[en] Sustainable agricultural and forest production depends on soil properties and on soil quality status. Variability in soil properties has a big interest, because site specific management may allow a reduction of production costs, while fully exploiting raw materials and the use of agricultural machinery. Using tehcniques such as localized application of fertilizers, plant protection products and new methods for measuring soil properties, precison agriculture therefore seekd to increase economic return., while decreasing environmental impacts. The main objective of this doctoral was the analysis of the statistical and spatial variability of both general soil properties and extractable elements in a agricultural field tought to be representative of the conditions of the Terra Cha district; these also focuses on mapping the spatial variability of the soil varibles studied. In addition potential relationships between soil apparent electrical conductivity soil general properties and extractable elements. In this way both, general soil properties and extractable elements are correlated with both soil veritcal and horizontal electrical conductivity (ECa). Soil samples were taken in 80 positions within the study filed at 0-20 and >20 cm depth, covering the whole A Horizon. Soil samples wer analyzed for: OM content, pH, Ca, Mg, K, Al, H+Al, SB, CEC, V, clay, silt and sand. Extractions have been performed using two different methods, Mehlich-3 (Ca, P, K, Fe, Mn, Zn, Cu, Cd, Cr, Ni y Pb) and DTPA (Fe, Mn, Zn, Cu, Cd, Cr, Ni y Pb). Coefficients of variation of general soil properties ranked as: pH<ECH<CEC<OM<H+Al<ECV<SB <K<Ca<V<Al<Mg. Moreover, coefficients of variation of elements extracted using Mehlich-3 ranked as: pH<ECH<CEC<OM<H+Al<ECV<SB<K<Ca<V<Al<Mg. When using DTPA, coefficients of variation ranked as: Cd<Ni<Fe<Cu<Pb<Mn<Zn<Cr. Significant lineal correlations have been found between ECH to OM (negative), clay, sand (negative), PMehlich-3 and NiDTPA. In turn, ECV was correlated to OM (negative), Ca, P , SB, clay, sand (negative) FeDTPA, CdDTPA, NiDTPA, PbDTPA, CdMehlich-3, NiMehlich-3 y PbMehlich-3. Both ECH and ECV showed a strong spatial dependence, which was modelled by a semivariogram nugget effect plus a spherical component. Spatial dependence was also demonstrated by 10 out of the 14 soil properties studied and it was strong for OM, pH, P, clay and sand; in these cases, patterns of spatial dependence were modelled by a nugget effect plus five spherical and five exponential semivariograms. When using Mehlich-3, 10 out of the 11 extracted elements showed spatial dependence, which was modelled by a nugget effect plus 8 exponential and 3 spherical models; the patterns of spatial dependence were stronger for K, Cd, Fe, P, Pb, Cr, Cu and Mn. When using DTPA, 4 out of the extracted elements also showed spatial dependence, which was modelled by three Exponential models and one Gaussian model; patterns of spatial were stronger for Mn and Fe.

[gl] A sostibilidade da produtividade agrícola e forestal depende das propiedades e da boa calidade do solo. O estudio da variabilidade das propiedades do solo resulta interesante, posto que realizando un manexo localizado do mesmo, favorécese a redución de custos de produción aproveitándose mellor as materias primas e o uso da maquinaria agrícola. A agricultura de precisión busca, mediante técnicas de aplicación localizada de fertilizantes, fitosanitarios e novos métodos de medida das propiedades dos solos, un maior rendemento económico da zona cultivada así como un menor impacto ambiental. Esta tese doutoral ten como obxectivo estudar a variabilidade estatística e espacial das propiedades xerais do solo e dos elementos extraidos nunha parcela representativa da Bisbarra de Terra Chá (ademais de crear mapas de variabilidade espacial dos mesmos). Ademais, estúdanse as posibles relacións entre a condutividade eléctrica aparente (CEa) do solo, as propiedades xerais e os elementos extraidos. Relaciónanse tanto as propiedades xerais como os elementos extraidos coa condutividade eléctrica aparente (CEa) do solo (horizontal e vertical). A toma de mostras realizouse unha vez obtida a rede de mostraxe optimizada en función das medidas de CEa. Obtivéronse 80 puntos de mostraxe a unha profundidade de 0 a 20 cm e >20 cm no Horizonte A. Nestes puntos foron amostradas as seguintes propiedades xerais: MO, pH, Ca, P, Mg, K, Al, H+Al, SB, CIC, V, arxila, limo e area. Os elementos foron extraídos nestes puntos mediante dous métodos, con Mehlich-3 (Ca, P, K, Fe, Mn, Zn, Cu, Cd, Cr, Ni e Pb) e DTPA (Fe, Mn, Zn, Cu, Cd , Cr, Ni e Pb). Os coeficientes de variación das propiedades xerais ordénanse do seguinte xeito: pH<CEaH<ICC<MO<H+Al<CEaV<SB<K<Ca<V<Al<Mg; os elementos obtidos por Mehlich-3: Fe<Ni<Cr<Cu<Cd<Pb<K<P<Ca<Zn<Mn e para os extraídos con DTPA: Cd<Ni<Fe<Cu<Pb<Mn<Zn<Cr. A CEH presenta correlacións lineais altamente significativas coa MO (negativa), arxila, area (negativa), PMehlich-3 e NiDTPA e a CEaV amosou correlación coa MO (negativa), Ca, P, SB, arxila, area (negativa) , FeDTPA, CdDTPA, NiDTPA, PbDTPA, CdMehlich-3 , NiMehlich-3 e PbMehlich-3. A dependencia espacial da CEaH y CEaV é forte en ambos os casos, axustándose ao modelo esférico de semivariograma. Respecto ás propiedades xerais, 10 de 14 presentan dependencia espacial (cinco modelos esféricos e cinco exponenciais) sendo forte para MO, pH, P, arxila e area. Dos elementos extraidos por Mehlich-3 presentan dependencia espacial 10 de 11 (oito modelos exponenciais e dous esféricos) sendo forte a dependencia para K, Cd, Fe, P, Pb, Cr, Cu e Mn. Dos elementos extraidos por DTPA catro de oito presentan dependencia espacial (tres modelos Exponenciais e un Gaussiano) sendo esta forte no caso do Mn e o Fe.