| Soil moisture is one of the most important factors that affects the growth of crops,the absorption of moisture and nutrients utilization. Soil moisture characteristic curve is a graph of non-saturated soil water though which can be qualitatively analyzed of the relationship between soil moisture content and soil water potential,thus providing information of water requirement for water-saving irrigation. In this paper, Brassica campestris L. and Orychophragmus violaceus were selected as materials to research the growth in two different kinds of soil under drought condition.This study mainly includes two experiments. Experiment 1: Soil moisture characteristic curves of the two kinds of soil which were loam and loamy clay respectively and moisture losing time with four levels of soil water content in each kind of soil. Experiment 2: the growth of Brassica campestris L. and Orychophragmus violaceus under different soil moisture conditions. The results are as follows:1、 Based on the formula of Gibbs free energy,the model of Soil moisture characteristic curves was derived:(7)(8)(7)(8)S 01(10)P y(28)y(10)kln 1(10)P. The fitting results showed that the equation can well express the relationship of the relationship between soil water content and water potential,which indicates that the equation of Gibbs free energy posesses good practicability in the expression of Soil moisture characteristic curve. According to this equation, list the corresponding relationship as a table to find the soil water content by soil water potential. By this equation,the relational tables of the appropriate soil water content and water potential could be listed to check the soil water content by soil water potential.2、The relationship between soil water potential and moisture losing time fitted with the 4-parameter Logistic equation. The fittingresults showed that the Logistic equation well fit the relationship between soil water potential and moisture losing time, and the correlation coefficient R was 0.996 or more. The soil water content calculated by the soil water potential with changing time can also be a good fit with Logistic equation.3、The Brassica campestris L. and Orychophragmus violaceus were cultivated with four levels of soil water content of each soil,and the variation of physiological indexes in the continuous drought was Monitored. The physiological indexes included net photosynthetic parameters, water use efficiency, leaf water potential and fluorescence parameters.AS to Brassica campestris L.under loam cultivation conditions,the net photosynthetic rate of T1 decreased by 12.84% compared with the control group, and decreased by 12.84% with loamy clay cultivation conditions. But, the moderate drought group, Brassica campestris L. photosynthetic rate decreased by 34.63% and 26.02% comparing with control group with loam and loamy clay cultivations. The net photosynthetic rate was no significant difference under the same moisture gradient of two species of soil. Under continuous drought, the Brassica campestris L. net photosynthetic rate had a descending trend, and its decline rate was slower than the decline rate of loamy clay condition. The changing trend of Orychophragmus violaceus net photosynthetic rate was consistent with the changing trend of Brassica campestris L.. The difference was that the photosynthetic rate of Brassica campestris L. decreased by 6.81% comparing the control group, the decline range was significantly lower than that of Brassica campestris L.. It indicated that the soil moisture of T1 had little effection on the growth of Orychophragmus violaceus. The F0 of Brassica campestris L. and Orychophragmus violaceus had trended down with soil water decrease. The time of F0 rapid increase(Brassica campestris L.) was consistent with the time of rapid decline of transpiration rate, which indicated that F0 would be greatly affected when the loam moisture content was less than 15.9%~17.8%(loamy clay moisture content was less than 24.1%~27.1%). The changes of Fv/Fm、q P and ETR showed the opposite trend. With the decrease of soil water, Fv/Fm、q P and ETR decreased gradually.4 、 The transpiration rates of Brassica campestris L. and Orychophragmus violaceus had trended down with soil water decrease. When the soil(loam) moisture content was 15.9% ~ 17.8%, the transpiration rate had rapid declines. Howere, when the loamy clay moisture content was 24.1% ~ 27.1%, the transpiration would downhill quickly. The transpiration rate of Orychophragmus violaceus decreased rapidly when loam water content was 15.8%~18.2%, and loamy clay water content was 24.8%~27.3%.5、The trend of leaf water use efficiency was first increasing and then decreasing with soil water decrease. When the soil(loam) moisture content was less than 13%(loamy clay moisture content less than 22%), the leaf water use efficiency decreased rapidly. The leaf water use efficiency of Orychophragmus violaceus decreased rapidly when loam water content was less than 10%, and loamy clay water content was less than 19%. When the soil(loam) water content was 18%(corresponding soil water potential was-0.72Mpa) and the soil(loamy clay) water content was 27%(corresponding soil water potential was-0.75Mpa), the leaf water potential of Brassica campestris L. began to decline rapidly; While, when the leaf water potential of Orychophragmus violaceus began to decline rapidly,the soil(loam) water content was 16%(corresponding soil water potential was-0.91Mpa) and the soil(loamy clay) water content was 26%(corresponding soil water potential was-0.85Mpa). IX... |
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