Soil test phosphorus dynamics in animal waste amended soils: using P mass balance approach

Soil test phosphorus (STP) is commonly used for phosphorus (P) fertilizer recommendations in agriculture and in risk assessment of offsite P movement from environmental perspectives. Present guidelines do not differentiate between the P sources and assume that P added to the soil would behave alike. The objective of this study was to understand the influence of different animal P sources applied at three different rates on changes in STP in many different soils using P mass balance approach. Six P sources consisting of three types of monogastric, two ruminant and triple super phosphate (TSP) applied at 0, 50, and 150 mg P kg(-1) in six different soils. Corn (Zea mays L.) was used to remove P and total of seven harvests were achieved. The STP (Bray 1P) was monitored at T(0) and after each harvest and relationship was developed between STP and net P addition/removal to compute the slope. Prior to crop P removal, the Turkey (Meleagris gallopava) litter (TL) produced the smallest slope at both rates and across all soils. Most P sources resulted large slope values in the Woodson soil. The slope value progressively decreased from higher rate to lower rate to the control treatment in P mass balance study. Soil clay content, initial STP, soil pH, and soil organic matter levels were involved in explaining variations in slope value in TL, while initial STP and clay content in Hog (Sus scrofa) manure (HM) and biosolid (SS) amended soils in net P addition/removal study.