Development of protofragipanic horizon after severe degradation processes of greenhouses soil

Abstract

Plant growing in greenhouses and plastic tunnels has some advantages: obtaining early production, plant protection against hail, hoarfrost, late spring and early autumn frosts. The main criteria considered for setting greenhouses are the existence of heating and water sources. Due to the compulsory location imposed by the above conditions, many greenhouses were placed on soils having low capability. After application of ameliorative measures some satisfactory results could be obtained on a relatively short period. Our studies on some soils in greenhouses and plastic tunnels in Romania have shown that after 15-20 years of the intensive exploitation an impermeable soil horizon with brittle blocky angular structure aggregates was formed at depth of circa 25-37 cm. The formation of this horizon is due to some pedogenenetic factors excluding compaction by soil tillage. The impermeable horizon shows some similar features to a fragipan (dense and brittle pan) that have been identified both in acid, neutral and even slight alkaline greenhouses soils: (i) evidence of pedogenesis within the aggregates; (ii) firm or firmer rupture-resistance class and a brittle manner of failure when soil is moist; (iii) restrict the entry of roots into (inactive and etiolated roots are distributed only on the structural aggregates). Nevertheless, some properties are not similar with a typical fragipan: (i) the diameter of soil aggregates frequently is lower than 5 cm; (ii) the structural aggregates are brittle on the moist state but are not submerged in water. Since this impermeable horizon has only some properties of fragipan we suggest to define it as horizon with protofragipanic characteristics. Moreover, due to the anthropogenic origin, these soils could be classified as Protofragipanic Hortic Anthrosol.