[Estimation of sugar to nitrogen ratio in wheat leaves with near infrared spectrometry].

The soluble sugar to nitrogen ratio reflects the coordination degree of carbon (C) and nitrogen (N) metabolism. Precise and real-time monitoring of soluble sugar to nitrogen ratio is of significant importance for nitrogen diagnosis and management regulation in wheat production. In this study, time-course near infrared spectroscopy and soluble sugar to nitrogen ratio of fresh and dry leaves were obtained under different field experiments with varied years and cultivar and N rates. The methods of partial least squares (PLS), back-propagation neural network (BPNN) and wavelet neural network (WNN) were used to develop the calibration models with the preprocessed spectra, respectively, and the dataset selected randomly was used to evaluate the constructed models. The results showed that the performance of the models for fresh-leaves was not satisfied, but good for dry-leaves with the root mean square errors of prediction (RMSEP) by PLS, BPNN and WNN models based on 1655-2378 nm less than 0.3% and with the coefficients of determination (R2) over than 0.9, respectively. In comparison, the model based on WNN was the best one. All these indicated that near infrared spectrometry could be applied to estimating the soluble sugar to nitrogen ratio in plant. The results provided the theoretical basis and technological approach for diagnosing crop C/N.

[Quantitative relationships between satellite channels-based spectral parameters and wheat canopy leaf nitrogen status].

Using space-borne remote sensing information to monitor the crop canopy nitrogen status and crop productivity in a large-scale is of great significance and application prospect i1 modern agriculture. With the hyper-spectral reflectance data from the wheat canopy under different nitrogen fertilization levels, this paper constructed the spectral indices (including the single wavelength, ratio spectral index, and normalized difference spectral index) simulated by satellite channels, and established the nitrogen estimation equations by quantifying the relationships between the simulated channels spectral indices and the leaf nitrogen index. The results indicated that the spectral indices based on NDVI (MSS7, MSS5), NDVI (RBV3, RBV2), TM4, CH2, MODIS1, and MODIS2 could be reliably used for estimating the leaf nitrogen content (LNC), with R2 over 0.60, and the spectral indices based on NDVI (PB4, PB2), NDVI (CH2, CHl1), NDVI (MSS7, MSS5), RVI (MSS7, MSS5), MODIS1, and MODIS2 could be accurately used for predicting the leaf nitrogen accumulation (LNA), with R2 greater than 0.86. Comparatively, NDVI (MSS7, MSS5) and NDVI (PB4, PB2) could be the more suitable spectral indices for predicting the wheat canopy LNC and LNA, respectively.

[Relationships of rice canopy PAR interception and light use efficiency to grain yield].

Taking two rice cultivars (Liangyoupeijiu and Wuxiangjing 14) with different plant types as test materials, a 2-year field experiment was conducted to study the relationships of rice canopy photosynthetically active radiation (PAR) interception and light use efficiency to grain yield under three planting densities and five nitrogen (N) application rates. From tillering to maturing stage, the average PAR reflectance in all treatments was 3.45%. The ratio of reflected PAR to the total loss of PAR from tillering to heading stage was 10.90%, which was significantly lower than that (22.06%) from heading to maturiting stage. The PAR conversion efficiency from tillering to maturing stage decreased with increasing planting density but increased with increasing nitrogen rate, and the conversion efficiency was significantly higher from tillering to heading than from heading to maturing stage. The PAR use efficiency from tillering to maturing stage increased with the increase of planting density and nitrogen application rate, and the average PAR use efficiency of Liangyoupeijiu (1.83 g x MJ(-1)) was significantly higher than that of Wuxiangjing 14 (1.42 g x MJ(-1)). Due to the longer growth period of Wuxiangjing 14, its incident PAR and intercepted PAR under midium and high planting densities were higher, as compared with Liangyoupeijiu. The grain yield was significantly positively correlated with the canopy PAR interceptance and use efficiency at different growth stages, but less correlated with the PAR conversion efficiency. To increase the canopy PAR use efficiency and conversion efficiency on the basis of maintaining higher PAR interception rate could be an effective way to increase rice yield.

