Xiaoli Xie

Effects of Long-Term Fertilization on the Distribution of Carbon, Nitrogen and Phosphorus in Water-Stable Aggregates in Paddy Soil

Abstract We investigated the size distribution of water-stable aggregates and the soil carbon, nitrogen and phosphorus concentration over aggregate size fractions based on a long-term (1990-2006) fertilization experiment in a reddish paddy soil. The results showed that the largest water-stable aggregate (WSA) (>5 mm) and the smallest WSA ( 2 mm) and decreased the proportion of the small WSA (

EFFECTS OF LONG-TERM FERTILIZATION ON SOIL CARBON, NITROGEN, PHOSPHORUS AND RICE YIELD

□ Fertilization plays an important role in soil fertility and rice yield. A long-term (1990–2006) field experiment was conducted at a typical subtropical hilly agriculture region in south central China. The objectives of this study are to investigate the effects of long-term fertilizations on i) accumulations and distributions of soil carbon (C), nitrogen (N) and phosphorus (P) in different sizes of water-stable aggregates (WSA); ii) dynamic change of soil C, N, and P over years; and iii) the rice yield. Application of organic materials (OM), especially in combination with chemical fertilizers, increased soil organic C (SOC), soil total N (NT), and soil total P (PT) concentrations in all sizes of WSA, and they more concentrated in WSA (>1 mm). However, single chemical fertilizers had little impact on SOC and NT. There were significantly positive correlations between SOC and NT in each size of WSA, (r≥0.977, n = 15, P < 0.01). It illuminated that application of organic materials benefited the conservation of soil nitrogen. However, application of organic materials had less impact on PT. Variation of C/P was larger than C/N. PT was mainly affected by input of phosphorus. Data over years showed that SOC and NT continued to rise, whereas PT tended to decline irrespective of treatments. Furthermore, economical chemical fertilizers application combining with green manure and half straw returning (NPKe + SR) can produce approximate effects on PT as conventional dose of chemical fertilizers (NPKc). Average rice yield of NPKc for 17 years was 9399 kg ha−1. Compared with NPKc, OM decreased yield by only 4.4%, which indicated that traditional organic fertilization could obtain relatively high yield. NPKe + SR obtained approximate yield as NPKc did, which showed that green manure and half amount of straw effectually reduced chemical fertilizers by about one third.

Mitigating effects of ex situ application of rice straw on CH4 and N2O emissions from paddy-upland coexisting system.

The in situ application of rice straw enhances CH4 emissions by a large margin. The ex situ application of rice straw in uplands, however, may mitigate total global warming potential (GWP) of CH4 and N2O emissions from paddy-upland coexisting systems. To evaluate the efficiency of this practice, two field trials were conducted in rice-rice-fallow and maize-rape cropping systems, respectively. Year-round measurements of CH4 and N2O emissions were conducted to evaluate the system-scaled GWP. The results showed that CH4 accounted for more than 98% of GWP in paddy. Straw removal from paddy decreased 44.7% (302.1 kg ha−1 yr−1) of CH4 emissions and 51.2% (0.31 kg ha−1 yr−1) of N2O emissions, thus decreased 44.8% (7693 kg CO2-eqv ha−1 yr−1) of annual GWP. N2O accounted for almost 100% of GWP in upland. Straw application in upland had insignificant effects on CH4 and N2O emissions, which increased GWP only by 91 kg CO2-eqv ha−1 yr−1. So, the transfer of straw from paddy to upland could decrease GWP by 7602 kg CO2-eqv ha−1 yr−1. Moreover, straw retention during late rice season contributed to 88.2% of annual GWP increment. It is recommended to transfer early rice straw to upland considering GWP mitigation, nutrient recycling and labor cost.

Microstructure studies of PdGe/Ge ohmic contacts to n-type GaAs formed by rapid thermal annealing

A low resistance and shallow ohmic contact to n-GaAs is performed by using Ge/Pd/GaAs trilayer structure and rapid thermal annealing process. The dependence of specific contact resistivity on the temperature of rapid thermal annealing is investigated. A good ohmic contact is formed after annealing at 400-500 degrees C for 60 s. The best specific contact resistivity is 1.4 x 10(-6) Omega cm(2). Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM) are used to analyze the interfacial microstructure. A strong correlation between the contact resistance and the film microstructure is observed.

Net global warming potential and greenhouse gas intensity as affected by different water management strategies in Chinese double rice-cropping systems

This study provides a complete account of global warming potential (GWP) and greenhouse gas intensity (GHGI) in relation to a long-term water management experiment in Chinese double-rice cropping systems. The three strategies of water management comprised continuous (year-round) flooding (CF), flooding during the rice season but with drainage during the midseason and harvest time (F-D-F), and irrigation only for flooding during transplanting and the tillering stage (F-RF). The CH4 and N2O fluxes were measured with the static chamber method. Soil organic carbon (SOC) sequestration rates were estimated based on the changes in the carbon stocks during 1998–2014. Longer periods of soil flooding led to increased CH4 emissions, reduced N2O emissions, and enhanced SOC sequestration. The net GWPs were 22,497, 8,895, and 1,646 kg CO2-equivalent ha−1 yr−1 for the CF, F-D-F, and F-RF, respectively. The annual rice grain yields were comparable between the F-D-F and CF, but were reduced significantly (by 13%) in the F-RF. The GHGIs were 2.07, 0.87, and 0.18 kg CO2-equivalent kg−1 grain yr−1 for the CF, F-D-F, and F-RF, respectively. These results suggest that F-D-F could be used to maintain the grain yields and simultaneously mitigate the climatic impact of double rice-cropping systems.

Photosynthetic and yield responses of rice (Oryza sativa L.) to different water management strategies in subtropical China

An experiment was performed to study gas exchange and chlorophyll fluorescence responses of rice (Oryza sativa L.) to various regimes, such as flooding–midseason drying–flooding (FDF), flooding–midseason drying–saturation (FDS), and flooding–rain-fed (FR) regimes. Compared to FDF, FR resulted in an obvious decrease in net photosynthetic rate (PN), due to the decrease in stomatal conductance and the increase in stomatal limitation. In contrast, FDS plants did not suffer stomatal limitation and had comparable PN with FDF plants. For diurnal light-saturated electron transport rate and saturation irradiance, FDF performed the best, which was followed by FDS and FR successively. FR and FDS plants tended to suffer from midday depression. FDS reduced irrigated water by 17.2% compared to FDF for comparable yields. The results suggested that FDS can be an effective irrigation regime to save water.