A comparison between nutritive value of enriched straw by two different methods ( routine and mechanical method )

Nutritional value of cereal straw can be increased by urea treatment process as ammonia resources. The conventional treatment of this process is rewetting the straws by urea solution. Because this method is a laborious, tedious and time-consuming task, it is essential to work on mechanized treatment. The objectives of this research were to mechanize the urea treatment of wheat straw by a baler through investigating the effects of nozzle type and spray flow rate on the moisture characteristics of wheat straw, and finally design, fabrication and evaluation of straw urea treatment machine (SUTM). Experiments were carried out in two sections: study of moisture characteristics of wheat straw and performance of the SUTM including nutritional value of treated straw, distribution of moisture in treated straw bales, machine capacity and required power. In static condition, the effects of nozzle type, spray flow rate and the amount of straw compaction and in dynamic condition the effects of straw conveying velocity, number and positions of nozzles on moisture characteristics of wheat straw were considered. The static experiments were conducted in a completely randomize factorial design with 3 replications. The experimental parameters were: four levels of straw densities (5, 50, 85 and 120 kg.m-3), three levels of water flow rates (400, 600 and 800 g.min-1) and two types of nozzles (conical and t-jet). The result of analysis of variance showed that, the density, flow rate, and nozzle type had significant effect on the amount of straw moisture before drainage, final moisture content, saturated moisture and drainage quantity (P ¡Ü 0.01). The combination of 5 kg.m-3 and 800 g.min-1 with t-jet nozzle, because of the highest water content and lowest drainage, was selected as the best condition for mechanized treatment of wheat straw. After manufacturing the experimental apparatus for dynamic test, straw rewetting experiments were performed with different number of t-jet nozzles and straw conveying velocities. These experiments were conducted in a completely randomize factorial design with 3 replications. The experimental parameters were selected at six levels of straw conveying velocities (3, 3.4, 3.8, 4.3, 4.8 and 5.2 km.h-1) and three levels of number of nozzles (8, 14 and 20 nozzles). The highest quantity of retained moisture was 43.5% and the lowest runoff was 1.75% by using 20 nozzles at 3 km.h-1 straw velocity. Results of straw rewetting on static and dynamic conditions showed that the conveying and feeding unit of baler is suitable for installation of 20 nozzles in the STUM. Pump type, power transmission, size and type of frame, type and volume of urea solution tank and installation position of the tank and nozzle on the baler were selected in the basis of technical calculations. For construction the SUTM, first the spray system was installed on baler model 349-T, made of Iran combine manufacturing company, and then was tested by Messy Ferguson 285 tractor. The machine was tested in the field to prepare treated straw bales at three urea concentration levels (3,4 and 5 percent). At the same time the conventional method was used for treating the chopped straw and the samples were compared with the mechanized treated straw. Analysis of variances showed that the interactions of treatment methods and urea concentration on some chemical compositions (DM, Ash, CP, CF and ADL) were not significant. But the effects of these factors on the other chemical compositions (NDF, ADF) and straw digestibility (DMD, OMD and DOMD) were significant (P0.05). Also there was no significant difference between DM, Ash, CP and ADL in two treatment methods (conventional and mechanized). These results showed that the designed system (SUTM) could spray urea solution on the straw with the same quality as in conventional method. For studying the uniformity and moisture distribution, the moisture in the side and center of the treated bales were measured and compared with t-test. The mean of moisture in the side and center of bales was 52.53 and 48.40%, respectively. In spite of the higher moisture content in the side of the bales, the differences were not significant (P0.05). The maximum required power for running the installed systems (SUTM), was about 5.07 kW, 3.3 kW of which was attributed to the weight of spraying systems on the baler and the rest to the running of the pump. The experiments result of using the STUM in the actual field showed that the designed machine could treat and baled the cereal straw in the field condition.