Effect of the calcium/magnesium ratio in soil acidity correctives on the initial growth and mineral nutrition of coffee

Exchangeable cations are often overestimated especially in salt-affected soils due to the presence of high levels of soluble ions in soil solution. Thus, quantitative analysis of the soil exchangeable cation based on ammonium acetate extraction method {(Exch. Cation)total} requires additional process to remove the free ions (pre-washing) in soil with distilled water or alcohol {(Exch. Cation)pw} or subtraction of the soluble ion contents from the total exchangeable cations {(Exch. Cation)ref}. In this research, we compared the three different methods for the determination of exchangeable cations in soils affected by different types of salt accumulation such as the soils from upland, plastic film house, and reclaimed tidal land. In upland soils, non-saline and non-sodic soils, the regular ammonium acetate extraction method did not have any problem to determine the content of exchangeable cations without any additional process such as the pre-washing method or the subtraction method. However, the contents of exchangeable cations in the salt-affected soils might be determined better with the pre-washing method for the plastic film house soils and with the subtraction method for the reclaimed tidal land soils containing high Na.

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated with high exchangeable Mg levels in soils relative to soil K and Ca. A greenhouse experiment was set up to test the hypothesis that the equilibrium between soil exchangeable K, Ca, and Mg ions influences the growth and nutrient status of sugar maple seedlings. Also tested was whether endomycorrhization can alter nutrient acquisition under various soil exchangeable basic cations ratios. Treatments consisted of seven ratios of soil exchangeable K, Ca, and Mg making up a total base saturation of 58%, and a soil inoculation treatment with the endomycorrhizal fungus Glomus versiforme (control and inoculated), in a complete factorial design. Sugar maple seedlings were grown for 3 months in the treated soils. Plant shoot elongation rate, dry biomass and nutrient concentrations in foliage were influenced by the various ratios of soil cations. The predicted plant biomass and foliar K concentration were highest at a soil Ca saturation of 38%, a soil K saturation of 12%, and a soil Mg saturation of 8%. Potassium concentration in foliage was dependent on the level of Ca and Mg saturation in the soil when soil K saturation was close to 12%. Foliar Ca and Mg levels were more dependent on their corresponding levels in soil than foliar K. Colonization by G. versiforme did not influence seedling growth and macronutrient uptake. The results confirm that growth and nutrition of sugar maple are negatively affected by imbalances in exchangeable basic cations in soils.

The increase in global food demand imposes pressure on agricultural soils, leading to soil fertility decline, particularly in African countries.Organic soil conditioners have been used to improve soil fertility although they are not stable and decompose with time.Zeolite is a stable inorganic material that is gaining popularity as a soil conditioner for its ion exchange capacity and high cation exchange capacity (CEC).Zeolites are aluminosilicate minerals, having a negative charge which is balanced by cations.The nature of zeolite in soil needs to be understood as it has a bearing on soil fertility and agricultural potential.A greenhouse pot experiment was conducted at the Agricultural Research Council, Stellenbosch to assess the residual effects of zeolite on soil exchangeable cations (Ca, Na, Mg, and K) and soil CEC.The exchangeability of all soil cations and CEC was increased with zeolite application.Soil exchangeability of Na, Mg, and K in the second growing season was generally reduced (p<0.05) on the zeolite-amended treatments, compared to the first growing season.However, the CEC of all treatments was larger in the second season compared to that of the first growing season.The results of this study show that zeolite can be used to improve sandy soil fertility.However, in continuous cropping systems some of the base cations will require replenishment.