[Responses of wheat seedlings root growth and leaf photosynthesis to drought stress].

Taking drought-sensitive wheat cultivar Wangshuibai and drought-tolerance cultivar Luohan 7 as test materials, a hydroponic experiment was conducted to study the effects of drought stress on root system morphology, physiological characteristics and leaf photosynthesis of wheat seedlings, aimed to elucidate the adaptation mechanisms to drought stress. Under drought stress, the root vitality of the cultivars increased markedly, but the root number and root surface area decreased. Drought stress decreased relative water content and increased the ratio of bound water to free water in leaves of Wangshuibai, but had less effects on Luohan 7. Drought stress decreased, the leaf chlorophyll content, Pn g(s), Ci, and transpiration rate of the two cultivars, but had no significant effects on leaf chlorophyll content and Pn of Luohan 7. Drought stress decreased the leaf area of the two cultivars and the root biomass, shoot biomass, and plant biomass of Wangshuibai, but had no significant effects on Luohan 7. The results indicated that under drought stress, drought-tolerant wheat cultivar was able to compensate decreased root absorption area and retain higher root water uptake capability via enhancing root vitality and maintaining higher root biomass, and further, to keep higher leaf photosynthetic area and Pn to mitigate the inhibition of drought on wheat seedlings growth.

[Accumulative nitrogen deficit models of wheat aboveground part based on critical nitrogen concentration].

Based on three-year field experiments, three models of critical nitrogen concentration dilution curve, nitrogen nutrition index, and accumulative nitrogen deficit were constructed for the aboveground dry matter in medium protein wheat variety Yangmai 16 and low protein wheat variety Ningmai 13, respectively. The critical nitrogen concentration dilution curve model had specific biological meaning, i. e., there existed a negative power function correlation between shoot maximum dry matter (DM) and critical nitrogen concentration (Ncnc) (Yangmai 16: Ncnc = 4.65DM(-0.4); Ningmai 13: Ncnc = 4.33DM(-0.45)), the nitrogen nutrition index model could be used for accurate diagnosis of wheat plant nitrogen status, and the accumulative nitrogen deficit model could be used for quantitative regulation of nitrogen fertilizer management. The tests of the derived equations with independent experiment data (2007-2008) showed higher accuracy and reliable prediction, suggesting that the present models could be used for the diagnosis and regulation of wheat nitrogen nutrition, providing a key technical approach to precise fertilization management in wheat production.

[Dynamic simulation of wheat stem-sheath angle based on process].

Based on the field experiments with different plant-type wheat (Triticum aestivum) cultivars and varied population densities, the time-course changes in the angle between stem and sheath (stem-sheath angle) on main stem were observed, and a process-based model was developed for simulating the growth dynamics of stem-sheath angle on the main stem by using system analysis method and dynamic modeling technology. The stem-sheath angle increased with the growth of corresponding leaves, and decreased with increasing population density. The maximum stem-sheath angle decreased with increasing leaf position, except for the first leaf on main stem. The growth dynamics of stem-sheath angle could be described with Logistic equation, and the changes in the maximum stem-sheath angle with leaf position could be quantified with two different equations. The maximal value of stem-sheath angle at the second leaf position was considered as the cultivar parameter to reflect the genetic differences, and the plant number per unit area was used to quantify the effects of population density. The independent field experiment dataset of different wheat cultivars was used to test the model, and the average RMSE between estimated and observed values was 1.7 degrees, suggesting that the present model had good performance and reliability on predicting the growth dynamics of wheat stem-sheath angle, and provided a key module for wheat plant-type simulation and visualization.

[Effects of atmospheric CO2 concentration enhancement and nitrogen application rate on wheat grain yield and quality].

