The Impact of Different Techniques of Soil Management on Soil Fertility and the Associated Bacterial Communities in Semi-arid Olive Tree Fields

Abstract

A remarkable decrease in olive production has been observed in Tunisia since 2000, particularly in the semi-arid region. This downfall was mainly due to a notable change in climatic conditions as a result of wind erosion and over cultivation. The aim of this work was to study the biological, physical, and chemical properties of several semi-arid soils from olive tree fields subjected to different farming practices, such as crop time and type of crop, olive mill wastewater (OMW) application rates, and tillage timing and depth (deep or conventional plowing). We noted that hydraulic conductivity (HC) was proportional to the age of the soil tillage, and the highest values were recorded in the soil cultivated for 100 years, with an average value of 33.05 ± 0.02 mm h −1. An important increment of the iron soil content was observed, especially after the fig tree introduction among the olive trees (12,094 ng μL −1) in 2007. Also, a significant increase of the organic matter (OM) content (up to2.6 mg-OM/g-soil) was identified in soil treated with OMW compared to the lowest OM content (0.83 mg-OM/g-soil) recorded in the soil cultivated since 1901. The bacterial communities of the different soils were characterized by 454 pyrosequencing technology, and showed an important diversity, mainly corresponding to Proteobacteria, Actinobacteria, and Acidobacteria. Many operational taxonomic units (OTUs) are raretons, indicating a high resilience of the soil bacterial communities. Statistical analyses showed significant correlations with the different soil parameters. However, an unexpected correlation was determined between soil respiration and OM (r = − 0.583*), suggesting that OM increases the retention of CO 2 , a greenhouse gas. The farming techniques analyzed in this study resulted in a reduction of the bacterial diversity, even though the total bacterial biomass augmented. Keywords Olive tree. Olive mill wastewater. Farming soil management. Semi-arid crop culture. 454 pyrosequencing * Haifa Rajhi

Temporal dynamics of total and active prokaryotic communities in two Mediterranean orchard soils treated with solid anaerobic digestate or managed under no-tillage

“…In both orchard soils, we found that the resident total bacterial community was largely affiliated with ubiquitous Actinobacteria and Proteobacteria (especially copiotrophic (Janssen 2006) including Mediterranean orchard soils (Curiel Yuste et al 2014;Siles et al 2014;Bastida et al 2017;Rajhi et al 2020). These taxa are widely distributed, inhabit nutrient-rich soils, participate in C, N, and S cycling, drive organic matter turnover and decomposition, regulate soil-plant interactions, release extracellular enzymes, and produce secondary metabolites (Spain et al 2009;Fausto et al 2018).…”

Organic Amendments and Sampling Date Influences on Soil Bacterial Community Composition and Their Predictive Functional Profiles in an Olive Grove Ecosystem

“…Regarding olive agroecosystems, it has been shown that organic amendments increase bacterial richness without affecting fungal richness [17]. Conversely, the use of fresh organic amendments such as oil mills wastewater, combined with other agricultural methods such as tillage, shows an increase in bacterial biomass but a reduction in bacterial diversity in the semiarid soils of olive groves [18] Additionally, shifts in soil microbial community composition have been associated with seasonality and sampling date in Mediterranean ecosystems, often linked to changes in soil management [19,20]. Understanding the role of both is critical to elucidate their effect on microbial biodiversity.…”