Nitrogen (N) is an essential macronutrient for plant function and growth and a key component of amino acids, which form the building blocks of plant proteins and enzymes. However, misuse and overuse of N can have many negative impacts on the ecosystem, such as reducing soil exchangeable base cations (BCs) and causing soil acidification. In this research, we evaluated clonal Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) seedlings grown with exponentially increasing N fertilization (0, 0.5, 1, 2 g N seedling-1) for a 100-day trial in a greenhouse. The growth of seedlings, their nutrient contents, and soil exchangeable cations were measured. We found that N addition significantly increased plant growth and N content but decreased phosphorous (P) and potassium (K) contents in plant seedlings. The high nitrogen (2 g N seedling-1) treated seedlings showed a negative effect on growth, indicating that excessive nitrogen application caused damage to the seedlings. Soil pH, soil exchangeable base cations (BCs), soil total exchangeable bases (TEB), soil cation exchange capacity (CEC), and soil base saturation (BS) significantly decreased following N application. Our results implied that exponential fertilization resulted in soil acidification and degradation of soil capacity for supplying nutrient cations to the soil solution for plant uptake. In addition, the analysis of plants and BCs revealed that Na+ is an important base cation for BCs and for plant growth in nitrogen-induced acidified soils. Our results provide scientific insights for nitrogen application in seedling cultivation in soils and for further studies on the relationship between BCs and plant growth to result in high-quality seedlings while minimizing fertilizer input and mitigating potential soil pollution.

To compare the dynamic effects of straw and corresponding biochar on soil acidity, nutrients, and exchangeable capacity in red soil, a pot experiment was performed. The treatments included control (CK), rice straw (R1B0), rice straw biochar prepared at 350℃ (R1B1) and 550℃ (R1B2), rape stalk (R2B0), and rape stalk biochar prepared at 350℃ (R2B1) and 550℃ (R2B2). Straw at 1% and corresponding biochar were added to a strongly acidic red soil. The rice was planted as the experimental crop. Soils were collected at the seedling, tillering, filling and mature stages of rice growth, respectively. The changes in soil pH, exchangeable acidity, organic matter, nutrients (NH4+-N and NO3--N), and exchangeable cations in soils were measured. The results showed that soil pH, NH4+-N, and NO3--N concentrations decreased with the growth period of rice, while the organic matter content and cation exchange capacity (CEC) increased. Direct returning of straw and biochar could increase soil pH, organic matter content, and exchangeable cations content, and reduce the total amount of exchangeable acids. In the mature stage of rice, rice straw and rape stalk biochar at 350℃ increased the soil pH by 0.29 and 0.42, respectively, compared to the control treatment. Similarly, biochar decreased the exchangeable acidity and exchangeable Al3+ content significantly compared to the direct returning treatments of straw. The exchangeable acidity and exchangeable Al3+ contents of soils in R1B2 and R2B1 treatments decreased by 54.8% and 58.9%, respectively, compared to the control treatment. The soil organic matter (SOM) content and CEC in biochar treatments were significantly higher than those in direct returning treatments of straw. Overall, the effects of rape stalk biochar on soil properties were slightly stronger than those of rice straw. The correlation analysis showed that soil exchangeable acids had a significantly negative correlation with organic matter (R=-0.912, P<0.01), and CEC (R=-0.866, P<0.05). The CEC in soils was positively related to organic matter (R=0.833, P<0.05). Direct returning of straw and biochar applications can effectively improve soil acidity and increase nutrient contents. The effects of straw biochar on soils were stronger than the direct returning of straw in decreasing soil acidity, and increasing soil organic matter content and exchangeable capacity in acidic soils.

This paper aims to identify the spatial distribution of exchangeable base cations in soils on an acid hillslope and to investigate possible cation release processes from slope soils to the stream. The basic assumption underlying this research is that the amount of exchangeable cations in soils reflects the nutrient stores and cation leaching processes across the slope where vegetation and parent materials are similar. The distribution of exchangeable Ca2+, Mg2+, K+ and Na+ has been investigated on a three-dimensional hillslope on the Quantock Hills, Somerset, UK. A two-way ANOVA shows that soil depth is predominant in explaining the total variance of exchangeable bases, despite the steep slope gradient and clear podzolic catena development. Major nutrient base cations, such as Ca2+, Mg2+ and K+, display homogeneous topsoil storage right across the slope. This spatial pattern may indicate that the spatial distribution of major nutrient cations is tightly controlled by the soil–vegetation system in nutrient-poor heathland environments. Na+ is an exception to this vegetation-controlled spatial distribution, because of its small involvement in the soil–vegetation and soil exchangeable systems. In subsurface soils, cations liberated from the soil–vegetation system are subject to redistribution over the slope according to the hydrological flowpaths operating on the slope, with some eventually released into the stream. The saturated wedge developed at the base of the slope plays a key role in the storage and release processes of base cations from slope soils to the stream. Ca2+, Mg2+ and Na+ carried by throughflow are stored in the saturated wedge and gradually released into the stream at times of high flow. K+, however, shows an apparently different spatial behaviour, being deficient in the saturated wedge. Copyright © 1999 John Wiley & Sons, Ltd.

