Vertical variation and storage of nitrogen in an aquic brown soil under different land uses

The vertical variation and storage of nitrogen in the depth of 0-150 cm of an aquic brown soil were studied under 14 years of four land use patterns, i.e., paddy field, maize field, fallow field and woodland in Shenyang Experimental Station of Ecology, Chinese Academy of Sciences in November of 2003. The results showed that different land uses had different profile distributions of soil total nitrogen (STN), alkali N, ammonium (NH4+-N) and nitrate (NO3--N). The sequence of STN storage was woodland >maize field > fallow field > paddy field, while that of NO3--N content was maize field > paddy field > woodland > fallow field, suggesting the different root biomass and biological N cycling under various land uses. The STN storage in the depth of 0-100 cm of woodland averaged to 11.41 thm-1, being 1.65 and 1.25 times as much as that in paddy and maize fields, respec-tively, while there was no significant difference between maize and fallow fields. The comparatively higher amount of NO3--N in maize and paddy fields may be due to nitrogen fertilization and anthropogenic disturbance. Soil alkali N was significantly related with STN, and the correlation could be expressed by a linear regression model under each land use (R20.929, p<0.001). Such a correlation was slightly closer in nature (woodland and fallow field) than in agro ecosystems (paddy and maize fields). Heavy N fertilization induced an excess of crop need, and led to a comparatively higher amount of soil NO3--N in cultivated fields than in fallow field and woodland. It is suggested that agroforestry practices have the potential to make a significant contribution to both crop production and environment protection.

Effects of Grazing Exclusion on Soil Carbon and Nitrogen Storage in Semi-arid Grassland in Inner Mongolia, China

The semi-arid grasslands in Inner Mongolia, China have been degraded by long-term grazing. A series of ecological restoration strategies have been implemented to improve grassland service. However, little is known about the effect of these ecological restoration practices on soil carbon and nitrogen storage. In this study, characteristics of vegetation and soil properties under continued grazing and exclusion of livestock for six years due to a nationwide conservation program—′Returning Grazing Lands to Grasslands(RGLG)′ were examined in semi-arid Hulun Buir grassland in Inner Mongolia, China. The results show that removal of grazing for six years resulted in a significant recovery in vegetation with higher above and below-ground biomass, but a lower soil bulk density and pH value. After six years of grazing exclusion, soil organic C and total N storage increased by 13.9% and 17.1%, respectively, which could be partly explained by decreased loss and increased input of C and N to soil. The effects of grazing exclusion on soil C and N concentration and storage primarily occurred in the upper soil depths. The results indicate that removal of grazing pressure within the RGLG program was an effective restoration approach to control grassland degradation in this region. However, more comprehensive studies are needed to evaluate the effectiveness of the RGLG program and to improve the management strategies for grassland restoration in this area.

Characteristics of soil organic carbon andtotal nitrogen storages for differentland-use types in Central Yunnan Plateau

Two-factor analysis of variance and redundancy analysis were used to analyze the characte-ristics of soil organic carbon total nitrogen storage in garden land,forestland,grassland,farmland,and bare land in the Dachunhe watershed of Jinning District,Kunming City,Yunnan Province,China.The effects of the soil organic carbon,total nitrogen stratification ratio,soil physical and chemical factors on the storage characteristics of organic carbon and total nitrogen of different land-use types were analyzed.The results show that the rates of carbon and nitrogen stratification in soil from 0-20 cm and 40-60 cm of the same land-use types differed are statistically significant(P<0.05).The organic carbon and total nitrogen stratification ratio SR1 of garden land soil are 38.5%and 25.3%,respectively,which are higher than SR^(2).The soil organic carbon and total nitrogen stratification ratio SR^(2) of different land-use types are greater than SR1.There are statistically significant differences in the SR^(2) soil organic carbon and total nitrogen stratification ratios(P<0.05).Soil organic carbon and total nitrogen storage of diffe-rent land-use types gradually decrease with increasing soil depth,with the maximum soil organic carbon and total nitrogen storage in the 0-20 cm soil layer.Soil organic carbon and total nitrogen sto-rage at the same soil depth are significantly different(P<0.05).Soil organic carbon and total nitrogen storage in the garden land are greater than those in the other land-use types.Soil organic carbon and total nitrogen storage in 0-20 cm garden land are 4.96 and 3.19 times than those in bare land,respectively;soil organic carbon and total nitrogen storage are explained by 93.66%and 1.53%in redundancy analysis RDA1 and RDA2,respectively.All physicochemical factors except Available Phosphorus and pH are statistically significance with carbon and nitrogen storage(P<0.05).Soil cationic exchange capacity,Available Phosphorus,C/N ratio,and Moisture Content are positively correlated with organic carbon and total nitrogen storage.In contrast,soil Bulk Density is negatively correlated with organic carbon storage and total nitrogen storage.Available Phosphorus,C/N ratio,and Moisture Content are the main factors promoting soil organic carbon and total nitrogen accumulation.