نشریه پژوهش های حفاظت آب و خاک
سال هفدهم شماره 3 (پاییز 1389)

The main aim of this study was to evaluate sensitivity of ET0 values estimated by Penman-Monteith FAO 56 (PMF-56) and Hargreaves (HG) models to the mean maximum (Tmax) and mean minimum air temperatures (Tmin) in humid regions of northern Iran. For this purpose, a 50-year meteorological quality controlled data from 6 synoptic stations were applied and their daily ET0 values were estimated by PMF-56 and HG methods for the same period. The average Tmax and Tmin values were then altered from 2 to 10 percents under various scenarios and the corresponding ET0 values were recalculated and compared with the initial ET0 values. The results showed that the maximum relative increase of ET0 values is observed in summer months by 10% increase in Tmax. In general, the sensitivity of both ET0 models to the maximum temperature was higher than minimum temperature. In contrast, a 10% increase in Tmin during summer months caused up to 7% drop in ET0. It is shown that in small temperature variations (less than 8%), the response of the ET0 models is linear. However, higher temperature variations (more than 10%) caused non-linear results. The comparison of HG and PMF-56 results revealed that the sensitivity of PMF-56 aerodynamic model to the Tmin and Tmax flactuations was more realistic than the HG model, because of considering outgoing long-wave radiation and vapor pressure deficit in PMF-56 model. The results indicated that the sensitivitiy of the HG and PMF-56 models to the temperature parameters depend on the geographical location and the season. When the effect of teleconnection events (ENSO, NAO, MJO) on ET0 variability is studied, the application of Hargreaves model is not recommended.

In order to prevent land degradation and soil and water pollution, realizing the respective processes and quantifying their relationships is unavoidable. Infiltration process is one of the most important components of the hydrological cycle. On the other hand, the direct measurement of infiltration process is laborious, time consuming and expensive. In this study, the possibility of predicting cumulative infiltration in specific time intervals, using readily available soil data and Pedotransfer Functions (PTFs) was investigated. For this purpose, 210 double ring infiltration data were collected from different regions of Iran. Soil texture ranged from loam to clay. Basic soil properties of the two upper pedogenic horizons including initial water content, bulk density, particle-size distributions, organic carbon, gravel content, CaCO3 percent and soil water contents at field capacity and permanent wilting point were determined on each soil sample. The parametric PTFs were then developed to predict the cumulative infiltration at times 5, 10, 15, 20, 30, 45, 60, 90, 120, 150, 180, 210, 240, 270 minutes after the start of the infiltration test and the time of basic infiltration rate, using the stepwise regression method. The results of reliability test indicated that all derived PTFs underestimated the cumulative infiltration. Also, the obtained RMSEs at small times were lower than those obtained at the ending times of the infiltration process. EF statistic had positive values and increased with time increasing. The EF values indicated that the efficiency of the derived PTFs improved during the time increasing. Also, developed PTFs had a mean RMSD of 6.90 cm in estimating the cumulative infiltration curve. Results indicated that at the 1% probability level, the estimated cumulative infiltration curve can be accepted as one of the replicates of a reliable infiltration test.

Qanat or Kariz is one of the most surprising collective works of human history that is used for water supply in water shortage regions in order to provide water for drinking, agriculture and livestock in these regions. One of the main problems of Qanat is permanent exit of water. Use of underground dams on Qanat could produce a new method as a solution for this problem. Thus Qanat water is stored in alluvium behind the dam and improve groundwater reservoir of Qanat. But using this technology requires comprehensive studies to determine the suitable site of underground dam construction on Qanat. In this research in order to determine the suitable sites of underground dam construction, a case study on Dahan Chenar Qanat in Kalat watershed of Gonabad is presented. At first the suitable span of Qanat that has initial conditions for underground dams construction is identified and determined. Then in every one of the length span determined suitable sites that have best conditions for construction of underground dams were proposed. At the final stage for all proposed sites the best point for underground dam construction on Qanat via Alluvial Capacity Index was determined. The results of this study showed from total 1000 m length of surveyed Qanat there are only 2 points for construction of underground dams that are the best point determined via Alluvial Capacity Index.

