Monitoring Water Status In Rice And Growth Parameters In Rice And Wheat With Canopy Spectral Reflectance

Management and regulation of crop water is the most important technique in crop production. Non-destructive monitoring crop water status is a significant research area in remote sensing and informational agriculture, and is essential for optimization of crop irrigation and precision farming management. In this study, the relationships between canopy spectral reflectance and water and growth status in rice were clarified with different pot and pool experiments, and models were developed for monitoring rice water status, growth parameters and leaf photosynthesis in rice and wheat, protein and starch accumulation in wheat grains.Relationship between canopy reflectance characteristics and plant water status under different water and nitrogen levels was studied. Near infrared reflectance (NIR) of rice canopy increased with the decreasing soil water content, while short-wave infrared reflectance (SWIR) exhibited the opposite pattern. With the same soil water treatment, the visible reflectance and SWIR under high nitrogen level was lower than that under low nitrogen, and NIR exhibited the reversed pattern. The ratio vegetation index (R810/R460) after jointing stage was linearly related to canopy leaf water content and plant water content, and the ratio of RVI and NDVI was linearly related to leaf water potential and leaf relative water content. So water status in rice plant can be indicated by canopy spectral reflectance.Dynamic changes of water content, nitrogen content, SPAD value and photosynthesis of each functional leaf on main stems of rice under different soil water and nitrogen levels were investigated. Distribution of leaf water content on main stems under all treatments was: WL1SPADL3>SPADL4 before heading, but after heading, the pattern was SPADL1PSL2>PSL3>PSL4. Distribution of leaf nitrogen content on main stems had the same trend with the SPAD. All patterns were consistent under high and low soil nitrogen conditions. Ratio or difference of water contents in different position leaves were significantly related to canopy leaf water content, canopy leaf nitrogen content andphotosynthesis.The quantitative relationship between canopy spectral reflectance and leaf photosynthetic characteristics under different water and nitrogen levels was determined. The results showed that the ratio vegetation index R810/R460 was linearly related to leaf photosynthetic characteristics in rice, and there was an exponential relationship between R610/R460 and leaf group photosynthesis potential in wheat. The models were validated using two rice experiments and one wheat experiment with different soil water and nitrogen conditions in different years respectively. It is concluded that the ratio vegetation index can be used to monitor leaf photosynthetic characteristics at different growth stages of rice and wheat.Temporal changes in canopy spectral reflectance in rice and wheat under different soil water and nitrogen levels were studied and relationships between canopy spectral reflectance and LAI & biomass were established. The results showed that under the same soil water status, the daily changing pattern for visible reflectance (450~700nm) and short-wave infrared reflectance (SWIR) (1200~1700nm) was R14>R12>R10, but for near red reflectance (NIR) (700-1100nm) it was R14>R10>R12 under adequate water supply and R10>R14>R12 under soil water stress. Over growth period, visible reflectance exhibited a lower value at the initial stages with lowest value at jointing, and then became higher gradually in rice, whereas in wheat visible reflectance showed a similar pattern, but NIR always went down over growth stages in wheat. Ratio vegetation index R760/R710 or R810/R710 after joint...