FACE platform was applied to study the effects of elevated atmospheric CO2 concentration on wheat grain yield and quality under two nitrogen (N) application rates. Elevated atmospheric CO2 concentration and applying N increased the grain yield, spike number, grain number per spike, and biomass significantly, but elevated CO2 concentration had no significant effects on harvest index (HI). Under elevated CO2 concentration, there was a significant decrease in the protein, gliadin, gluteinin, and glutein contents of the grain and the sedimentation value of the flour, and a significant increase in the starch and its components contents of the grain; under N application, an inverse was observed. The dough stability time and the dough viscosity characteristics, such as peak viscosity, final viscosity, and setback value, increased significantly under elevated CO2 concentration and high N application rate. The interaction of atmospheric CO2 concentration and N application rate had significantly positive effects on wheat grain yield and biomass, but less effect on grain quality. Therefore, with elevated atmospheric CO2 concentration in the future, maintaining a higher N application level would benefit wheat grain yield and paste characteristics, and mitigate the decline of grain quality.

[Defining of wheat growth management zones based on remote sensing and geostatistics].

Taking the winter wheat planting areas in Rugao City and Haian County of Jiangsu Province as test objects, the clustering defining of wheat growth management zones was made, based on the spatial variability analysis and principal component extraction of the normalized difference vegetation index (NDVI) data calculated from the HJ-1A/B CCD images (30 m resolution) at different growth stages of winter wheat, and of the soil nutrient indices (total nitrogen, organic matter, available phosphorus, and available potassium). The results showed that the integration of the NDVI at heading stage with above-mentioned soil nutrient indices produced the best results of wheat growth management zone defining, with the variation coefficients of NDVI and soil nutrient indices in each defined zone ranged in 4.5% -6.1% and 3.3% -87.9%, respectively. However, the variation coefficients were much larger when the wheat growth management zones were defined individually by NDVI or by soil nutrient indices, suggesting that the newly developed defining method could reduce the variability within the defined management zones and improve the crop management precision, and thereby, contribute to the winter wheat growth management and process simulation at regional scale.

[Three-dimensional morphological modeling and visualization of wheat root system].

Crop three-dimensional (3D) morphological modeling and visualization is an important part of digital plant study. This paper aimed to develop a 3D morphological model of wheat root system based on the parameters of wheat root morphological features, and to realize the visualization of wheat root growth. According to the framework of visualization technology for wheat root growth, a 3D visualization model of wheat root axis, including root axis growth model, branch geometric model, and root axis curve model, was developed firstly. Then, by integrating root topology, the corresponding pixel was determined, and the whole wheat root system was three-dimensionally re-constructed by using the morphological feature parameters in the root morphological model. Finally, based on the platform of OpenGL, and by integrating the technologies of texture mapping, lighting rendering, and collision detection, the 3D visualization of wheat root growth was realized. The 3D output of wheat root system from the model was vivid, which could realize the 3D root system visualization of different wheat cultivars under different water regimes and nitrogen application rates. This study could lay a technical foundation for further development of an integral visualization system of wheat plant.

[Effects of shading on the nitrogen redistribution in wheat plant and the wheat grain quality].

Taking winter wheat (Triticum aestivum L.) cultivars Yangmai 158 (shading-tolerant) and Yangmai 11 (shading-sensitive) as test materials, this paper studied the effects of shading at the stages from jointing to maturity on the plant N redistribution, grain yield, and grain- and dough quality of the cultivars. The treatments were non-shading, 22% shading, and 33% shading. Under shading, the grain yield and its protein content of Yangmai 158 and Yangmai 11 decreased by 4.1%-9.9% and 3.0%-8.3%, and 15.3%-25.8% and 10.4%-14.1%, respectively, compared with non-shading. With the increase of shading intensity, the grain N content was increasingly dependent on the N accumulated after anthesis. Shading decreased the redistribution of N stored pre-anthesis in the vegetative organs to the grain, but increased the redistribution efficiency of N accumulated pre-anthesis (RENP) in leaves while decreased the RENP in sheathes and stems, and in hulls and rachises. Therefore, the mean RENP in the vegetative organs was not essentially altered by shading. The grain protein content increased significantly under shading, which could be related to the "condense effect", i.e., the decrement of grain protein content was much less than that of grain yield. In addition, shading had less effects on the contents of grain albumin and globulin but increased the contents of grain gliadin and glutinin significantly, and accordingly, the grain wet gluten content, dough development time, and dough stability time increased, while the dough softening degree decreased.

[Dry matter accumulation in rice aboveground part: quantitative simulation].

