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ABSTRACT: In the coastal Batinah plain of Oman, a litterbag experiment was carried out in an irrigated field, investigating the effects
of organic fertilization and mineral fertilization on the cultivation of carrots and cauliflower. Two straw varieties and
two green-harvested crops were used, simulating the properties of green manures. The loss of C in the litterbags declined
in the order maize (−94%) > alfalfa (−89%) > wheat (−80%) > canola (−69%). For all these materials, the concentration of muramic
acid, as an indicator of bacterial C, as well as galactosamine was generally increased in comparison with the initial values.
In contrast, fungal glucosamine and consequently also the ratio of fungal C/bacterial C declined for canola and wheat straw.
The loss of N, P, and S was generally smaller than that of C and showed strong substrate-specific patterns. Fertilization
and crop cultivation had no effect on C losses. Organic fertilization resulted in significant increases in S, Mg, and Al in
the litterbags in comparison with mineral fertilization. Cultivation of carrots led to significantly lower ash, N, P, Ca,
K, Na, and Al concentrations than cultivation of cauliflower. Organic fertilization and carrot cultivation both led to stronger
fungal colonization of the litter retained in the litterbags in comparison with mineral fertilization and cauliflower cultivation,
respectively. More information is required on the interactions between initial plant surface colonizing microorganisms and
soil-derived colonizers.
KeywordsLitter quality–Decomposition–Nutrient release–Microbial C–Fungal C–Amino sugars–Litterbag
Biology and Fertility of Soils 04/2012; 47(1):71-80. · 2.32 Impact Factor
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ABSTRACT: Many microbial turnover processes in acidic sandy subtropical soils are still poorly understood. In a 59-day pot and a 189-day
laboratory incubation experiment with two West African continuous cereal soils, the effects of 2mg g−1 root residues were investigated on growth of sorghum seedlings, soil microbial biomass and activity indices, using cowpea,
groundnut, pearl millet, maize and sorghum. The effects of root residues were compared with mineral P or mineral P + N treatments
and with a non-fertilized control treatment. On the Alfisol (Fada, Burkina Faso), shoot dry mass was always significantly
higher than on the Ultisol (Koukombo, Togo). Highest shoot dry mass was observed after application of mineral P + N on the
Alfisol and after mineral P alone on the Ultisol. The application of legume root residues led to small and non-significant
increases in dry mass production compared to the non-amended control, whereas the application of cereal root residues led
to a decline, regardless of their origin (millet, maize or sorghum). Contents of microbial biomass C, microbial biomass N
and ergosterol were 75 to 100% higher in the Alfisol than in the Ultisol, while ATP was only 36% higher. Organic amendments
increased ergosterol concentrations by up to 145% compared to the control and mineral P application. Microbial biomass C and
microbial biomass N increased by up to 50% after application of root residues, but ATP only up to 20%. After application of
legume root residues, cumulative CO2 production was similar in both soils with an average of 370 µg CO2-C g−1 over 189days. After application of cereal root residues, cumulative CO2 production was higher in the Alfisol (530 µg g−1) than in the Ultisol (445 µg g) over 189days.
Plant and Soil 04/2012; 325(1):145-156. · 2.73 Impact Factor
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ABSTRACT: “Effective microorganisms” (EM) are a poorly defined mixture of supposedly beneficial microorganisms that are claimed to enhance microbial turnover in compost and soil. In Costa Rica, EM are used to produce organic compost (bokashi) from banana residues (Musa ssp.). Given the scarcity of scientific data about the effects of EM on the mineralization of plant residues, this study aimed at investigating the effects of EM addition on the decomposition of banana residues during Bokashi production. To this end, the following non-EM treatments were compared to EM Bokashi: Bokashi produced with water (W), with molasses (M) as an EM additive, and with sterilized EM (EMst). Subsequently, the effects of the resulting Bokashi treatments on the growth of young banana plants were evaluated. Compared with non-EM controls, the effect of EM on the mineralization of banana material was negligible. Dry-matter losses of the composts with different EM treatments were similar, with about 78% over 5 weeks. Ergosterol concentration was highest in EM Bokashi (77 µg (g dry soil)–1) and lowest in EMst Bokashi (29 µg (g dry soil)–1). Microbial biomass carbon (Cmic) and microbial biomass nitrogen (Nmic) were both lowest in EM (Cmic = 3121 µg g–1; Nmic = 449 µg g–1), while Cmic was highest in Bokashi produced with molasses (3892 µg g–1) and Nmic was highest in EMst (615 µg g–1). Treatment effects on adenylate concentrations and adenylate energy charge were negligible. Application of all Bokashi variants to young banana plants significantly increased shoot growth under greenhouse conditions compared to plants grown in a control soil without amendments. However, these effects were similar for all Bokashi treatments, even if EM Bokashi increased the K concentrations in banana leaves significantly compared to Bokashi produced with EMst and the control. Bokashi produced with only molasses and EM Bokashi decreased the number of root nematodes under greenhouse conditions compared to the control. Overall, the results confirmed the expected influence of composting on the degradation of organic material and the effect of compost application on plant growth. Hower, under the conditions of this study, EM showed no special effects in this, except for increasing the K concentrations in the leaves of young banana plants.
