1 Organic carbon in water-stable aggregates as affected by long-term nitrogen fertilization and liming. 1 Aboveground (shoot), belowground (root) and litter biomass as affected by long-term liming and N application.
- Background
- Justification of the study
- Research question
- Objectives
The impact of liming on soil C storage varies with soil type, land use, climate and management factors (Holland et al., 2018). For example, co-application of lime and mineral fertilizers reduced C stocks in Rengen Grassland experiment (Sochorová et al., 2016) and potentially changed plant elemental composition.
Introduction
Maintaining soil quality and long-term productivity of a sustainable grassland farming system has been the main goal (Mayel et al., 2021). Greater knowledge of soil response to grazing management is essential to evaluate different techniques for achieving a long-term sustainable agroecosystem of soils.
Grassland management practices
- Grazing
- Mowing
- Burning
- Fertilization
The effect of mowing on plant diversity differs per height, grassland type, fertilization percentages and mowing dates (Tälle et al., 2016). The species richness under mowing management is comparable to that under grazing (Socher et al., 2013).
Effect of grass management on plant production
- Effect of grazing and mowing
- Effect of burning
- Effect of fertilization
The intensity of grazing on plant species richness and composition is well known (Arévalo et al., 2007). The elemental composition and stoichiometric ratio of plant tissue is affected by mowing and grazing (Turner et al., 1993).
Effect of grassland management practises on soil properties
- Grazing
- Mowing
- Burning
There are conflicting reports in the literature on soil C-stocks and N with increasing grazing intensity (Steffens et al., 2008). Indirect impacts take place in the long term, influenced by the transformation of organic matter, compatibility and reduced porosity (Alcañiz et al., 2018).
Soil response to grassland fertilization
- Physical properties
- Chemical properties
- Biological properties
Differences in aggregation exist between mineral and organic fertilizers due to organic matter composition (Pachepsky et al., 1996). Increased enzyme activity (Keeler et al., 2009) is linked to high soil moisture due to high OM.
Soil response to grassland liming
- Physical properties
- Chemical properties
- Biological properties
Several soil microbial communities exist that are closely related to plant species (Kourtev et al., 2003). Field studies showed that N enrichment favors fungal communities rather than bacterial communities (Wang et al., 2017a; van der Bom et al., 2018) (Table 2.3). Studies have shown a positive (Yandong et al., 2005), negative (Sarathchandra et al., 2001) and neutral (Johnson et al., 2005) response of soil microbial biomass (SMB) to grassland fertilization.
The variations depend on various soil properties, including pH, total N, moisture, organic matter and rate of N addition, among others (Drenovsky et al., 2004; He et al., 2013). Lime formation increases the stability of aggregates in soils with high clay content and aggregate stability (Keiblinger et al., 2016). Supplying Ca2+ cations with lime neutralizes the effect of H+ ions in the soil solution and leads to an increase in soil pH (Holland et al., 2018).
Increasing SOC due to liming has been shown to increase C sequestration and C stocks in a 129-year grassland experiment through increased root mass and root exudates (Fornara et al., 2011). Carbon storage in grasslands is achieved through physical protection of microaggregate fractions associated with stable OM (Egan et al., 2018a). A decrease in microbial biomass C in a 2-year experiment was associated with low basal respiration (Johnson et al., 2005), while a 5- and 34-year experiment reported increases in MBC and soil respiration (Aye et al., 2016 ).
Conclusion
The effect of liming on soil biological properties is through increased soil pH and microbial activity. Liming has been shown to increase ammonia-oxidizing bacteria, archaeal and bacterial abundance, arbuscular and mycorrhizal fungal organisms (Heyburn et al., 2017a; Egan et al., 2018a; Egan et al., 2018b) due to the positive effect of soil pH on root secretions that promote the decomposition of bacteria. The abundance of fungi and AM fungi is mostly dominant in acidic soils (Bothe 2015), which explains the decline of calcareous grasslands (Millard and Singh 2010; Egan et al., 2018b). 2018) pointed out that the abundance of root colonization by AM fungi increases at pH 5-6, while a decline is observed at soil pH.
Given the variation in the response of soil biota to lime formation, there is a significant impact on soil biological processes (Table 2.4). An extensive literature on lime-induced elevation of soil pH has a cascading effect on soil N and C transformation, which in turn affect N and C supply and cycling. It is likely that continuous liming will increase mineralization, but the overall impact depends on the C:N ratio of plant debris returned to the soil (Bailey 1995).
Limiting the effect of mowing involves minimizing the use of machinery, cutting grass to the prescribed height and reduced frequency. Nutrient cycling depends on biomass production and microbial activity, while C and N storage depends on the physical stability of aggregates.
- Introduction
- Materials and Methods
- Study site
- Experimental design
- Soil sampling and analysis
- Statistical analysis
- Results
- Discussion
- Conclusion
Prolonged fertilization (135 years) in Rothamsted experiments resulted in an increase in TN and available N overtime, but did not affect SOC overtime (Glendining et al., 1996). High Fe and Al concentrations due to N-induced soil acidity affect soil P solubility through sorption reactions (Ahmed et al., 2019). Micronutrient biogeochemical cycles influence soil fertility in terrestrial ecosystems (Richardson et al., 2017).
The opposite effect of nitrogen addition on soil exchangeable bases and trace elements can lead to nutrient imbalances with serious implications for ecosystem function (Feng et al., 2019). Hejcman et al., (2009) reported reduced mobility of Cd, Fe, Mn and uptake of Zn on limed soils due to increase in pH. According to Silvertown et al. 2006) ecosystems take time to stabilize in response to fertilization, implying the importance of long-term responses.
