Effects of free iron oxyhydrates and soil organic matter on copper sorption-desorption behavior by size fractions of aggregates from two paddy soils

Effects of free iron oxyhydrates （Fed） and soil organic matter （SOM） on copper （Cu^2＋） sorption-desorption behavior by size fractions of aggregates from two typical paddy soils （Ferric-Accumulic Stagnic Anthrosol （Soil H） and Gleyic Stagnic Anthrosol （Soil W）） were investigated with and without treatments of dithionite-citrate-bicarbonate and of H2O2. The size fractions of aggregates were obtained from the undisturbed bulk topsoil using a low energy ultrasonic dispersion procedure. Experiments of equilibrium sorption and subsequent desorption were conducted at soil water ratio of 1：20, 25℃. For Soil H, Cu^2＋ sorption capacity of the DCB-treated size fractions was decreased by 5.9% for fine sand fraction, by 40.4% for coarse sand fraction, in comparison to 2.9% for the bnlk sample. However, Cu^2＋ sorption capacities of the H2O2-treated fractions were decreased by over 80% for the coarse sand fraction and by 15% for the clay-sized fraction in comparison to 88% for bulk soil. For Soil W, Cu^2＋ sorption capacity of the DCB-treated size fraction was decreased by 30% for the coarse sand fraction and by over 75% for silt sand fraction in comparison to 44.5% for the bulk sample. Cu^2＋ sorption capacities of the H2O2-treated fractions were decreased by only 2.0% for the coarse sand fraction and by 15% for the fine sand fraction in comparison to by 3.4% for bulk soil. However, Cu^2＋ desorption rates were increased much in H2O2-treated samples by over 80% except the clay-sized fraction （only 9.5%） for Soil H. While removal of SOM with H2O2 tendend to increase the desorption rate, DCB- and H2O2-treatments caused decrease in Cu^2＋ retention capacity of size fractions, Particularly, there hardly remained Cu^2＋ retention capacity by size fractions from Soil H after H2O2 treatment except for clay-sized fraction. These findings supported again the dominance of the coarse sand fraction in sorption of metals and the preference of absorbed metals bound to SOM in differently stabilized status among the size fractions. Thus, enrichment and turnover of SOM in paddy soils may have great effects on metal retention and chemical mobility in paddy soils.

Effects of Organic Amendments on Soil Physical Attributes and Aggregate-Associated Phosphorus Under Long-Term Rice-Wheat Cropping

The quantification of phosphorus(P) in bulk soil and P distribution in different size fractions of water-stable aggregates(WSAs)are important for assessing potential P loss through runoff. We evaluated available and total P distribution within WSAs of a sitty clay to clay soil in a long-term fertility experiment of a rice-wheat cropping system in India. Surface soil samples were collected from seven plots amended with NPK fertilizers in combination with or without organic amendments, farmyard manure(FYM), green manure(GM), and paddy straw(PS). The plot with no NPK fertilizers or organic amendments was set as a control. The soil samples were separated by wet sieving into four soil aggregate size fractions: large macroaggregates(> 2.0 mm), small macroaggregates(0.25–2.0 mm), fine microaggregates(0.05–0.25 mm), and a silt + clay-sized fraction(< 0.05 mm). Structural indices were higher in the soil receiving organic amendments than in the soil receiving inorganic fertilizer alone. Organically amended soil had a higher proportion of stable macroaggregates than the control and the soil receiving inorganic fertilizer alone, which were rich in microaggregates. Total and available P contents within WSAs were inversely related to the aggregate size, irrespective of treatment. The distribution of available and total P in the soil aggregate size fraction was as follows: silt + clay-size fraction > small macroaggregates > fine microaggregates> large macroaggregates. Within a size class, aggregate-associated available and total P contents in the organically amended soil were in the following order: FYM > PS ≥ GM. The available P content of the microaggregates(< 0.25 mm) was 8-to 10-times higher than that of the macroaggregates(> 0.25 mm), and the total P content of the microaggregates was 4-to 5-times higher than that of the macroaggregates. Cultivation without organic amendments resulted in more microaggregates that could be checked by the application of organic amendments such as FYM and GM, which increased the proportion of water-stable macroaggregates by consolidating microaggregates into macroaggregates.

Effects of Integrated Soil-Crop System Management on Soil Organic Carbon Characteristics in a Primosol in Northeast China

A synchronous increase in crop productivity, nutrient use efficiency, and soil carbon(C) sequestration is important from the point of view of food security and environmental protection. In recent years, integrated soil-crop system management(ISSM), which uses crop models and advanced nutrient management to redesign cropping systems, has been successfully demonstrated to achieve both high crop productivity and high nutrient use efficiency in China, but the effects of ISSM on soil organic C(SOC) characteristics remain unknown. In this study, the effects of current farmers' practice(FP), high-yielding practice(HY), which maximizes yields without considering costs, and ISSM on the content and chemical composition of SOC were studied in a 4-year(2009–2013) field plot experiment with maize(Zea mays L.) monoculture in an Alluvic Primosol in Northeast China. The ISSM resulted in higher soil total organic C(TOC), water-soluble organic C, easily-oxidizable organic C, particulate organic C, and humic acid C compared with HY and FP in the region. The SOC contents in aggregate size fractions generally followed a similar pattern to TOC. Compared with FP,HY decreased the mean weight diameter, geometric mean diameter, percentage of > 0.25-mm water-stable aggregates, and the stability ratio of water-stable aggregates, and increased the structure-deterioration rate and index of unstable aggregates. The opposite trend was observed between ISSM and HY. Solid-state ^(13)C nuclear magnetic resonance spectra of bulk soil showed that ISSM had higher O-alkyl C and aliphatic C/aromatic C ratio, but lower aromatic C, carbonyl C, and alkyl C/O-alkyl C and hydrophobic C/hydrophilic C ratios than HY and FP. Our results suggest that ISSM improves the quantity and quality of SOC and has a positive effect on soil aggregation and aggregate stability.