Predicting Phosphorus Availability from Soil‐Applied Composted and Non‐Composted Cattle Feedlot Manure

Abstract

Prediction of phosphorus (P) availability from soil‐applied composts and manure is important for agronomic and environmental reasons. This study utilized chemical properties of eight composted and two non‐composted beef cattle ( Bos taurus ) manures to predict cumulative phosphorus uptake (CPU) during a 363‐d controlled environment chamber bioassay. Ten growth cycles of canola ( Brassica napus L.) were raised in pots containing 2 kg of a Dark Brown Chernozemic clay loam soil (fine‐loamy, mixed, Typic Haploboroll) mixed with 0.04 kg of the amendments. Inorganic P fertilizer (KH 2 PO 4 ) and an unamended control were included for comparison. All treatments received a nutrient solution containing an adequate supply of all essential nutrients, except P, which was supplied by the amendments. Cumulative P uptake was similar for composted (74 mg kg −1 soil) and non‐composted manures (60 mg kg −1 soil) and for the latter and the fertilizer (40 mg kg −1 soil). However, the CPU was significantly higher for organic amendments than the control (24 mg kg −1 soil) and for composted manure than the fertilizer. Apparent phosphorus recovery (APR) from composted manure (24%) was significantly lower than that from non‐composted manure (33%), but there was no significant difference in APR between the organic amendments and the fertilizer (27%). Partial least squares (PLS) regression indicated that only two parameters [total water‐extractable phosphorus ( ) and total phosphorus (TP) concentration of amendments] were adequate to model amendment‐derived cumulative phosphorus uptake (ACPU), explaining 81% of the variation in ACPU. These results suggest that P availability from soil‐applied composted and non‐composted manures can be adequately predicted from a few simple amendment chemical measurements. Accurate prediction of P availability and plant P recovery may help tailor manure and compost applications to plant needs and minimize the buildup of bioavailable P, which can contribute to eutrophication of sensitive aquatic systems.