JWSS - Journal of Water and Soil Science

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Iran with a cultivation area of 45000 ha and production of 150 ton/year is the number one saffron producer in the world. Planting of large size corms will increase flowering, but production of corms (number and size) may be affected by irrigation method or frequency. In this research which is performed in the farm of College of Agriculture, Shiraz University, the effects of method and frequency of irrigation on corm production, and the effect of produced corms on flowering were evaluated in two consecutive years. Two irrigation methods (basin and furrow) with four levels of irrigation frequencies (12, 24 and 36 days and dryland farming) were applied. In August of 2000 sample corm was taken from every plot, and the effect of applied treatment from previous growing period on corm production and the effect of produced corms on future flowering were evaluated and analyzed. Based on the results, in furrow irrigation, total number of corms and total number of corms smaller than 4 gr is significantly higher than basin irrigation. In all of the above cases, irrigation frequencies did not show a meaningful difference between themselves or in comparison with dryland farming treatment. Total weight of corms and number and weight of corms larger than 8 gr in basin irrigation were more than furrow irrigation. This is to the extent that it is considered as the main reason for the difference in the flowering of corms, and has caused the flowering of basin irrigation to be significantly higher than furrow irrigation. In basin irrigation, irrigation frequencies of 12 and 24 days had the highest amount of flowering. No significant difference was observed on average corm production between the treatments in the two irrigation methods. However, irrigation treatments in both irrigation methods showed significant differences when compared with dryland farming treatment. So, basin irrigation with irrigation frequency of 24 days is preferred over furrow irrigation due to lower water consumption and production of larger size corms which is effective in flowering.

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In the present research, for the development of Fars province minimum temperature atlas, minimum daily temperature data of 20 evaporative stations of Fars Regional Water Organization and five synoptic stations of Fars Meteorological Organization were used. At first, two starting times were selected for all of the stations. The first was the first day of Farvardin for analyzing the spring frost and the secend was the first day of Mehr for analyzing the autumn and winter frost. Also, the temperature range of 0 to –1.5 was classified as mild frost or freeze, the temperature range of -1.5 to –3 as the moderate frost or freeze and temperature below –3 as severe frost or freeze. The data of minimum temperatures, the first and the last days in which the three temperature ranges occurred and the day of the lowest temperature based on the two starting times were recorded. The selected number of days (dates) were fitted to the distribution functions by SMADA software and the best distribution function was identified using the statistical parameter Root Mean Square. The best fitted distribution functions were Pearson type III and log Pearson type III. Then, based on the fitted distribution function, the number of days for the occurrence of the first and last frost and number of days for the occurrence of the first lowest temperature were determined at 50 and 70% probability levels. Finally, each of these occurrence dates was plotted with Surfer software using the geographical positions of each station (longitude and latitude) for Fars province. Based on these plotted maps, the best days of planting and harvesting of the crops can be determined throughout the Fars province.

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Agricultural investigations use computer models for simulation of crop growth and field water management. By using these models, the effects of plant growth parameters on crop yields are simulated, hence, the experimental costs are reduced. In this paper, the model of MSM (Maize Simulation Model) was calibrated and validated for the prediction of maize forage production at Agricultural College, Shiraz University in 1382 and 1383 by using maize forage yield under furrow irrigation with four irrigation and three nitrogen treatments. Irrigation treatments were I4, I3, I2, and I1, with the depth of water 20% greater than, equal to, 20% and 40% less than potential crop water requirements, respectively. Nitrogen treatments were N3, N2, and N1, with the application of N as urea equal to 300, 150, and 0 kg N ha^-1, respectively. After calibration and validation of MSM, it was used to estimate suitable planting dates, forage yield and net requirement of water discharge for planting at different dates. The results indicated that the net requirement of water discharge was reduced by gradual planting at different planting dates. By considering different planting dates for maize, from Ordibehest 20th to Tir 10th, the planting area might be increased 17.9%, compared with single planting date on Ordibehesht 30th under a given farm water discharge and full irrigation.

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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 (ET_p) 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 ET_p by MSM model, calculated ET_p by Penman-Monteith, and measured irrigation water and soil water content indicated that the prediction of ET_p by MSM model was satisfactory. Model prediction of seasonal ET_p, potential transpiration (T_p) 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 ET_p, T_p 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 ET_p, 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 ET_p by Penman-Monteith method using single crop coefficient were 615 and 632 mm in 2003, and 2004, respectively. Comparison between the results of predicted ET_p by MSM model, calculated ET_p 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 ET_p.

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Many experiments have been carried out to decrease the negative effect of drought stress and obtain suitable growth under water deficit conditions. Application of plant growth regulators (especially growth retardants) is one of the proposed methods. This study was conducted to investigate the effect of Cycocel application on growth of two olive cultivars (Shengeh and Roghani) under water stress condition. The design of experiment was completely randomized with six replications (Factorial arrangement). Treatments included irrigation intervals (2, 4, 6, 8 weeks) and Cycocel concentrations (0, 500,1000,2000,4000 mg per litter). Some indices such as height, chlorophyll, leaf area, root, and shoot weight (fresh and dry) were measured. Results indicated that interaction of C.C.C treatment and irrigation intervals on height of olive cultivars was not significant, probably due to the response of these cultivars to concentrations of C.C.C. Although drought stress decreased the number of leaves in both cultivars, the application of CCC (500 mg per litter) thwarted the adverse effects of drought stress. Cycocel increased chlorophyll content significantly (500 mg per litter in Roghani and Shengeh and 6 weeks irrigation interval). Cycocel application decreased leaf area, but in Shengeh cultivar increased leaf area in 6 week irrigation interval. Overall, the results indicated that the application of Cycocel with concentration of 500 mg per litter in 6 week irrigation intervals in both cultivars (Roghani and Shengeh) was the best treatment for controlling the adverse effects of drought. Also, results indicated that such changes were dependent on Cycocel concentration and drought level.

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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.

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In the present research, the performances of six empirical models, i.e., simple threshold exceedance, fixed proportion exceedance, quadratic function of storage, power function of storage, cubic function of storage, and exponential function of storage were investigated for estimation of groundwater potential recharge in a semi-arid region. First, the FAO Dual Crop procedure was used to calibrate evaporation from bare soil during the occurrence of potential recharge period. Then, the empirical models were calibrated utilizing soil moisture and potential recharge data. For validation of empirical models, soil moisture and potential recharge were simultaneously estimated for an independent event. Results indicated that 5 of the six models (except for the simple threshold exceedance model) were able to estimate potential recharge with a reasonable accuracy, showing the maximum computed value of NRMSE (Normalized Root Mean Square Errors) of 24.4 percent. According to validation results, exponential, cubic, and power function models provided better estimation of potential recharge in comparison with the linear models. Also, all of the applied empirical models were able to simulate soil moisture during the recharge period with an acceptable accuracy. Finally, the exponential model with minimum NRMSE value for soil water simulation and also acceptable performance of potential recharge estimation was recommended for estimation of potential recharge in the study area.

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