Soil Tillage and Denitrification: Source from Depollution the Soil, Subsoil and Aquifer Water— Description, to Conduct and Control

Abstract

Denitrification is generally considered as a way of losing nitrogen in the soil. In recent years, increased nitrate pollution has made denitrification a natural process, possibly directed, to reduce this pollution from soil, subsoil and aquifer water (groundwater). In any farming system, it is important to determine the meaning and rate of changes of nitrogen compounds that take place in the soil under the influence of different technological systems and cultural practices. Due to the meteorological difficulties and the long time objective required to research the synthesis and decomposition of organic substances, mineralization, accumulation and loss of nitrogen, quantitatively and qualitatively, experimental data worldwide are fragmented and do not cover the whole diversity of situations encountered in agricultural practice. Based on the main considerations of these issues, this chapter analyzes them. This paper summarizes the results of the researches performed and quoted in the literature, supplemented with the results from the researches conducted at the University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Romania, regarding the possibility of controlling and directing the processes of nitrification-denitrification from the soil through factors with direct influence: the existing microflora, the level anoxia, availability in oxidized nitrogen and in carbon substrate; or factors with indirect influence: soil tillage system, soil humidity, application of fertilizers and organic matter. The soil tillage system changes the biological processes in the soil. This is accomplished by physical, hydrophysical and other system-specific factors. The conventional soil tillage (with plow) leads to quite a low denitrification; the repeated aeration of the soil being the first limiting factor. Here, nitrogen losses through denitrification are generally 3-10 kg/ha/year. Summer ploughing, compared to autumn ploughing, leads to a higher amount of nitrates in the soil. Soil conservation tillage (minimum tillage, no-tillage) requires minimal soil processing and an increased percentage of remaining vegetal incorporated in the soil to at least 30-50%. As a result, there are important changes in soil condition, water stability and organic carbon content in the soil depending on the soil tillage system. The higher percentage of not decomposed vegetal debris, a weaker soil settlement, better structure and therefore an increase in capillary porosity results in a balance between humification and mineralization, with an increase in the percentage of organic carbon, and at the same time a more intense denitrification activity. The soil surface mulch favors lower temperatures and diminution of amplitudes (denitrification is favored by temperatures around 25°C and nitrification at temperatures of 30-32°C). Theoretically, this would mean less nitrate leaching.