3. Results and discussion
Table 1 shows the physicochemical properties of both soils col-lected in 2011 and 2012. Note the higher pH for YS as comparedwith NYS in 2011 in both years. Thus, the higher pH of YS must bedue to the yeast residue.A remarkable note was the increase of OC content of both soilsover just one year (20%) in situ. This must be due to the frequentapplications of EMA. On the contrary, YS stored at 4◦C during 1 yearlost 17% OC whereas NYS kept the original value. This might indi-cate a mineralization process in YS at the temperature of storage. Astudy of carbon and nitrogen mineralization in soil after the addi-tion of compost – made of brewing yeast and lemon tree prunings– showed there was a high release of CO2at early stages of biosta-bilization. Mineralization of organic carbon was around 25% in 70days of incubation [18]. In our work, the composting process wasjust 4 to 5 days. The same probably did not occur in the field due toEMA applied after the yeast, thus neutralizing the negative effectof yeast.Something striking was to find no CFU g−1in newly collectedsoil (Table 1). Only after 1 year of storage, colonies were possibleto be counted. Fig. 1A and B shows the p − t curves obtained during25 h for both soils at FCH supplemented with different amountsof glucose. Specific thermal power (p) − time (t) curves obtainedwith soil amended with glucose did not show the typical shape ofmicrobial growth curves.These curves show that the optimum concentration of glucosefor YS was 5 mg g−1(curve c of Fig. 1A) due to the higher p val-ues. However, the optimum glucose concentration for NYS was3 mg g−1as observed in Fig. 1B, curve a. Due to the strange shape ofthese curves, we decided to measure specific thermal power during100 or more hours and also, to measure the evolution of CO2onceor twice a day. Both soils were tested at different periods of timeduring 1 year. Fig. 2 shows the p − t curves obtained.Note the similarity among the p − t curves of each soil during2011 (Fig. 2, curves a–c). However, a difference can be observedbetween the soils. The most striking difference was that of YS andNYS collected in 2012 (curve d, Fig. A and B, respectively). Themicroflora responsible for the peak at 80 h in NYS is not presentin YS.Table 2 shows the thermodynamic parameters calculated fromthe curves in Fig. 2.
3. ผลลัพธ์ และสนทนาTable 1 shows the physicochemical properties of both soils col-lected in 2011 and 2012. Note the higher pH for YS as comparedwith NYS in 2011 in both years. Thus, the higher pH of YS must bedue to the yeast residue.A remarkable note was the increase of OC content of both soilsover just one year (20%) in situ. This must be due to the frequentapplications of EMA. On the contrary, YS stored at 4◦C during 1 yearlost 17% OC whereas NYS kept the original value. This might indi-cate a mineralization process in YS at the temperature of storage. Astudy of carbon and nitrogen mineralization in soil after the addi-tion of compost – made of brewing yeast and lemon tree prunings– showed there was a high release of CO2at early stages of biosta-bilization. Mineralization of organic carbon was around 25% in 70days of incubation [18]. In our work, the composting process wasjust 4 to 5 days. The same probably did not occur in the field due toEMA applied after the yeast, thus neutralizing the negative effectof yeast.Something striking was to find no CFU g−1in newly collectedsoil (Table 1). Only after 1 year of storage, colonies were possibleto be counted. Fig. 1A and B shows the p − t curves obtained during25 h for both soils at FCH supplemented with different amountsof glucose. Specific thermal power (p) − time (t) curves obtainedwith soil amended with glucose did not show the typical shape ofmicrobial growth curves.These curves show that the optimum concentration of glucosefor YS was 5 mg g−1(curve c of Fig. 1A) due to the higher p val-ues. However, the optimum glucose concentration for NYS was3 mg g−1as observed in Fig. 1B, curve a. Due to the strange shape ofthese curves, we decided to measure specific thermal power during100 or more hours and also, to measure the evolution of CO2onceor twice a day. Both soils were tested at different periods of timeduring 1 year. Fig. 2 shows the p − t curves obtained.Note the similarity among the p − t curves of each soil during2011 (Fig. 2, curves a–c). However, a difference can be observedbetween the soils. The most striking difference was that of YS andNYS collected in 2012 (curve d, Fig. A and B, respectively). Themicroflora responsible for the peak at 80 h in NYS is not presentin YS.Table 2 shows the thermodynamic parameters calculated fromthe curves in Fig. 2.
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