Since sodium dithionite (Na2S2O4) is often contaminated with zinc (Zn) and can form metal sulfide precipitates, it is not suitable for solubilizing iron (Fe) oxides in fractionation schemes for soil microelements. The objective was to find an alternate method to solubilize crystalline Fe oxides that would fit into a scheme including extractants for amorphous Fe and manganese (Mn) oxides. Three soils were extracted with seven reagents designed to remove amorphous and/or crystalline Fe or Mn oxides [0.1M Na4P2O7, pH 10.0; 0.2M (NH4)2C2O4 in 0.2M H2C2O4, pH 3.0 (oxalate); 0.1M NH2OH‐HCl, pH 2.0; 1.0M NH2OH‐HCl in 25% acetic acid; 0.1M ascorbic acid in the oxalate solution; 0.1 g SnCl2 per gram of soil in the oxalate solution; and 1.0 g dithionite per gram of soil in citrate buffer]. The Na4P2O7, an extractant for elements associated with the organic fraction, extracted amounts of Fe similar to that for the oxalate solution. The two NH2OH‐HCl extractants solubilized very little Fe (<1% total), but NH2OH‐HCl alone solubilized as much Mn as most of the other extractants indicating that it is specific for Mn oxides. The ascorbic acid‐oxalate and SnCl2‐oxalate experimental methods extracted amounts of Fe similar to the dithionite method and amounts of Al higher than the dithionite method. Of the amorphous Fe‐oxide extractants, the oxalate solution solubilized the most Zn and Cu, whereas of the crystalline Fe‐oxide extractants, the ascorbic acid‐oxalate solubilized the highest amounts of Zn and Cu. The extractants suggested for a fractionation scheme are NH2OH‐HCl for Mn oxides, oxalate solution shaken with the soil in the dark for amorphous Fe oxides, and ascorbic acid‐oxalate for crystalline Fe oxides.
Organic soil amendments can ameliorate metal toxicity to plants by redistributing metals to less available fractions. The objective of this study was to determine the effects of organic amendments on Zn distribution among soil fractions. Two soils (fine‐textured and coarse‐textured) were amended with five organic waste materials (some of which contained Zn) or commercial humic acid with and without 400 mg kg−1 Zn, incubated, and fractionated using a sequential extraction technique. Where no Zn was added most of the metals were in the residual fraction. Commercial compost, poultry litter, and industrial sewage sludge increased Zn in the exchangeable (EXC), organic (OM), and manganese oxide (MnOx) fractions due to Zn in the materials. Spent mushroom compost (SMC) redistributed Zn from the EXC fraction to the MnOx fraction for the coarse‐textured soil. Where Zn was added, most of the metal was in the EXC and OM fractions. The SMC and humic acid lowered Zn in the EXC fraction and increased Zn in the other fractions. Effects of the organic materials on Zn in soil fractions were more evident for the sandy soil dominated by quartz in the clay than for the finer‐textured soil dominated by kaolinite in the clay‐size fraction. It was concluded that organic materials high in Zn can increase Zn in the EXC, OM, and MnOx fractions where the soil is not contaminated and others such as SMC and HA can lower the potential availability of Zn in contaminated soils by redistributing it from the EXC to less soluble fractions.
Intensively managed golf courses are perceived by the public as possibly adding nutrients to surface waters via surface transport. An experiment was designed to determine the transport of nitrate N and phosphate P from simulated golf course fairways of 'Tifway' bermudagrass [Cynodon dactylon (L.) Pers.]. Fertilizer treatments were 10-10-10 granular at three rates and rainfall events were simulated at four intervals after treatment (hours after treatment, HAT). Runoff volume was directly related to simulated rainfall amounts and soil moisture at the time of the event and varied from 24.3 to 43.5% of that added for the 50-mm events and 3.1 to 27.4% for the 25-mm events. The highest concentration and mass of phosphorus in runoff was during the first simulated rainfall event at 4 HAT with a dramatic decrease at 24 HAT and subsequent events. Nitrate N concentrations were low in the runoff water (approximately 0.5 mg L-1) for the first three runoff events and highest (approximately 1-1.5 mg L-1) at 168 HAT due to the time elapsed for conversion of ammonia to nitrate. Nitrate N mass was highest at the 4 and 24 HAT events and stepwise increases with rate were evident at 24 HAT. Total P transported for all events was 15.6 and 13.8% of that added for the two non-zero rates, respectively. Total nitrate N transported was 1.5 and 0.9% of that added for the two rates, respectively. Results indicate that turfgrass management should include applying minimum amounts of irrigation after fertilizer application and avoiding application before intense rain or when soil is very moist.
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