Study On The Irrigation Technology For Lettuce Cultivation In Greenhouse Based On The Substrate Wetting And Root Growth Characteristics

The organic matrix cultivation has become an effective technique to avoid continuous cropping obstacle in protected horticulture. But there is little research for the matrix moisture characteristic and its detecting method, this leads to the water irrigation in matrix is not reasonable and accurate, effects the crop growth and yield. How to monitor the moisture content in the matrix accurately and realize intelligent water-saving irrigation is an urgent problem to solve. In view of the existing problems, we deeply study the matrix moisture monitoring sensor, the matrix wetting body variation characteristics, the matching of the wetting body and the lettuce root, Put forward the irrigation control strategies in matrix cultivation and development of intelligent irrigation control system. The main research works are:1) Through the analysis of the existing soil moisture sensor,and features of facilities substrate cultivation,the article selected EC-5capacitive sensor to detect the moisture content of the substrate. Analysis the type of substrate, substrate temperature, substrate density and conductivity of the substrate effecting on detecting precision of EC-5moisture sensor, determine the main factors and proposes a simple correction method of sensor. Through the dynamic monitoring of moisture of cross-section substrate and the variability and correlation analysis of matrix moisture at different depths, the article uses cluster analysis to determine the final layout position of EC-5sensor.2) Study on the influence of irrigation flow, drip lasted, drip irrigation initial water content of the matrix on matrix wetting body and water distribution under drip irrigation. The results show that:the wetting body shape of the matrix is similar to the paraboloid of revolution under drip irrigation. The maximum radius of level infiltration is not on the substrate surface, but3-6cm under the surface of the matrix. The size of the wetting body is T4>T3>T2>T1when drip flow, matrix initial water content and drip duration are the same. The horizontal infiltration distance at0.15L/h is more23.3%than at0.5L/h at least,the vertical infiltration distance is more5.5%than at0.5L/h at most under the same irrigation amount and different drip flow. The horizontal infiltration distance at0.5L/h is1.04times of0.15L/h at at least, and the vertical infiltration distance is1.34times of0.15L/h at at least under the same irrigation duration (60min)and different drip flow, the maximum matrix moisture increased9%-13.5%. The vertical infiltration distance is more62%than the horizontal infiltration distance at least, and the matrix water content is increased30%under the same drip flow and different irrigation duration (60min and198min). The horizontal infiltration distance increased31%and the vertical infiltration distance decreased13%with the matrix initial water content increase under the same irrigation duration.3) This paper studies the effects of the initial moisture content of matrix and micro sprinkler irrigation amount on vertical infiltration distance and water distribution of matrix in micro-sprinkler case. The results showed that:each matrix treatment appear the middle layer in the vertical direction about4～10cm range,and the matrix moisture content changes larger in the layer. In the same matrix intial water content, the vertical infiltration distance increases with the amount of irrigation, the average matrix water content in the layer at the irrigation perod (30min) was more22%than at15min at least. In the same micro-sprinkler irrigation amount, the average vertical migration rate of T2,T3and T4increased56%with the increase of the matrix initial water content, but the vertical migration rate of T1was more56%than compound matrixs at the low matrix initial water content,but the matrix moisture content contour density decrease with the initial water content increase.4) The matrix characteristic value model and matrix wetting body semi empirical model were established using dimensionless analysis method. The results show that the correlation coefficient between the prediction value and the actual value of the horizontal infiltration distance and vertical infiltration distance for4kinds of matrixs were was more than0.8, the RMSE and the ME were were1.06cm,1.18cm and-0.154,-0.53cm for drip irrigation; The correlation coefficient between the prediction value and the actual value of the vertical infiltration distance for4kinds of matrixs were was more than0.9, the RMSE and the ME were were1.06cm and1.3cm for micro-irrigation; It show that the models have high accuracy for prediction the matrix wetting front.5) Analysis the factors of influence the root growth and distribution characteristics for lettuce. Models for lettuce root length, root growth and root zone were established using the accumulated temperature. The results show that the effects of matrix types can be ignored; Under different irrigation methods, lettuce root length density is mainly concentrated in the0-6cm matrix layer and accounting for more than70%of the total, and the microsprinkler irrigation is advisable under the high temperature season for lettuce cultivation with matrix. The RMSE and RE between predictive value and actual value for lettuce root length, root depth and root zone radius were290cm,0.81cm0.63cm and15%,12%,13%, The model can predict the root growth of lettuce well.6) According the requirement of the irrigation control system using in the matrix cultivation to present the design principle. Using visual studio as the software development tool, c#as the programming language, sqlserver as database, design a irrigation control system using in the matrix cultivation based on ZigBee technology, analysis of the factors influencing the irrigation control and estimation the evapotranspiration. Prent the matching principle and the drip irrigation strategy based on the evapotranspiration,the overlap of section area of lettuce root and wetting body, and the microspray irrigation strategy based on the evapotranspiration,the overlap of the lettuce root depth and matrix vertical wetting front, then start the comprehensive irrigation control.As a consequence, according the flow information to estimate the change of the matrix wetting body after irrigation began and the growth time after lettuce planting to estimate the changes of lettuce root. Using the preset irrigation control strategy to decision whether irrigation and irrigation quantity in order to achieve the purpose of accurate irrigation.