A field experiment with four rice (Oryza sativa L.) cultivars and different nitrogen application rates was conducted, with the dry matter accumulation (DMA) in the cultivars aboveground part measured at their main growth stages. The dynamic model of relative dry matter accumulation (RDMA) was established with the normalized DMA and TEP (product of thermal effectiveness and PAR) from emergence to maturity, and the temporal characteristics of DMA changes was quantitatively analyzed based on the RDMA model. The dynamic changes of the RDMA could be well described with Richards equation, i. e., RDMA = 1.0157/(1 +e(3.6329-7.5907xRTEP)) 1/0.5574 (r = 0.9938). The model was validated with independent field experiment datasets, involving different eco-sites, cultivars, and nitrogen application rates. The RMSE (root mean square error) between the simulated and observed values of DMA at varied RTEP was 0.86 t x hm(-2). According to the two inflexion points of dry matter accumulation rate equation, the whole process of dry matter accumulation could be divided into early, middle, and late phases. The maximum dry matter accumulation rate (AR(max)), relative TEP at AR(max), and relative dry matter accumulation at AR(max) were found to be 2.24, 0.56, and 0.46, respectively.

[Comparison of spatial interpolation methods for daily meteorological elements].

A comparative study was made to evaluate the methods of inverse distance weighting (IDW), co-kriging (CK), and thin plate spline (TPS) in interpolating the average meteorological elements (including maximum air temperature, minimum air temperature, sunshine hours, and precipitation) of the 15th day per month from the 1951-2005 comprehensive observation data of 559 meteorological stations in China. The results showed that the RMSEs for the maximum and minimum air temperature in a year interpolated by TPS were the smallest (1.02 degrees C and 1.12 degrees C, respectively), and the R2 between the observed and predicted values were the highest (0.9916 and 0.9913, respectively), compared with those interpolated by IDW and CK. In four seasons, the smallest RMSEs for the maximum and minimum air temperature interpolated by TPS were observed in autumn (0.83 degrees C) and summer (0.86 degrees C), respectively, and the R2 between the observed and predicted values interpolated by TPS were higher in autumn than in other seasons. The RMSEs for the sunshine hours and precipitation in a year interpolated by TPS were the smallest (0.59 h and 1.01 mm, respectively), and the R2 between the observed and predicted values were the highest (0.9118 and 0.8135, respectively), compared with those interpolated by IDW and CK. In four seasons, the RMSE for the sunshine hours in winter interpolated by TPS was the smallest (0.49 h), and the R2 between the observed and predicted sunshine hours was the smallest (0.9293). The RMSE for the precipitation in winter interpolated by TPS was the smallest (0.33 mm), while the RMSE for the precipitation in summer interpolated by IDW was the smallest (2.01 mm). The R2 between the observed and predicted precipitation in winter interpolated by CK was the highest (0.8781). It was suggested that TPS could be the optimal spatial interpolation method in interpolating and rasterizing the daily meteorological elements in China.

[Model designing for suitable nitrogen index dynamics of rice and wheat].

By analyzing and extracting the quantitative relationships of suitable nitrogen index dynamics of rice and wheat to their cultivar types, cultural techniques, and eco-environments, a design model for the suitable nitrogen index dynamics of rice and wheat was developed. The model was driven by the physiological development time-based relative growing degree days, with the relative nitrogen indices as modeling parameters, and could be used to generate the time-course indices such as the nitrogen accumulation and concentration of rice and wheat under different growth conditions. Case studies with the datasets from 3-year field experiments in Nanjing showed that the average RMSEs of the simulated to measured plant nitrogen accumulation and concentration were 0.1245 and 0.1316 for rice, and 0.1166 and 0.1301 for wheat, respectively. It was suggested that this model could reliably guide the dynamics of major nitrogen indices of rice and wheat, which would help with the quantitative nitrogen diagnosis and precision nitrogen management of rice and wheat under different eco-environments, cultivar types, and production conditions.

[Morphological and physiological differences of wheat genotypes at seedling stage under water stress].

