Effects Of Fertilization On Kinetic And Thermodynamic Parameters Of Soil Urease In Paddy Fields

Urease is the key enzyme in the translation of nitrogen, and the dynamics and thermodynamics of urease can reflect the urease activity and enzymatic reaction process mechanism in the certain degree. This paper mainly discussed what effects of fertilization would be made on soil urease dynamics and thermodynamics characteristics. The study included:1) The dynamics and thermodynamic characters of urease of soil showed that the urease content of rice paddy soil was the least and the enzymatic reaction was the least likely to happen, compared with vegetable field and bamboo forest soil. The Km value of it was the biggest, with 29.1 mmol·L-1,22.5 mmol·L-1 and 17.8 mmol·L-1 corresponding to 27℃,37℃and 47℃. But the Vmax and K value of it was the smallest. Under 27℃,37℃and 47℃, the Vmax values were 1.1 ug·g-1·h-1,3.6 ug·g-1-h-1and 4.5 ug-g-1·h-1, with 2.25×10-6 h-1,4.84×10-6 h-1 and 8.85×10-6h-1for K value. The Ea,ΔH,ΔG andΔS values of paddy soils were the largest. The Ea value of paddy soil, vegetable plots and bamboo forest soil were 77.79 kJ·mol-1,59.64 kJ·mol-1 and 62.07 kJ·mol-1. Under 27℃,37℃and 47℃, theΔH values of paddy soil were 77.07 kJ·mol-1,76.99 kJ·mol-1 and 76.91 kJ·mol-1. TheΔG values were 124.99 kJ·mol-1,125.83 kJ·mol-1 and 128.48 kJ·mol-1. TheΔS values were-159.72 J·mol-1,-157.53 J·mol-1 and-167.17 J·mol-1.2) All the dynamics and thermodynamic characters revealed that the urease enzymatic reaction was more likely to occur, and the less energy barrier needed to overcome in the soil applied with organic fertilizer than urea. The three times of fertilization made different effects on the parameters of urease. After the three times of fertilization, the Vmax and K values of soil applied with organic fertilizer were bigger than urea, but not the Ea,ΔH,ΔG andΔS values. Especially after the first time fertilization, under 47℃, the Vmax, K, Ea,ΔH andΔS values of soil applied with organic fertilizer were 31.2 ug·g-1-h-1,5.16×10-5h-1,33.91 kJ·mol-1, 33.66 kJ·mol-1 and-176.9 J·mol-1. The Vmax, K, Ea,ΔH andΔS values of soil applied with urea were 7.2 ug·g-1·h-1,2.99×10-5h-1,51.45 kJ·mol-1,51.21 kJ·mol-1 and-176.9 J·mol-1.The maximum difference of these paremeters of the two soil were 24 ug·g-1·h-1,2.10-5h-1,17.5 kJ·mol-1,17.5 kJ·mol-1 and 54 J·mol-1. The Km vaules of the two soil samples were incomparable.3) Adding biochars to soil was beneficial to soil enzymatic reaction, and they can improve the content of urease and reduce the energy needed for the happening of the reaction. The kinetics and thermodynamics indicators of the soil shows that adding biochars to soil maked soil enzymatic reaction occur more easily. Among 3 kinds of biochar, the 30 g/kg BCB imposed the best effect on activating urease. The BCB600℃can reduce the Km value around by 54.9%, both Ea andΔH value arond by 80%,ΔG by 4.7%, andΔS by 37%, but enhance the Vmax and K value by around 169% and 474%. The LB imposed the worst effect on it, and RSB was placed in the middle. The biochar made under 600℃had the better effect on urease than the ones made under 500℃to some degree, with the more 0.8ug·g-1h-1 and 3.0×10-6h-1 for the augment of Vmax and K value, the more 1.4 mmol·L-1,2.0 kJ·mol-1 and 0.6 kJ·mol-1 for the reduction ofΔH andΔG values. The dynamics and thermodynamics parameters of the soil cultivated for the relatively long time (60days) displayed superiority over the ones cultivated for the relatively short time(7days), which meaned the higher incidence of enzymatic reaction.4) Fertilization could impose influence on the soil urease enzymatic reaction apparent constant K. The results showed that the transformation of nitrogen of paddy fields was the weakest, and the decompositon time of it was the longest. From 27℃to 47℃, the decomposition time reduced from 998 h to 253 h, dropping by 294%.The K values of soil applied with organic fertilizer were 0.41×10-3 h-1-2.78×10-3 h-1 higher than soil applied with urea, with less decompsiton time from 19 h to 237 h. Especially after the third time of fertilization, under 47℃, the K value of soil applied with organic fertilizer were 6.62×10-3h-1, and the K value of soil applied with urea were 3.84×10-3h-1, appearing the maximum difference with 2.78×10-3 h-1. Adding biochars would increase K value and reduce the decomposition time. Especially, the BCB600℃could incease it to the highest growing rate around 230%. The biochar made under 600℃had the better effect on urease than the ones made under 500℃. The relatively long time (60days) revealed superiority over the ones cultivated for the relatively short time (7days). The maximum difference of the K value aimed at these two cultivating time reached 1.7×10-3 h-1, with 118 h for the decomposition time T.