فصلنامه تحقیقات مهندسی کشاورزی
سال پانزدهم شماره 2 (تابستان 1393)

Subsurface drip irrigation can increase irrigation and water use efficiency. This irrigation method distributes water into the soil, leaving the surface of the soil dry and decreasing evaporation. In the design of subsurface drip irrigation (SDI) systems, the dimensions of the wetted onion determine the installation depth and spacing of the drippers. Several models have been developed to simulate soil moisture patterns and the wetting front using soil hydraulic parameters, emitter discharge rate and volume of water discharged. The present study used the powerful numerical model HYDRUS-2D and dimensional analysis, which requires fewer parameters to predict the wetted zone using the empirical method. The predicted values for wetting depth (upward, downward) and horizontal dimensions were compared with those obtained by laboratory testing conducted in loamy soil at 40 cm in depth. R2 varied from 0.88 to 0.97 for HYDRUS-2D and 0.94 to 0.98 for the empirical model. The results showed that the simulated andexperimental results were in very good agreement and that the empirical model better predicted the dimensions of the wetted onion.

The effective parameters of the present study on wheat yield were the optimum use of residue and water. The effects of residue management and post-irrigation methods on raised bed planting systems were evaluated for irrigated wheat. This study was a split-block design with three replications. The levels of residue management considered as main plots were burned straw (B), partial removal of straw + stalk shredder (R), and partial removal of straw + stalk shredder + moldboard plowing (RP). The effects of delayof post-irrigation was measured at 7 d (I7), 14 d (I14), and 21 d (I21) after planting for the sub-plots. The soil cone index, moisture content, percentage of plant emergence, percentage of surface residue cover, weight of 1000 kernels, water use, and wheat yield were measured. The results indicated that treatment RP decreased the cone index 18.8%, plant emergence 7%, surface residue cover 63%, and water use 5%, and increased organic matter 3.5%, wheat yield 5%, and water use efficiency based on wheat yield 11.3% compared to treatment B. The results also showed that timing of post-irrigation had no significant effect on wheat yield. This indicates that post-irrigation can be delayed until 21 d after planting, which effectively eliminates the need for post-irrigation.

Near-infrared spectroscopy (NIRS) combined with chemometric methods of spectral pre-processing and multivariate modeling is popular non-destructive method for measuring quality attributes of fruits and vegetables. The present study investigated the feasibility of reflectance NIRS in a spectral range of 930 1650 nm for non-destructive prediction of soluble solids content (SSC) and titratable acidity (TA) in Thomson oranges. The effect of spectral pre-processing methods on the accuracy of multivariate predictor models was also assessed. Partial least squares (PLS) multivariate calibration models were developed using the reference measurements and pre-processed spectra. The following methods were used: smoothing (moving average (MA), Savitzky-Golay (SG), wavelet transform (WT)); normalizing (multiplicative scatter correction (MSC), standard normal variate (SNV)); and increasing the spectral resolution (the first and second derivatives (D1, D2)) to predict the SSC and TA of oranges. The results indicate that reflectance NIRS plus chemometrics gives the potential for non-destructive prediction of SSC and TA in oranges. Preprocessing methods directly affected the results of the PLS models. The best prediction results for SSC (RMSEC = 0.430, rc = 0.923, RMSEP = 0.451, rp = 0.936, SDR = 2.798) and TA (RMSEC = 0.133, rc = 0.883, RMSEP = 0.177, rp = 0.863, SDR = 1.853) were achieved based on a combination of the MA + SNV pre-processing methods.

Paddy rice residue covers more than 60000 ha of the Khuzestan plain. High soil moisture content (low evaporation and heavy soil texture), time limitations, and the likelihood of rainfall make conventional tillage methods unsuitable for wheat cultivation after the rice harvest. The present study investigated the best residue management method, and fuel and time savings, to produce acceptable yields and improve the physical properties of the soil. The study was conducted on silty-clay soil from 2010-2012 at Shavoor Agricultural Research Station in northern Ahwaz province in Iran. Testing was conducted in strip plots using a randomized complete block design with three replications. The main plots were tillage T1 = conventional plow + disc harrow + leveler; T2 = chisel plow + disc harrow + leveler; T3 = chisel plow + rotavator; T4 = disc harrow + rotavator; T5 = two passes of disc harrow + leveler; T6 = one pass of rotavator; and T7 = no tilling or drilling. Subplots combine two rice residue cover varieties (LD183 and Anboory) with two rice-growing methods (paddling and dry seeding). The results showed that the highest (49.1 l/ha) and lowest (20 l/ha) fuel consumption were recorded for T1 and T7, respectively. Fuel consumption decreased 35% for T2, 20% for T3, 31% for T4, 50% for T5, 44% for T6, and 59% for T7 over T1. T1 at 4.3 h/ha and T7 at 0.5 h/ha had the highest and lowest total operation times, respectively. Total operational time decreased 46% for T2, 35% for T3, 39% for T4, 70% for T5, 53% for T6, and 88% for T7 over T1. Total operational cost of conservation tillage methods decreased 20% to 33% over T1. Type of rice residue and rice growing method had no significant effect on wheat grain yield or on other parameters. There was a significant difference between tillage methods versus seeding depth and soil versus residue break-up. Wheat grain yield for the first year of testing was significant and 9.6% higher than for the second year. The results for sowing wheat after rice harvest in silty-clay soil in Khuzestan provinceusing available machinery recommends tillage methods T7, T5, T2 or T6 instead of conventional method T1.

