File Name: soil ph and nutrient availability .zip
Soil pH is a master variable in soils because it controls many chemical and biochemical processes operating within the soil. It is a measure of the acidity or alkalinity of a soil. The study of soil pH is very important in agriculture due to the fact that soil pH regulates plant nutrient availability by controlling the chemical forms of the different nutrients and also influences their chemical reactions.
In the natural environment, soil pH has an enormous influence on soil biogeochemical processes. This paper discusses how soil pH affects processes that are interlinked with the biological, geological, and chemical aspects of the soil environment as well as how these processes, through anthropogenic interventions, induce changes in soil pH. Unlike traditional discussions on the various causes of soil pH, particularly soil acidification, this paper focuses on relationships and effects as far as soil biogeochemistry is concerned.
Firstly, the effects of soil pH on substance availability, mobility, and soil biological processes are discussed followed by the biogenic regulation of soil pH. It is concluded that soil pH can broadly be applied in two broad areas, i.
To many, soil pH is only essential for the chemistry and fertility of soils. However, the recognition of soil functions beyond plant nutrient supply and the role soil as a medium of plant growth required the study of the soil and its properties in light of broader ecosystem functions through a multidisciplinary approach.
This allows scientists to view processes from landscape to regional and global levels. One process that denotes the multidisciplinary approach to soil science is soil biogeochemistry, which studies biogeochemical processes. The ecosystem functions of soil, to some extent, have a strong relationship with soil biogeochemical processes, which are linkages between biological, chemical, and geological processes [ 1 ].
The soil is the critical element of life support systems because it delivers several ecosystem goods and services such as carbon storage, water regulation, soil fertility, and food production, which have effects on human well-being [ 2 — 4 ]. These ecosystem goods and services are broadly categorized as supporting, provisioning, regulating, and cultural services [ 5 ]. According to the Millennium Ecosystem Assessment [ 5 ], the provisioning and regulating functions are said to have the greatest impact on the components of human well-being in terms of safety, the basic material for a good life, health, and good social relations.
In the natural environment, the pH of the soil has an enormous influence on soil biogeochemical processes. Soil pH is compared to the temperature of a patient during medical diagnoses because it readily gives a hint of the soil condition and the expected direction of many soil processes lecture statement, Emeritus Prof.
Eric Van Ranst, Ghent University. On the other hand, pH controls the biology of the soil as well as biological processes. Consequently, there is a bidirectional relationship between soil pH and biogeochemical processes in terrestrial ecosystems, particularly in the soil.
In this sense, the soil pH influences many biogeochemical processes, whereas some biogeochemical processes, in turn, influence soil pH, to some extent, as summarised in Figure 1. For many decades, intensive research has revealed that soil pH influences many biogeochemical processes.
Recent advances in research have made intriguing revelations about the important role of soil pH in many soil processes. This important soil property controls the interaction of xenobiotics within the three phases of soil as well as their fate, translocation, and transformation. Soil pH, therefore, determines the fate of substances in the soil environment.
This has implications for nutrient recycling and availability for crop production, distribution of harmful substances in the environment, and their removal or translocation. This functional role of soil pH in soil biogeochemistry has been exploited for the remediation of contaminated soils and the control of pollutant translocation and transformation in the environment. Unfortunately, in many studies, soil pH is often measured casually as a norm without careful consideration for its role in soil.
This paper seeks to explore the importance of pH as an indicator of soil biogeochemical processes in environmental research by discussing the biogeochemical processes that are influenced by soil pH, the biogeochemical processes that also control soil pH, and the relevance of the relationship for future research, planning, and development.
Simultaneously, in accordance with biochemical changes, physicochemical processes, including dissolution, precipitation, adsorption, dilution, volatilization, and others, influence leachate quality [ 9 ]. Soil pH controls the solubility, mobility, and bioavailability of trace elements, which determine their translocation in plants [ 10 ]. This is largely dependent on the partition of the elements between solid and liquid soil phases through precipitation-dissolution reactions [ 10 , 11 ] as a result of pH-dependent charges in mineral and organic soil fractions.
For instance, negative charges dominate in high pH whereas positive charges prevail in low pH values [ 12 ]. Additionally, the quantity of dissolved organic carbon, which also influences the availability of trace elements, is controlled by soil pH.
At low pH, trace elements are usually soluble due to high desorption and low adsorption. At intermediate pH, the trend of trace element adsorption increases from almost no adsorption to almost complete adsorption within a narrow pH range called the pH-adsorption edge [ 13 ].
