Subjects: Biology >> Ecology submitted time 2017-11-29 Cooperative journals: 《中国生态农业学报》
Abstract： Nitrogen (N) mineralization is an important process of nitrogen cycling in terrestrial ecosystems and significantly influences the availability of soil N. In this paper, we studied the change of soil mineral N and the mineralization rates of N in sloping soils of the northern Loess Plateau respecting to the vegetation types, sampling locations (under canopy vs. outer canopy) and slope positions (upper, middle and lower positions) during the growing season. The objectives were to understand dynamics of N mineralization during growing season and their influencing factors. Sloping lands with Chinese Pine (Pinus tabulaeformis) and Korshinsk Peashrub (Caragana korshinskii), respectively, were selected in the Liudaogou catchment, and an in situ mineralization methods was used to measure the mineralization of soil N from April to October. The measurement were conducted in upper, middle and lower positions of the slope, under and outer of the canopy at the 0-10 and 10-20 cm soil depths. Soil mineral N in the growing season was dominated by ammonium, which accounted for 61% and 70% of total mineral N at the 0-10 and 10-20 cm soil depths, respectively. Meanwhile, the proportion of ammonium to total mineral N increased with the development of growing season. Soil ammonium in the upper and middle slope positions was significantly higher than that in the lower slope position for Chinese pine slopes, but was not affected by slope positions in for Korshinsk Peashrub slopes. Furthermore, soil ammonium was not affected by sampling locations in both Chinese Pine and Korshinsk Peashrub slopes. Soil nitrate and total mineral N were affected by vegetation type and sampling location, rather than by slope positions. Soil nitrate under canopy was similar to that from outer canopy in Chinese Pine slope, but was greater than that from outer canopy in Korshinsk Peashrub. The mineralization of soil N during growing season was mainly resulted from the nitrification at the 0-10 cm soil depth, but caused by both nitrification and ammonification at the 10-20 cm soil depth. Ammonification rate was significantly high at the early growing season, but low at the middle growing season. Moreover, ammonification rate was affected by slope position, vegetation type and sampling location. Nitrification and net N mineralization rate in soils under canopy were similar to soils of outer canopy in Chinese Pine slopes, but were greater than that in soils of outer canopy in Korshinsk Peashrub slopes. Additionally, when comparing with other slope positions, nitrification and net mineralization rate of N were the highest in lower slopes in soils under canopy, but the lowest in lower slopes in both Chinese Pine and Korshinsk Peashrub slopes. The results from this study suggested that Korshinsk Peashrub enhanced nitrification and mineralization of N in soils under canopy, while the effects of Chinese Pine on soil mineral N and mineralization were not affected by sampling location.
Subjects: Biology >> Ecology submitted time 2017-11-29 Cooperative journals: 《中国生态农业学报》
Abstract： On the Loess Plateau, maize morphological structure and yield performance were restricted by rainfall capacity and soil nutrient status. Resource competition in intercroped cultivation can provide a postive effect on the individual establishment and biomass allocation of maize cultivars. The research on root morphology and biomass allocation of maize under integrated influence of annual rainfall level, planting densities and intercropped cultivation aimed for clear and definite the necessity and importance of intercropped models on the grain yield and water use efficiency (WUE) increase. Field experiment was conducted at a classic dry farmming region in a semi-arid region of Loess Plateau in Northwest China. Two maize cultivars (Zhengdan 958, Z958 and Shendan 16, S16) with two planting densities as 45000 plants. hm-2 and 75000 plants .hm-2, intercroped planting in two rows interlaced, above- and belowground competitive growth and biomass accumulation were measured and analyzed for assessing the correlation among biomass allocation, root distribution, grain yield and WUE. The results showed as: (1) Soil water deficiency showed an effective force to root surface area (SA) decrease of S16 at flowering stage under low intercroped density, and SA of Z958 decreased by 30.5% under high intercroped density, water competition was intensified with the intercropped density increase. Over two experimental years, Z958 and S16 intercropping increased root length density (RLD) in 0-20 cm soil layer significantly, denstiy increase and rainwater deficiency both stimulated root growing deeper for water uptaking which then enhanced root competition for water, finally, caused the RLD obvious increase in 30-40 cm soil layer and Z958 appeared deeper root distribution capacity than S16 in two planting densities. (2) Biomass accumulated advantage under intercroped planting had a gentype difference, Z958 appeared growing promotion during vegetative period and that of S16 was during reproductive period. Individual biomass of two maize cultivars decreased with the intercroped density increase, and there had a increase in S16 dry weight during during reproductive growing period compared with that of Z958 in 2011under low intercroped planting density; with high density and more drought condition, maize cultivars intercrops decreased individual biomass accumulation after flowering. (3) the high intercroped density system obtained a increase of harvest index (HI) by 6.0% averagely over two different rainfall years, and ample rain promoted the HI of intercroped group. Root and shoot could grow normally due to inefficient light competition under the sufficient precipitation and low planting density; Soil drought and high intercroped density resulted in the significant decrease of root to shoot rate (RSR) in Z958 because the root competition for water was enhanced. (4) In the drought year (2011), competitive advantage was fully appeared in the two intercroped systems, showed as final yield and WUE increased by 10.3 and 21.4% , 28.2 and 42.0% respectively in the two intercroped densities, furthermore, yield and WUE of Z958 under mixed system were 17.6 and 50.0% higher than S16 over two years. Finally, Z958 showed reasonal biomass distribution and response mechnisim to soil drought under intercropping with S16, through decreased root redundant growth and useless resouces consume. Effective root morphological adjustment and biomass distribution of Z958 were responsible for yield and WUE increase.
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