Lime and calcium-magnesium silicate in the ionic speciation of an Oxisol

Plant residues and certain fertilizers accelerate soil acidification and increase the levels of aluminum-Al+3 in soils under no-tillage (NT). Silicates act as acidity amendments and as a source of silicon as in H4SiO4. An increase in the pH of soil solution causes the deprotonation of H4SiO4 and generates the anionic form (H3SiO4−). The aim of this study was to evaluate the ionic speciation of Si, Al, Ca, Mg and K in aqueous extracts by means of a software calculation. Since 2006, a field experiment has been under way on an Oxisol under NT subjected to lime and calcium-magnesium silicate applications under four crop systems. The amendments were applied in Oct 2006 and in Oct 2011, aiming to raise base saturation to 70 %. Soil samples were collected in Oct 2013, at depths of 0-5, 5-10, 10-20, 20-40 and 40-60 cm. Both Ca and Mg formed complexes with dissolved organic carbon (DOC) whereas the same was not observed for potassium. These three basic cations were mostly in their free forms regardless of treatment, while Al was mostly complexed with DOC even at the lowest depths (40-60 cm). The highest value of free Al form was 15 %. Si was almost 100 % as H4SiO4, and its activity was similar to its concentration in solution for all crop systems and at all depths, regardless of amendment applied. The percentages of H3SiO4− and Al-H3SiO42+ were irrelevant, providing more phytoavailable H4SiO4 in soil solution

Atributos eletroquímicos e disponibilidade de nutrientes, elementos tóxicos e metais pesados em solos tropicais

As propriedades eletroquímicas dos solos tropicais são muito importantes para entendimento dos fenômenos físico-químicos que afetam a fertilidade do solo e a disponibilidade dos nutrientes das plantas. Essa revisão destaca os atributos eletroquímicos de solos e o comportamento e a disponibilidade de nutrientes, elementos tóxicos e metais pesados no solo, especialmente aqueles com predominância de minerais com cargas variáveis. A disponibilidade dos elementos é relacionada com a troca iônica, especiação da solução e propriedades adsortivas eletrostáticas e específicas do solo. Modelos empíricos e de complexação de superfície são brevemente descritos, e são apresentados resultados de sua aplicação em solos tropicais. É necessário um melhor entendimento do papel da dupla camada difusa de cargas e da CTC na disponibildade de nutrientes em solos altamente intemperizados, assim como uma melhor compreensão dos modelos de complexação de superfície, a fim de melhorar o entendimento do comportamento dos ânions no solo. Mais estudos devem ser conduzidos para gerar resultados que tornem possível o uso de conceitos de especiação química e o cálculo de diversas constantes usadas em modelos de complexação, especialmente para solos altamente intemperizados do trópico úmido. Deve haver um contínuo desenvolvimento de programas computacionais que já tenham incorporado os conceitos de especiação e modelos de adsorção no estudo da disponibilidade de nutrientes, elementos tóxicos e metais pesados no sistema solo-planta.Electrochemical properties of soils are very important for the understanding of the physico-chemical phenomena which affect soil fertility and the availability of nutrients for plants. This review highlights the electrochemical properties of tropical soils, the behavior and the availability of nutrients, toxic elements and heavy metals in the soil, especially for soils with predominant variable charge minerals. Availability of the elements is related to ionic exchange, solution speciation, and electrostatic and specific adsorptive soil properties. Empirical and surface complexation models are briefly described, and some results of their application in tropical soils are presented. A better understanding of the role of the double diffuse layer of charges and CEC on nutrient cation availability for highly weathered soils is required, as well as a solid comprehension of surface complexation models, in order to improve the knowledge regarding the behavior of anions in soils. More studies have to be conducted to generate results that enable the use of chemical speciation concepts and calculation of several constants used in surface complexation models, especially for highly weathered soils from the humid tropics. There has to be a continuing development and use of computer softwares that have already incorporated the concepts of chemical speciation and adsorption models in the study of nutrients, toxic elements and heavy metal availability in the soil-plant system

