Phosphorus accumulation and leaching in two irrigated soils with incremental rates of cattle manure

Abstract

The risk of P leaching increases on land that receives manure at rates sufficient to meet crop N requirements, but calcareous subsoils may minimize P loss due to P adsorption. An 8-yr field experiment was conducted to determine the effects of different rates of manure on the accumulation and leaching of soil P in a coarse-textured (CT) soil and a medium-textured (MT) soil under typical irrigation management in southern Alberta. Treatments included a non-manured control and four rates of cattle (Bos taurus) manure (20, 40, 60, and 120 Mg ha-1 yr-1, wet-weight basis). In manured treatments, P addition ranged from about 80 to 450 kg P ha-1 yr-1, while P removal by annual cereal silage crops ranged from 15 to 22 kg P ha-1 yr-1. High soil test P (STP) concentrations occurred to a depth of 0.6 m at the CT site and 0.3 m at the MT site. Increase in STP concentration to 0.6 m was equivalent to 43% of net P input, and increase in total soil P was equivalent to 78% of net P input. Non-recovery of net P input suggests that P loss by leaching occurred at these sites and that leaching was more prevalent at the CT site. These calcareous soils have considerable potential to hold surplus P, but may still allow P leaching.Key words: Manure, phosphorus dynamics, soil test phosphorus, phosphorus leaching, soil texture