Search

This paper demonstrated how a modeling approach can be used to find the optimal mix of farmers' water management practices to improve irrigation efficiency at the tertiary level in collective canal schemes. The approach is developed for the case of the Office du Niger and based on a field study of 3 years. First, a simulation model is presented in which all relevant physical and social aspects of water management at the farmers' level are considered. Next, simulations are performed to evaluate the impact on performance of different combinations of management practices and different external conditions. Finally, the combinations are selected that succeed in limiting seasonal water consumption to 1,400 mm and avoiding irrigation problems, but which are also realistic from a farmer's point of view. Results demonstrate that in the Office du Niger, where seasonal water consumption per hectare should be reduced by about 30%, a tight control of the tertiary intake in combination with a good maintenance of the tertiary canal should be proposed. Although the model software is built especially for the case of the Office du Niger, the concept of the model can be transferred to other irrigation schemes, as it uses only simple hydraulic principles and limited data input. DOI: 10.1061/(ASCE)0733-9437(2009)135:1(50) CE Database subject headings: Irrigation; Agriculture; Simulation models; Africa.

This paper presents a model to estimate the soil salinity for different on-farm management strategies under irrigated conditions. It is based on research in the Manitoba irrigation scheme in northeast Brazil, where upward flow from the shallow water table is the main cause of soil salinization. The model calculates soil water and salt balances for the topsoil. It is calibrated for the topsoil of abandoned plots and for the root zone (0.9 m) of mango trees. Simulating the effect of different management scenarios on soil salinity may help to organize the switch from intensive surface irrigation to more efficient irrigation practices. DOI: 10.1061/(ASCE)0733-9437(2005)131:4(351) CE Database subject headings: Irrigation systems; Irrigation efficiency; Saline ground water; Salinity; Simulation models; Water balance; Brazil.

The crop coefficient during the initial period ([K.sub.c ini]) varies with wetting frequency, evaporative demand, and water-holding capacity of the tipper soil layer. It is possible to develop a semitheoretical integrated function to predict the average [K.sub.c ini] representing the initial period of a growing season when the soil is mostly bare and that incorporates these three factors. The function is based on a two-stage evaporation function as used in the Food and Agriculture Organization Irrigation and Drainage Paper No. 56 (FAO-56) dual crop coefficient method. Parameters in the integrated equation are soil based and can be calculated a priori without field measurements. The procedure can be used to produce graphical figures similar to that introduced in FAO-24 for [K.sub.c ini]. Similar to FAO-24, the function utilizes the mean time between wetting events and reference evapotranspiration. In this paper, the development of the procedure and figures for [K.sub.c ini] are described. Comparisons with measured evaporation and [K.sub.c ini] in southern California indicate relatively good performance by the function without calibration. DOI: 10.1061/(ASCE)0733-9437(2005) 131:1(14) CE Database subject headings: Evapotranspiration; Crops; Evaporation; Soil water.

Crop coefficient curves provide simple, reproducible means to estimate crop evapotranspiration (ET) from weather-based reference ET values. The dual crop coefficient ([K.sub.c]) method of the Food and Agricultural Organization of the United States (FAO) Irrigation and Drainage Paper No. 56 (FAO-56) is intended to improve daily simulation of crop ET by considering separately the contribution of evaporation from soil. The dual method utilizes 'basal' crop coefficients representing ET from crops having a dry soil surface and separately predicts evaporation from bare soil based on a water balance of the soil surface layer. Three extensions to the evaporation calculation procedure are described here that are intended to improve accuracy when applications warrant the extra complexity. The first extension uses parallel water balances representing the portion of the soil surface wetted by irrigation and precipitation together and the portion wetted by precipitation alone. The second extension uses three 'stages' for surface drying and provides for application to deep cracking soils. The third extension predicts the extraction of the transpiration component from the soil surface layer. Sensitivity and analyses and illustrations indicate moderate sensitivity of daily calculated ET to application of the extensions. The dual [K.sub.c] procedure, although relatively simple computationally and structurally, estimates daily ET as measured by lysimeter relatively well for periods of bare soil and partial and full vegetation cover. DOI: 10.1061/(ASCE)0733-9437(2005) 131:1 (2) CE Database subject headings: Evapotranspiration; Evaporation; Crops; Crop moisture index; Soil water.

The current intensive use of agricultural land is affecting the land quality and contributes to climate change. Feeding the world's growing population under changing climatic conditions demands a global transition to more sustainable agricultural systems. This requires good insight in land cultivation practices at the field to global scale. This study outlines a spatially distributed version of the field-scale crop model AquaCrop version 6.1, to simulate agricultural biomass production and soil moisture variability over Europe at a relatively fine resolution of 30 arcseconds (~1 km). A highly efficient parallel processing system is implemented to run the model regionally with global meteorological input data from the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2), soil textural information from the Harmonized World Soil Database, version 1.2 (HWSDv1.2), and generic crop information. Daily crop biomass production is evaluated with the Copernicus Global Land Service dry matter productivity (CGLS-DMP) data. Surface soil moisture is compared against NASA Soil Moisture Active Passive surface soil moisture (SMAP-SSM) retrievals, the Copernicus Global Land Service surface soil moisture (CGLS-SSM) product derived from Sentinel-1, and in situ data from the International Soil Moisture Network (ISMN). Over central Europe, the regional AquaCrop model is able to capture the temporal variability in both biomass production and soil moisture, with a spatial mean correlation of 0.8 (CGLS-DMP), 0.74 (SMAP-SSM) and 0.52 (CGLS-SSM), respectively. The higher performance when evaluating with SMAP-SSM compared to Sentinel-1 CGLS-SSM is largely due to the lower quality of CGLS-SSM satellite retrievals under growing vegetation. The regional model further captures the interannual variability, with a mean anomaly correlation of 0.46 for daily biomass, and mean anomaly correlations of 0.65 (SMAP-SSM) and 0.50 (CGLS-SSM) for soil moisture. It is shown that soil textural characteristics and irrigated areas influence the model performance. Overall, the regional AquaCrop model proves to be useful in assessing crop production and soil moisture at various scales and could serve as a bridge between point-based and global models. [ABSTRACT FROM AUTHOR]