Abstract
Soils are considered as an important source for NO emissions, but the uncertainty in quantifying these emissionsa worldwide remains large due to the lack of field experiments and high variability in time and space of environmental parameters influencingNOemissions. In this study, the development of a relationship forNOflux emission from soil with pertinent environmental parameters is proposed. An Artificial Neural Network (ANN) is used to find the best non-linear regression between NO fluxes and seven environmental variables, introduced step by step: soil surface temperature, surface water filled pore space, soil temperature at depth (20.30 cm), fertilisation rate, sand percentage in the soil, pH and wind speed. The network performance is evaluated each time a new variable is introduced in the network, i.e. each variable is justified and evaluated in improving the network performance. A resulting equation linking NO flux from soil and the seven variables is proposed, and shows to perform well with measurements (R2 = 0.71), whereas other regression models give a poor correlation coefficient between calculation and measurements (R2 ≤ 0.12 for known algorithms used at regional or global scales). ANN algorithm is shown to be a good alternative between biogeochemical and large-scale models, for future application at regional scale.
Highlights
Nitric oxide (NO) emissions from soils represent an important part of total NO emissions (Davidson and Kingerlee, 1997; Delmas et al, 1997).NO is produced in the soil upon microbial processes referred to as nitrification and denitrification
Soil moisture influence was emphasized in tropical soils, introducing the notion of pulse effect (Johansson et al, 1988; Yienger and Levy, 1995), but the same kind of soil moisture effect may occur when fertilization is applied in temperate soils before rain events
Results are presented in a sequential manner, where parameters are added one after the other and in the following order: soil surface temperature and surface Water Filled Pore Space (WFPS) at first, soil temperature at depth, fertilization rate, pH, percentage of sand and wind speed
Summary
Nitric oxide (NO) emissions from soils represent an important part of total (anthropogenic plus biogenic) NO emissions (around 40%, an amount comparable to fossil fuel combustions) (Davidson and Kingerlee, 1997; Delmas et al, 1997).NO is produced in the soil upon microbial processes referred to as nitrification and denitrification. The rate of nitrification and denitrification depends on the type of soil and on the nutrient content, and the exact role of each process in producing NO has been proven difficult to assess (Conrad, 1996). NO emissions from soils have been shown to be influenced by soil water content and soil temperature. The importance of soil temperature has been firstly considered, mostly in temperate soils (Williams et al, 1992; Martin et al, 1998). Increasing temperature was shown to increase NO emission, (Williams et al, 1992; Martin et al, 1998), whereas in some particular tropical conditions, the daily variation of fluxes with temperature could not be highlighted (Cardenas et al, 1993; Serca et al, 1994). A certain threshold in water filled pore space, the emission increases (Otter et al 1999; Meixner and Yang, 2004 )
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