Nutrient Dynamics in a Highly Weathered Soil Under No-Till and Heavy Metal Phytoavailability as Affected by Biochar Amendment

The nutrient dynamics in soils are affected by cropping systems, soil properties and environmental conditions. A field experiment under NT has been conducted in an Oxisol, which assesses rates of inorganic P and K fertilizers for soybean production in conjunction with liming since 1995. The objectives were to evaluate the effect of rates of P and K fertilizers on soybean yields, and to access the P species in solid state by X-ray fluorescence (P-XANES). The optimum amounts of P and K fertilizers were revealed, which will help farmers improve their crop yields while minimize the impact of fertilization on soil and water quality. The long-term mineral phosphate fertilizer application led to P stabilization in soils under more thermodynamically stable forms, such as P-Fe and P-Al, in spite of the effects that soil organic matter (SOM) might have on P reactivity. A second project studied the heavy metal (HM: Zn, Pb and Cd) dynamics in a contaminated soil of NE Oklahoma. High concentrations of HM in soils have negative impacts on plants, human health and the environmental quality. The purpose was to evaluate the effects of biochars on the Zn, Pb and Cd phytoavailability in Tar Creek contaminated soils, as well as on the growth and uptake of these elements by perennial ryegrass (Lolium perenne). Biochars produced from switchgrass (SGB) and poultry litter (PLB) feedstocks at 350 and 700 °C (pyrolysis temperatures) were characterized as their potential use as soil amendment. Those pyrolyzed at 700 oC were used to investigate their effect on ryegrass dry matter yield and the accumulation of HM in shoots and roots. Biochars were applied to the soil at 0, 0.5, 1, 2 and 4% (w/w) and the soils were extracted by DTPA to estimate the available HM contents. Soils amended with low amounts of biochars reduced HM phytoavailability thus reduced plant metal uptake. Biochar also increased plant biomass but reduced metal transfer from roots to shoots. It is effective using readily available bioproducts to remediate HM contaminated soils and to enhance ryegrass forage yield with acceptable amount of HM in the shoots

Exploration of Ion Species in Agricultural Subsurface Drainage Waters

Assessing the effectiveness of management strategies to reduce agricultural nutrient efflux is hampered by the lack of affordable, continuous in-situ monitoring systems. Generalized water quality monitoring is possible using electrical conductivity. However environmental conditions can influence the ionic ratios, resulting in misinterpretations of established electrical conductivity and ionic composition relationships. Here we characterize the specific electrical conductivity of agricultural drainage waters to define these environmental conditions and dissolved constituents that contribute to electrical conductivity. Results from a field investigation revealed that bicarbonate, calcium, nitrate, magnesium, chloride, sodium, and sulfate (in order of decreasing ppm concentration) are primary dissolved constituents that contribute to the electrical conductivity of agricultural drainage waters. Analysis of seasonal drainage samples showed that bicarbonate, calcium, and magnesium were present at greater concentrations during the post growing season, while nitrate and chloride were greatest in the growing season. Seasonal variability of sulfate and sodium was negligible. Continuous corn and corn in annual rotation with soybeans had greater magnesium and chloride concentrations than that of soybeans in annual rotation with corn. Conversely, calcium was greater among soybean cropping systems compared to that of corn cropping systems. Bicarbonate and nitrate were not significantly different among any of the cropping systems. These changes in the ionic composition resulted in significantly different ionic ratios among the growing and post growing season samples, but not among cropping systems

Iron isotope fractionation in soil and graminaceous crops after 100 years of liming in the long‐term agricultural experimental site at Berlin‐Dahlem, Germany

