| Solos

Carbon source

Study shows that the soil emits CO2 at a rate 10 times greater than all industrial activities combined.

10.11.2015 | 21:59 (UTC -3)

Soils used for agricultural exploration are generally devoid of vegetation for a period of time, waiting for the rainy season, before planting. During this period, this environment is basically an emitter of CO2 into the atmosphere, as no vegetation is present and no photosynthesis occurs. Soil is one of the main components in the carbon cycle, as it is the largest emitter of this element in the biosphere. To give you an idea, all industrial activity in the world releases approximately 5 billion tons of carbon into the atmosphere per year, while soil respiration, without taking into account the process of root respiration, emits around 50 billion tons of carbon per year, that is, an emission 10 times greater than that caused by all industrial pollution.

In recent centuries, activities such as soil management have influenced the dynamics of soil-atmosphere carbon emissions, causing an increase in such emissions. These processes are directly related to the greenhouse effect, placing agricultural activities as one of the main responsible for the recent change in the planet's climate.

Thus, a strategy that has been suggested to reduce global warming would be to rationalize some agricultural activities, in particular soil preparation methods, seeking to reduce the loss of carbon from the soil to the atmosphere. Despite all efforts, it is necessary to relate the influence of management systems to the amount of additional carbon emitted, especially in tropical soils.

One of these results was recently obtained from experiments carried out between 2000 and 2002 at FCAV-UNESP, Jaboticabal campus, SP, under the supervision of professors Prof. Dr. Afonso Lopes (Department of Rural Engineering) and Prof. Dr. Newton La Scala Júnior (Department of Exact Sciences) and the collaboration of students from the Agronomy course at this faculty. The teachers studied the immediate emission of CO2 from the soil after various preparations, such as: Rotary hoe, Scarifier, Disc plow followed by leveling harrow and Plow harrow followed by leveling harrow. In these surveys, care is taken to keep portions unchanged, called undisturbed. Once the soil preparation procedure was completed, we waited 24 hours to begin measuring the CO2 flux.

CO2 emissions from the soil were evaluated using a portable camera model 6400-09 (LI-COR, NE, USA), instrumentation acquired through the project financed by FAPESP (97/12009-8). The operation of the equipment is simple, and prevents the accumulation of CO2 inside the chamber, operating between a maximum and minimum concentration of CO2 inside, around the ambient concentration. To take readings, the camera is placed on PVC collars installed on the ground, and data on the CO2 flow emitted at each point is computed using the LI-6400 equipment (photosynthesis system).

Figure 1 (

) presents the results obtained over a 2-week period. In the first 24 hours that the management was carried out, emissions were as high as 0 g CO64 m-2 h-2 and 1 g CO0,47 m-2 h-2 in the scarified and plowed plots plus leveling harrow, respectively, and as low as 1 g CO0,27 m-2 h-2 in the unprepared plot. During the 1-week period, no rain occurred at the site and in the last days of the study, CO2 emissions converged to the same value of 2 g CO0,22 m-2 h-2 for all treatments. Statistical analysis demonstrated that CO1 emissions are significantly different (P

In more recent work, carried out in mid-2002, the aforementioned professors were able to prove that differences in the settings of a rotary hoe also significantly affect CO2 emissions from the soil to the atmosphere. Figure 2 shows this effect where emissions are compared after preparation with a rotary hoe in four adjustment forms: 1) without disturbance. 2) rotor rotation 122 rpm and rear bulkhead position raised. 3) 153 rpm and bulkhead raised 4) 153 rpm and bulkhead lowered 5) 216 rpm and bulkhead lowered. CO2 emission after preparation was monitored for 30 days and compared with the results of the portion without mobilization. The results showed that changing the settings on the same rotary hoe caused significant differences in CO2 emissions from the soil, as well as those caused by the different types of equipment, as shown in Figure 1.

In this way, the researchers remember that this line of studies meets new trends in agronomic practices considering environmental preservation. Such experiments will be enabling decision-making on sustainable development projects in the near future, with minimal transfer of carbon from the soil to the atmosphere after soil preparation, with the possibility of financial capture through so-called “carbon credits”.