Tropentag, October 6 - 8, 2009 in Hamburg "Biophysical and Socio-economic Frame Conditions for the Sustainable Management of Natural Resources"

Estimating Nutrient and Carbon Losses on an Irrigated Sandy Soil in Northern Oman

¹University of Kassel, Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Germany
²University of Kassel, Department of Grassland Science and Renewable Plant Resources, Germany
³Royal Gardens and Farms, Royal Court Affairs, Oman

Abstract

Little is known about gaseous and leaching losses of carbon (C) and nitrogen (N) in irrigated agriculture of the hyperarid Arabian Peninsula. Therefore, gaseous emissions of NH₃, N₂O, CO₂ and CH₄ were measured on an experimental field near Sohar (Oman) with an INNOVA photo-acoustic infrared multi-gas monitor connected to a custom made cuvette (closed chamber system). Conducted on an irrigated sandy soil with four replications the experiment comprised two manure types (characterised by a C/N ratio of 24 with high fibre content and a C/N ratio of 15 with low fibre content) and a control treatment with equivalent levels of mineral nitrogen (N), phosphorus (P) and potassium (K). These three fertility treatments were factorially combined with a crop rotation at two levels comprising cauliflower (Brassica oleracea) and carrot (Daucus carota subsp. sativus) each preceded by a crop of radish (Raphanus sativus). Experimental leaching losses were calculated using the solute concentrations of N, P and K in leachate samples and the cumulative amount of leached solutes determined by ion"=exchange resin cartridges. Seepage was estimated with the software Hydrus 1d using estimates of crop-specific evapotranspiration.
Gaseous N emissions averaged 27 kg N ha^-1 (60% NH₃-N, 40% N₂O-N) for a cropping period of 120 days, with little variations between treatments. During the same period C emissions were 6 t C ha^-1 (99% CO₂-C, 1% CH₄-C) on plots treated with organic manures. Plots treated with mineral fertiliser had a mean emission rate of 3 tons C ha^-1. Repeated measurement analysis of the gas emission data revealed significant effects of crop rotation and manure treatment for NH₃-N and CH₄-C. Crop rotation had a significant effect on emissions of CO₂-C and N₂O-N. Cumulative leaching averaged 5 kg N ha^-1 for plots treated with organic manure of low C/N, 28 kg N ha^-1 for plots treated with organic manure of high C/N and 15 kg N ha^-1 for the control treatment.

Keywords: Hydrus 1d, INNOVA multi-gas monitor, leaching, organic agriculture

Contact Address: Andreas Buerkert, University of Kassel, Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Steinstraße 19, 37213 Witzenhausen, Germany, e-mail: tropcropsuni-kassel.de