Quantity-intensity (Q/I) curves and their derived parameters provide general information about soil K availability. The present study was conducted to assess the potassium Q/I parameters including readily exchangeable K (∆Ko), equilibrium activity ratio (ARek), specific K sites (Kx), lineare potential buffering capacity (PBCk), energy of exchange of K (Ek) and their relationships with forms of potassium, clay mineralogy and the properties of 18 surface soils samples belonging to four main subgroups: Typic Endoaquepts, Fluventic Haploxerepts, Typic Calcixerepts and Typic Haploxerepts in the vineyard growing areas of Western Azarbaijan province. X-ray diffraction analysis showed that illite and chlorite were the dominate clay minerals. The ARek values ranged from 0.0014 to 0.019 (moles/L)0.5. The readily exchangeable K (∆Ko) varied from 0.020 to 0.85 (cmol/kg soil). The values of soil solution K (So-K), exchangeable K (Ex-K) and non exchangeable K (NEx-K) varied from 0.070 to 0.56, 0.42 to 1.4 and 0.2 to 2.6 (cmol/kg soil), respectively. There was highly significant positive relationship between NEx-K and illite contents (R2=0.82, P≤0.001). Significant positive correlation observed between PBCK and clay content (r=0.90, P≤0.001) and CEC (r=0.80, P≤0.001). The highest PBCK values were associated with the Typic Calcixerepts soils which had the greatest clay contents and CEC. The highest AReK value was observed in the Typic Calcixerepts soils with high values of exchange also solution potassium while the lowest values was observed in Typic Endoaquept soils with higher chlorite content in the clay fraction. The soils showed high capacities to maintain the potential of K against depletion, as they represented high potential buffering capacities (PBCk) [18-103 (cmolc/kg)/(mol/L)0.5]

Soil organic matters (SOM) like soil mineral components also play an important role in soil chemistry. Soils responses are affected by the type and quantity of SOM. Decomposition of SOM is the most important factor in the production of acids in soil, which cause weathering of clay minerals (main resource of NEK) and releasing NEK. Besides the NEK quantity, the rate of potassium release and its availability in plant growth period are significantly important. The experiment was carried out as a factorial in completely randomized design including two factors, with three replications. First factor included four dominant soil series of Golestan province and the second factor contained blank, removal of SOM through H2O2 and NaOCl treatments. The results showed that NaOCl removed more SOM than H2O2. This means that H2O2 has less ability in the removal of SOM. The rate of NEK release was determined in soils with and without SOM. Kinetic experiments results indicated that total quantity of NEK from the soils in all treatments was maximum in Aliabad series at the end of extraction. The rates of NEK release were minimum at blank in Kordkoy series and in both SOM removed treatments in Daland series. More K was released in all soils in H2O2 removed treatment; whereas less K was released in NaOCl treatment. Consequently, SOM has direct and indirect effects on the chemical forms of K quantity and its kinetic release.

Soil loss is commonly predicted using the revised universal soil loss equation (RUSLE) worldwide. Soil erodibility (K) is one of factors affecting soil loss essential to predict water erosion. In this study, soil loss was measured under 41 natural rainfall events at standard plots located in 36 different fallow lands with 9% slope in Hashtroud, a semi-arid region in the northwestern of Iran from March 2005 to March 2007. Soil erodibility factor (K) values were measured based on the soil loss per unit of rainfall-runoff erosivity factor (R) and also estimated on the basis of geometric mean diameter of soil particles (Dg) for 36 lands. Estimated K value (0.038703 t h MJ-1 mm-1) was on average 50.98 times higher than the measured value (0.000483 t h MJ-1 mm-1) in 36 lands. Regression analysis indicated that the measured K is significantly (P<0.001, R2=90) related to the aggregate stability and soil permeability. Relationship between the measured K value and easily-measurable soil properties (mineral particles, gravel, organic matter, lime and potassium) was analyzed. Results showed that the measured K value is significantly (P<0.001, R2=0.82) influenced by Dg, organic matted and lime. This study revealed that the aggregate stability and soil permeability are the two important dependent soil properties affecting soil erodibility (K), affected by mineral particles, organic matter and lime. Soil properties that increase the aggregate stability and permeability can decline the soil erodibility. Lime is one of the soil properties that has an important role in declining the soil erodibility in soils of the semi-arid regions.

Vegetation as one of the main effective factors in the flow resistance directly influence the flow velocity by increasing the surface roughness. The calculation of flow velocity in hydraulic, hydrology science and all water projects, particularly river engineering, flood control, also for hydraulic and hydrologic modeling is necessary. One of the methods used for determing the velocity of flow is using the manning equation. In this research, some field experiments have been carried out to simulate runoff flow on two slops in order to determine the effects of vegetation on manning roughness coefficient on the hillslope of Aghghala in Golestan province. These experiments have been done on two rectangular plots, with a width of 2 meters, length of 18 meters, on two different slops i.e. 4.1, 12.9 percent. The runoff was generated by pumping water out of a reservoir. The experiments were done firstly with vegetation and then the vegetation was removed from the plots and the experiments were repeated. Totally, these experiments were repeated 20 times. The slope, vegetation percentage, flow discharge rate for the hillslope were measured. Then, in each repetition, the flow velocity was calculated and also the hydraulic radius in 6 sections were determined. The manning roughness coefficient, with vegetation and without vegetation, determined using the manning equation for the two hillslopes was 0.0557, 0.0510 for low slope hill and 0.0652, 0.0564 for the high slope hill. After the calculation of manning coefficient of all repetitions, the T test results showed that the vegetation can significantly increase the roughness coefficient. The structure of the field experiments as well as the fact that sheet flow runoff and unsubmerged vegetation being the focus of the study were new in this research and there is no enough knowledge on them.

