The traditional qualitative analysis of the individual factors on the kinetic parameters cannot sufficiently reveal the mechanism underlying urea hydrolysis in soil.This study aimed at revealing the coupling effects of the three factors on urease activity(V_(0)),hydrolysis rate constant(K_(u)),and activation energy(Ea)and establishing the quantitative model for K_(u) under the coupling condition.Laboratory culture experiments were conducted under different temperatures(T)(15℃,20℃,25℃,and 35℃),moisture contents(θ)(60%,80%,and 100%of field capacities),and nitrogen application rates(F)(247 mg/kg,309 mg/kg,371 mg/kg,and 433 mg/kg).The urea content was measured daily.Results showed that the effects of moisture content,temperature,nitrogen application rate,and their interaction on V_(0) and K_(u) were in the descending order:T,F,T^(*)F,θ,T^(*)θ,F^(*)θ,T^(*)θ^(*)F.The effect of single factor and two-factor coupling on V_(0) was extremely significant(p<0.01),whereas the effect of the three-factor coupling on V_(0) was negligible.The effects of three factors and their interaction on K_(u) were extremely significant(p<0.01).The effects of moisture content,nitrogen application rate,and their interaction on Ea were in the descending order:F,θ,F^(*)θ.The effects of two factors and their interaction on Ea were not significant.The mean absolute percentage error(MAPE)values of the established K_(u-1)(θ,T,F)and K_(u-2)(θ,T,F)models were 3.14%and 4.60%,respectively.The MAPE of the traditional Arrhenius model K_(u-3)(T)was 6.75%.The accuracy of the proposed three-factor interaction model was superior to that of the traditional single factor model.The results supplemented the mechanism of urea hydrolysis and improved the prediction accuracy of K_(u).
Tao LeiQiongqiong GuXianghong GuoJuanjuan MaYong ZhangXihuan Sun
The traditional qualitative analysis of the individual factors on the kinetic and thermodynamic parameters cannot sufficiently reveal the mechanism underlying ammonia volatilization in soil.This study aimed to determine the effects of temperature,moisture content,and their interaction on the kinetic and thermodynamic parameters,which revealed the key control mechanism underlying ammonia volatilization,modified the traditional Arrhenius model,and established a quantitative prediction model of cumulative NH_(3)-N loss(CNL).Laboratory culture experiments were conducted under different temperatures(T)(15℃,20℃,25℃and 35℃)and moisture contents(θ)(60%,80%,and 100%field capacities).Soil ammonia volatilization was also measured every 2 d.Results showed that the effects of individual factors and their interaction on the values of reaction rate(K_(N)),Activation free energy(ΔG),and activation entropy(ΔS)followed the descending order of T>θ>T·θ,whereas those of activation enthalpy(ΔH)and activation degree(lgN)followed the descending order ofθ>T>T·θ.The interaction showed significant effect on K_(N)value and insignificant effect on all the thermodynamic parameters.The effects of water and temperature were mainly observed during the preparatory stage and the most critical transition state stage of the chemical reaction,respectively.Given thatΔH>0,ΔG>0,andΔS>0,ammonia volatilization is found to be an endothermic reaction controlled by enthalpy.The new K_(N)(T)-2 model with the determination coefficient(R^(2))of 0.999 was more accurate than the traditional Arrhenius model with the R^(2)of 0.936.The new NH_(3)(T,θ)model with the mean absolute percentage error(MAPE)of 4.17%was more accurate than the traditional NH_(3)(T)model with the MAPE of 7.11%.These results supplemented the control mechanism underlying ammonia volatilization in soil fertilized with urea and improved the prediction accuracy of CNL.
Lei TaoGuo XianghongMa JuanjuanSun XihuanFeng YangWang Hongyu
Crop root system plays an important role in the water cycle of the soil-plant-atmosphere continuum. In this study, com- bined isotope techniques, root length density and root cell activity analysis were used to investigate the root water uptake mechanisms of winter wheat （Triticum aesfivum L.） under different irrigation depths in the North China Plain. Both direct inference approach and multisource linear mixing model were applied to estimate the distribution of water uptake with depth in six growing stages. Results showed that winter wheat under land surface irrigation treatment （Ts） mainly absorbed water from 10-20 cm soil layers in the wintering and green stages （66.9 and 72.0%, respectively）; 0-20 cm （57.0%） in the jointing stage; 0-40 （15.3%） and 80-180 cm （58.1%） in the heading stage; 60-80 （13.2%） and 180-220 cm （35.5%） in the filling stage; and 0-40 （46.8%） and 80-100 cm （31.0%） in the ripening stage. Winter wheat under whole soil layers irrigation treatment （Tw） absorbed more water from deep soil layer than Ts in heading, filling and ripening stages. Moreover, root cell activity and root length density of winter wheat under TW were significantly greater than that of Ts in the three stages. We concluded that distribution of water uptake with depth was affected by the availability of water sources, the root length density and root cell activity. Implementation of the whole soil layers irrigation method can affect root system distribution and thereby increase water use from deeper soil and enhance water use efficiency.