Taking thirty six wheat cultivars bred in different era and ecological regions as test materials, their seedlings growth under water stress was investigated, and their drought resistance was evaluated by gray correlation grade analysis. Significant difference was observed in the drought resistance among the cultivars. The weighted drought resistance index ranged from 0.6580 to 0.2434. Among the test seventeen morphological and physiological traits, shoot dry mass had the greatest correlation degree (0.9473) with drought resistance, while SPAD had the smallest one (0.5356). The test cultivars were clustered into three groups, among which, eight cultivars belonged to strong drought resistance group, twenty three cultivars belonged to medium drought resistance group, and five cultivars belonged to drought-sensitive group. The shoot dry mass, root dry mass, plant dry mass, plant height, root nitrogen accumulation, leaf area, and tiller number per plant differed significantly among the three groups, which could be used for evaluating the drought resistance of wheat cultivars at seedling stage.

[Simulation model of barley leaf area index].

To simulate leaf area index (LAI) accurately is the key for the prediction of crop growth and yield in a crop growth model. Based on the analysis of the dynamic changes in the LAI of high-yielding barley cultivars in Wuhan and Yangzhou, a simulation model of barley LAI was established, in which, the LAI was the function of expansion coefficient of LAI for cultivar genetic property, climatic factors such as daily air temperature difference, sunshine hours, and accumulation of photosynthetic available radiation after sowing (sigma PAR), and limitation indices of water and nutrients. It was indicated that the maximum LAI and optimal LAI at the stages of booting and heading were not the same conception, but differed significantly. The model was tested by the field experiments with different barley cultivars under different sowing dates and nitrogen application rates in Yangzhou, Nanjing, and Kunming. The results showed that this model gave the good predictions of LAI at different development stages, with the RMSE values ranged in 0.742 and 2.865, and averaged 1.348. The simulated and observed LAI values were significantly positively correlated, and the correlation coefficient from y = x regression analysis was between 0.511 and 0.954.

[Estimation of optimum normalized difference spectral index for nitrogen accumulation in wheat leaf based on reduced precise sampling method].

Four independent field experiments with 6 wheat varieties and 5 nitrogen application levels were conducted, and time-course measurements were taken on the canopy hyperspectral reflectance and leaf N accumulation per unit soil area (LNA, g N x m(-2)). By adopting reduced precise sampling method, all possible normalized difference spectral indices [NDSI(i,j)] within the spectral range of 350-2500 nm were constructed, and the relationships of LNA to the NDSI(i,j) were quantified, aimed to explore the new sensitive spectral bands and key index from precise analysis of ground-based hyperspectral information, and to develop prediction models for wheat LNA. The results showed that the sensitive spectral bands for LNA were located in visible light and near infrared regions, especially at 860 nm and 720 nm for wheat LNA. The monitoring model based on the NDSI(860,720) was formulated as LNA = 26.34 x [NDSI(860,720)](1.887), with R2 = 0.900 and SE = 1.327. The fitness test of the derived equations with independent datasets showed that for wheat LNA, the model gave the estimation accuracy of 0.823 and the RMSE of 0.991 g N x m(-2), indicating a good fitness between the measured and estimated LNA. The present normalized hyperspectral parameter of NDSI(860,720) and its derived regression model could be reliably used for the estimation of winter wheat LNA.

[A near-infrared spectral index for estimating soil organic matter content].

Taking the air-dried samples of five soil types from middle and eastern China as test materials, the correlations of their organic matter content with the spectral reflectance of near-infrared (1000-2500 nm), and with the ratio index (RI), difference index (DI), and normalized difference index (ND) of the first derivative values of the reflectance between two bands were studied. Based on this, the key spectral indices and the quantitative models for estimating soil organic matter (SOM) content were developed. After corrected with Multiplicative Scatter Correction (MSC) and Savitzky-Golay (SG) smoothing methods, the spectral reflectance of near-infrared had an obviously high correlation with SOM, compared with the original spectral reflectance, while the corrected spectral indices of the first derivative values of the reflectance between two bands took the intermediate position. The correlation of the spectral indices with SOM was in the order of was DI > RI > ND, regardless the composition of the original spectral reflectance or the first derivative spectra. The DI of the reflectance of near-infrared between 1883 and 2065 nm corrected with MSC and SG smoothing methods [DI(CR1883, CR2065)] had the best linear correlations with SOM. The test of the monitoring model based on DI(CR1883, CR2065) with the independent datasets of SOM showed that the R2 and RMSE validation values were 0.837 and 4.06, respectively. Comparing with the results from the Partial Least Square (PLS) method, the monitoring model based on DI (CR1883, CR2065) was somewhat inferior. However, the DI(CR1883, CR2065) only needed two reflectance bands, and the monitoring model was simpler, being able to provide more available information for developing portable instruments, and a good spectral index for estimating SOM content.