Journal of Plant Nutrition and Soil Science 10/2007; 170(5):649 - 656. · 1.60 Impact Factor
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ABSTRACT: An important feature of maintaining the agricultural stability in millennia-old mountain oases of northern Oman is the temporary abandonment of terraces. To analyse the effects of a fallow period on soil microbial performance, i.e. microbial activity and microbial biomass, samples of eight terrace soils abandoned for different periods were collected in situ, assigned to four fallow age classes and incubated for 30days in the laboratory after rewetting. The younger fallow age classes of 1 and 5years were based on the records of the farmers recollections, the two older fallow age classes of 10–20 and 25–60years according to the increase in the d -to- l
ratio of valine and leucine enantiomers. The increase in these two ratios was in agreement with that of the d
-to- l ratio of lysine. The strongest relationship was observed between the increase in the d -to- l
ratio of lysine and the decrease in soil microbial biomass C. However, the most stringent coherence between the increase in fallow age and soil properties was revealed by the decreases in cumulative respiration and net N mineralisation rates with decreasing availability of substrate to soil microorganisms. During the 30-day incubation following rewetting, relative changes in microbial activity (respiration and net N mineralisation) and microbial biomass (C and N) indices were similar in the eight terrace soils on a fallow age-class-specific level, indicating that the same basic processes occurred in all of the sandy terrace soils investigated.
Biology and Fertility of Soils 04/2004; 39(6):398-406. · 2.32 Impact Factor
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ABSTRACT: Our knowledge of the agricultural sustainability of the millennia-old mountain oases in northern Oman is restricted in particular with respect to C and N turnover. A laboratory study was conducted (1) to analyse the effects of rewetting and drying on soil microorganisms after adding different manures, (2) to investigate the effects of mulching or incorporating of these manures, and (3) to evaluate the relationships between C and N mineralisation rates and manure quality indices. During the first 9-day rewetting and drying cycle, i.e. the mulch period, the content of extractable organic C decreased by approximately 40% in all four treatments. During the second 9-day rewetting and drying cycle, i.e. the incorporation period, this fraction decreased insignificantly in almost all treatments. The control and mature manure treatments form the first pair with a low percentage of total organic C evolved as CO2 (0.3% in 18days) and a considerable percentage of total N mineralised as NH4 and NO3 (1% in 18days), the fresh and immature manure treatments form the second pair with a higher amount of total organic C evolved as CO2 (0.5% in 18days) and no net N mineralisation. During the first 9-day rewetting and drying cycle, the contents of microbial biomass C and biomass N increased by approximately 150% in all four treatments. During the second 9-day rewetting and drying cycle, no further increase was observed in the control and immature manure treatments and a roughly 30% increase in the other two treatments.
Biology and Fertility of Soils 01/2004; 39(3):165-171. · 2.32 Impact Factor
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ABSTRACT: For millennia oasis agriculture has been the backbone of rural livelihood in the desertic Sultanate of Oman. However, little is known about the functioning of these oasis systems, in particular with respect to the C turnover. The objective was to determine the effects of crop, i.e. alfalfa, wheat and bare fallow on the CO2 evolution rate during an irrigation cycle in relation to changes in soil water content and soil temperature. The gravimetric soil water content decreased from initially 24% to approximately 16% within 7 days after irrigation. The mean CO2 evolution rates increased significantly in the order fallow (27.4 mg C m−2 h−1) < wheat (45.5 mg C m−2 h−1) < alfalfa (97.5 mg C m−2 h−1). It can be calculated from these data that the CO2 evolution rate of the alfalfa root system was nearly four times higher than the corresponding rate in the wheat root system. The decline in CO2 evolution rate, especially during the first 4 days after irrigation, was significantly related to the decline in the gravimetric water content, with r=0.70. CO2 evolution rate and soil temperature at 5 cm depth were negatively correlated (r=−0.56, n=261) due to increasing soil temperature with decreasing gravimetric water content.
