**1. Introduction**

Nitrogen (N) plays a key role in the growth and development of wheat; thus, wheat's growth and quality might be modified through N fertilization [48]. However, cultures use N inefficiently, and, in general, 50% of the applied N is not used by plants [12, 41]. Therefore, N losses take place, both gaseous and leached, which cause economic and environmental costs.

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Within the economic costs, that caused due to diminished N use efficiency stands out. Among the environmental costs, the contribution of some N-based gaseous compounds that play a role in the greenhouse effect [10], acid rain [23, 24] and the contamination and eutrophication of waters due to nitrate leaching further than the root zone [1, 17] are notable. In this sense, in Álava, Arrate et al. [6] describe a series of changes in the management of arable land in the years 1967–1997 (wetland drainage, application of large quantities of fertilizers, phytosanitary products etc.) that progressively increased the concentration of N compounds in subsurface waters. Due to such reasons and by application of the European Directive 88/778/ EEC related to water for human consumption [13], the zone related to the Eastern sector of the quaternary aquifer of Vitoria was designated as vulnerable to nitrate pollution in the year 1999 [14]. This zone comprises 38% of the area where wheat is grown in Alava, 9500 ha approximately. In this zone, the N fertilization is as much as 140 kg N ha−1 depending on the previous culture and soil richness; N fertilization is not allowed at a distance closer than 3 m of any water course.

can occur simultaneously in the soil since the aerobic and anaerobic conditions can simultane-

The N balance allows the knowledge of the N evolution at the soil–plant system in a settled period of time. It also enables the knowledge of the sources of N other than fertilization, and the rate of transfer between the different components of N, the main mechanisms of N loss, and what amount of N is not likely to be recovered [30]. Therefore, determining the balance of N in a culture system helps explain certain parameters that determine the dose of N needed by the cereal [28, 49], optimizing the nitrogenous nutrition of the plant and reducing the dan-

The goal of this work was to ascertain the quantity of N lost by leaching or by being released to the atmosphere and to study the factors that have an effect on such losses. Also, the N bal-

A nitrogen fertilization experiment was carried out in Gauna, Álava (average annual rainfall of 779 mm and average annual temperature of 11.5°C) from November 2001 to February 2004 in three consecutive seasons. The assay was conducted in the Western Sector of the quaternary aquifer of Vitoria, adjacent to the area vulnerable to the contamination of nitrates of agricultural origin. The trial was organized in random blocks with four repetitions in which

classified as Aquertic Eutrudept [40] and was planted with wheat. Some of the soil properties are shown in **Table 1**. Data regarding when sowing, the first, second, and third N broadcast-

O ha−1 were applied as 0-14-14. Nitrogen doses of 0, 140, and 220 kg N ha−1

ings, and the harvest took place are shown in **Table 2**. Before sowing, 90 kg ha−1 of P<sup>2</sup>

Depth (cm) 0–30 30–60 Sand (%) 45.18 48.25 Silt (%) 27.14 39.21 Clay (%) 27.67 12.49 pH 7.98 8.13 Organic matter (%) 2.12 1.52 Phosphorous (P) (mg kg−1) 43.30 32.53 Potassium (K) (mg kg−1) 135.00 93.00 Carbonates (%) 11.90 22.00

. The soil on which the trial was established was

Nitrogen Losses: Gaseous and Leached Nitrogen Balance

http://dx.doi.org/10.5772/intechopen.75801

81

O5 ha−1

ously take place at the same soil aggregate [26].

ance in the soil–plant system was to be determined.

each elementary plot covered an area of 50 m<sup>2</sup>

**Table 1.** Soil properties of the experiment in Gauna (Álava).

ger of contamination.

**2. Materials and methods**

**2.1. Assay establishment**

and 90 kg ha−1 of K<sup>2</sup>

Nitrous oxide (N<sup>2</sup> O) is not a very reactive gas; it persists in the atmosphere for as much as 150 years [47]. This gas adsorbs electromagnetic radiation in various wavelengths in the infrared region between 7.7 and 17 μm [35] and its greenhouse effect per mass unit is some 300 times larger than that of CO<sup>2</sup> [36]. In this sense, it is estimated that in the last 100 years, N<sup>2</sup> O has contributed approximately 5% to the warming up of the planet [42, 43]. The origin of 90% of the N<sup>2</sup> O emissions is anthropogenic, and agriculture is its main source [22]. N<sup>2</sup> O in soils can be produced both due to nitrification and denitrification (**Figure 1**). Nitrification is a microbial aerobic process in which ammonium first oxidizes to nitrite and then to nitrate. In this ammonium to nitrate oxidation process, N<sup>2</sup> O can be released into the atmosphere [46]. On the other hand, denitrification is a microbial anaerobic process in which organic carbon is used as the energy source and the nitrate as the last electron acceptor so that it reduces to the last nitrogenous gaseous compounds N<sup>2</sup> O and N<sup>2</sup> . The nitrification and denitrification processes

**Figure 1.** Transformations of mineral nitrogen in the soil [46].

can occur simultaneously in the soil since the aerobic and anaerobic conditions can simultaneously take place at the same soil aggregate [26].

The N balance allows the knowledge of the N evolution at the soil–plant system in a settled period of time. It also enables the knowledge of the sources of N other than fertilization, and the rate of transfer between the different components of N, the main mechanisms of N loss, and what amount of N is not likely to be recovered [30]. Therefore, determining the balance of N in a culture system helps explain certain parameters that determine the dose of N needed by the cereal [28, 49], optimizing the nitrogenous nutrition of the plant and reducing the danger of contamination.

The goal of this work was to ascertain the quantity of N lost by leaching or by being released to the atmosphere and to study the factors that have an effect on such losses. Also, the N balance in the soil–plant system was to be determined.
