Effects of animal effluents on the phosphorus sorption characteristics of soils

Abstract

Two groups of soils were examined to determine the effects of dairy, pig, or sewage effluent and other materials containing phosphorus (P) on their P sorption characteristics, using the Langmuir equation to estimate values of both sorption capacity and sorption strength. There were 19 soils (0-15 cm) from 6 sites in the Williams River catchment and 3 soils (0-100 cm) from Bermagui, all from coastal New South Wales. Effluent usually decreased P sorption capacities of the Williams River soils, and in 3 soils the capacities were reduced to zero. Sorption strength was reduced substantially by effluent treatment in all soils except one, which had received effluent for only 3 years. Sorption strength, but not necessarily capacity, was also lower after treatment with poultry manure or chicken litter than after treatment with superphosphate only. Where effluent did not decrease sorption capacity there was a substantial increase in total carbon and iron, both of which could increase sorption capacities. After 3 years of effluent treatment of the Bermagui soil, sorption capacities had been reduced in the top 70 cm depth, the extent of the reduction varying from 17% at 0-7 · 5 cm depth to 38% at 40-70 cm depth. Sorption strength was reduced in the top 40 cm depth only. After 12 years of effluent treatment, sorption capacities and strength had also decreased at the deeper sampling depths (to 100 cm), and the average reduction in capacity was about 40%. These results suggest that P leaching will begin well before the total sorption capacity has been saturated. There was a direct and significant correlation between the sorption strength of the untreated soil and the percentage saturation reached before leaching began. Further saturation of the sorption complex appears to be slow after this degree of saturation has been reached, and it seems that P leaching exceeds adsorption during this phase. There was also a negative correlation between sorption strength and KCl-soluble P in all soils, suggesting that soil P solubility and potential saturation are both controlled by this characteristic.

Phosphorus adsorption characteristics of a constructed wetland soil receiving dairy farm wastewater

“…The soils used in the present study had an organic matter content ranging from 6.7%, for the background soil, to between 5 and 10% for the highly variable wetland soils. Holford et al (1997) also found that effluent treated soils have the lowest P adsorption capacities, as well as decreased adsorption strength. Holford et al (1997), however, also stated that the blocking of P adsorption sites by organic anions in wastewaters may be partially offset by the creation of new sites on enlarged organic matter-Fe surface complexes, but these sites adsorb P very weakly and probably allow for subsequent desorption to occur.…”

“…P would have already saturated some of the wetland adsorption sites, thereby reducing the S max in the wetland soils. As well, organic anions, such as those found in wastewater, can form complexes with Fe and Al, thereby reducing the effectiveness for P retention in a soil (Holford et al 1997;Reddy et al 1998). Wetlands with predominately mineral soils are better P storage sinks than peatlands, which are characterized by a high organic content, and other organic soils (Reddy and Graetz 1981;Richardson 1985).…”

“…Under alkaline conditions, precipitation as insoluble Ca-phosphates becomes more dominant (Faulkner and Richardson 1989;Verhoeven and Meuleman 1999). It is possible that organic anions in animal effluent will affect P adsorption characteristics by blocking soil sorption sites and lowering P sorption strength by organic anion interaction (Holford et al 1997).…”

Pig effluent-P application can increase the risk of P transport: two case studies

“…Several processes are not represented by the laboratory sorption procedure and may result in such accumulation, for example, precipitation, evaporative concentration of P in solution at the soil's surface, slow sorption processes (as discussed by Barrow 1992 andHolford 1997), and effects on sorption capacity related to the addition of effluent constituents (e.g. formation of complexes between P, P-reactive cations, and effluent OC, as suggested by Holford et al 1997). Desorption studies were directed at finding information about the nature of P storage in these piggery effluent irrigated soils (Fig.…”

“…Unfortunately, the study described in Holford et al (1997) was unable to quantify P additions, other than those in the form of superphosphate, making comparisons between treatments difficult.…”