Long term impact of different tillage systems on carbon pools and stocks, soil bulk density, aggregation and nutrients: A field meta-analysis
Introduction
Conservation tillage systems, here outlined as no-tillage (or zero tillage) with residue retention, has been accepted as a promising strategy (and a key management system) that preserve and restore soil physical and soil organic pools and dynamics (Vazquez et al., 2019). Due to their convenience in minimizing input costs, improving water storage and preserving soil carbon (C), conservation tillage is recognized as a long-term sustainable practice for agricultural ecosystems (Li et al., 2019). As in most parts of Europe, the application of conservation tillage in Romania is limited but the interest is growing continuously.
In the context of conservation agriculture practices, no-tillage system can also enhance soil quality by improving soil structure, intensifying soil biological activity, improving the nutrient cycle, increasing the soil water holding capacity and the water infiltration characteristics (Hellner et al., 2018, Borges et al., 2018) and also plays a crucial role in sustaining agricultural productivity and preserving environmental quality (Raus et al., 2016, Amezketa, 1999). Lampurlanes et al., 2016, Jat et al., 2019, Zuber and Villamil, 2016, Li et al., 2018 found that conservative tillage showed promising trends in improving soil enzyme and microbial activity and enhance soil structure and crop yields. An issue based on long-term tillage in North America showed that the larger SOC content in the 21–35 cm soil under CT did not completely equilibrate the gain in the 0–20 cm soil under NT (Angers and Eriksen-Hamel, 2008). The main challenges with the adoption of NT include soil compaction, weed management, and stratification of organic matter and nutrients. Therefore, further research is still needed to evaluate the effects and mechanisms of conservation tillage practices on changes in soil quality along the soil profile (Angers and Eriksen-Hamel, 2008).
Soil physical property dynamics within different tillage system are well documented but a systematic synthesis is needed to enhance how these practices affect soil physical properties on a global scale and how these changes in soil physical properties are linked to multiple ecological components at cropping system level (Li et al., 2019).
Soil structure, the spatial arrangement of primary soil particles and aggregates with associated pore networks, is a key parameter for soil sustainability management; it provides vital functions and acts as an optimum medium for plant growth (Lehmann et al., 2017). Soil aggregation plays an important role in soil structure and organic matter stabilization, which furthermore supports soil fertility through minimizing soil erosion, mediating air permeability, infiltration and nutrient cycling (Zhang et al., 2018). In addition, soil aggregate stability can defend soil organic carbon from mineralization because it physically reduces the accessibility of organic compounds for microorganism, enzymes and oxygen. The process of soil carbon associated aggregate destabilization vary with macro and microaggregates. The degree of mineralization can be intensified by macroaggregate conversion to dimension of microaggregates (Jat et al., 2019). The soil organic matter associated with macroaggregates was more labile and less processed than that associated with the microaggregates. Organic matter is also an important agent responsible for binding soil mineral particles together (Jat et al., 2019).
Conventional tillage usually involves heavy tillage practices down to 20–25 cm soil depths (Pittelkow et al., 2015); this reliable management practice has resulted in reduced soil bulk density, increased porosity, and improved weed control (Pagliai et al., 2004). Conventional tillage can also adversely affect soil structure, when the process of aggregate formation is disturbed due to destruction of aggregates (Six et al., 2002). Soil aggregates are directly affected through physical disturbance of the macroaggregates and indirectly by alteration of biological and chemical factors (Gupta Choudhury et al., 2014, Li et al., 2019, Bronick and Lal, 2005).
Poor aggregate structure and stability can decrease water infiltration and reduce soil carbon and nutrients in macro and microaggregates. Higher soil aggregation can be achieved by decreasing tillage and increasing residue retention through conservation tillage. Gupta Choudhury et al. (2014) found that the applications of the organics in the form of residues combined with conventional or conservative tillage improved the percent of macroaggregates compared to microaggregates. A positive correlation was reported between aggregate size and soil organic carbon content, so the larger aggregate with higher soil organic carbon minimized the intensity of disintegration of aggregate exposed to water (Blevins et al., 1998).
Soil physical quality has been widely approached by bulk density, to evaluate various soil processes or to estimate soil carbon reserves (Vereecken et al., 2016). Generally, bulk density might be considered an important parameter that reflect soil structure, being an indicator of soil compaction related to total soil and pore space volume (Hernanz et al., 2000).
In addition to environmental services, soil organic carbon is a valuable indicator which maintain soil fertility, soil sustainability, crop yield, and contributes to mitigate climate warming and ensure food safety. Conservation agriculture has proved to be an excellent alternative to conventional agriculture in the long term of sustainable crop production and SOC sequestration. No-tillage/ reduced tillage decreases the carbon oxidation process and soil disturbance with the loss of soil organic carbon and nutrient availability (Kan et al., 2020, Modak et al., 2019). Crop residues behave as a barrier between soil and environment which may have a great role in soil erosion reduction and soil quality indicators (Jat et al., 2019). Maintained good physical, chemical and biological properties particularly those related to soil carbon sequestration are necessary for production sustainability (Martin et al., 2019).
The general objective of this study was the assessment of soil quality-based management practices and parameter identification that are sensitive to soil disturbance. The specific objectives were to investigate the impact of long-term tillage systems on soil aggregate stability, nutrient availability and soil carbon storage pools and dynamics. We hypothesized that the conservation tillage improves soil physical properties and organic carbon stocks.
Section snippets
Study site description
This study was part of a long field experiment conducted during 2009–2019, at the Research Farm of the Agricultural University Iasi - Romania (47°07′ N latitude, 27°30′ E longitude). The climate in the experimental area is a temperate-continental type; the mean values precipitation of the last 20 years at this site reaches 517.8 mm with an average air temperature of 9.4 °C. Significant deviations from the long-term average and temperature have been observed in the last 10 years. The
Carbon fraction and C-stabilization
Tillage and cropping system significantly influenced TOC content and C-fractions, C-pools and C-management indices in the 0–10 cm depth soil layer (Table 3 and Fig. 2). The concentration of TOC (p < 0.05) in the surface soil 0–10 cm was maximum (37.0 g kg−1) in no-tillage variant with similar values at the sub-surface depth 10–20 cm (31.4–31.6 g kg−1) in both the conservative treatments. The increase of TOC under reduced tillage was more in surface soil 0–10 cm than of 10–20 cm and 20–30 cm
Conclusions
The results obtained maintain the assumption that conservation tillage can improve soil physico-chemical properties, especially by reducing bulk density and increasing stability of aggregates and soil total organic carbon. The addition of crop residues in chisel and no-tillage treatments, increased non labile C fraction Cfrac4 in 0–20 cm depth. The effect of tillage practices on total organic carbon and soil available nutrients was notable after ten-year rotation. The effect was intense for
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Authors acknowledge the logistic support from Competitiveness Operational Programme (COP) 2014 – 2020, under the project number 4/AXA1/1.2.3. G/05.06.2018, SMIS2014+ code 119611, with the title “Establishing and implementing knowledge transfer partnerships between the Institute of Research for Agriculture and Environment - IAȘI and agricultural economic environment”.
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