Journal of Water Research in Agriculture
Year:2010 | Volume:24 | Issue:1|Papers Count:7

Hydraulic conductivity (K) of unsaturated and saturated soils and the pore size distribution parameter (Gardner a) are important hydraulic parameters for understanding some aspects of unsaturated soil water flow. These parameters vary with time as well as spatial position. For To investigate these changes, field measurements were performed using disc infiltrometer at matric potentials of -15, -10, -6, -4, -3, and 0 cm water were in three times periods from June to August in 2009. The measurements were made in four fields under different land uses as including winter barley, silage single cross corn, apple orchard, and uncultivated land in the agricultural fields of Urmia University, Iran. Five replicate sequences of infiltration rate tests were conducted for each measurement set and land use. Soil texture at these sites was classified as clay. The study was conducted employing split plot in time experiment. Results of ANOVA showed that land use, time period, and their interaction had significant impact (at one per cent level) on K values (except at matric potential of -15 cm). At matric potential of -15 cm, the average K displayed significant variation (at five per cent level). Therefore, land use and time period showed the least impact on K15. Values of Gardner a had significant differences (at one per cent level) with respect to land use and time, but showed no significant difference (at five per cent level) with respect to their interaction. Results of this study showed that the initial soil moisture had an important role on the rate of temporal variation of soil k.

To evaluate seven equations for computing evapotranspiration over a grass reference crop (ETo)., this experiment was carried out in a greenhouse at the a the Plant Pathology Research Institute located in Tehran, Iran (latitude 35 41 N, altitude 51 19 E; 1190.8 meter above sea level). Meteorological parameters (solar radiation, air temperature, air humidity and wind speed) were recorded manually on a daily basis in order to calculate evapotranspiration. Additionally, one microlysimeter were was installed inside the greenhouse to measure grass reference evapotranspiration. Results indicated that there was a reasonable correlation between ETo values measured by microlysimeter and that estimated by FAO-Penman-Monteith equation with a root mean square error and coefficient of determination of 1.39 mm.d-1 and 0.69, respectively. In comparison, the relationship between ETo values measured by Microlysimeter and that estimated by Belaney-Ceriddle equation was the weakest, with a root mean square error and coefficient of determination of 1.54 mm.d-1 and 0.49, respectively. In addition, by using a small evaporation pan in during the study, pan coefficient was found to be 0.4562, with a coefficient of determination was of 0.82.

High evaporation, insufficient and non-uniform rainfall, and traditional irrigation methods are the most important limiting factors for the agricultural development in Bushehr Province in southern Iran, wich has the third rank of date production in Iran. Therefore, to prevent irrigation water loss, application of pressurized irrigation methods and accurate determination of water requirements for irrigation schedueling seem necessary. In order to determinate irrigation water requirements for drip-irrigated date palms (Kabkab cv) in bearing in Bushehr Province, a study was conducted using randomized complete blocks design with 4 levels of calculated irrigation water based on Class A pan evaporation ( 100%, 80%, 60% and 40%) with three replications during 4 years (2003-2007 ). Irrigation interval was based on 20mm evaporation from a class a pan and the amounts of applied water were measured by a water meter. According to the results, higher water consumption was associated with higher fruit yield and lower WUE. However, there was not any significant yield reduction in the treatment that received 80% of the calculated irrigation water. Also, irrigation treatments of 80% and 40% did not have significantly different effects on WUE and irrigation treatments had no significant effects on the quality parameters of the fresh fruit such as pH and TSS. Therefore, in conditions similar to the experimental site, for achieving an average fruit yield of 29.68 kg/tree and WUE of 0.62kg/m3, the seasonal water consumpion is recommended at the rate of 7535.6 m3/ha.

To study the effects of irrigation treatments on yield, water use efficiency (WUE), and quality characteristics of bread wheat, an experiment was conducted based on randomized complete blocks as a split plot design with 4 replicates, at the experimental farm of Agricultural and Natural Resources Research Center of Yazd, during 2006-2007. The main plots were allocated to four irrigation frequencies (8, 10, 12 and 14 days) and the sub plots were planted to four bread wheat cultivars (Backcross Roshan, Sistan, WS-9 and Pishtaz). The results indicated that the irrigation intervals and cultivars had significant effect (P<0.01) on grain yield, WUE, grain protein, and grain wet gluten. Also, interaction between treatments had significant effects on grain yield, WUE and grain wet gluten (P<0.01), but not on grain protein. The highest average grain yield and WUE were produced in 8-day irrigation interval (and were, respectively, 3258 kg/ha and 0/.65 kg/m3), However, 14-day irrigation frequency had the highest grain protein content at at 17/.28% followed by WS-9 cultivar (16/.67%). The latter cultivar contained the highest grain wet gluten equal to 53/.08%. Under 8-day irrigation treatment, Sistan cultivar produced the maximum grain yield (3875 kg/ha) and WUE (0/.77 kg/m3). The greatest percent of grain protein belonged to WS-9 cultivar under 14-day irrigation frequency (17/.79 %), while Sistan cultivar under the same irrigation had the maximum percent of grain wet gluten (55.42 %). The results of the experiment indicated that 8-day and 14-day irrigation intervals were favourable irrigation frequencies for production of the maximum grain yield and quality, respectively. Finally, based on the results, various varieties are suggested and for different production aims or irrigation management.

