Unravelling of Soil pH Dynamics under Flooded Environment: A Review
Abstract
Global climate change has increase the frequency and severity of extreme weather conditions including heavy rainfall followed by subsequent flooding. Soil pH is one of the most influential chemical parameters that have an impact on directly affecting the nutrient availability status, microbial activity and overall plant health. During the flooding period of paddy crop the soil pH for initially < 6.5 it was increased to approximately 7.0. Rice cultivated under continuous flooded conditions when soil pH became varied from 6.1 to 6.5 throughout the crop growth period. Agricultural crops such as rice benefit from mild increases of soil pH in submerged conditions to enabling improved nutrient solubility and reduced aluminum toxicity. In this contrast, crops like maize, wheat and legumes are inhibited the growth and nutrient uptake under flooded soil due to shifting of soil pH environments. Future research and development must focus on deeper understanding and management of these soil chemical shifts to ensure resilient cropping systems.
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Introduction
Global climate change has increase the frequency and severity of extreme weather circumstances with heavy rainfall followed by subsequent flooding. It is a direct effect of prolonged waterlogging and inundation stress altering soil physio-chemical and microbial changes in agricultural soils. Consequently, the understanding of how soil pH responds to these conditions has become critical. Flooding-related disruptions due to soil pH changes can lead to substantial agricultural losses. When soil pH shifts from the optimal range typically 6.0–7.0 for most crops, nutrient solubility becomes impaired, toxic elements may become bioavailable (e.g., aluminum, manganese) and microbial function is inhibited. Global estimated acid sulfate soils alone affect over 49 million hectares, predominantly in Asia. Where water management is key challenges cause significant crop failure due to post-flood pH depression (Dent, 1986). In India, economic losses due to reduced soil productivity under waterlogged and pH-altered conditions in lowland rice fields are estimated in the billions of rupees annually (Singh & Sharma, 2016). Horticultural crops like tomatoes, chillies, and bananas, which are particularly sensitive to pH changes, often exhibit stunted growth and fruit loss in these settings (Yadav et al., 2017). Moreover, these losses are increased by input cost especially for lime application in acidic soils or sulfur amendments in alkaline soils and long-term degradation of soil fertility. The most immediate effect of anaerobic soil conditions on plant is a reduction in aerobic respiration in roots. The particular end product of anaerobic respiration is partially dependent on soil pH. At a pH above neutrality, lactate fermentation is dominant, and as pH decreases (due to partially lactate fermentation), ethanol fermentation is induced. Rapid drop in cytosolic pH called acidosis is thought to be one of the main reasons why cells die in response to flood. In flood tolerant plants the pH drop may be counteracted by an alkaline process (Crawford et al. 1994).
Soil pH is one of the most influential chemical parameters that have an impact on directly affecting the nutrient availability status, microbial activity and overall plant health. Alteration of soil pH has a significant role on the sustainable cultivation of agricultural and horticultural crop production under flooded conditions. In this present review is mainly focused on critical examination of the mechanisms behind the modification of the soil pH under the flooding conditions. To assess the impact of soil pH changes on different crop species and explore soil management practices that mitigate adverse environmental effects
Conclusion
Flooding alters the soil environment drastically and one of the most significant consequences is shifting of soil pH due to oxygen depletion and redox reaction activities. Under flooded conditions, soils transition from aerobic to anaerobic condition to prompting a cascade of microbial and chemical changes that impact nutrient availability based on soil pH status (Ponnamperuma, 1984; Reddy & Delaune, 2008). The direction of pH change occurring, whether increasing or decreasing the soil pH depends on soil type, initial pH, soil buffering capacity and the duration including frequency of flooding (Patrick & Delaune, 1977). Whereas, the acidic soils are typically experience a temporary increase of soil pH due to proton consumption during reduction reaction process, while alkaline soils may acidify due to organic acid production and CO₂ accumulation (Brady & Weil, 2017).
Agricultural crops such as rice benefit from mild increases of soil pH in submerged conditions to enabling improved nutrient solubility and reduced aluminum toxicity. In this contrast, crops like maize, wheat and legumes are inhibited the growth and nutrient uptake under flooded soil due to shifting of soil pH environments (Setter & Waters, 2003). The effects on nutrient solubility such as iron, manganese, phosphorus and sulphur are sensitive to soil pH, leading to either deficiencies or toxicities depending on the redox-pH dynamic potential (Fageria et al., 2011). This emphasises are the importance of managing soil pH to sustain crop productivity during and after flooding events.
Horticultural crops, which generally require soil pH for optimal growth. The crops like tomatoes, citrus, grapes and peppers show chlorosis, stunted growth or even plant death when pH moves outside optimal threshold level (Ehret et al., 2010; Zhang et al., 2019). In addition, microbial shifts in the rhizosphere also affect nutrient cycling and disease susceptibility in these high-value crops. Flooding not only changes the crop root-zone soil pH but also alters beneficial symbiotic microorganism such as mycorrhizae and rhizobia, which are crucial role in nutrient uptake in many horticultural crops (Kozlowski, 1997). To mitigate these effects, strategic management practices such as lime application, raised beds, controlled drainage and the use of pH-tolerant crop varieties are essential for maintain the soil pH. Also monitoring real-time soil redox activities and soil pH changes can guide fertilizer application and drainage strategies to minimize long-term degradation (Pezeshki, 2001; Sharma et al., 2005). This is more helpful for understanding the dynamic relationship between soil pH, flooding and crop responses for ensuring resilient agricultural and horticultural systems in flood-prone conditions.
VIII. FUTURE PROSPECTS Future prospects of soil pH under flooded conditions in agricultural and horticultural crop cultivation. In the global climate change has marked by increasing frequency and intensity of rainfall pattern is making flooding or waterlogging is more common in many agricultural crop cultivated lands. One of the key challenges under these conditions is the rapid and often unpredictable fluctuation of soil pH. Future research and development must focus on deeper understanding and management of these soil chemical shifts to ensure resilient cropping systems (Ponnamperuma, 1984; Reddy & Delaune, 2008).
One of the most promising areas lies in advanced soil monitoring technologies. Precision agriculture tools, especially Internet of Things (IoT)-enabled soil sensors, now offer the possibility of continuously monitoring soil pH, redox potential (Eh) and moisture in real time. These tools could allow farmers to respond to unfavorable soil pH shifts with lime or sulfur applications, drainage modifications or chancing of fertilization schedules. Additionally, artificial intelligence (AI) models could predict soil pH trends based on real-time flooding events, enabling proactive soil pH correction strategies (Gebbers & Adamchuk, 2010; Sudduth et al., 2013).
Breeding of agriculture and horticulture crops varieties which more scope for flood-resilient and pH-tolerant are another critical path. In the case of rice, extensive studies have shown its unique adaptations like aerenchyma formation and root oxygenation. These traits, along with rhizosphere acid–base balancing mechanisms, need to be bred into other cereals and horticultural crops like tomato, citrus and eggplant. Modern genomic tools, especially CRISPR/Cas9, offer the potential to accelerate development of such crops by targeting genes related to pH tolerance, nutrient uptake under flooding and organic acid metabolism (Setter & Waters, 2003; Zhang et al., 2019; Chen et al., 2019).
Finally, there is a need for policy support and farmer-level capacity building. Flood-induced soil pH stress is often underappreciated at the policy level and many farmers are unaware of how waterlogging changes soil chemistry. Governments and institutions must invest in farmer training, soil testing infrastructure and incentives for adopting sustainable water and soil pH management practices. Focused research on local soil types and crop responses to flooding across different agro-ecological zones will be crucial informing future flooding issues eradication strategies (FAO, 2020).
