DSpace Collection: Journal of the King Saud University - Agricultural Sciences

Measured and estimated crop et and kc for wheat and barley in central Saudi Arabia

Wed, 01 Jan 2003 00:00:00 GMT

Title: Measured and estimated crop et and kc for wheat and barley in central Saudi Arabia

Authors: Alazba, A..A.; Alghobari, H.M.; Mohammad, F.S.; Alomran, A.M.

Abstract: A field experiment was conducted at the educational farm. King Saud University (central region of SaudiArabia) to measure crop evapotranspiration (ETC\ for wheat and barley crops. The measurements of alfalfa reference ET werecoupled with the measured crop ET(ETC) to obtain the crop coefficients (A'r). Also, three models for estimation of referenceET (ETnf) were examined to assess their suitability for prediction of ETC under local climate conditions The measurementswere accomplished using nine non-weighting lysimeicrs constructed with reinforced concrete. The lysimetcrs were randomlyand evenly planted with the selected crops, wheat and barley, and with alfalfa reference crop. The research outputs revealedthat the seasonal E7\ for wheat and barley are 898 and 930 mm, respectively. The maximum daily ETC rates never exceeded11 mm/day for both crops. The average maximum daily ET, was 10.34 and 10.21 mm/day for wheat and barley, respectively.For wheat crop, the A',, values for initial, mid-season, and late-season stages have been found to equal 0.63, 1.38, and 0.41 forthe three stages, respectively On the other hand, the Kt values for barley were 0 60, 1.39, and 0.29, for the initial, mid andlate-season stages, respectively, The tested models for predicting ET, gave almost identical estimates. The standard errors ofestimates (SEE) lor the three models were in the vicinity of 1.7 mm/day.

Estimation of pomegranate shape and size by machine vision

Wed, 01 Jan 1997 00:00:00 GMT

Title: Estimation of pomegranate shape and size by machine vision

Authors: Hobani, Ali I.; Al-Janobi, A.

Abstract: A simplified machine vision system for estimating shape and size of pomegranates was developed. The system allows the estimation ofvolume, surface area, and weight ofthe fruit using predic-tion equations developed from the relationship between projected area and shape and size. This proce-dure resulted in excellent values of the coefficient of determination and can be used to estimate volume, surface area, and weight of Banati and Manfaluti pomegranates. The analysis of variance indicated that there was no significant difference in shape between Banati and Manfaluti cultivars at the 95% confidence level. A power law equation was obtained to describe the relationship between volume, surface area, and weight and the projected areas. The average measurement error of prediction was in the 1.5. 0.7 and 2.0% - range for volume, surface area, and weight of Banati pomegranate, respectively:'The Maiif'aluti pomegra-nate had average measurement errors in the range of 1.1, 1.4 and 3.2% for volume, surface area, and weight, respectively.

Mechanical deterioration of polyethylene greenhouses covering under arid conditions

Tue, 01 Jan 2008 00:00:00 GMT

Title: Mechanical deterioration of polyethylene greenhouses covering under arid conditions

Authors: Alhamdan, Abdullah M.; Al-Helal, Ibrahim M.

Abstract: One of the most common greenhouse covering materials in Saudi Arabia is polyethylenefilm. However, polyethylene films are susceptible to mechanical failure due to harsh conditionsof high temperature, solar radiation, and wind as occurs in Riyadh, Saudi Arabia. Thisstudy examined effects of ambient conditions on the deterioration of mechanical propertiesof polyethylene films over 14 months, using an experimentally cooled empty greenhouse(3.6m length, 2.4m width, and 3.6m height) covered with a single layer of 200- m thickpolyethylene.Three mechanical tests were conducted on the polyethylene samples: penetration, shear,and tension utilizing a SMS texture analyzer. The force–distance curves produced werecharacterized by two stages, the elastic and plastic regions. Mechanical properties weredetermined, including modulus of elasticity, rupture point, and total work for each stage ofthe three tests. Generally, mechanical resistance of the samples decreased with increasedexposure time. The results of the tension tests were preferable to penetration and sheartests. For tension tests, work decreased from 21,693Nmm for new samples, to 6658Nmmafter 14 months. Based on elongation at break data, the shelf life of polyethylene coverswas 12 months under the tested environmental conditions. This illustrates the effect of aridconditions and age on the mechanical deterioration of polyethylene films. The presenteddata can be utilized to predict the deformation and mechanical behavior of greenhousepolyethylene covers at different exposure times under arid conditions.

Description: Department of Agricultural Engineering, College of Food and Agricultural Sciences,King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia

Cryogenic freezing of fresh soft dates

Wed, 01 Jan 1992 00:00:00 GMT

Title: Cryogenic freezing of fresh soft dates

Authors: Hassan, B.H.; Al-Mohizea, I.S.

Abstract: Seven cultivars of widely consumed fresh soft dates, at two stages of maturity, i.e.. Kutab (fullyripe) and Munassif (half ripe), have been cryogenically frozen using liquid nitrogen. The cultivars were:Sukkari. Nabt Sultan. Nabt Saif. Maneefi. Sillaj. Reziz. and Khalas, all purchased fresh from the localmarket during the 1989 dale production season. The experimental time-temperature data of the fresh softdates during the cryogenic freezing process were generated and compared with the conventional freezinglime-temperature data. The initial freezing points of the date cultivars were in the range -16 to -18°C.Quality attributes of the thawed dates kept frozen at -S0°C for 12 months were compared with their freshcultivars counterparts. Significant differences ( P < 0.05) were detected by sensory panelists, in color, texture,flavor, and overall acceptability of most cryogenically frozen cultivars at their Munassif stage ofmaturity. Panelists were nol able to detect significant differences (P < 0 05) while scoring for the overallacceptability of all cultivars at their Rutab stage of maturity. except Nabt Saif. Cryogenically frozen NabtSaif cultivar at the Munassif stage of maturity was not significantly different (P < 0.05) from its fresh onein color, texture, flavor, and overall acceptability.