Grasslands on Acid Soils: Use of Different Amendments in the Context of Galicia

Abstract

The large importance of the bovine sector in Galicia, which situate it among the top 10 dairy regions in Europe, would explain the high agricultural area that is occupied by grasslands (70% of the usable agricultural area). These grasslands are, in most cases, placed on unproductive and acid soils, whereby the addition of amendments and fertilizers is essential. Since last mid-century numerous research studies about the impact of liming and fertilization practices on different Galician soils have been performed. In this chapter, the main results from three different studies related with amendment addition in grassland soils are presented chronologically, including pictures that help to recognize the edaphic and landscape context where these grasslands develop. The first study investigated the residual effect of CaCO₃ addition, at different doses (0.75, 1.5, 3.0, 6.0 and 12 Mg ha⁻¹), on different parameters of grassland soils developed on three lithological materials (granite, slate and gabbro). Starting from 3.0 Mg ha⁻¹ of limestone, a residual effect was observed even 6 or 7 years after the amendment application, with tenfold higher Ca and a decrease in Al saturation up to 50% in the plots with the highest doses, compared with the control ones. In the second study the possibility to replace, as regular liming product, the commercial limestone with mussel shell, a very abundant residue in the region, was investigated. Tests were performed using mussel shell (grinded or calcined) with different particle size. The mussel shell applied doses (3.0 Mg ha⁻¹) was enough to increase Ca and to decrease Al saturation, from 60% in the control soils to less than 20% in the non-rhizosphere soil and to less than 5% in the rhizosphere. These results, together with plant production ones, were similar to those obtained with commercial limestone. The third study, performed in 2009/2010, analysed the fertilizing and liming capacity of several mixtures prepared with residues from the canning and forestry industries. The results from plots where these mixtures were added, plots with just NPK fertilization, plots with NPK and mussel shell addition (NPK + MS) and control plots, were compared both in the rhizosphere and non- rhizosphere area. The NPK + MS treatment was the one that caused the better soil chemical conditions, but the mixtures also significantly improved the acidic conditions of these soils compared with the control and NPK treatments. The production of the species sowed in the plots with mixtures and with NPK + MS was similar and significantly higher than in the plots with NPK and the control ones. The rhizosphere area presented better conditions for plant growth than the non- rhizosphere soil in all the plots, proving the importance of the study of this root contact area in these grassland soils.