Characteristics of Nitrogen Loss in Sloping Cropland of Purple Soil during Maize Growth Stage Under Rainstorm
Scientia Agricultura Sinica,Vol 51,No. 04
【Abstract】 [Objective] The characteristics of soil erosion and nitrogen loss in sloping cropland of purple soil during maize ( Zea mays L.) growth stage under the rainstorm were investigated to provide a theoretical basis for the prediction and effective prevention of nitrogen loss. [Method] Simulated rainfall combined with runoff plot experiments were employed during maize seedling stage (1th May), elongation stage (26th May), tasseling stage (27th June) and maturity stage (4th August). According to the feature of the stormy summer months in the purple soil region of Sichuan Province, the characteristics of nitrogen loss in surface runoff, interflow, and sediment were studied during maize growth stage under rainfall intensity of 1.5 mm·min −1 and the slope gradient of 15°. [Result] (1) The rate of surface runoff and sediment yield increased with the increasing rainfall duration during maize growth stage, which were the highest within seedling stage, and the lowest within tasseling stage, but the rates of interflow within tasseling stage and maturity stage were the highest and lowest, respectively. (2) The rate of nitrogen loss in surface runoff increased with the increasing rainfall duration and became stable after the rainfall duration of 36 min. The average total nitrogen and dissolved total nitrogen were up to 5.24 mg·m −2·min −1 and 4.74 mg·m −2·min −1 in seedling stage, respectively. The rate of nitrate nitrogen reached stable after the rainfall duration of 30 min, and the rate of ammonium nitrogen showed volatility with rainfall duration. The rates of nitrate nitrogen and ammonium nitrogen were up to 3.90 mg·m −2·min −1 and 0.14 mg·m −2·min −1 in elongation stage, respectively. The regression relationships of total nitrogen, dissolved total nitrogen and nitrate nitrogen with surface runoff during maize growth stage were extremely significant. (3) The rate of nitrogen loss in the interflow increased slowly with increasing the rainfall duration. The rates of dissolved total nitrogen and nitrate nitrogen showed the same trend with nitrogen loss within seedling stage, elongation stage and maturity stage, while the rate of ammonium nitrogen showed volatility with time. The rates of total nitrogen, dissolved total nitrogen, nitrate nitrogen and ammonium nitrogen were up to 25.04, 20.34, 16.20 and 0.22 mg·m −2·min −1 within elongation stage, respectively. The regression relationships of total nitrogen, dissolved total nitrogen and nitrate nitrogen with interflow during maize growth stage were significant, and the slope of linear relationship was the biggest within elongation stage. (4) The rate of nitrogen loss in sediment yield increased with the increasing rainfall duration, but the increase was the highest in seedling stage, which was up to 0.92 mg·m −2·min −1. The regression relationship between nitrogen loss and sediment yield during maize growth stage was extremely significant. (5) The forms of nitrogen loss in the surface runoff reached the highest in seedling stage and elongation stage. The nitrogen loss in the interflow reached maximum in elongation stage and tasseling stage. The nitrogen loss in sediment yield reached the highest in seedling stage. Interflow was the main source for nitrogen loss and accounted 64.07%–83.39% of the total nitrogen loss. Dissolved total nitrogen was the main form of nitrogen loss in surface runoff and interflow, and nitrate nitrogen was the main form. [Conclusion] Under the rainfall intensity of 1.5 mm·min −1, the nitrogen losses in surface runoff and interflow were the highest within seedling stage and elongation stage, respectively. The dissolved total nitrogen and nitrate nitrogen were the highest in elongation stage, which could easily lead to the eutrophication in waters. Thus, it is necessary to control surface runoff in seedling stage and interflow in elongation stage to reduce nitrogen loss in the purple soil region.
