Design and test of bacteria spraying device for harvest ditch and stalk-disposing machine

Abstract: In the rice-wheat crop rotation and double cropping area, there is a new straw-returning method named collecting straw to return to the ditch (CSRD). It can absorb nutrients, increase the field fertilizer input and promote the crop yield as well as realize the carbon sequestration and emission reduction. The CSRD adapts well to the full amount of straw returning. Based on this returning method, a multifunctional machine was developed, which could realize ditching, harvesting and straw returning simultaneously. But the long-term practice showed that the straw collected and returned into ditch by the multifunctional machine was difficult to be decomposed timely due to its stable internal environment. This problem not only affects the normal growth of the crop beside the ditch, but also obstructs the mid-term field managements. Thus, on the basis of the catalytic straw-decomposition characteristics of bacteria (yeast, actinomycetes, bacillus licheniformis and bacillus subtilis) and the structure of the multifunctional machine, a new device of bacteria spray was designed to address this problem. The spray device would spray bacteria solution with a concentration of 154 mL/L to prompt straw decomposition when the straw was collected into the ditch. In the performance test, Ponceau-S solution was used to simulate and trace the droplet motion of bacteria solution. To evaluate spray penetration and coverage results, several pictures were taken at 5 different straw layers, i.e. 0, 5, 10, 15 and 20 cm. The straw decomposing rate was calculated by using the mesh bag weighing method. In order to be helpful to the comparison of the performance, the same method was used when adopting the common knapsack sprayer. The results showed that the multifunctional machine coupled with bacteria spray device could work synchronously and coordinately because of a reasonable configuration. The nozzles (rotary cage centrifugal atomizers) were not jammed during working process, and the nozzles were suitable to the bacteria solution. In terms of working performance, when the multifunctional machine was operated at the speed of 0.27 m/s, there was a continuous and uniform liquid droplet of bacteria. The spray coverage rates at different layers were 67.5%, 37.4%, 39.4%, 32.2% and 18.6%, respectively. When it came to the common knapsack sprayer, the spray coverage rates were 38.6%, 4.8%, 2.9%, 4.0% and 3.8%, respectively. It showed that the performance of multifunctional machine coupled with bacteria spray device was better than the common knapsack sprayer, while the average loss rate outside the ditch with the new spray device was 21.3% which was slightly higher than the common knapsack sprayer. Through the comprehensive comparison, it could be concluded that the performance of the bacteria sprayer of the multifunctional machine was superior to the common knapsack sprayer. Finally, several contrast tests were used to evaluate the decomposition rate with different spray rates, and when the spray rate was 0.078 L/kg, the decomposition rate of the straw was the maximum and tended to be stable with the travel speed of 0.27 m/s. This result can serve as the guidance for the bacteria solution spraying under this working condition. This study provides a new way to extend the function of the multifunctional machine, and it provides a technical support for the further research on the promotion of CSRD as well.