The size distribution of water-stable aggregates and the variability of organic C,N and P contents over aggregate size fractions were studied for orchard,upland,paddy,and grassland soils with high,medium,and low fertility levels.The results showed that > 5 mm aggregates in the cultivated upland and paddy soils were 44.0% and 32.0%,respectively,less than those in the un-tilled orchard soil.Organic C and soil N in different size aggregate fractions in orchard soil with high fertility were significantly higher than those of other land uses.However,the contents of soil P in different size aggregates were significantly greater in the paddy soil as compared to the other land uses.Soil organic C,N and P contents were higher in larger aggregates than those in smaller ones.The amount of water-stable aggregates was positively correlated to their contribution to soil organic C,N and P.For orchard and grassland soils,the > 5 mm aggregates made the greatest contribution to soil nutrients,while for upland soil,the 0.25-0.053 mm aggregates contributed the most to soil nutrients.Therefore,the land use with minimum disturbance was beneficial for the formation of a better soil structure.The dominant soil aggregates in different land use types determined the distribution of soil nutrients.Utilization efficiency of soil P could be improved by converting other land uses to the paddy soil.
LIU Xiao-LiHE Yuan-QiuH. L. ZHANGJ. K. SCHRODERLI Cheng-LiangZHOU JingZHANG Zhi-Yong
通过盆栽和模拟实验探讨了水分状况和施磷量对红壤有效磷的影响。结果表明,水分状况和施磷量均显著地影响红壤有效磷含量,二者的交互作用达极显著水平;同时也均显著地影响水稻生物量和对磷的吸收量,二者的交互作用达显著和极显著水平。红壤有效磷含量基本上随红壤水分含量和施磷量的增加而提高,随水稻生长时间的延长而降低;水稻的生物量和对磷的吸收量均随施磷量的增加和水稻生长时间的延长而增加,但以中水条件下最高。在保证80%的饱和持水量和常规氮、钾等养分投入条件下,施磷量为67.5 kg hm-2就可以满足水稻旱作的生长需求。
Biologically active soil organic carbon （BASOC） is an important fraction of soil organic carbon （SOC）, but our understanding of the correlation between BASOC and soil aggregate stability is limited. At an ecological experimental station （28° 04＇-28° 37＇ N, 116° 41＇-117° 09＇ E） in Yujiang County, Jiangxi Province, China, we analyzed the dynamic relationship between soil aggregate stability and BASOC content over time in the red soil （Udic Ferrosols） fertilized with a nitrogen-phosphorus-potassium chemical fertilizer （NPK） without manure or with NPK plus livestock manure or green manure. The dynamics of BASOC was evaluated using CO2 efflux, and soil aggregates were separated according to size using a wet-sieving technique. The soils fertilized with NPK plus livestock manure had a significantly higher content of BASOC and an improved aggregate stability compared to the soils fertilized with NPK plus green manure or NPK alone. The BASOC contents in all fertilized soils decreased over time. The contents of large aggregates （800-2 000 μm） dramatically decreased over the first 7 d of incubation, but the contents of small aggregates （〈 800 μm） either remained the same or increased, depending on the incubation time and specific aggregate sizes. The aggregate stability did not differ significantly at the beginning and end of incubation, but the lowest stability in all fertilized soils occurred in the middle of the incubation, which implied that the soils had a strong resilience for aggregate stability. The change in BASOC content was only correlated with aggregate stability during the first 27 d of incubation.
LI Cheng-LiangXU Jiang-BingHE Yuan-QiuLIU Yan-LiFAN Jian-Bo