From this point onwards, the elements are completely adsorbed [ 13 ]. For instance, Bradl [ 13 ] found that at pH 5. The fate of readily available trace elements depends on both the properties of their ionic species formed in the soil solution and that of the chemical system of soil apart from soil pH itself [ 14 ].
Research has established that with increasing soil pH, the solubility of most trace elements will decrease, leading to low concentrations in soil solution [ 14 ]. Any increase or decrease in soil pH produces distinct effects on metal solubility.
This may probably depend on the ionic species of the metals and the direction of pH change. Rengel [ 15 ] observed that the solubility of divalent metals decreases a hundred-fold while trivalent ones experience a decrease of up to a thousand-fold.
Aside from adsorption, trace element concentrations at high soil pH may also be caused by precipitation with carbonates, chlorides, hydroxides, phosphate, and sulphates [ 11 , 16 ]. Apatite and lime applied to soils produced the highest effect on pH and simultaneously decreased the concentrations of available, leachable, and bioaccessible Cu and Cd [ 16 ]. Soil organic matter exists in different fractions ranging from simple molecules such as amino acids, monomeric sugars, etc.
These occur together with undecomposed and partly decomposed plant and microbial residues [ 17 ]. The solubility and mobility of the fractions differ during and after decomposition and could lead to the leaching of dissolved organic carbon and nitrogen in some soils.
Dissolved organic carbon is defined as the size of organic carbon that passes through a 0. Soil pH increases the solubility of soil organic matter by increasing the dissociation of acid functional groups [ 19 ] and reduces the bonds between the organic constituents and clays [ 20 ]. Thus, the content of dissolved organic matter increases with soil pH and consequently mineralizable C and N [ 20 ].
This explains the strong effects of alkaline soil pH conditions on the leaching of dissolved organic carbon and dissolved organic nitrogen observed in many soils containing substantial amounts of organic matter [ 19 , 21 ]. The same observation has been made on the dissolved organic carbon concentration in peatland soils [ 22 ]. The pH-dependence of dissolved organic carbon concentration gets more pronounced beyond pH 6 [ 23 ].
Within the pH condition in a specific soil system, the solubility of organic matter is strongly influenced by the type of base and is particularly greater in the presence of monovalent cations than with multivalent ones [ 23 ]. According to Andersson and Nilsson [ 24 ] and Andersson et al. The former is found to be more pronounced than the latter [ 19 ]. Ecophysiology is an interlinkage between cell-physiological functioning under the influence of environmental factors [ 25 ].
It is estimated using the metabolic quotient q CO 2 as an index [ 25 ] to show the efficiency of organic substrate utilization by soil microbes in specific conditions [ 26 ]. A decrease in microbial community respiration makes C available for more biomass production, which yields higher biomass per unit [ 27 ]. The metabolic quotient is, therefore, described as a cell-physiological entity that reflects changes in environmental conditions [ 25 ].
This implies that any change in environmental conditions towards the adverse state will be indicated by the index [ 25 ]. This is controlled by soil pH [ 28 ]. Soil pH as a driving force for microbial ecophysical indices stems from its influence on the microbial community together with the maintenance demands of the community [ 28 ] and was among the predictors of the metabolic quotient [ 29 , 30 ]. The metabolic quotient was found to be two-and-a-half times higher in low pH soils compared to neutral pH soils [ 28 ].
This has been associated with the divergence of the internal cell pH usually kept around 6. It is observed from the literature that soil pH conditions required for microbial activity range from 5. Thus, soil respiration often increases with soil pH to an optimum level [ 26 ]. This also correlates with microbial biomass C and N contents, which are often higher above pH 7 [ 26 ].
In low pH conditions, fungal respiration is usually higher than bacterial respiration and the vice versa [ 25 ] because fungi are more adapted to acidic soil conditions than bacteria.
Extracellular enzymes are produced by soil microorganisms for the biogeochemical cycling of nutrients [ 33 ]. Soil pH is essential for the proper functioning of enzyme activity in the soil [ 34 , 35 ], and may indirectly regulate enzymes through its effect on the microbes that produce them [ 36 ].
However, there are myriad of enzymes in biological systems which assist in the transformation of various substances. Besides, enzymes are of different origins and with differing degrees of stabilization on solid surfaces. Thus, the pH at which they reach their optimum activity pH optima is likely to differ [ 33 ].
