Low Slope Tea Plantation Moisture Migration Characteristics And Sprinkler Irrigation Automatic Control System

Drought stress on tea plant impedes the growth and causes decline in tea quality and yield.Sprinkler irrigation is often adopted to provide the moisture needed for the growth of the tea plant.But its control often relys on experience(such as soil water content)which is easy to cause excessive irrigation,and distribution range of irrigation water in different slope is different in tea plantation.As the research target of sprinkler irrigation automatic control technology in Jiangsu Province low slope hilly tea plantation,the Special Fund of Non-profit Scientific Research for Agriculture provided funds for the design and development of an adjustable cultivation box frame and field irrigation testing system.Soil moisture migration characteristics of low slope tea plantation were studied.Subsequently,a model about water infiltration wetted depth under different slopes and sprinkler irrigation intensities was developed.Furthermore,irrigation control strateg was formulated.The irrigation control system was developed.Finally,the model and water saving performance were verifyed through field test.The main research work and findings are as follows:(1)Tea plant root distribution and sprinkler irrigation system design The Anji White tea was chosen as the research object.A total of three tea plants from different locations were observing using the whole plant excavation method and the root system distribution was measured.Results showed that the tea plant roots in the experimental area reached 40 cm,which named the expected wetted depth of test area was 40 cm.More than 50% of the tea tree root distribution was in 10~20 cm.The range of test tea plantations slope was measured.Therefore an adjustment cultivation box frame was designed which could realize 0~15° slope adjustment to simulate a real tea plantation slope conditions.With the hydraulic calculation,a chamber and a field sprinkler irrigation testing system with intensity of 6 mm/h were developed.(2)Low slope tea plantation soil water infiltration depth model research Nine different test processings were set up successively in the box frame with slope and sprinkler irrigation intensity as factors and wetted depth as an index.With conditions of tea plant,the influence of slope and irrigation intensity to the infiltration rate on the soil water infiltration process and the influence of slope and irrigation intensity to the wetted depth on the moisture redistribution process were studied respectively.Thereby a model about the water infiltration depth was set up.In addition,the differences of water migration in the soil with and without tea plantation were compared.Based on the established soil water infiltration depth model,the required infiltration depth was corrected and verified by experiments.The results showed that,wetting front migration rate was positively correlated with irrigation intensity and negatively correlated with the slope.In the process of moisture redistribution,the ratio of infiltration depth and wetted depth was positively related to the irrigation intensity,and negative correlation with slope.It showed the smaller sprinkler irrigation intensity was,the greater the slope was,the better water vertical movement was.Within the range of study slope,the critical slope value making variation tendency of wetting front migration rate and slope change was existed when there was no tea plant.With tea plant,the critical slope value had not been found.At low slope,root system of tea plant reduced the wetted depth of redistribution.At large slope,the root system of tea plant increased the wetteddepth of redistribution.The water lose of 0~10 cm soil layer was positively correlated to air temperature,solar radiation and wind spreed.With verification,the relative error of infiltration depth estimated by the model and true value was 1.71%.The relative error of required wetted depth and true value was 2.92%.Result of field experiment about water infiltration depth model showed that the calculated infiltration depth was 21.52 cm,measured infiltration depth was 22.69 cm,and the error was 5.44%.The expected wetted depth was 40 cm,measured wetted depth was 38.91 cm,and the error was 2.73%.This showed that the model could be better applied to the selected test tea plantation.(3)Tea plantation irrigation control system development and field experiment The control process of the system was:(1)the sprinkler irrigation would work when the water intensity in a certain depth was smaller than the expected value under a certain circumstance containing the slope and irrigation intensity;(2)the control core would calculate the sprinkler irrigation time of the system based on the above water infiltration depth model;(3)repeating the process of(1)and(2).Based on the above control technology,PLC,soil moisture sensor and touch screen were chosen to develop tea plantation sprinkler irrigation control system.Slope of tea plantation,irrigation intensity(based on features of nozzle parameters)and depth of tea plant root were the input parameters to execute the irrigation operation.In field experiments,the experimental results showed that: the error of measured infiltration depth under the tea plantation sprinkler irrigation control system and calculated value was 2.60%.The error of measured wetted depth and expected value was 3.40%.So the tea plantation sprinkler irrigation control system could achieve the expected sprinkler irrigation effect.In contrast test,the water consumption based on tea plantation sprinkler irrigation control system was 7.252 m~3.Water consumption of traditional irrigation methods was 11.378 m~3,and water-saving percentage reached 36.26%.