A procedure for the rapid determination of basic exchangeable cations in soils that uses the copper(1) complex with thiourea is described and tested. The results obtained compared favourably with values obtained by displacement of cations with pH 8.5, 1M NH4Cl and 0.01 M silver thiourea.

This paper aims to identify the spatial distribution of exchangeable base cations in soils on an acid hillslope and to investigate possible cation release processes from slope soils to the stream. The basic assumption underlying this research is that the amount of exchangeable cations in soils reflects the nutrient stores and cation leaching processes across the slope where vegetation and parent materials are similar. The distribution of exchangeable Ca2+, Mg2+, K+ and Na+ has been investigated on a three-dimensional hillslope on the Quantock Hills, Somerset, UK. A two-way ANOVA shows that soil depth is predominant in explaining the total variance of exchangeable bases, despite the steep slope gradient and clear podzolic catena development. Major nutrient base cations, such as Ca2+, Mg2+ and K+, display homogeneous topsoil storage right across the slope. This spatial pattern may indicate that the spatial distribution of major nutrient cations is tightly controlled by the soil–vegetation system in nutrient-poor heathland environments. Na+ is an exception to this vegetation-controlled spatial distribution, because of its small involvement in the soil–vegetation and soil exchangeable systems. In subsurface soils, cations liberated from the soil–vegetation system are subject to redistribution over the slope according to the hydrological flowpaths operating on the slope, with some eventually released into the stream. The saturated wedge developed at the base of the slope plays a key role in the storage and release processes of base cations from slope soils to the stream. Ca2+, Mg2+ and Na+ carried by throughflow are stored in the saturated wedge and gradually released into the stream at times of high flow. K+, however, shows an apparently different spatial behaviour, being deficient in the saturated wedge. Copyright © 1999 John Wiley & Sons, Ltd.

The relationship between water soluble and exchangeable cations (Ca, Mg, Na, and K) was investigated for surface horizons of 195 soils including many taxonomic categories and a wide range in physical and chemical properties from around the world. This will provide information on exchangeable soil cation solubility for use in estimating plant uptake and leaching potential. Amounts of water soluble and exchangeable cations were not consistently related (r2 of 0.50, 0.08, 0.77, and 0.49 for Ca, Mg, Na, and K). High correlations were biased by high water soluble and exchangeable cation levels of a few soils that had 3.8‐ and 2.5‐fold greater mean than median values. The ratio of exchangeable to water soluble cations was closely related to cation saturation (r2 of 0.87, 0.95, 0.95, and 0.93 for Ca, Mg, Na, and K, respectively). As the degree of saturation of the exchange complex by a certain cation increased, solubility Increased. A change in saturation had less effect on K than on Na, Mg, and Ca solubility. Only exchangeable soil cations (NH4OAc extractable) are routinely measured and reported in soil survey reports, thus, water soluble levels may be determined from cation saturation. This will allow estimation of the amounts of cation that can potentially move in solution through the soil or be taken up by plants. Use of cation saturation, in addition to exchangeable content, will better characterize soil cation availability by representing quantity, intensity, and buffer factors.