The soil is derived from localized dolerite intrusions in a shale parent material (Rutherford et al., 2006). Bulk density is dependent on factors such as organic matter, texture and nutrient content (Chaudhari et al., 2013). Furthermore, an increase in total soil N can be due to large returns of organic N to soil roots and litter (Glendining et al., 1996).
- Introduction
- Material and methods
- Site description
- Soil sampling and analysis
- Results
- Mean weight diameter and weight of water-stable aggregate fractions
- Organic carbon in water-stable aggregates
- Discussion
- Conclusion
Despite many studies on the effect of N enrichment on bulk soil C dynamics, there is a lack of evidence for the mechanisms that explain the response of soil aggregates (Lu et al., 2021). Grasslands and grasslands are exposed to acidic conditions due to fertilizers or extensive cation leaching (Paradelo et al., 2015). However, conflicting results have been reported where low soil pH was associated with high aggregate stability (Bethlenfalvay et al., 1999).
Adsorption of NH4+ (low hydration energy) instead of cations with high hydration energy (e.g. Mg2+ and Ca2+) results in interlayer collapse (Rigol et al., 1999) due to NH4+-induced dispersion. A review by Paradelo et al. 2015) showed that multiple factors determine the net effect of calcification on SOC. Despite many studies on the effect of N enrichment on the C dynamics of bulk soils, there is a lack of evidence for the mechanisms explaining the response of soil aggregates (Lu et al., 2021).
Aggregate stability was determined using the wet sieving method as described by (Six et al., 2000a). Soil pH-mediated effects due to N fertilization can increase mineral surface activity leading to an increase in mineral-associated SOM (Riggs et al., 2015). Carbon in microaggregates is protected from microbial attack and therefore has a longer residence time compared to that stored in macroaggregates (Six et al., 2000b).
- Introduction
- Material and methods
- Site description
- Soil sampling and analysis
- Cold-water extractable carbon (CWEOC)
- Above-ground biomass and below-ground biomass sampling
- Statistical analysis
- Results
- Cold water extractable organic C
- Plant biomass
- Plant elemental stoichiometry
- Correlation analysis
- Discussion
- Conclusion
Forage production was increased in Arraba temperate montane grasslands (Mijangos et al., 2010) due to species adaptation. Higher C:N ratios have been shown to slow down the mineralization process (Tong et al., 2009). More resource allocation to belowground biomass under ammonium sulfate and lime treatments may be a result of nutrient deficiency (Ai et al., 2017).
In general, observed differences in plant biomass between aboveground and belowground organs are a reflection of the balance between aboveground resources (i.e., light and CO2) and belowground resources (water and nutrients) (Yang et al., 2010). The distribution of plant biomass is the key information linking aboveground productivity and C sequestration (Hovenden et al., 2014). This may be because the photo-assimilates were transported to the underground parts of the plants (Domanski et al., 2001; Kuzyakov 2001).
Plant tissue nitrogen concentration can also be influenced by plant-specific nitrogen use strategies and efficiency (Zhang et al., 2004). The pattern of P allocation depends on soil P availability and affects the photosynthetic rates of plant species leaves (Guilherme Pereira et al., 2018). The change in the N:P ratio could reflect the ecological strategies and growth rate capabilities of the species (Zechmeister-Boltenstern et al., 2015).
Summary of findings
This means that ammonium fertilizers increase the soil's susceptibility to erosion and compaction while liming maintains structural stability. The carbon distribution in aggregates was attributed to the change in the proportion of each aggregate fraction with N addition rather than change in soil C content. This stems from the evidence that soil C levels did not differ between treatments, suggesting that the soil has reached C saturation.
Any of the carbon added in a form of litter accumulates on the soil surface and slowly decomposes over time, but the soil can no longer store any of the added C. Even the C stock stored with respect to each treatment is not significantly different from the control. This is also observed in the relationship between root N:P ratio with labile C in the form of CWEOC.
However, there was no relationship between plant stoichiometry and SOC, implying that any added C in a form of plant debris does not change soil carbon content. While N increased leaf C content, N was not changed, resulting in a high shoot C:N ratio in AS70 and no change was detected on N:P and C:P. N uptake was not significantly different from the control expectation for AN211 and AS211L treatments, which means that C accumulation in the shoots exceeds N accumulation resulting in a high C:N ratio.
Conclusions
Effect of nitrogen (N) in fertilizer on soil organic carbon, total N and soil pH in long-duration continuous winter wheat (Triticum aestivum L.). Effect of long-term liming on soil organic carbon and aggregate stability in low-acid soils. Interaction of long-term nitrogen fertilizer application, crop rotation and tillage system on soil carbon and nitrogen dynamics.
Effect of long-term grazing on soil organic carbon content in semiarid steppes of Inner Mongolia. Long-term effects of grassland management on soil microbial abundance: implications for soil carbon and nitrogen storage. The effects of long-term applications of inorganic nitrogen fertilizer on soil nitrogen in the Broadbalk Wheat Experiment.
Effects of soil structure and pasture management on soil organic C and N and mineralization rates of C and N. Effects of nitrogen fertilization on soil microbial biomass and community functional diversity in temperate grasslands in Inner Mongolia, China. . The effect of grassland management on soil carbon sequestration in the states of Rondônia and Mato Grosso, Brazil.
Effects of prescribed fire on soil quality in Mediterranean grasslands (Prades Mountains, northeastern Spain). Modeling the long-term impacts of fertilization and liming on soil acidification at Rothamsted Experimental Station.
