KONRAD SIEGFRIED1, HERBERT DIETZ2, EVA SCHLECHT3, ANDREAS BUERKERT1
1University of Kassel, Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Germany
2Royal Gardens and Farms, Royal Court Affairs, Oman
3University of Kassel / University of Göttingen, Animal Husbandry in the Tropics and Subtropics, Germany
Information about gaseous losses of carbon (C) and nitrogen (N) in irrigated organic agriculture in northern Oman is scarce. To fill this gap of knowledge a field experiment was carried out in an experimental farm near Sohar, during which applications of two bovine manure types (a C/N ratio of 39 at high fibre content and a C/N ratio of 31 with a low fibre content) and a control treatment (mineral fertilisers with equivalent levels of N and P and K) were factorially combined with two crop rotations comprising cauliflower (Brassica oleracea) and carrot (Daucus carota subsp. sativus) each preceded by a crop of radish (Raphanus sativus). Concentrations of soil-surface emitted NH3, N2O, CO2 and CH4 were determined using an INNOVA photo"=acoustic infrared multi-gas monitor within a closed chamber system and acumulative leaching losses through cartridges filled with cation/anion"=exchange resins.
Cumulative gas emissions during a 90 day cropping period attained a total of 14 kgNha-1 (68% NH3, 32% N2O) and 2,254 kgCha-1 (98% CO2, 2% CH4) for plots treated with organic manure of high C/N and high fibre as compared to equal 14 kgNha-1 and 1,889 kgCha-1 for plots treated with organic manure of low C/N and low fibre content.
Emission rates declined between irrigation events, most likely due to decreasing soil moisture. The significant effect of time on gaseous emissions determined for N2O (p=0.0266), CO2 (p=0.001) and CH4 (p=0.001) was likely due to changing soil moisture and relative humidity.
Cumulative N-leaching was with a total 13 kgha-1 higher on plots amended with organic manure of high C/N and high fibre in comparison to leaching losses of 6 kg N ha-1 on plots with organic manure of low C/N and low fibre content. Cumulative N leaching losses were higher on plots planted with cauliflower than on carrot plots. This may be due to differences in the rooting system and uptake dynamics of both crops.
Keywords: Oman, organic agriculture, vertical nutrient fluxes