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Wu Y.-F.,Chinese Academy of Agricultural Sciences | Dong Y.-W.,Chinese Academy of Agricultural Sciences | Hu X.,Shangqiu Academy of Agriculture and Forestry science | Lu G.-H.,Chinese Academy of Agricultural Sciences | And 2 more authors.
Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis | Year: 2015

At field scale, surface soil had special characteristics of volumetric moisture content (VMC) with a relatively little difference and spatial heterogeneity induced by physical and chemical properties, roughness, straw residues, etc. It has been a great challenge for near infrared diffuse reflectance spectroscopy (NIR-DRS) measurement of surface soil moisture in situ. In this study, exonential decay models based on seven water-related wavelengths (1200, 1400, 1450, 1820, 1940, 2000 and 2250 nm), linear models of normalized difference soil moisture index (NSMI) and relative absorption depth (RAD) based on wavelength combinations, linear or quadratic model of width of the inflection (σ), center amplitude of the function (Rd) and area under the Gaussian curve (A) from soil moisture Gaussian model (SMGM), and partial least square (PLS) regression models based on bands were used to quantify VMC. The results indicated that (1) of all the single wavelengths, 2000 nm showed the best validation result, indicated by the lowest RMSEp (2.463) and the highest RPD value (1.060). (2) Comparing with RAD, the validation of NSMI was satisfactory with higher R2 (0.312), lower RMSEp (2.133) and higher RPD value (1.224). (3) In the validation results of SMGM parameters and PLS fitting, Rd was found to produce the best fitting quality identified by the highest R2 (0.253), the lowest RMSEp (2.222), and the highest RPD value (1.175). (4) Comprehensively, a linear model based on NSMI showed the highest validation accuracy of all the methods. What is more, its calculation process is simple and easy to operate, and therefore become the preferred method to quantify surface soil moisture content in situ. © 2015, Science Press. All right reserved. Source


Wu Y.-F.,Chinese Academy of Agricultural Sciences | Hu X.,Shangqiu Academy of Agriculture and Forestry science | Lu G.-H.,Chinese Academy of Agricultural Sciences | Ren D.-C.,Shangqiu Academy of Agriculture and Forestry science | And 2 more authors.
Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis | Year: 2014

In the present study, late frost experiments were implemented under a range of subfreezing temperatures (-1~-9°C) by using a field movable climate chamber (FMCC) and a cold climate chamber, respectively. Based on the spectra of winter wheat canopy measured at noon on the first day after the frost experiments, red edge parameters REP, Dr, SDr, Drmin, Dr/Drmin and Dr/SDr were extracted using maximum first derivative spectrum method (FD), linear four-point interpolation method (FPI), polynomial fitting method (POLY), inverted Gaussian fitting method (IG) and linear extrapolation technique (LE), respectively. The capacity of the red edge parameters to detect late frost stress was explicated from the aspects of the early, sensitivity and stability through correlation analysis, linear regression modeling and fluctuation analysis. The result indicates that except for REP calculated from FPI and IG method in Experiment 1, REP from the other methods was correlated with frost temperatures (P<0.05). Thereinto, significant levels (P) of POLY and LE methods all reached 0.01. Except for POLY method in Experiment 2, Dr/SDr from the other methods were all significantly correlated with frost temperatures (P<0.01). REP showed a trend to shift to short-wave band with decreasing temperatures. The lower the temperature, the more obvious the trend is. Of all the REP, REP calculated by LE method had the highest correlation with frost temperatures which indicated that LE method is the best for REP extraction. In Experiment 1 and 2, only Drmin and Dr/Drmin calculated by FD method simultaneously achieved the requirements for the early (their correlations with frost temperatures showed a significant level P<0.01), sensitivity (absolute value of the slope of fluctuation coefficient is greater than 2.0) and stability (their correlations with frost temperatures always keep a consistent direction). Dr/SDr calculated from FD and IG methods always had a low sensitivity in Experiment 2. In Experiment 1, the sensitivity of Dr/SDr from FD was moderate and IG was high. REP calculated from LE method had a lowest sensitivity in the two experiments. Totally, Drmin and Dr/Drmin calculated by FD method have the strongest detection capacity for frost temperature, which will be helpful to conducting the research on early diagnosis of late frost injury to winter wheat. Source


Wu Y.F.,Chinese Academy of Agricultural Sciences | Zhong X.L.,Chinese Academy of Agricultural Sciences | Hu X.,Shangqiu Academy of Agriculture and Forestry science | Ren D.C.,Shangqiu Academy of Agriculture and Forestry science | And 3 more authors.
New Zealand Journal of Crop and Horticultural Science | Year: 2014

The influence of frost stress during the jointing stage in winter wheat was examined for original tillers (OT), regenerated tillers (RT) and the yield components of the cultivars Yumai 18, Zhoumai 18 and Yanzhan 4110. Ear number per plant, kernel number per ear, 1000-kernel weight and yield per plant were recorded under a range of subfreezing temperatures (-1,-3,-5,-7 and-9°C). The results were modelled by linear and quadratic regression. In the quadratic model, ear number per plant and yield per plant of the three cultivars were all significant (P < 0.001) and their fitted curves showed a concave-downward parabolic trend as the subfreezing temperature decreased. By analysing the change characteristics of ear number and yield per plant of OT and RT following frost treatment, it was found that OT decreased and RT increased resulting in the concave-downward parabolic yield trend. Final ear number and yield were the result of these opposing behaviours with OT and RT partly offsetting one another and thus tending to stabilize yield loss. The resulting compensatory behaviour of the three cultivars showed obvious differences with the RT of Yumai 18 making the greatest contribution to grain yield. The work offers the potential for creating a rational basis for selecting cultivars having improved frost resistance based on recording their tillering behaviour under low-temperature conditions. © 2014 The Royal Society of New Zealand. Source


Liu J.,China Agricultural University | Wang N.,China Agricultural University | Wang P.,China Agricultural University | Hu X.,Shangqiu Academy of Agriculture and Forestry science | Huang J.,China Agricultural University
Nongye Jixie Xuebao/Transactions of the Chinese Society for Agricultural Machinery | Year: 2015

The air temperature within near-ground layer is an important surrounding factor that can affect winter wheat growth. The simultaneous heat and water (SHAW) model, which is a detailed process model of heat and water movement in the plant-snow-residue-soil system, was evaluated in simulating the air temperature within near-ground layer from 0 cm to 40 cm at after-jointing stage of winter wheat. Field experiment was taken in Shangqiu City, Henan Province to observe the winter wheat growth and surrounding factors, such as air temperature. The SHAW model was calibrated and driven with inputs of part of field experiment data and empirical parameters. The results showed that the SHAW model performed well in simulating air temperature within near-ground layer in winter wheat field, with 48% of the absolute error of simulated values was less than 1℃, 75% of the absolute error of simulated values was less than 2℃, and the model efficiency at different heights was higher than 0.94. The simulated values had higher biases during the day than those at night and they were increased with the increase of height from ground, and their biases generally reached the largest value during 11:00 and 14:00. The daily mean values of the simulated and observed air temperature values were basically the same, while the daily lowest values were overestimated and the daily highest values were underestimated. The model had better effects at jointing, filling and dough stages than those at booting, blooming and heading stages. © 2015, Chinese Society for Agricultural Machinery. All right reserved. Source

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