Madras Agric. J. 92 (7-9) : 599-602 July-September 2005
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Research Notes
KAU micro sprinklers - a promising irrigation technique P. SUSEELA1 AND M.V. RANGASWAMI 2 l. Asst, Prof, WMRU, Kerala Agrl. University, Vellanikkara. 2. Prof and Head, Dept. of SWCE, TNAU, Coimbatore
Good scientific water management involves adoption of right method of irrigation consistent with the topography of the field to supply water to the crop at right time and the required quantity. Micro irrigation can be considered as an efficient irrigation method, which is economically usable, technically feasible and socially acceptable. Unfortunately, the sophisticated design of the system components, frequent clogging of emitters apart from its prohibitive initial cost become major constraints in the adoption of this technology for many of the farmers (Post et al 1986 and Sreekumaran et al, 1996). In this study, an attempt was made to develop an improved low cost micro sprinkler and was found operating satisfactorily. It is very cheap, simple in design and is almost intermediary system between the drip & sprinkler. This system was designed to operate clog free and ensuring the complete wetting of the basin area of the crop due to its rotating action. It allows fertilizer application, cooling of green houses, poultry houses, cowsheds etc. Initial investment, running cost and maintenance cost is comparatively less. Various sizes of low cost micro sprinkler units were fabricated by using the LDPE pipes. Performance evaluation of various sprinkler heads were made and two units, that provided best performance, were selected. The experiment was conducted at the Water Management Research Unit, working under Kerala Agricultural University, Vellankkara, Low cost micro sprinkler heads were fabricated using 8-mm, 12-
mm and 16-mm diameter LDPE pipe cuttings. 5cm, 8-cm and 12-cm length of pipe cuttings from each diameter pipes were used to fabricate the sprinkler heads. Sprinkler heads were provided with lmm, 2mm and 3mm diameter nozzles. Totally 45 types of micro sprinkler heads were fabricated. The basic principle of the KAU micro sprinkler is - moment of the couple constituted by the, streams of water coming out of the nozzles, caused the emitter to rotate, while in operation. Based on the performance study of 45 sprinkler heads developed, two sprinkler heads; MS8, 5N1,1 (Sprinkler head having 8mm diameter, 5cm length with 1 number of nozzle having lmm diameter) and MS 12, 8N 1, 1 which gave best performance and ideal for the crops growing in Kerala were selected. Hence these two sprinkler heads were recommended to the farmers. A 0.5 hp monoblock centrifugal pump set (25 mm*25 mm) was utilized to provide sufficient pressure required for operating the sprinkler heads. The discharge line consisted of a main line of 25 mm diameter PVC pipe and 16-mm diameter LDPE laterals. A ball valve and pressure gauge were used to set the required operating pressure by controlling the flow. 6 mm diameter micro tubes were connected to the lateral pipes by using the micro tube tap connectors. Sprinkler heads were then connected to the micro tubes by using micro tube pin connector. In order to minimize the runoff & percolation loss and also to reduce the operating cost of the
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Fig. 1. Variation of discharge with pressure
Fig. 2. Variation of effective wetting radius with pressure
KAU micro sprinklers - a promising irrigation technique
system, a through knowledge of discharge availability of sprinkler head is required. The variation of discharge of sprinkler head with pressure was found out and curves showing their relationship are shown in Fig. 1. Since these low cost micro sprinklers were developed for the farmers with small/marginal land holdings, a low operating pressure within a range of 0.3kg/cm2 to 1.7 kg/cm2 was fixed for the present study. In both the sprinkler heads, discharge was found to increase with increase of pressure. These results were more or less in conformity with the result obtained by Boman, (1991) who have conducted study with commercially available microsprinklers At lower pressures, the discharge of MS 12,8N 1, l was found to be more than MS8, 5N1, 1. The difference in discharge between two sprinkler heads was found to decrease with increase of pressure and was found to be the same at higher pressures. The volume of MS 12,8N 1, 1 is more than MS8,5N 1,1 Hence the amount of water coming out of the nozzle is more in the case of MS 12,8N1, 1 than MS8,5N1,1. But at higher pressure, the force with which the water entering into both the sprinkler heads and coming out through the nozzle is comparatively high. Since the volume of MS8,5N1,1 is less than MS 12,8N 1,1; it will contain less volume of water and hence the weight of the unit along with water will be comparatively less. So MS8,5Nl,l was found to rotate at higher rate than MS 12,8N 1, l . Hence at higher pressure the effect of volume of sprinkler head reduces and hence discharge coming out from both the sprinklers became almost the same. Variation of effective wetting radius (average distance from the emitter to the most distant 5% of the containers, which received water) with pressure was noted at different pressures, viz.,0.3Kg/cm2, 0.5Kg/cm 2 0.7Kg/cm2, lKg/cm 2 1.5kg/cm 2 and l.7Kg/cm2 and the results of the same is shown fig.2. During the study, height of the riser pipe was
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maintained at 60cm, which is suitable for most of the crops. Effective wetting radius was found to increase considerably with increase of pressure. Effective wetting radius of MS8,5N 1,1 was found to be much more than MS 12, 8N 1,1 and for a particular operating pressure, MS8,5N 1,1 gave comparatively fine spray than MS 12,8N 1, l This may be due to the fact that the energy required to rotate MS8, 5N1,1 along with water is considerably small and with the same energy it will throw water to a greater distance which resulted greater effective wetting radius. A multiple regression analysis was done for both the sprinkler heads to develop an equation which help to find out the operating pressure of the system to get a particular discharge and wetting radius needed for a particular crop P = -0.4938 + 0.165 Q + 0.0036 WR - for MS8, 5N 1, l P = - 0.834377 + 0.0193 Q + 0.0073 WR for MS 12, 8N 1, l
Where P = operating pressure, kg/cm 2 , Q = discharge, lit/hr; WR = wetting radius, cm The regression analysis showed that the operating pressure has significant influence on both discharge and wetting radius. Hence after selecting the sprinkler head, based on the type of crop, the operating pressure can be determined and based on that we can select the pump. This will help to reduce the initial cost, cost of operation, wastage of water and make the system more economical. Micro sprinkler irrigation system never shows the clogging problem, which is the major problem in the drip irrigation. The experiences in the farmer's fields as well as in the fields of the research station found that there is no need to install the filter in this irrigation system. Hence, while installation of KAU micro sprinkler irrigation system,
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filters can be avoided which will further reduce the cost of the system. The economic study revealed that KAU micro sprinkler irrigation system is comparatively cheaper than drip system especially in close growing crops.
References Boman, B.J. (1991). Microtubing effects on microsprinkler discharge rates. Transactions of ASAE 34(6): 2453 - 2458.
Post, E.C., Peck, D.E., Brendler, R.A, Sakovitch, N.J. and Waddle, L. (1986). Evaluation of low-flow sprinklers. California Agriculture. July-August, pp. 27 - 29. Sreekumaran, V., Santhakumari, G., Jayakrishnakumar, V., and Raghu, P.K. (1998). Bubbler Irrigation System-An Innovative Micro irrigation Method Proceedings of the Kerala Science Congress, Kozhikode pp : 494 - 496. (Received : February 2004 Revised : March 2005)
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