Heavy metals in pastureland soils situated in A Pastoriza (NW Spain) treated with cattle slurry and NPK fertilizers

Abstract

In Galicia (NW Spain), pasturelands cover a broad extension and are mainly used to feed cattle. Farms are managed in an intensive manner, using cattle slurry and inorganic fertilizers to increase pasture production, but also increasing risks of heavy metal pollution. In this work we studied the influence of fertilization practices on total concentrations and in-depth distribution of heavy metals and related elements (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn) in two forest soils (SN1, SN2) and five pastureland soils (P1-P5) fertilized with cattle slurry and NPK, in a broadly exploded farmland area (A Pastoriza, Lugo). Soils SN2 and P4 were developed over slate, whereas soils SN1, P1, P2, P3 and P5 evolved on Candana quartzite. Forest soils presented acid pH (4.58-4.68), high Al saturation (75-90%), and low available P concentration (4.78-11.96 mg kg<sup>-1</sup>), whereas those parameters exhibited better scores in the pastureland soils, due to previous amendment and fertilization practices, thus giving pH 5.17-7.02, Al saturation 0.58-59.24%, and available P 5.24-42.07 mg kg<sup>-1</sup>. Regarding heavy metals, soil depth did not affect significantly to total concentrations, contrary to that happening with parent material, with higher As, Cu, Fe, and Ni concentrations found in soils over slate (possibly due to the presence of pyritic materials). In most cases, heavy metal total concentrations were lower than that considered as reference background levels for soils developed over each of the parent materials, and were always lower than that considered phyto-toxic. In this study, natural soils usually presented heavy metal total contents similar or even higher than that of the fertilized soils (unless Zn in the P4 pastureland), thus indicating that the spread doses of fertilizers did not influence significantly their concentration levels.

Forms of Toxic and Trace Metals in Grassland Soils of Galicia, Spain

“…In the case of manganese, 39% of the samples analysed, mainly in the surface soil, had a pseudo-total concentration higher than the GRL. The values were higher than those reported by Seco-Reigosa et al (2015) for pasture and forest soils of the same area and similar to those reported by Caridad-Cancela et al (2002) for natural soils in Galicia. Moreover, the maximum allowable concentration range for Mn (1,500-3,000 mg kg −1 , according to Kabata-Pendias and Szteke ( 2015)) was never exceeded.…”

“…Thus, iron will be considered mainly in its micronutrient condition. The concentrations were higher than the total concentrations, determined by X-ray fluorescence, reported by Seco-Reigosa et al (2015) for four pasture soils of the same area. In the case of manganese, 39% of the samples analysed, mainly in the surface soil, had a pseudo-total concentration higher than the GRL.…”

“…Twelve percent of the samples exceeded the GRL for Cr (85 mg kg −1 ). Seco-Reigosa et al (2015) reported Cr concentrations above the GRL for pasture and forest soils of the same area. The GRL for Co and Ni (40 and 80 mg kg −1 , respectively) were never exceeded, consistently with Seco et al (Seco-Reigosa et al, 2015).…”

“…In Galicia (NW Spain), the application of cattle slurry to pastureland is a common practice (Franco-Uria et al, 2009), which provides the soil with macro and micronutrients as well as organic matter. Few published data exist relative to the presence of toxic and trace metals in Galician soils treated with cattle slurry (Paz-González et al, 2000;Caridad-Cancela et al, 2002;Lopez-Mosquera et al, 2005;Franco-Uria et al, 2009;Seco-Reigosa et al, 2015).…”

Application of organic wastes to soils and legislative intricacies in a circular economy context

“…As exposed previously for other European regions, this legislative spectrum often results confusing for farmers (Ortolano et al 2009) and in the common thought that fertilization strongly correlates with the crop yield, organic and inorganic fertilization is carried out following their own criteria. In Galicia, annual doses of 40 m3 ha −1 of poultry manure were addressed by Conde-Cid et al (2018) in agriculture areas, 100 m3 ha −1 for cattle slurry and 1000 kg ha −1 for mineral fertilizer NPK 8:24:16 were reported in pasturelands (Seco-Reigosa et al 2015), and over 200 kg N ha-1 and 50 kg P kg ha −1 for grasslands (Paz-Ferreiro et al 2010). On the other hand, the addition of organic materials different from manures on Galician soils was widely studied by different authors (Santalla et al 2011;Paz-Ferreiro et al 2012;Pousada-Ferradás et al 2011) before and after the appearance of Decree 125/2012 that regulates the usage of organic wastes in Galicia.…”