Applications of poultry litter and triple superphosphate fertilizer to a sandy soil: effects on soil phosphorus status and profile distribution

To determine P loadings, added through poultry litter, sufficient to cause downward movement of P from the cultivated layer of a sandy soil, six rates of poultry litter were applied annually for four years to a site in centra l England. (total loading 0 - 1119 kg P ha(-1)). A single extra plot also r eceived an extra 1000 kg ha(-)1 as triple superphosphate (TSP; total loadin g 2119 kg P ha(-1)) and three other treatments received 200 - 800 kg ha(-1) P as TSP only. Annual soil sampling in 30-cm increments to 1.5-m depth pro vided information on P build-up in the topsoil and P movement to depth. The re were strong linear trends between P balance (P applied - P removed in cr ops) and total P, Olsen bicarbonate extractable P and water-soluble P in th e topsoil. Phosphorus from TSP and poultry litter fell on the same regressi on lines, suggesting that both would be equally effective as fertilizer sou rces. We calculated that 100 kg ha(-1) surplus total P would increase the O lsen extractable P content by c. 6 mg kg(-1) and the water-soluble P by c. 5 mg kg(-1). Thus, relatively large amounts of P would need to be applied t o raise soil P status. We found some evidence of P movement into the soil l ayers immediately below cultivation depth. However, neither soil sampling n or soil solution extracted through Teflon water samplers showed evidence of movement into the deep subsoil (1 m) despite large P loadings.