[Quantitative relationships between hyper-spectral vegetation indices and leaf area index of rice].

Based on field experiments with different rice varieties under different nitrogen application levels, the quantitative relationships of rice leaf area index (LAI) with canopy hyper-spectral parameters at different growth stages were analyzed. Rice LAI had good relationships with several hyper-spectral vegetation indices, the correlation coefficient being the highest with DI (difference index), followed by with RI (ratio index), and NI (normalized index), based on the spectral reflectance or the first derivative spectra. The two best spectral indices for estimating LAI were the difference index DI (854, 760) (based on two spectral bands of 850 nm and 760 nm) and the difference index DI (D676, D778) (based on two first derivative bands of 676 nm and 778 nm). In general, the hyper-spectral vegetation indices based on spectral reflectance performed better than the spectral indices based on the first derivative spectra. The tests with independent dataset suggested that the rice LAI monitoring models with difference index DI (854,760) as the variable could give an accurate LAI estimation, being available for estimation of rice LAI.

[Exploring novel hyperspectral band and key index for leaf nitrogen accumulation in wheat].

The objectives of the present study were to explore new sensitive spectral bands and ratio spectral indices based on precise analysis of ground-based hyperspectral information, and then develop regression model for estimating leaf N accumulation per unit soil area (LNA) in winter wheat (Triticum aestivum L.). Three field experiments were conducted with different N rates and cultivar types in three consecutive growing seasons, and time-course measurements were taken on canopy hyperspectral reflectance and LNA tinder the various treatments. By adopting the method of reduced precise sampling, the detailed ratio spectral indices (RSI) within the range of 350-2 500 nm were constructed, and the quantitative relationships between LNA (gN m(-2)) and RSI (i, j) were analyzed. It was found that several key spectral bands and spectral indices were suitable for estimating LNA in wheat, and the spectral parameter RSI (990, 720) was the most reliable indicator for LNA in wheat. The regression model based on the best RSI was formulated as y = 5.095x - 6.040, with R2 of 0.814. From testing of the derived equations with independent experiment data, the model on RSI (990, 720) had R2 of 0.847 and RRMSE of 24.7%. Thus, it is concluded that the present hyperspectral parameter of RSI (990, 720) and derived regression model can be reliably used for estimating LNA in winter wheat. These results provide the feasible key bands and technical basis for developing the portable instrument of monitoring wheat nitrogen status and for extracting useful spectral information from remote sensing images.

[Effects of shading on wheat grain starch quality and redistribution of pre-anthesis stored nonstructural carbohydrates].

This paper studied the effects of shading in the period from jointing to maturity on the grain yield, starch content, and starch paste traits of two winter wheat (Triticum aestivum L.) cultivars, shading-tolerant Yangmai 158 and shading-intolerant Yangmai 11, and analyzed the relationships of the redistribution of total soluble sugars stored before anthesis in vegetative organs with the grain yield, starch content, and starch paste parameters of the cultivars. The results showed that shading decreased the redistribution of pre-anthesis stored total soluble sugars in vegetative organs to reproductive organ, resulting in the decrease of grain yield, and significantly decreased the amylopectin content but had no effects on the amylose content in grains, inducing a significant decrease in the ratio of amylopectin to amylase content in the grains. Shading also decreased the grain starch peak viscosity of the cultivars. Under shading, Yangmai 11 had a decrease of its grain starch through viscosity and an increase of starch pasting temperature, while Yangmai 158 had lesser responses in the two parameters.