Nutrient cycling and field-based partial nutrient balances in two mountain oases of Oman

Little is known about nutrient fluxes as a criterion to assess the sustainability of traditional irrigation agriculture in eastern Arabia. In this study GIS-based field research on terraced cropland and groves of date palm (Phoenix dactylifera L.) was conducted over 2 years in two mountain oases of northern Oman to determine their role as hypothesized sinks for nitrogen (N), phosphorus (P) and potassium (K). At Balad Seet 55% of the 385 fields received annual inputs of 100-500 kg N ha(-1) and 26% received 500-1400 kg N ha(-1). No N was applied to 19% of the fields which were under fallow. Phosphorus was applied annually at 1-90 kg ha(-1) on 46% of the fields, whereas 27% received 90-210 kg ha(-1). No K was applied to 27% of the fields, 32% received 1-300 kg K ha(-1), and the remaining fields received up to 1400 kg ha(-1). At Maqta N-inputs were 61-277 kg ha(-1) in palm groves and 112-225 kg ha(-1) in wheat (Triticum spp.) fields, respective P inputs were 9-40 and 14-29 kg ha(-1), and K inputs were 98-421 and 113-227 kg ha(-1). For cropland, partial oasis balances (comprising inputs of manure, mineral fertilizers, N-2-fixation and irrigation water, and outputs of harvested products) were similar for both oases, with per hectare surpluses of 131 kg N, 37 kg P, and 84 kg K at Balad Sect and of 136 kg N, 16 kg P and 66 kg K at Maqta. This was despite the fact that N2-fixation by alfalfa (Medicago sativa L.), estimated at up to 480 kg ha(-1) yr(-1) with an average total dry matter of 22 t ha(-1), contributed to the cropland N-balance only at the former site. Respective palm grove surpluses, in contrast were with 303 kg N, 38 kg P, and 173 kg K ha(-1) much higher at Balad Sect than with 84 kg N, 14 kg P, and 91 kg K ha(-1) at Maqta. The data show that both oases presently are large sinks for nutrients. Potential gaseous and leaching losses could at least partly be controlled by a decrease in nutrient input intensity and careful incorporation of manure. (c) 2004 Elsevier B.V. All fights reserved.