A study of the impact of initial conditions on the predictability of a warm-sector torrential rain over South China
Acta Meteorologica Sinica,Vol 76,No. 03
【Abstract】 The warm-sector torrential rain in South China often occurs in the warm sector 200–300 km ahead of a cold front or without a cold front. Because of the lack of distinct synoptic systems, the predictability of this type of rain is at a very low level. To discuss the impact of initial moisture condition on warm-sector convection triggering and development, two numerical experiments (the control run CTRL and the cloud analysis run CLD) were designed to study a case occurred over the western coast of Guangdong Province on 16 May 2015. These experiments were conducted using 3-km resolution mesoscale Global/Regional Assimilation and PrEdiction System (GRAPES) model and ARPS Data Analysis System (ADAS) complex cloud analysis system. Results showe that: (1) the initial condition of cloud analysis run CLD is characterized by higher moisture content, more instable stratification, larger convective available potential energy, increased K index and precipitable water, lower lifting condensation level and convective inhibition, and smaller LI index. Thereby, the vertical velocity is enhanced and the convection is triggered more quickly; (2) there exist some differences between the mechanisms for the warm-sector convection triggering and development, i.e., the triggering is enhanced by latent heat released from water vapor condensation, which contributes to the positive buoyancy force; during the convection development period, convergence is caused by the outbreak of the surface cold pool and the warm advection from the sea. Sensitivity experiments further indicate that when reducing the water vapor content to 70%, the initial convergence is weakened, and the convection triggering is subsequently weakened, while the dissipation is also delayed. These results can increase our understanding of the predictability of warm-sector torrential rain in South China. Specifically, results of the present study can be used as a reference for future development of operational cycling assimilation system.
Characteristics of temporal and spatial distribution of regional rainstorm processes to the east of 95°E in China during 1981–2015
Acta Meteorologica Sinica,Vol 76,No. 02
【Abstract】 The events of the regional rainstorm processes (RRP) to the east of 95°E in China over 1981–2015 were constructed based on intensive daily observations of precipitation in China and NCEP/NCAR reanalysis data by means of subjective and objective analyses. Temporal and spatial characteristic distributions of RRP in China were further investigated using the methods of wavelet power spectrum, nine-point binomial smoothing and Ward cluster analysis. The main conclusions are as follows. (1) The annual average number of RRP to the east of 95°E in China was nearly 30. RRP in the Yangtze–Huaihe River valley occurs most frequently among the six subareas with an annual average number of about 19, followed by that in South China and eastern part of Southwest China with annual average numbers of 10.5 and 5.8 times respectively. Annual average number of RRP is only about 1–3 in other subareas. (2) The inter-annual and inter-decadal variations of the annual number of RRP exhibit distinct fluctuation characteristics. The inter-annual and inter-decadal fluctuating variation in the Yangtze–Huaihe River valley is the most consistent with that to the east of 95°E in China. Moreover, the fluctuating variations have a significant positive correlation between South China and eastern part of Southwest China, and also between Northeast China and North China. The annual number of RRP over the east of 95°E in China and its subareas demonstrates a periodic variation of 2–4-a, and also a periodic variation of 6–10-a in the Yangtze–Huaihe River valley, South China and eastern part of Northwest China, while a 13–17-a oscillation can be found in North China. (3) On the whole, the occurrence frequency of RRP to the east of 95°E in China is the most in summer (especially in July), the least in winter, and higher in spring than in autumn. The months when RRP occur most frequently are June and July in the Yangtze–Huaihe River valley and eastern part of Southwest China, and May and June in South China. RRP mainly appear in July and August in other subareas. (4) The distribution patterns of RRP to the east of 95°E in China are divided into 7 types. The heavy precipitation areas for patterns I–IV migrate northward step by step from South China and southern part of Yangtze River valley to Huanghe–Huaihe Basin and eastern part of Sichuan Basin. The heavy precipitation areas of patterns V–VII all are located at the coastal region of Southeast China. The precipitation areas of pattern V are concentrated from the eastern part of South China to Huaihe River. The precipitation areas of pattern VI are located from the northern part of Huanghe–Huaihe Basin to central-southern part of Northeast China. The precipitation areas of pattern VII are concentrated over the western part of Huanghe–Huaihe Basin and central-southern part of North China.