The effect of 6 solvents with different polarities on the extraction of pomegranate seed extracts was studied. Extraction efficiency, reducing activity, radical scavenging properties and the effect of each extract on thermal resistance (oxidative stability index) of antioxidant-free soybean oil were analyzed using a factorial test in a completely randomized design with 3 replications. The results showed that the highest extraction yield from pomegranate seeds was hexane extract and from defatted seeds was acetone extract. The antioxidant properties of the different extracts were analyzed using FRAP and DPPH and revealed that methanol seed extract had the highest antioxidant properties. The antioxidant efficiency of the seed extracts prepared using solvents in combination with antioxidant-free soybean oil was measured using a Rancimat. The results showed that methanol seed extract increased the oxidative stability of the oil sample.

Parboiling of paddy rice is a three-step hydrothermal process consisting of soaking, heating and drying. Parboiling decreases the percentage of broken rice and increases the nutritional value of the rice. The present study examined the Tarom, Shirody and Fajr rice varieties. The rice was parboiled, then milled and the variables for parboiled and non-parboiled rice were recorded. The most significant change was the decrease in broken rice in the Shirody and Fajr varieties, and a decrease in whiteness and solids and an increase in hardness in all parboiled rice varieties.

Tomatoes are an economically important crop in Iran. Approximately 30% of the crop is lost from the consumption chain during harvest. The high production of ethylene by tomatoes is the main reason for rapid ripening and consequential loss. The present study tested various concentrations of 1-MCP gas in a tomato storage jar. The tomato cultivar Rapsona was harvested at the breaker stage of ripening for use in this study. The results demonstrated that the presence of 1-MCP in the storage atmosphere controlled the ethylene, extended the ripening time of green tomatoes, delayed softening of texture and changes the surface color of the fruit to red. The effectiveness of these parameters depended on 1-MCP concentration and length of contact of the fruit with the activated gas. Ripening of treated tomatoes was delayed for 15-18 d with the application of ≥0.7 μl/l 1-MCP and an exposure time of 24 h. Despite the success in controlling and delaying fruit ripening, the use of 1.35 μl/l 1-MCP is not recommended because of the lack of uniformity in the fully-ripened red tomatoes, which decreases utility and production of a market-friendly product.

The present study used a constant level of citric acid and polyvinyl alcohol and different amounts of nanocrystalline cellulose (CNC) and TiO2 nanoparticles to improve the properties of starch film. The effect of different amounts of glycerol was also examined. The results of differential scanning colorimetry demonstrated that the addition of CNC increased the melting and glass transition temperatures and the addition of high levels of TiO2 decreased the melting temperature and increased the glass transition temperature. The effects of these three compounds on the hydrophobicity and color of bionanocomposite plasticized starch were studied and their optimum values determined using a central composite design in response surface methodology. Water uptake data showed that the quadratic effect of TiO2 concentration and the linear and quadratic effects of CNC and GLY concentrations were significant. The optimum levels for TiO2, CNC and GLY for minimum water uptake were 0.118, 0.3 g and 1.36 ml, respectively. Quadratic CNC concentrations and linear glycerol concentrations were significant for water solubility. The optimum levels of TiO2, CNC and GLY for minimum water solubility were 0.235, 0.30 g and 1.36 ml, respectively. The CNC concentration had linear and quadratic effects on the yellowness index (YI) of the bionanocomposite. There was a significant interaction between TiO2 and GLY. The optimum levels of TiO2, CNC and GLY for minimum YI were as 0.235, 0 g and 1.06 ml, respectively.