h.a. alizadeh

Water and nitrogen are the main limiting factors affecting agricultural production in arid and semiarid regions. Therefore, improving the efficiency of these factors is very important. The method of fertilizer application is affecting water and fertilizer use efficiency. The objective of this study was to investigate the effect of furrow fertigation on fertilizer use efficiency (FUE), water use efficiency (WUE), and corn yield. A field experiment was carried out in furrows which have 165m length and 0.006 (m/m) slope in Karaj. The corn Hybrid 370 double-cross was planted on June 2008. A factorial design based on randomized complete block design with 4 replicates. Four levels (0, 60, 80 and 100%) of the recommended fertilizer value and four levels (60, 80, 100, and 120%) of the irrigation water requirement were applied. These 16 treatments were compared with traditional fertilizer application method. Fertilizer treatments were accomplished in four critical stages of the growth (before cultivation, in seven leaves stage, shooting stage and Flowering stage) for fertigation treatments and two stages (before cultivation and seven leaves stage) for the traditional method. Results showed that effects of levels of different water and fertilizer on yield component were significant. Water use efficiency (WUE) was significantly affected by nitrogen rate. On the other hand, water treatments significantly affected fertilizer use efficiency. Increasing fertilizer increased water use efficiency. Increasing water levels to 100% of ETC resulted in increasing fertilizer use efficiency. Highest yield was obtained from the full irrigation treatments (W100%). Albeit the difference among W120%, W100% and W80% was not significant (P=0.05), because W100% was always higher than W120%, treatment of W80% recommends as optimum water level for arid and semi arid region. The maximum and minimum WUE was 2.24 and 0.66 (kg/m3) in W80%N100% and W100%N60%, and The maximum and minimum FUE was 29.85 and 8.52 (kg/kg) in W100%N100% and traditional method, respectively.

Use of deficit irrigation to conserve water by minimizing leaching fraction during an irrigation season, or even across several irrigation seasons causes salt accumulate within the root zone. Naturally, salinization of the root zone is exacerbated when marginal waters are used. In this situation plants are experiencing simultaneously drought and salinity stress. Various mathematical models are exist for plants response to combined drought and salinity stress and its corporation in water uptake. The reduction functions are classified as additive, multiplicative and non coseptive models. Because transpiration is the largest component of the water budget in arid systems, the efficacy of models to simulate water and salt movement is depended on their ability to predict transpiration. In this study six different macroscopic reduction functions; Van Genuchten (additive and multiplicative), Dirksen et al., Van Dam et al, Skaggs et al and Homaee were evaluated in greenhouse condition using tomato data were exerted. This experiment was performed based on completely randomized design with three replicates and eight levels of salinity (0.75, 1.5, 2.5, 3.5, 4.5, 6, 8 and 10 dS/m) .Drought levels carry out as matrix potential during the experiment. The result of this study indicated that without salinity stress, all reduction function have a good agreement with measured data. Also, The result of this study indicated that the crop response to drought and salinity stress is additive low salinity level and is multiplicative at salinity level above 3.5 dS/m. among multi model, reduction function of Skaggs et al and Homaee's models were better fitness to measured data than the other functions.

Determining saturated hydraulic conductivity (Ks) is one of the important soil characteristics that its estimation is important in soil and water studies. There are several methods for estimating Ks in unsaturated conditions. These methods include the inversed-auger-hole method, the double-ring infiltrometer and the single-ring pressure infiltrometer. The measurement of Ks by these methods requires large volumes of water and long period of time. The Simplified Falling Head (SFH) technique is for rapid determination of Ks, using small volumes of water and easily transportable equipments. The SFH technique appears hopeful and suitable for detailed and repeated sampling, also, over large areas. In this study, Ks was measured by SFH method, double-ring and single-ring pressure infiltrometers for evaluating SFH method. Results showed that in a loam soil, the SFH method estimate higher values for Ks, compared with the double-ring and the single-ring pressure infiltrometers (respectively 9.6% and 18.5%). Statistical analysis of the results of above methods showed that there is no significant difference between Ks values (P