Adjacent plots (1 m2) with and without communities of dwarf bamboo (Sasa), i.e. Sasa- and ref-plots, were selected in mountainous areas, which were relatively low in soil buffer capacity. The following parameters were studied: chemical properties of surface (0-30 cm) soil (at 6 sites), elemental abundances in the soil-Sasa ecosystem (at 6 sites), effect of artificial acid rain on the above two parameters (at 1 site), and chemical properties of throughfall and stemflow of Sasa (at 2 sites including one on a plain). Average values of pH(H2O), base saturation and the ratio of exchangeable (K+Mg+Ca)/exchangeable Al in surface soil were 4.35±0. 53, 25.2±14.3% and 0.41±0.28, respectively, in Sasa-plots and 4.26±0.63, 20.0±9.6%, and 0.28±0.13, respectively, in ref-plots. Though not significant, all soil parameters had higher values in Sasa-plots, i.e. Δx = ca. 0.1 unit, 5% and 0.13, respectively. When the abundance of elements (exchangeable cations in soil of 30 cm depth plus elements in litter and Sasa biomass) in the ecosystem was compared between the two plots, K (and often other basic cations) was higher in Sasa-plots than in ref-plots, whereas Al was lower. Artificial acid rain (1.5 L of 0.05 M H2SO4 applied monthly for 10 months) induced a reduction of Na, K, Mg and Ca in a ref-plot, but in a Sasa-plot only Na and K were reduced whereas Mg and Ca were completely retained. The composite samples of throughfall and stemflow of Sasa were ca. 0.5 higher in pH and richer in K, Mg and Ca than the ambient precipitation. The amounts (equivalents) of elements released by Sasa were in the order K > Ca > Mg. It was determined that about 87% and 98% of K, 76% and 87% of Ca, and 39% and 93% of Mg were of Sasa origin in the composite samples at a mountainous site (cambisol soil type) and a plain site (andosol soil type), respectively. Sasa communities may have a significant role in retention of basic cations in surface soil and prevention of soil acidification because of recycling elements in the soil-Sasa ecosystem.

The long-term productivity of a soil is greatly influenced by cation exchange capacity (CEC). Moreover, interactions between dominant base cations and other nutrients are important for the health and stability of grassland ecosystems. Soil exchangeable base cations and cation ratios were examined in a 11-year experiment with sheep manure application rates 0–1,500 g/(m2·a) in a semi-arid steppe in Inner Mongolia of China, aiming to clarify the relationships of base cations with soil pH, buffer capacity and fertility. Results showed that CEC and contents of exchangeable calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+) were significantly increased, and Ca2+ saturation tended to decrease, while K+ saturation tended to increase with the increases of sheep manure application rates. The Ca2+/Mg2+ and Ca2+/K+ ratios decreased, while Mg2+, K+ and Na+ saturations increased with increasing manure application rates. Both base cations and CEC were significantly and positively correlated with soil organic carbon (SOC) and soil pH. The increases of SOC and soil pH would be the dominant factors that contribute to the increase of cations in soil. On a comparison with the initial soil pH before the experiment, we deduced that sheep manure application could partly buffer soil pH decrease potentially induced by atmospheric deposition of nitrogen and sulfur. Our results indicate that sheep manure application is beneficial to the maintenance of base cations and the buffering of soil acidification, and therefore can improve soil fertility in the semi-arid steppes of northeastern China.

Core Ideas Exchangeable cations are important in water sorption, hydraulic conductivity, swelling, flocculation–deflocculation, and fertility. Intrinsic relationship exists between matric potential and cation hydration at very low water contents. Proposed model predicts soil water content at low matric potentials for different exchangeable cations in soil. Model is applicable for soil water retention models and quantification of different types of exchangeable cations. The origin of matric potential in the tightly adsorbed soil water retention (SWR) regime, where matric potentials are generally less than −150 MPa, remains unsettled. Surface tension in soil pores and van der Waals attraction (VDW) near particle surfaces are known, respectively, as the sources of matric potential for capillary and adsorbed film water. However, theories based on VDW fail to predict the SWR for matric potentials less than −150 MPa. Recent studies show that cation hydration occurs at matric potentials much lower than those predicted by considering a particle surface hydration originating from the VDW forces. With this basis, a theoretical soil water retention curve (SWRC) model for drying path is proposed to quantify matric potential and its retained water by accounting for all water sorption mechanisms on or within soil particles, particularly the cation–water molecule or charge–dipole interaction. It is found that clays at very low soil water content, typically less than a few percentage gravimetric, charge–dipole interaction energy, dominate matric potential. Experimental SWR data for various cation‐exchanged soils confirms the validity of the theoretical SWRC model and its accuracy, indicating that cation hydration is mainly responsible for SWR for matric potentials less than −150 MPa. Furthermore, the predicted lowest matric potentials at zero water content for various soils agree well with experimental data. The lowest matric potential of a soil depends mainly on the type of exchangeable cations and thus is not a universal constant for all soils. These results have potential applications in using SWRC for the determination of cation exchange capacity and types of exchangeable cations in soils.

