The soil organic carbon (SOC) plays a vital role in plant growth and development, and therefore is considered as one of the most important indicators of soil quality. This study was carried out in the central region of Saudi Arabia to explore the potential of spectroscopy in determining the SOC concentration in low-fertility soils. Spectral reflectance data were collected, under the controlled laboratory conditions on 39 air-dried 2.0 mm sieved soil samples, using a handheld spectroradiometer of a wavelength range between 350 nm and 2500 nm in the direct contact probe mode. The concentration of the SOC was determined using the Walkley and Black (W&B) and the UV-VIS spectrophotometric methods. The increase in the concentration of SOC was associated with a decrease in the corresponding spectral reflectance. Regression analysis showed linear relationships with high significant correlation between the spectral reflectance and the SOC measured by both the UV-VIS (Model-1: R 2 =0.46, p=0.00015 and RMSE=6.6 g/kg) and the W&B (Model-2: R 2 =0.48, p=8.92E-05 and RMSE= 2.8 g/kg) methods. For these models, two wavebands with wavelengths of 2167 nm (Model-1) and 1359 nm (Model-2) were identified as the most sensitive bands to the SOC concentration. The cross-validation confirmed the validity of Model-1 with R 2 , p and RMSE values of 0.50, 0.0099 and 6.6 g/kg, respectively. The validation results of the Model-2 showed values of R 2 , p and RMSE of 0.72, 0.00023 and 4.0 g/kg, respectively. Results of this study revealed the possibility and the potential of using the spectral reflectance technique in predicting the concentration of SOC.
Maintaining the homogeneity of soil nitrogen (N) and plant vigor across agricultural fields is a major concern for farmers and agricultural scheme planners, particularly fields that are irrigated through pressurized systems, such as center pivots. Therefore, this study was carried out on a 30 hm 2 potato field located 650 km south of Riyadh, the capital city of the Kingdom of Saudi Arabia, to investigate the impacts of the center pivot irrigation distribution uniformity on the crop development and the spatial distribution of residual soil N. Irrigation performance test was designed to investigate water application rate and distribution uniformities. The overall water application uniformity coefficients (Cu), determined through Christiansen (Cud) and Heerman (CuH) methods, were determined at 81.29% and 80.64%, respectively. However, the overall water distribution uniformity (Du) was determined at 70%. A considerable variability in the distribution uniformity of irrigation water was observed across the experimental field (a Du value of 67% over the medium spans compared to a Du value of 88% over the inner spans). Results of this study showed a linear correlation between the irrigation water distribution uniformity and the soil N (R 2 = 0 .88). On the other hand, the vegetation cover distribution, indicated by the Cumulative Normalized Difference Vegetation Index (CNDVI), was not found to be much responsive to the irrigation distribution uniformity (R 2 = 0 .11). A time series of successive NDVI maps extracted throughout the potato crop growth stages showed a consistent trend in the distribution of NDVI across the field, with R 2 values that ranged between 0.25-0.73.
Background:In the developing countries, Tuberculosis is one of leading causes of morbidity and mortality. The detection and identification of Mycobacterium tuberculosis is considered a great challenge for clinical microbiologists. Albeit Ziehl-Neelsen (ZN) smear is being a rapid diagnostic tool for TB, the culture on Lowenstein Jensen (LJ) medium is considered the golden diagnostic tool for TB in the developing countries.Objectives: To evaluate the validity and reliability of ZN smear of acid-fast bacilli compared to the culture on LJ medium.
Patients and methods:The retrospective analytic comparative cross-sectional study included patients visiting TB OPD clinic at NCDC, including transferred patients from other healthcare facilities and hospitals. A total of 2783 specimen of suspected pulmonary TB cases were processed for both direct smear and culture. The direct smears were stained with ZN method (1% Carbolfuchsin, 3% Hydrochloric acid Ethanol and 0.1% methylene blue). Specimens were observed under 100-x oil immersion lens, whilst cultures were inoculated on LJ medium after digestion and decontamination of the clinical specimens.Results: Of total 2783 study subjects, 203 (7.29%) were smear positive while 327 (11.74%) were culture positive. Out of 203 smear positive pulmonary cases, 154 (47.094%) were found to be positive on LJ culture. A total of 2407 pulmonary cases were negative on the smear and LJ culture for Mycobacterium tuberculosis.Conclusion: This preliminary study indicated the low sensitivity of sputum smear direct microscopy for early diagnosis of TB, while culture on LJ remains the golden standard modality.
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