Abstract
A research was conducted to improve spray deposition on rice field. In this connection, a survey was performed to identify the knowledge of farmers on spray practices and present status of sprayer use in Laguna province, Philippines and Munshiganj district of Bangladesh. It was found that the knowledge of 38% of farmers in the Philippines and 68% of farmers in Bangladesh were poor. The general linear model of survey data indicated that the farmer's education (p = 0.006) and training (p = 0.019) can increase the knowledge of efficient spraying. It was also observed that 98.7% of farmers in selected areas of the Philippines applied a number of pesticides by using top lever operated knapsack (LOK) sprayer with double orifices cone fixed nozzle (DN). On the other hand, 69 % farmers of Bangladesh used single orifice cone fixed nozzle (SN). However, it was found that the performance of LOK sprayers with traditional nozzles were poor due to variation of spraying pressure (CV-20%), flow rate (CV=11%), nozzle heights (CV =60%), forward speed of the operator (CV = 28%), application rate of active ingredient etc. All of the above factors influenced on uneven spray distribution, off-target deposition, and drift. Therefore, traditional LOK sprayer was modified by adding a controlled flow valve (CFV) in the lance and a boom with four and eight XR11001 nozzles instead of lance to improve spray deposition. Different spraying parameters such as spraying pressure, discharge rate, spray distribution, spray coverage, deposition and drift were determined in the laboratory. It was observed that different improved sprayers gave more coverage, high deposition onto the target, less drift, and more uniformity than those from LOK with traditional nozzles. The above improved sprayers arranged in different combinations with/without valve, with/without trained operator, boom etc to conduct the experiment on spray deposition. Thus, experiments were conducted to determine spray deposition in eight different techniques in randomised complete block design with three replications in the rice field of IRRI. The result showed that the deposition from different spray techniques increased by 1.04 to 1.98 times than the deposition from LOK with traditional nozzles. On the other hand, 4 to 98% of pesticides were saved by using improved LOK spray techniques when optimum depositions were considered from LOK sprayer with traditional nozzles. Besides LOK spraying, a hand held ultra low volume applicator (ULVA) set in 9 different combinations of disc speeds (3500 rpm, 4849 rpm, and 5873 rpm) and application rates (20 l/ha, 30 l/ha and 60 l/ha) to determine spray deposition at IRRI rice field in RCBD with 3 replications. The depositions from ULVA were 1.11-3.18 times higher than the deposition of LOK with traditional nozzles. The ULVA was also tested in the laboratory to determine the effect of voltage on disc speed, power consumption, VMD of droplets, life of batteries, spray coverage, deposition and drift. The ergonomic study on heart and respiration rate showed that none of any spray techniques except LOK with 8 nozzles made stress on the operator. Among different improved techniques of LOK, a boom with four XR11001 nozzles gave the best performance (deposition increased to 1.49-1.98 times, pesticides saved to 49-98%, cost reduced to 65-94%, and operator's contamination decreased to 25-14% than those from LOK sprayer with traditional nozzles). On the other hand, ULVA gave the best performance with a spray recovery efficiency of 53%, when it was operated in 6V (disc speed 4849 rpm), VMD of droplets 117μm, 150 ml/min flow rate, and application rate of 20 l/ha. Finally, The comparison of performances of different spray techniques indicated that a mini-boom with four XR11001 nozzles attached with the traditional LOK and ULVA (operated in 6V with 20L/ha application rate) could be used in the rice field for pesticide spraying. These improved sprayers will provide an even spraying, proper dose, more deposition, less drift, and less contamination. On the other hand, it will decrease the amount of pesticides used. This will save the foreign currency to buy the pesticides. Thus the improve spray techniques will protect the environment from misuse of agrochemical and save money.