Although coupling of transport processes in soil has been studied for some time using the principles of irreversible thermodynamics, its importance with respect to coupled diffusion of cations in soil has not yet been fully determined. The purpose of this study was to evaluate the importance of coupled diffusion of cations in a sandy soil in which the pH‐dependent charge from organic matter represented a major proportion of the total cation‐exchange capacity. The degree of coupling was evaluated by determining what effect counterdiffusion of exchangeable K and Ca had on the distribution of exchangeable Na when the latter was initially at a uniform concentration throughout the system. Coupling was evidenced by a Na flux that was counter to, and ranged from 16 to 28% as large as, the K flux. The simultaneous diffusion of Ca, K, and Na was modeled by assuming that the coupling resulted from a diffusion potential arising from the counterdiffusion of K and Ca. Intrinsic diffusion coefficients required in the model were estimated from conductance data. Predicted and measured cation concentrations showed a highly significant linear correlation, with predicted concentrations averaging 96% of measured concentrations for all three cations.

Desenvolveu-se um experimento de campo com o intuito de verificar o efeito da irrigação por microaspersão, utilizando-se água de condutividade elétrica média de 1,42 dS m-1, sob as propriedades químicas de um Neossolo Flúvico cultivado com cenoura cv. Brasília. A área foi dividida em dois setores (S1 e S2), com 900 m² cada um (30 x 30 m) e texturas contrastantes; no S2 adicionou-se cobertura morta aos 23 dias após a semeadura (DAS) e se adotou uma fração de lixiviação de 0,20 para os dois setores. Realizaram-se duas amostragens de solo, antes da semeadura e a 96 DAS, nas camadas de 0-20 e 20-40 cm, em 49 pontos no S1 e 52 pontos no S2, segundo uma malha de 5 x 5 m. No extrato da pasta saturada foram medidos o pH e a condutividade elétrica (CEes), e determinadas as bases solúveis; determinou-se, ainda, as bases trocáveis, calculando-se a relação de adsorção de sódio e a percentagem de sódio trocável. Os dados foram analisados por estatística descritiva e geoestatística. Considerando-se a camada de 0-40 cm, a área salina no S1, inicialmente de 7,98%, aumentou para 15,09% ao final do ciclo cultural. Para o S2, a área salina passou de 5,97 para 5,52%; verificou-se, assim, a influência decisiva da textura e da cobertura morta no controle da salinidade do solo.

The amelioration effects of crop straws and their biochars on an acidic ultisol were compared in incubation experiments to determine suitable organic amendments for acid soils. Four crop straws, including non-legumes (canola straw and rice straw) and legumes (soybean straw and pea straw) were used to prepare biochars using a low temperature (350°C) oxygen-limited pyrolysis method. Two application rates of 1% and 2% were used for both crop straws and their biochars in incubation experiments lasting 90 days. Soil pH (1:2.5 soil to water), soil exchangeable acidity, soil exchangeable base cations, and soil cation exchange capacity (CEC) were determined to evaluate the amelioration effects of these crop straws and their biochars on an acidic ultisol. The incorporation of crop straws increased or decreased the soil pH depending on the relative contribution of alkalinity of the straws, mineralization of organic N and nitrification of NH4 +. The incorporation of biochars produced from crop straws increased the soil pH, and their ameliorating effects increased with the application rates of biochars. The biochars from legume straws induced more increase in soil pH than non-legume biochars. The addition of both crop straws and their biochars decreased soil exchangeable acidity and exchangeable Al3+, and increased soil exchangeable base cations and base saturation degree. The biochars (especially legumes) induced a greater decrease in soil exchangeable acidity and a greater increase in soil exchangeable base cations compared to their feedstock due to their much higher contents of base cations. The CEC of biochars were 10–20 times that of soil CEC and thus biochar incorporation increased the soil CEC significantly, as well as the retention of Ca2+, Mg2+, K+, and NH4 + by acid soils. The biochars produced from legume crop straws were better choices as amendments for acid soils than their feedstock. Organic anions and carbonates were the main forms of alkali in the biochar; both contributed to neutralizing soil acidity and increasing soil pH. The incorporation of biochar cannot only neutralize soil acidity, but can also improve soil fertility.