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Background Even though extensive work has been done on P interactions with free Al-and Fe-hydroxide minerals, limited or no information exists on sorption/desorption processes of organic and inorganic phosphate forms with soil hydroxy-interlayered minerals.Purpose The purpose of this study was to assess the potential of soil clays rich in hydroxy-interlayered vermiculite (HIV) and smectite (HIS) minerals to adsorb and release inorganic and organic P forms as compared to geological reference gibbsite and goethite minerals. Methods Seven-day P adsorption/desorption experiments were conducted involving six soil clays containing >40% HIV, two soil clays containing >55% HIS, and two reference goethite and gibbsite clays equilibrated with P pools consisting of 10 mg P g -1 clay from KH 2 PO 4 or inositol hexakisphosphate. Results The results indicated a strong tendency for HIV and HIS minerals to sorb P at amounts equivalent to or even higher than those sorbed by gibbsite or goethite minerals. Organic P was sorbed at higher quantities and was retained with greater energy than inorganic P forms. Ammonium oxalate-treated samples produced a clearer picture of the net contribution of hydroxy-interlayered minerals to P sorption capacity compared to free Al/Fe hydroxide components, but the degree of Al-hydroxy-interlayering somewhat obscured P-sorption mineral quantity correlations. Increasing Psorption equilibration times generally increased total inorganic and organic-sorbed P loads only of the ammonium oxalate treated samples, suggesting increased P interaction with less accessible interlayer reactive sites. Reaction times had no significant effect on P desorption characteristics, although some samples released less P at longer equilibration times probably due to readsorption processes. Conclusions The findings suggest that soils containing high amounts of hydroxy-interlayered minerals may act as good P sinks and tolerate higher organic P loads than free Al or Fe hydroxides without increasing risks of P contamination.

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Low-phosphorus (P) litter, a manure treatment byproduct, can be used as an organic soil amendment and nitrogen (N) source but its effect on N mineralization is unknown. A laboratory incubation study was conducted to compare the effect of adding untreated (fine or pelletized) broiler litter (FUL or PUL) versus extracted, low-P treated (fine or pelletized) broiler litter (FLP or PLP) on N dynamics in a sandy soil. All four litter materials were surface applied at 157 kg N ha−1. The soil accumulation of ammonium (NH4+) and nitrate (NO3−) were used to estimate available mineralized N. The evolution of carbon dioxide (CO2), ammonia (NH3), and nitrous oxide (N2O) was used to evaluate gaseous losses during soil incubation. Untreated litter materials provided high levels of mineralized N, 71% of the total N applied for FUL and 64% for PUL, while NH3 losses were 24% to 35% and N2O losses were 3.3% to 7.4% of the total applied N, respectively. Soil application of low-P treated litter provided lower levels of mineralized N, 42% for FLP and 29% for PLP of the total applied N with NH3 losses of 5.7% for FLP for and 4.1% for PLP, and very low N2O losses (0.5%). Differences in mineralized N between untreated and treated broiler litter materials were attributed to contrasting C:N ratios and acidity of the low-P litter byproducts. Soil application of treated low-P litter appears as an option for slow mineral N release and abatement of NH3 and N2O soil losses.

Ash from power plants that incinerate poultry litter has fertilizer value, but research is lacking on optimal land application methodologies. Experiments were conducted to evaluate calcitic lime and flue gas desulfurization gypsum (FGDG) as potential fillers for poultry litter ash land applications. The ash had phosphorus (P) and potassium (K) contents of 68 and 59 g kg−1, respectively. Soil extractable P and K were measured in an incubation pot study, comparing calcitic lime to FGDG at filler/ash ratios of 1:3, 1:2, 1:1, 2:1, and 3:1. After one month, soils were sampled and annual ryegrass (Lolium multiflorum Lam.) seeds were planted to investigate how plant growth and uptake of P and K were influenced by the fillers. Application of ash alone or with fillers increased soil extractable P and K levels above unamended controls by 100% and 70%, respectively. Filler materials did not affect biomass or P and K concentration of the ryegrass. A field study with a commercial spinner disc fertilizer applicator was conducted to compare application uniformity of ash alone and filler/ash blends. Overall, test data suggested that uniform distribution of ash alone or with fillers is feasible in field applications using a commercial fertilizer spreader.

Repeated land application of dairy manure can increase soil phosphorus above crop requirements because of manure’s low nitrogen (N) to phosphorus (P) ratio (N:P < 4:1). This soil P build-up can lead to off-site P transport and impairment of surface water quality. We evaluated a treatment process to extract P from manures, called Quick Wash, integrated with a double-stage solids separation system to recover coarse and fine manure solids. The Quick Wash process uses a combination of acid, base, and organic polymers to extract and recover P from manures, improving the N:P ratio of recovered manure solids (RMS). Results showed that coarse RMS could have use as bedding materials for dairy cows, and the fine acidified RMS with N:P > 10:1 can be used as a low-P organic soil amendment. A soil incubation test showed that acidified RMS stimulated N mineralization and nitrification having higher nitrate levels than untreated dairy slurry when incorporated into soil. Our results suggest that the inclusion of Quick Wash in a dairy manure management system can improve manure’s value, lowering costs of bedding material and manure hauling, and recover P for use as fertilizer while reducing the environmental impact of land spreading manure P.