In order to determine the effect of deficit irrigation on yield and water use efficiency of forage sorghum, this research was carried out in a randomized complete block design and a split plot arrangement with three replicates at Zahak Researh Station in Zabol, Iran, during 2004 and 2005 growing seasons. Basin and furrow methods were in the main plot and irrigation amounts consisting of T1=100%, T2=80%, and T3=60% of the crop water requirement were in the subplots. The combined results of the two-year experiment showed that the effect of irrigation methods was not significant, while irrigation amounts showed a significant effect on dry matter, at %1 probability level. The maximum yield was 22.18 t/ha and was obtained in furrow irrigation with T2 treatment. The interaction effect of irrigation method and amount of water applied on dry yield was significant at %1 probability level. However, there was no significant difference between different treatments of irrigation methods and irrigation amounts regarding fresh forage yield, at %5 probability level. But, the maximum fresh forage obtained was 105.6 t/ha and belonged to furrow irrigation with T1. The maximum and minimum water use efficiencies were obtained in basin irrigation method with T3 and T1 and were, respectively, 1.78 kg/m3 and 1.21 kg/m3.

Unsaturated soil hydraulic conductivity is an important soil hydraulic property that is widely used in the studies of water and solute transport in soils. However, its direct measurement is time consuming and expensive. In order to study pore connectivity factor (l) in the Burdine-Brooks-Corey Model (BBC), 59 soil samples from the GRIZZLY database were used in a sensitity avalysis to determine sensitive parameters of this model. To study pore connectivity factor, its different values e.g., 3, 2, 1, 0.5, 0, -0.5, -1 and results of sensitivity analysis showed that BBC model was more sensitive to the saturated water content and pore size distribution index than to pore connectivity factor and saturated hydraulic conductivity. The statistical parameters, e.g., sum of absolute error (SAE), root mean square error (RMSE), Akaike’s information criterion (AIC) and concordance correlation coefficient (rc) calculated in the estimation of unsaturated hydraulic conductivity indicated that the BBC model error with l=2 is was less than the other values. The results also showed that pore connectivity factor was linearly correlated with the power of BBC model with goodness of fit R2=0.96. Based on this approach, pore connectivity factor was removed from BBC model and a new empirical equation was developed to estimate unsaturated hydraulic conductivity. This model was verified using 33 samples of the UNSODA database. The results showed that the developed empirical equation estimated unsaturated hydraulic conductivity better than BBC model, in which pore connectivity factor was assumed to be equal to 2.

In this research, the effects of water stress on qualitative properties of winter wheat and potato were investigated in Shahrekord. For wheat, a completely randomized design, consisting of 9 irrigation treatments and 4 replications, was conducted at the Experimental Farm of Shahrekord University, on a sandy loam soil texture. The irrigation time was determined based on 50% depletion of soil water content in the full irrigation treatment. Depth of irrigation in this treatment was calculated based on the difference between water content at the time of irrigation and its amount at field capacity. For the other treatments, depths of irrigations were calculated by multiplying a coefficient by the depth of irrigation in the full irrigation treatment. This coefficient was more than one for T1 and T2 and less than one for the other treatments. Thus, T1 and T2 treatments were over-irrigated, T3 had full irrigation, and the other treatments were under different levels of deficit irrigation. The results showed that the effect of deficit irrigation on qualitative properties of winter wheat, consisting of percentage of starch, protein, and amylose, were not significant. In the case of potato, the alternate furrow irrigation method was applied. A randomized complete block design experiment, with three irrigation treatments and four replications, was conducted on potato at the Agricultural Research Center, Shahrekord. The irrigation treatments were: normal furrow irrigation (N), fixed alternate furrow irrigation (F) and variable alternate furrow irrigation (V). The frequency of irrigation was constant and its depth was calculated based on measurement of soil moisture, with the alternate furrow treatments receiving half of the water applied to the N treatment. After harvesting, starch and protein content were measured for each plot. Compared with the N treatment, the alternate furrow irrigation decreased the starch content significantly, while the V treatment increased the starch content significantly compared to the F treatment. There was no significant difference between the protein contents in the three treatments.