Flood irrigated date-palm orchards annually manured for 10 ( = Ulo), 50 ( = Use), 110 ( = U 1 lo) and 230 (U230) years together with a barren site in a nearby desert (= Uo), all on sandy soils, were analysed for total P (TP), organic P (OP), inorganic P extracted by 0.5 M H2S04 (Ca-P), inorganic P not extracted by 0.5 M H2SO4 (NP), total N (TN) and organic C (TC). Watering resulted in continuing CaC03 accumulation in the soils. TC and TN to 160 cm depth increased rapidly over the first 50 years (120 g C m-2 a-l and 9.7 g N m-' a-'), then the increases slowed. In contrast, TP continued to accumulate steadily (4.8 g P m-2 a-'). At Uo, TP to 160 cm depth was very small ( = 88 mg kg-') and dominated by Ca-P with OP as a minor component. At Ulo, OP and Ca-P were in equal proportions. The latter acquired increasing dominance with increasing period of treatment whereas OP reached a steady state. NP increased at a rate which decreased with time. It is likely that most of OP compounds have been leached down the profile where mineralization and subsequent immobilization, probably by Ca2+ ions from irrigation waters, have occurred.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.