Adsorption of P and forms of iron in no-tillage areas in the 'Cerrado' biome

The objective of this study was to evaluate the forms of iron extracted as sodium dithionite-citrate-bicarbonate (Fed), acid ammonium oxalate (Feo) and sodium pyrophosphate (Fep) and the relationship between these variables and the total organic carbon content and maximum adsorption capacity of P (MACP). The areas selected for this study had been using a no-tillage system (NTS) for varying periods of time: 3 years (NTS3), 15 years (NTS15) and 20 years (NTS20). These areas were compared with an area of native 'Cerrado' (CE) and a pasture area planted with Brachiaria decumbens (PA). The soil of the areas studied was classified as dystrophic oxisol. In each area, samples were collected at 0-5 cm and 5-10 cm. A correlation was observed between the C content and the different forms of Fe in the areas studied. There was a significant positive correlation between the carbon content and the forms of iron (Feo, Feo/Fed and Fep) and a negative correlation with the level of Fed. The areas of CE and PA had the highest MACP, which diminished as the amount of time of NTS use increased.

本研究旨在评估连二亚硫酸钠-柠檬酸钠-碳酸氢钠提取态铁（sodium dithionite-citrate-bicarbonate, Fed）、酸性草酸铵提取态铁（acid ammonium oxalate, Feo）及焦磷酸钠提取态铁（sodium pyrophosphate, Fep）的赋存形态，并探究上述铁形态变量与土壤总有机碳含量及磷最大吸附容量（maximum adsorption capacity of P, MACP）之间的关联。本研究选取的试验区域均采用免耕系统（no-tillage system, NTS），且免耕时长各异，分别为3年（NTS3）、15年（NTS15）及20年（NTS20）。将上述免耕试验区与原生塞拉多植被区（CE）及种植俯仰臂形草的牧草地（PA）进行对照。供试土壤均被归类为瘠薄氧化土。在每个区域内，分别于0-5 cm和5-10 cm土层采集土壤样品。研究发现，供试区域内土壤碳含量与不同形态铁之间存在相关性：碳含量与Feo、Feo与Fed的比值及Fep呈显著正相关，而与Fed含量呈显著负相关。CE与PA区域的MACP最高，且随着免耕种植时长的增加，MACP逐渐降低。