Study On Organic Carbon And Nutrient Status Of Soil Aggregates In Lou Soil Profile

Guanzhong Plain is an important grain production of Shaanxi Province,where the Lou soil is the main soil type.Aim at providing reasonable theoretical reference and data for the management of farmland resources at this area,we did a study about Lou soil in Wugong.The distribution of the soil water-stable aggregates was detected by wet sieve method,and the stability of the soil water-stable aggregates was analyzed by means of average weight diameter and fractal dimension.At the same time,the distribut ion and turnover mechanisms of macronutrients and micronutrients in soils were studied.The source of soil organic carbon was explored by combining with isotope mass spectrometry techniques.The main results were as follows:?1?In the plough horizon,ancient plough horizon and Calcic horizon,the content of soil water-aggregates showed a distribution of“high-low-high-low-high”with decreasing of particle size.In the argillic horizon and parent material layer,the content of soil water-aggregates is"low-high-low-high"distribution.The content of>5 mm particle size was mainly dominated in the plough horizon and the ancient plough layer,and<0.25 mm particle size was dominated in the parent material layer.In the argillic horizon and calcic horizon,>0.5 mm and<0.25 mm particle size were domianated.The average weight diameter and geometric mean diameter had a most s ignificant correlation with the content of>5 mm particle size,and also had significantly negaticely correlation with the content of<2 mm particle size,while the fractal dimension of the soil had a most negative correlation with the content of 2-5 mm particle size,and had a most significant correlation with<0.25 mm.?2?The content of soil organic carbon,total nitrogen,and microbial biomass carbon in Lou soil profile showed a decrease with the deepening of soil layer,and the decreasing speed slowed gradually.A higher content of phosphorus was showed at the tillage layer.The distribution of potassium was high-low-high-low-high with the deepening of soil.The distribution of calcium carbonate showed a“Calcic horizon>Parent material horizon>Ancient plough layer>Plough horizon>Argillic horizon”.According to the grading standard of second national soil nutrient census,the conte nt of organic carbon and total nitrogen in the soil was at a relatively low level,in which phosphorus was moderate and potassium was abundant.?3?The distribution and fractal dimension of soil water-stable aggregates and organic carbon and nutrients had a certain correlation in the soil.Specifically,the content of organic carbon and total nitrogen of aggregates had a most significant correlation with>5 mm particle size,and also had a significantly negaticely correlation with 0.5-1 mm,0.25-0.5 mm,and<0.25 mm particles.The content of total phosphorus showed a significantly positively correlation with>5 mm particle size,and showed a positively correlation with 0.5-5 mm particle size.The content of soil microbial biomass carbon was related to>5 mm particle size.The available phosphorus was related to 2-5 mm.The fractal dimension in soil had a significantly negaticely correlated with organic matter and total nitrogen,and also had a significantly positively correlation with total potassium,while showed irrelevant with the total phosphorus.Therefore,the status of soil organic carbon and nutrients can be reflected by using fractal dimensions.?4?For the contents of organic carbon and nutrient in soil water-stable aggregates,the contents of organic carbon and total nitrogen of<0.25 mm in the profile soil showed a first increase and then a decrease in soil depth.The total phosphorus in all particle sizes showed a distribution of"high-low-high"with the deeper of soil layer,while the content of total potassium in Lou soil profiles showed a distribution of“high-low-high-low”with the deepening of the soil.For the distribution of soil organic carbon and nutrients,>5 mm particle size became the main sites of soil organic carbon and nutrients,whic h showed a gradually decreasing with the deepening of the soil.The distribution of organic carbon and nutrients for<0.25 mm particle size showed the opposite change with the deepening of the soil.?5?The contents of soil iron,manganese,copper and zinc were between 3.47-4.12%,707-880 mg/kg,23.7-29.2 mg/kg and 67.4-97.6 mg/kg respectively,and both reached the highest in the argillic horizon.The content of trace element of different particles sizes of water-aggregates showed a difference in the soil profile.In the argillic horizon,calcic horizon and parent material layer,the content of iron and manganese in the<0.25 mm particle size was lower than that of other particle size aggregates,and the zinc content was higher than that of other particle size aggregates.The distribution of micro-elements of aggregates in different sizes showed a consistent with with the distribution of macronutrients.The content of copper and zinc in aggregates had a closely relation with the contents of organic carbon a nd total nitrogen.?6?The vertical distribution of?¹³C values for soil organic carbon showed a characteristic of increasing first and then decreasing,and the?¹³C values of organic carbon showed a difference with each particle sizes.About 55.91-84.09%of organic carbon in soil came from C₃ plants and about 15.911-44.09%of them came from C₄ plants,indicating that the soil organic carbon mainly comes from C₃ vegetation.During the periods of different soil formation,the proportion was different for the growing of C₃ and C₄ vegetations on the ground.The relationship between the content of soil organic carbon and?¹³C could reflect the degree of decomposition of organic matter,which showed that the degree of decomposition of soil organic matter was lower above the Calcic horizon and the degree of decomposition of soil organic carbon was higher below the Calcic layer,and the nature of organic carbon tend to stable.