Phosphorus Availability to Wheat From Biosolids.

Biosolids are an organic by-product of wastewater treatment (also called sludge). In the cleaning process, phosphorus (P) is removed from the water and concentrated in the biosolids. Previously conducted research has shown that when biosolids are applied to the soil, the phosphorus in them is partially available to the soil solution. However, research has found that the different methods of removing P used by wastewater treatment plants affects how available the P is (another words, for the same amount of total P in the biosolids, different levels of P become available in the soil). If biosolids are to be applied to fields to supply nutrients, farmers want to know if the P is available to their plants. The objectives of this research were to 1) to investigate P availability to soil and to wheat from biosolids with different treatment methods and 2) to determine if P availability is affected by soil pH. The study was conducted in the greenhouse. Winter wheat (Triticum aestivum) was grown in pots 15 cm in height and with an area of 43.33*10^-7 ha. Biosolids from three different wastewater treatment plants (lime, iron, biologically amended as P removal methods) as well as an inorganic P fertilizer (KH₂PO₄) were used as P sources. Phosphorus sources were applied at two total P rates (55 kg P ha^-1 and 110 kg P ha^-1) to a Plano silt loam soil adjusted to two pH values (~pH 6 and 7). All pots were supplied with 15 % nitrogen and kept at 70^o - 80^o F with light supplied by growing lights 15 hours per day. Four harvests were collected on Nov 19th, Dec 4th, Dec 26th 2009, and Feb 8th 2010. After each harvest, plant samples were analyzed for total P concentration and P uptake. Soil pH and Bray P1 were measured at the end of the experiment. In general, phosphorus was more available from the lime treated biosolids at pH 6 than at pH 7, whereas soil pH seemed to have no effect on the availability of P from the other biosolids. The iron treated biosolids were not consistent in P availability between pH levels. Finally, P concentration was higher at soil pH 7. In conclusion, P availability depends on the type of biosolid applied and the soil pH.