فصلنامه حفاظت منابع آب و خاک
سال سوم شماره 2 (پیاپی 10، زمستان 1392)

Leaf Area Index (LAI)، is a key component in estimating crop yield and environmental stresses. Given the importance of accurate determination of these parameters، the present study was aimed to estimate the LAI of rice plant. For this purpose، 20 paddy fields were selected. The data required to perform the operations in the study area were corrected by land impressions (direct method) and measured by AccuPAR (indirect method). Field work to gathering LAI were taken at intervals of 16 days from seedling stage to the flowering stage of rice plants. The results showed that the lowest and highest levels of LAI belongs to seedlings and flowering stages، respectively. The leaf area obtained by both methods، were almost the same for each farm during different stages of plant growth. Consistent with the obtained values by both methods، indicate that the index can be calculated from a derived empirical relationship. Based on this empirical formula for every stage of plant growth، weka3. 7 software was adopted to calculate the mentioned relationship.

Uneven distribution of precipitation in many arid and semi- arid regions like Iran، has led to water reserved for a reliable supply. Recently، large dam construction is more extended for water storage. Construction of the reservoir، while the high costs، it also has many environmental problems. Consecutive drought events have led to hedging rules is more considered by reservoirs operators. This study aimed to develop hedging policies for reducing stress during drought years through the water store before stress period. Therefore، Namroud storage dam river system was simulated using the MODSIM8. 1. After the calibration، hedging rule algorithm was coded in the model and it was run with and without hedging implementation. The system operation indices such as satisfaction، reliability، vulnerability، resiliency and sustainability of the system were calculated for two states. The results were shown that the developed hedging rule algorithm cause adjustment the big stress and uniformity distributed in operation period. With hedging rule implementation، reliability and system sustainability indices were increased 10 and 7 percent، respectively، and vulnerability and resiliency indices were decreased 18 and 9 percent respectively. These results were shown the indices were improved under hedging rule.

Soil hydraulic properties have important effects on describing water flow، solute and gass transports and also are important in hydrological studies. Although spectral information over visible near-infrared and shortwave infrared range، as a rapid، cost-effective and non-destructive method، has been recently applied to predict a number of soil properties، only few attempts have been conducted to predict soil hydraulic properties. The objective of this study was to assess whether inclusion of soil spectral data as a uniqe set of the predictors and alternative to basic soil properties would improve water retention predictions. Consequently، a number of 174 soil samples were taken and the spectral reflectances of the soils over 350 to 2500 nm range were measured، using a handheld spectroradiometer apparatus. The water retention at six matric potentials of -330، -1000، -3000، -5000، -10000 and -15000 cm were also measured by using preassure plate apparatus. Four scenarios including spectrotransfer functions (STFs)، pedotransfer functions (PTFs)، spectropedotransfer functions (SPTFs) and Rosetta PTFs were investigated. The transfer functions were first derived and compared with each other as well as with Rosetta PTFs afterwards. Based on the obtained results، basic soil properties and water retention parameters indicated high and significant (1% significancancy level) correlations with spectral reflectance values particularly in near and shortwave infrared ranges. The STFs indicated higher accuracy (R2>0. 60; RMSR<0. 011 cm3 cm-3) than the others especially at mid and dry end of retention curve. Although SPTFs and PTFs provided similar predictions، but PTFs were estimated narrowly better predictions at wet-end part of retention curve (-330 and -1000 cm). Weak predictions were obtained by Rosetta PTFs for all water contents particularly at the wet part of retention curve. These results suggest the efficacy of the spectral data، which can be used as an indirect method to predict soil water retention status.

Determination of soil fertility is very important to measure fertilization. Regardless of the level of soil fertility، the improper use of chemical fertilizers، not only the quantity and quality of agricultural products would not rise up، but also it makes imposed additional costs، disturb the balance of nutrients in the soil and environmental issues are also raised. Therefore، the assessment and mapping of soil fertility is essential. In this research، the fuzzy technique and the Analytic Hierarchy Process (AHP) were used for mapping soil fertility into Geographic Information System (GIS). The amount of available soil phosphorus and potassium، total nitrogen، soil organic carbon، pH and cation exchange capacity (CEC) obtained form 77 surface soil samples were used as the input data. In the first stage، the interpolation of data was done by Inverse Distance Weighting (IDW) model into GIS. Then a fuzzy membership function was defined for each factor according to Sys guideline. Finally، the map of soil fertility was prepared by using AHP technique into Expert Choice software with an inconsistency ratio of 0. 07. The results showed that soil organic carbon has the greatest impact on the soil fertility in the study area and for wheat cultivation، most area were classified into group of moderate suitable.

Identifying of effective parameters and planning for their management and coordinating agronomic operation with trend changes of effective parameters leads to improving production baseline and prediction for future. Plant growth and crop production under rainfed is a function of changes in climatic factors. In order to determination of climate-yield production functions، analyzed eight crop seasons data (1998-2006) of 25 climate parameters and rainfed barley grain yields of four cold and semi-cold regions of Lorestan province. These regions were including Aleshtar، Khoram-Abad، Aligodarz and Boroujerd. By path analysis method، correlation coefficient separated to direct and indirect effects. Results showed that in local and common models of production functions، the role of crop season vapor pressure deficit is very important. The local models necessary small input data but common model need more input data. Rain water productivity of all regions determined for eight crop seasons، and amounts of maximum، minimum and average of rain water productivity were 0. 3، 0. 15 and 0. 224 kg per cubic precipitation، which its average was 6 percent lower than national average (0. 239 kg. m-3). The maximum temperature، sunshine، absolute maximum temperature and crop season vapor pressure deficit parameters were the most sensitive parameters on grain yield prediction. We conducted the climate-yield models are useful tools to predict rainfed barley yield and so to assist managers and farmers for making decisions in rainfed agronomic activity under climate parameters changes.

Investigation on physical characteristics of suspended sediment is an important subject in river studies. The particle size distribution of the suspended sediment is one of these physical properties represents important links between sources and fluvial mechanisms in the watersheds. However، limited studies have been conducted in field of suspended sediment particle size distribution. The present study therefore aimed to investigate the particle size distribution of suspended sediments in Kojour River within the period of one year. Toward this attempt، 24 suspended sediment samples were collected at intervals of some 15 days. The particle size distribution was determined after necessary preparations by laser scattering particle size of HORIBA LA-950. The results showed that the suspended sediment diameter were in the range of 0. 82 to 353. 55 microns during time of sampling and in different conditions. Also، the silt particles with partial contribution of 97. 68 % had the largest contribution in the suspended sediment load. In addition، the results indicated that the precipitation and sand harvesting plays an important role in increasing the coarse particles of suspended sediment load.