Applied Soil Ecology.
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ABSTRACT: The Digital Elevation Model (DEM) derived from NASA's Shuttle Radar Topography Mission is the most accurate near-global elevation model that is publicly available. However, it contains many data voids, mostly in mountainous terrain. This problem is particularly severe in the rugged Oman Mountains. This study presents a method to fill these voids using a fill surface derived from Russian military maps. For this we developed a new method, which is based on Triangular Irregular Networks (TINs). For each void, we extracted points around the edge of the void from the SRTM DEM and the fill surface. TINs were calculated from these points and converted to a base surface for each dataset. The fill base surface was subtracted from the fill surface, and the result added to the SRTM base surface. The fill surface could then seamlessly be merged with the SRTM DEM. For validation, we compared the resulting DEM to the original SRTM surface, to the fill DEM and to a surface calculated by the International Center for Tropical Agriculture (CIAT) from the SRTM data. We calculated the differences between measured GPS positions and the respective surfaces for 187,500 points throughout the mountain range (ΔGPS). Comparison of the means and standard deviations of these values showed that for the void areas, the fill surface was most accurate, with a standard deviation of the ΔGPS from the mean ΔGPS of 69 m, and only little accuracy was lost by merging it to the SRTM surface (standard deviation of 76 m). The CIAT model was much less accurate in these areas (standard deviation of 128 m).The results show that our method is capable of transferring the relative vertical accuracy of a fill surface to the void areas in the SRTM model, without introducing uncertainties about the absolute elevation of the fill surface. It is well suited for datasets with varying altitude biases, which is a common problem of older topographic information.
ISPRS Journal of Photogrammetry and Remote Sensing.
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ABSTRACT: In the desert country of Oman, available water resources are scarce and scattered. In most locations where water can be accessed, this resource is harnessed by oases planted to date palm (Phoenix dactylifera L.) and other crops. So far, little is known about the site-specific conditions determining the existence, size and type of these oases. Remote sensing and image processing techniques were used to locate oases, to characterize the sites according to their topographic, hydrologic and geologic characteristics and to develop a typology of oases in northern Oman.To derive oasis positions, we calculated the Normalized Difference Vegetation Index (NDVI) of Landsat images covering all of northern Oman, subtracted a regional average NDVI, averaged the resulting grid over 3 × 3 pixels and extracted the brightest of five classes determined by a natural breaks algorithm. A buffer of six pixels was added to the oases and the vegetated area as determined by the NDVI was summarized for these polygons. The oasis detection procedure was validated using Google Earth Pro®. Topographic information was derived from data of the Shuttle Radar Topography Mission (SRTM), complemented by digitized Russian military maps, from which mean elevations and elevation range above the oases within a buffer of 2 km were extracted.Water contributing upslope area and distance to streams with catchments of 10 km2 and 100 km2 were derived from the same elevation model. All geologic formations of northern Oman were assigned to one of 7 groups and tested for influence on vegetation surrounding them. Four such geologic settings were identified and described by categorical variables. All input parameters were used to define oasis types based on cluster analysis.Our algorithm detected 2663 oases in northern Oman, of which 2428 had vegetated areas of more than 0.4 ha, the minimum size for reliable detection. The oases were subdivided into six groups. ‘Plain Oases’ (49% of all oases) lie mostly in the plains east and west of the mountains, and are fed by groundwater flow in Quaternary sediments. ‘Foothill Oases’ (46%) are scattered over the foothills, where they draw their water from groundwater flow that is channeled by rock formations. ‘Mountain Oases’ (3%) and ‘Kawr Oases’ (0.5%) lie in the mountains, close to an unconform boundary between limestones and confining rocks. ‘Drainage Oases’ (0.3%) are the largest oases in northern Oman. They lie close to a drainage channel, which drains the entire area west of the mountains. Finally, ‘Urban Oases’ (1.7%) consist of parks and sporting facilities, which do not lie in conclusive hydrologic settings.
Remote Sensing of Environment.
