Study On Technologies Of Monitoring Plant Water And Management Decision In Rice

As the core content of crop production and management, the precision water management is of great significance to ensure food security and save water resource. Remote sensing, crop model and decision support system are important tools for monitoring crop growth characters, water indices and irrigation management. In this study, a series of field experiments with rice were carried out, the change characteristics of growth, development and water content condition under different soil water levels were defined with the methods of information query, growth analysis, mathematical statistics and mathematical modeling. The quantitative relationships of canopy-air temperature difference(CATD), leaf-air temperature difference(LATD) with plant water status were confirmed. By studying quantitative relationship between plant water status and hyperspectra, spectral index, nondestructive models for monitoring plant and leaf water contents were developed. Based on the theory of soil water balance, a sub-model for water real-time regulation was established by quantifying the relationships between water demand of rice and environment factors. By further adopting the methodology of software component design and the technology of object oriented program, a model-based decision support system for rice water management was developed. This work has provided a basic theory and key technologies for monitoring water status and irrigation management.The dynamic characteristics of growth, development and water condition were studied under different soil water conditions and rice cultivars of Wuxiangjingl4 and Liangyoupeijiu. Results showed the plant height, panicle length, internodes length, number of primary and second branch, plant and total leaf water contents were remarkably affected by soil water in different water treatments, the treads were CK>W3>W2>W1. The distribution of leaf water contents on main stem in all treatments and development stages were WL1<WL2<WL3<WL4. The leaf area index, SPAD value of leaves and leaf photosynthesis were the highest under low-grade soil dry stress (W3) for it delayed aging of leaf. After heading stage, the SPAD values of leaves at upper position were higher than basal position, and the distribution of leaf photosynthesis at different positions were L1>L2>L3>L4. The yield tread in all treatments were W3>CK>W2>W1, W3 treatment had the highest yield.By applying the measuring instruments of THREMOCAM P25 and Raytec ST60, the change characteristics of canopy-air temperature difference(CATD) and leaf-air temperature difference(LATD), and their quantitative relationships of CATD, LATD with plant water content(PWC) and leaf water content(LWC) were studied. Results showed the values of CATD and LATD in all treatments and stages were W1>W2>W3>W4. The leaf-air temperature differences among upper three positions were very small, but varied distinctly with the upper forth leaf at all development stages. CATD or radio of L1/L3 LWC with PWC and canopy leaf water contents were significantly related. LATD with LWC, stomatic conductance and transpiration rate showed certain relativity. It is concluded that CATD, LATD and LWC can be used to monitor plant water conditions.The change characteristics of leaf hyperspectral reflectance and water content were studied. Ratio spectral indices (RSI), normalized difference spectral indices (NDSI) and difference spectral indices (DSI) with all combinations of two wavebands between 350 and 2500 nm were calculated, and the relationship between spectral indices and LWC was analyzed. The results indicated that the leaf spectral reflectance varied distinctly with soil water treatments and different top leaves, the sensitivity bands mostly occured within near-infrared and short-infrared spectral regions. The spectral indices as RSI (R1402, R2272) and NDSI (R1402, R2272) were linear with LWC, giving the determination coefficient of linear regression (S-R2) of 0.80, and the predicted R2 (P-R2) based on the testing performance with independent datasets as 0.86. It is concluded that the RSI (R1402, R2272) and NDSI (R1402, R2272) can be used to monitor leaf water content in rice.Based on the characteristic of canopy hyperspectra, the relationship between plant water condition and hyperspectral reflectance were analyzed. The results indicated that canopy spectral reflectance varied distinctly with soil water conditions. The sensitivity bands mostly occured within visible light region and near infrared region. The RSI (R773, R1287) were the most effective approach for predicting plant and canopy leaf water contents. The predicted R2 (P-R2) based on the testing performance with independent datasets were 0.802 and 0.774 respectively. It is concluded that the RSI (R773, R1287) can be used to monitor plant and canopy leaf water contents.Based on analysis and extraction of the research results in rice water management theories and technologies, further with plant water contents or soil water potential as the regulation indices, a sub-model for water real-time regulation in rice was developed by combining rice water indices nondestructive monitoring model, quantifying the relationships of water demand and cultivation technologies, variety traits, and eco-environments. Furthermore, guided by the methodology of software component design and the technology of object oriented program, based on rice knowledge model for water management, rice growth simulation model and weather data generating model, a model-based decision support system for rice water management was developed based on platform of Visual Studio. NET 2005. The system realized the functions as basal information management, dynamic water simulation, design of irrigation amount, real-time dynamic regulation and help, etc. The field comparison experiments showed that the average grain yields and irrigation water use efficiencies were improved in two eco-sites under the model-designed irrigation strategies, as compared to conventional irrigation regimes. It appears that the present model has good applicability and proper guidance for rice water irrigation management.