Selecting the designing rainfall is a basic step in many commonly used methods for estimation of design floods. Design rain that results in design flood has some characteristics such as time distribution of rainfall in rain period. In this research for derivation of time distribution of rainfall, the data of rain gauge station of Zabol station has been used. All severe rainstorms in each station is located in 1, 2, 3, 6, 9, 12, 14 hours duration. The Pilgrim method was used based on storms separation into four quarters and estimation of rainfall percentage for each quartile and ranking. By averaging ranks in each quartile, specifying index rank the final pattern of each time duration is obtained. To statistically evaluate the obtained patterns with durations of interest, Chi square test was used after establishing a contingency table. Based on Huff method, in every time duration based on this fact that in which quarter the maximum rain has happened, the first, second, third and fourth rainstorms were defined and the related charts with 10 to 90% probability were prepared. The result of two method comparisons shows that: The Pilgrim method is an easier and more expressive method than the Huff method and if suitable data are available, regardless of simplicity it is an accurate method. Comparison of Pilgrim temporal rainfall pattern with Huff, and fifty percent rainfall distribution probability curve, shows that the result of these two methods in every time distribution are the same pattern. The best design conditions of Huff probability curves in each quartile is to consider the first, second, third and forth quartile. In this condition determined curves will be more clear and accurate.

Freezing and thaw cycles that appear due to consistent decrease and increase of temperature in the short-term period are the important factors of damage to crop and garden plants in susceptible area. In this research to calculate the relative frequency of freezing and thaw cycles in the Khorasan Razavi province, the daily minimum and maximum temperatures of 9 synoptic stations were used over 20 statistic years (1989-2008). Also 6 distinct range of temperatures including: the minimum temperatures lower and equal to -2 and the maximum temperatures greater and equal to 2 (A), the minimum temperatures lower and equal to -3 and the maximum temperatures greater and equal to 3 (B), the minimum temperatures lower and equal to -5 and the maximum temperatures greater and equal to 5 (C), the minimum temperatures equal to -2 and the maximum temperatures greater than 2 (D), the minimum temperatures equal to -3 and the maximum temperatures greater than 3 (E) and the minimum temperatures equal to -5 and the maximum temperatures greater than 5 were presented. Following processing by a computer program in the FORTRAN space, the averages of monthly, seasonal and annual number of days with this phenomenon were calculated for each station and then the relative frequencies of monthly and seasonal were obtained. Results showed that, relative frequency of freezing and thaw cycles in winter is highest, but cold-season cereals and fruit trees show lower damage than spring and autumn seasons, because of cold acclimation phenomenon in this season. Monthly investigation showed that in October, the probability of damage to crop plants such as cotton or sugar beet in regions such as Sabzevar, Gonabad and Kashmar is less than regions such as Mashhad, Sarakhs and Neyshabur. In March and April, fruit trees may have faced with damage in Neyshabur, Torbat heydariye and Golmakan. Also in these months, early implant of cotton is risky in regions such as Sabzevar, Kashmar and Neyshabur.

Soil carbohydrate, particulate organic carbon and distribution of organic matter in different aggregate fractions are factors affecting soil structure. This study was initiated in a clayey soil in Javanmardi plain (East Lordegan, central Zagros) to evaluate 1) the influence of conversion of degraded pasture to cropland (wheat fields) on total organic carbon (TOC), particulate organic carbon (POC), total nitrogen (Nt), dilute acid extractable carbohydrate (CHda), hot water extractable carbohydrate (CHhw), and 2) the amount of TOC, Nt and CHda inside of aggregates. Soils of degraded pasture and cropland were sampled in two depths of 0-5 and 5-15 cm. The results showed that carbohydrates and POC represent 3.6-6.5% and 39-52% of TOC in soils, respectively. Conversion of degraded pasture to cropland resulted in an increase in TOC, POC, Nt, CHda, and CHhw contents. For the degraded pasture, the amount of TOC, N and CHda were significantly different in aggregate size classes, and appeared to increase as size increased from 0.05 to 1 mm diameter. Nonetheless, there was no clear relationship between the size of aggregates and organic matter content for cropland. The POC/TOC ratio was higher in cropland compared to the degraded pasture, reflecting the coarser nature of organic inputs under cultivation. In general, results indicated that the OC contents in the macroaggregates were higher than those in the microaggregates fractions. This may resemble that the factors controlling the stability or destruction of macroaggegates can control the OC stocks in soils too.

Potential evapotranspiration (ETp) rates are needed for irrigation scheduling. ETp rates are commonly estimated from weather parameters. The Fao-Penman Monteith, is now accepted for computation of ETp. This study examined the suitability of fuzzy logic for estimating daily potential evapotranspiration with grass reference crop compared with artificial neural networks, Fao-Penman Monteith and evapotranspiration pan. The daily climatic data of the Borojen station in Chaharmahale-Bakhtiari was used. The estimated ETp values from a fuzzy logic model using six input parameters resulted in RMSE=0.74 mm/day, R2=0.88 which has the highest correlation and the lowest error in comparison with other methods.