Showing 4 results for Soil Water Content
A. Majnooni-Heris, Sh. Zand - Parsa, A. R. Sepaskhah, A. A. Kamgar-Haghighi,
Volume 11, Issue 41 (10-2007)
Abstract
Optimal crop water requirement is needed for precise irrigation scheduling. Prediction of crop water requirements is a basic factor to achieve this goal. In this study, maize potential evapotranspiration (ETp) was prediced by maize simulation model (MSM). Then, it was evaluated and validated using experimental field data obtained in Agricultural Research Station of Shiraz University (Bajghah, Fars province) during 2003 and 2004. Comparison of measured volumetric soil water content with predicted values by MSM model in 2003 and 2004 indicated that this subroutine (prediction of maize evapotranspiration) did not need modification. Also, daily potential evapotranspiration of maize was estimated by using Penman-Monteith equation considering single and dual crop coefficients. Comparison between the results of predicted ETp by MSM model, calculated ETp by Penman-Monteith, and measured irrigation water and soil water content indicated that the prediction of ETp by MSM model was satisfactory. Model prediction of seasonal ETp, potential transpiration (Tp) and soil evaporation (E) were 831, 536 and 329 mm, respectively, in 2003, and 832, 518 and 314 mm, respectively, in 2004. The values of ETp, Tp and E calculated by Penman-Monteith method using dual crop coefficients were 693, 489 and 205 mm, respectively, in 2003, and 700, 487 and 213, respectively in 2004. Maximum rate of predicted potential ETp, Tp and E were 11.1, 8.2 and 5.1 mm d-1, respectively in 2003 and 13.0, 9.0 and 4.0 mm d-1, respectively in 2004. The values of calculated seasonal ETp by Penman-Monteith method using single crop coefficient were 615 and 632 mm in 2003, and 2004, respectively. Comparison between the results of predicted ETp by MSM model, calculated ETp by Penman-Monteith equation with single and dual crop coefficients (FAO-56) and measured values of irrigation water and soil water contents of root depth indicated that FAO-56 methods underestimated the ETp.
T. Honar, A. Sabet-Sarvestani, A. Sepaskhah, A. A. Kamgar-Haghighi1, Sh. Shams,
Volume 16, Issue 59 (4-2012)
Abstract
In recent years, simulatiom modelling of yield has been the focus of attention for many researchers. Because, while reducing adminestrative costs, it can easily provide simulation models of different situations. In this study, while a subroutine on simulation of canola was added to CRPSM model, effect of different water treatments on canola was also investigated. In this research, canola (Talaye) under 5 irrigation treatments (full irrigation treatment during the growing period, water stress treatment at the spring re-growth stage, the flowering stage and pod formation, the grain formation stage and dry land treatment) was sown in complete randomized block designs at the college of Agriculture, Shiraz University during 2007-2008, and then the model was calibrated based on available information (soil-location -plant-water). Review of statistical indicators between simulated and measured yield show high accuracy in the estimation of crop yield (R2=0.98) and soil water content. The result of model validation with independent data series also showed that the result of soil water content is desirable except in dry treatment, and the corrolation coeficient between simulated and measured crop yield (R2=0.98) was acceptable.
J. Asghari Meidani, E. Karimi, S. B. Mousavi,
Volume 16, Issue 60 (7-2012)
Abstract
This study was conducted to study and compare the effects of different tillage systems on soil physical properties and wheat yield in dryland conditions. The experiment was carried out in Maragheh Dryland Research Station with 5 treatments and 4 replications based on RCBD for 3 years (2001-2003). The results showed that difference between the treatments in terms of wheat yield was significant, and stubble chopping and chisel plow tillage in fall + sweep in spring + seed drill planting had the maximum yield (i.e. 1452 kg/ha), lower value for yield (1.077kg/ha) blonged to T1 treatment. Also the results showed that spike/plant and spike length were the main characters in yield increase. For the soil bulk density and water content, the difference between treatments was significant and in planting and flowering stages stubble chopping and chisel plow in fall + sweep in spring + planting by seed drill had the highest soil water content and the lowest bulk density
Sh. Zand-Parsa, S. Parvizi, A. R. Sepaskhah, A. A. Kamgar Haghighi,
Volume 22, Issue 1 (6-2018)
Abstract
In this study, the values of moisture and soil temperature were estimated at different depths and times under unsteady conditions by solving the Richards’ equation in an explicit finite difference method provided in Visual Studio C#. For the estimation of soil hydraulic parameters, including av and nv (coefficients of van Genuchten’s equation) and Ks (saturated hydraulic conductivity), soil moisture and temperature at different depths were measured by TDR probes and the stability apparatus, respectively. The objective function [equal to Root Mean Square Error (RMSE)] was minimized by the optimization of a parameter separately, using the Newton-Raphson method, while, the other parameters were considered as the constant values. Then, by replacing the optimized value of this parameter, the same was done for other parameters. The procedure of optimization was iterated until reaching minor changes to the objective function. The results showed that soil hydraulic parameters (coefficients of van Genuchten’s equation) could be optimized by using the SWCT (Soil Water Content and Temperature) model with measuring the soil water content at different depths and meteorological parameters including the minimum and maximum temperature,, air vapor pressure, rainfall and solar radiation. Finally, the measured values of soil moisture and temperature were compared to the depth of 70cm in spring, summer, and autumn of 2015. The values of the normalized RMSE of soil water content were 0.090, 0.096 and 0.056 at the soil depths of 5, 35 and 70 cm, respectively, while the values of the normalized RSME of soil temperatures were 2.000, 1.175 and 1.5 oC at these depths, respectively. In this research, the values of soil hydraulic parameters were compared with other previous models in a wider range of soil moisture varying from saturation to air dry condition, as more preferred in soil researches.
