Mid-long term effects of no tillage and Ca-amendment on degraded acid soils under contrasting weather conditions

Inadequate soil management such as excessive ploughing is one of the main problems affecting the sustainability of agroecosystems and may exacerbate problems in acid soils. The application of Ca-amendments to ameliorate acid soils and no tillage practices to recover degraded soils are common management strategies. However, few studies have focused on their interactive effects under conditions of variable rainfall. In this study, we assessed the changes in soil properties over a period of seven years in response to no tillage (NT) and tillage, with or without the application of a Ca-amendment (sugar beet foam and red gypsum). Our split-plot experiment, which started in 2005 was carried out in a degraded Palexerult in Southwestern Spain with an annual rainfed forage crop. The Ca-amendment increased soil pH, Ca content and ameliorated Al-toxicity down to a depth of 50 cm, even under NT, due to the relatively high solubility of the amendment. However, after seven years of experiment, soil organic matter variables were enhanced only to a soil depth of 0-5 cm: NT and the Ca-amendment increased total organic carbon by 31% and 25%, respectively, whereas particulate organic carbon was increased to a larger extent (by a factor of 2.5 and 2, respectively). The positive effect of NT on organic matter variables increased with time, whereas the beneficial effect of the Ca-amendment was stronger in the early years of the experiment. Adverse weather conditions, with either excessive precipitation in autumn-winter or scarce precipitation in spring, favoured biomass production under NT. Given that NT mitigated the adverse effects of both water excess and deficit on biomass, it constitutes a valuable tool to combine with Ca-amendment to maintain crop productivity and recover degraded acid soils. This is especially the case under the changing weather conditions of a Mediterranean climate or other climates with increasing occurrences of periods of drought and/or water excess.