It is striking that enzymes that act on the same substrates could vary considerably in their pH optima. This is evident in phosphorus enzymes, which have both acid and alkaline windows of functioning in the range of pH 3—5. In a study on the optimum pH for specific enzyme activity in soils from seven moist tropical forests in Central Panama, Turner [ 33 ] classified enzymes into three groups depending on their pH optima as found in the soils.
These were: a enzymes with acidic optima that appeared consistent among soils, b enzymes with acidic pH optima that varied among the soils, and c enzymes with optima in both acid and alkaline soil pH. Stursova and Walker [ 37 ] found that organophosphorus hydrolase has optimal activity at higher pH. For instance, glycosidases have an optimal pH range between 4 and 6 compared to proteolytic and oxidative enzymes whose optima was between 7 and 9 [ 35 , 36 , 38 ]. Shifts in microbial community composition could potentially influence enzyme production if different microbial groups require lower nutrient concentrations to construct biomass, or have enzymes which differ in affinity for nutrients [ 39 ].
Soil microorganisms are described as ecosystem engineers involved in the transformation of substances in the soil. One of such transformations is biodegradation, a process through which microbes remediate contaminated soils by transforming toxic substances and xenobiotics into least or more toxic forms.
Biodegradation is the chemical dissolution of organic and inorganic pollutants by microorganisms or biological agents [ 34 , 40 ]. Like many soil biological processes, soil pH influences biodegradation through its effect on microbial activity, microbial community and diversity, enzymes that aid in the degradation processes as well as the properties of the substances to be degraded.
Soil pH was the most important soil property in the degradation of atrazine [ 41 ]. Generally, alkaline or slightly acid soil pH enhances biodegradation, while acidic environments pose limitations to biodegradation [ 34 , 37 , 42 ].
Usually, pH values between 6. Within this range, specific enzymes function within a particular pH spectrum. The biodegradation process rather slowed down in three acidic United Kingdom soils pH 4. This was associated with the highest bacterial populations [ 34 ]. Furthermore, Houot et al.
They observed maximum soil respiration in atrazine-contaminated soils at soil pH values higher than 6. Organic matter mineralization is often expressed as carbon C , nitrogen N , phosphorus P , and sulphur S mineralization through microbial action. Soil pH controls mineralization in soils because of its direct effect on the microbial population and their activities.
This also has implications for the functions of extracellular enzymes that aid in the microbial transformation of organic substrates. Additionally, at a higher soil pH, the mineralizable fractions of C and N increase because the bond between organic constituents and clays is broken [ 20 ]. In a study on the mineralization of C and N in different upland soils of the subtropics treated with different organic materials, Khalil et al.
Similar results had earlier on been obtained by Curtin et al. Nitrification and denitrification are important nitrogen transformation processes of environmental concern.
Plant Physiological Ecology pp Cite as. Many methods have been developed for assessing the availability of soil nutrients, but for a variety of reasons none are universally applicable. In this chapter, we discuss the conceptual basis for measuring nutrient availability and describe the strengths and limitations of some of the methods for assessing nonagricultural soils. We also discuss methods for characterizing soil acidity, salinity and redox potential because they often control nutrient cycling and availability. Unable to display preview. Download preview PDF.
Soil pH affects nutrients available for plant growth. In highly acidic soil, aluminum and manganese can become more available and more toxic to plant while.
Jump to navigation Skip to Content. Deficiencies of major plant nutrients often occur in acidic soil because nutrients are less available to plants. The availability of nutrients to plants is altered by soil pH Figure 5. In acidic soils, the availability of the major plant nutrients nitrogen, phosphorous, potassium, sulfur, calcium, magnesium and also the trace element molybdenum is reduced and may be insufficient. In addition to being chemically less available to plants, nutrients may also be positionally less available due to poor root growth in acidic soils.
Biotech Articles. Publish Your Research Online. Article Summary: From the present study it can be concluded that the knowledge of interaction of availability of nutrient with soil pH give the information which nutrient apply which pH for maximum utilize by crop plants with minimum loss
Learn more. Having the correct pH is important for healthy plant growth. Being aware of the long-term effects of different soil management practices on soil pH is also important. Research has demonstrated that some agricultural practices significantly alter soil pH. A pH value is actually a measure of hydrogen ion concentration. Because hydrogen ion concentration varies over a wide range, a logarithmic scale pH is used: for a pH decrease of 1, the acidity increases by a factor of Therefore, at high alkaline pH values, the hydrogen ion concentration is low.
Skip to content. What is soil pH? As acidity increases, soil pH decreases.
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