kg x m(-2) > THR (0.21 +/- 0.06 kg x m(-2)), and TP density was in the order of SIHR (0.19 +/- 0.04 kg x m(-2)) > SUHR (0.11 +/- 0.03 kg x m(-2)) > THR (0.08 +/- 0.04 kg x m(-2)). The fine-scale landscape units (ecotopes) with the highest soil OC, TN and/or TP stocks were rainfed annual crops in SIHR, paddy rice in SUHR, and open canopy trees and brush in THR, respectively. In all hilly regions, paddy and forest land use classes had the highest soil OC and TN density, while mined areas had the lowest soil OC and TN density, with the distribution of TP density showing a more complicated pattern than that of OC and TN. Ecotope level analysis could reflect the soil organic carbon, nitrogen and phosphorus distribution in densely populated village landscape of hilly regions more comprehensively than land use or land cover analysis.