Akio Tada

Estimation of crop water requirements in arid region using Penman–Monteith equation with derived crop coefficients: a case study on Acala cotton in Sudan Gezira irrigated scheme

The recommended Penman‐Monteith reference crop evapotranspiration (ET0) with derived crop coefficients (Kc) from the phenomenological stages of Acala cotton is used to estimate the crop water requirements (CWRs) of Acala cotton in the Gezira area of Sudan. The published basal crop factors of Acala cotton were used with Penman‐Monteith equation as well to estimate ET. The results were compared with the current practice that uses Penman evaporation (E0) from free water surface and crop factors (Kf) derived by Farbrother [Farbrother, H.G., 1970. Irrigation practices on Gezira clay-rates and intervals. Gezira miscellaneous paper no. 94. Gezira Research Station, Wad Medani, Sudan] and still in use in Sudan. The two methods were compared with the actual ET of Acala cotton measured by Fadl [Fadl, O.A., 1987. Water use of Acala cotton. Annual report 1978‐1979. Gezira Research Station, Wad Medani, Sudan, pp. 143‐147]. Penman‐Monteith equation was found to be better than Farbrother method in terms of the total predicted CWR, coefficient of determination (r 2 ), the slope of the linear regression line and the standard error of estimate with both basal and derived (Kc) values. The trends of weather examined for the period 1966‐1993 showed an increasing ET0 during the rainy season due to the recent drought conditions that prevailed in the region. Care must be taken when predicting CWR during such period. # 2000 Elsevier Science B.V. All rights reserved.

Direct Observation Of Soil Water Movement Through Soil Macropores Using Soft X-rays And Stereographing

Water movement in soil was observed directly and recorded on videotape using soft X-ray technology with a liquid contrast agent and on continuous photos. The movement of soil water occurred in an Andosol sample, and quantitative analyses were carried out by image processing. The results shown here are:The fluids flowing in tubular macro pores connected with each other. The flow showed spatial motion in which the tubular pores were sometimes swollen. Soil water moved into small pores like a volcanic explosion and also moved, worm-like, according to the shape of the tubular pores. Soil water movement occurred only in some tubular pores. In most cases, soil water was not detected in the pores.The spatial structures of macropores shown in three-dimensional graphics were drawn from stereo-radiographs, based on the observation of the spatial contribution of soil pore structures and the calculation of their actual length and tortuousity.Applying Darcy’s law, various permeabilities (K2, K3, K4) of the soil were calculated using the diameters of the dominant macropores and actual velocities. The permeability was compared with the permeability (K1) tested independently by the constant head method. Differences among K1, K2, K3 and K4 were not significant.The validity of Darcy’s law was tested using the constant head tank at different heads and samples. Results show that the validity of Darcy’s law was not confirmed.The Reynolds number was calculated using the actual diameter of the tubular pores and velocities of the agent measured by the stereo-graph obtained by the video. The flow seemed to be transitional between laminar and turbulent.

Satellite-Based Mapping of Cultivated Area in Gash Delta Spate Irrigation System, Sudan

In this study, a simple methodology for mapping the seasonal cultivated area of the Gash Delta Spate Irrigation System based on satellite images was developed. The methodology combined information from multiple bands to characterize the land surface in terms of spectral indices (e.g., Normalized Difference Vegetation Index (NDVI), and surface temperature (Ts)). Visual interpretations of a conveniently selected image were undertaken to identify and select sample points of interest. The NDVI and Ts values (computed from multi-date images that represented the crop growing period) of the sample points were used to developed typical NDVI and Ts plots. By analyzing these plots and the cropping calendar, an NDVI and Ts threshold-based algorithm was developed to extract the cultivated area of a given season. Analysis of the developed algorithm showed that it was simple, easily modifiable, and had interpretable rules and threshold values. Comparing the extracted cultivated area with the field report area showed a promising application of the methodology to map and estimate the cultivated area from only remote sensing data.