Sustainable arable cropping relies on repeated liming. Yet, the associated increase in soil pH can reduce the availability of iron (Fe) to plants. We hypothesized that repeated liming, but not pedogenic processes such as lessivage (i.e., translocation of clay particles), alters the Fe cycle in Luvisol soil, thereby affecting Fe isotope composition in soils and crops. Hence, we analysed Fe concentrations and isotope compositions in soil profiles and winter rye from the long-term agricultural experimental site in Berlin-Dahlem, Germany, where a controlled liming trial with three field replicates per treatment has been conducted on Albic Luvisols since 1923. Heterogeneity in subsoil was observed at this site for Fe concentration but not for Fe isotope composition. Lessivage had not affected Fe isotope composition in the soil profiles. The results also showed that almost 100 years of liming lowered the concentration of the HCl-extractable Fe that was potentially available for plant uptake in the surface soil (0–15 cm) from 1.03 (standard error (SE) 0.03) to 0.94 (SE 0.01) g kg−1. This HCl-extractable Fe pool contained isotopically lighter Fe (δ56Fe = −0.05 to −0.29‰) than the bulk soil (δ56Fe = −0.08 to 0.08‰). However, its Fe isotope composition was not altered by the long-term lime application. Liming resulted in relatively lower Fe concentrations in the roots of winter rye. In addition, liming led to a heavier Fe isotope composition of the whole plants compared with those grown in the non-limed plots (δ56FeWholePlant_ + Lime = −0.12‰, SE 0.03 vs. δ56FeWholePlant_-Lime = −0.21‰, SE 0.01). This suggests that the elevated soil pH (increased by one unit due to liming) promoted the Fe uptake strategy through complexation of Fe(III) from the rhizosphere, which favoured heavier Fe isotopes. Overall, the present study showed that liming and a related increase in pH did not affect the Fe isotope compositions of the soil, but may influence the Fe isotope composition of plants grown in the soil if they alter their Fe uptake strategy upon the change of Fe availability.Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/50110000234

Authigenic apatite and octacalcium phosphate formation due to adsorption–precipitation switching across estuarine salinity gradients

Mechanisms governing phosphorus (P) speciation in coastal sediments remain largely unknown due to the diversity of coastal environments and poor analytical specificity for P phases. We investigated P speciation across salinity gradients comprising diverse ecosystems in a P-enriched estuary. To determine P load effects on P speciation we compared the high P site with a low P site. Octacalcium phosphate (OCP), authigenic apatite (carbonate fluorapatite, CFAP) and detrital apatite (fluorapatite) were quantitated in addition to Al/Fe-bound P (Al/Fe-P) and Ca-bound P (Ca-P). Gradients in sediment pH strongly affected P fractions across ecosystems and independent of the site-specific total P status. We found a pronounced switch from adsorbed Al/Fe-P to mineral Ca-P with decreasing acidity from land to sea. This switch occurred at near-neutral sediment pH and has possibly been enhanced by redox-driven phosphate desorption from iron oxyhydroxides. The seaward decline in Al/Fe-P was counterbalanced by the precipitation of Ca-P. Correspondingly, two location-dependent accumulation mechanisms occurred at the high P site due to the switch, leading to elevated Al/Fe-P at pH 6.6 (seaward; precipitation). Enhanced Ca-P precipitation by increased P loads was also evident from disproportional accumulation of metastable Ca-P (Ca-Pmeta) at the high P site. Here, sediments contained on average 6-fold higher Ca-Pmeta levels compared with the low P site, although these sediments contained only 2-fold more total Ca-P than the low P sediments. Phosphorus species distributions indicated that these elevated Ca-Pmeta levels resulted from transformation of fertilizer-derived Al/Fe-P to OCP and CFAP in nearshore areas. Formation of CFAP as well as its precursor, OCP, results in P retention in coastal zones and can thus lead to substantial inorganic P accumulation in response to anthropogenic P input

Lime induced changes in the surface and soil solution chemistry of variable charge soils

The study was conducted to improve lime recommendations as well as to design better management practices for acidic grasslands of Appalachian region. These goals were achieved by two experiments. In the first experiment, the accuracy of lime predictions by quick tests were improved by accounting soil order and develop equation based lime correlations for acidic pasture soils of West Virginia. In order to achieve this objective, 26 surface soil samples (0--7.5 cm) from three most important soil orders for the state (Alfisols, Inceptisols, Ultisols) from each of the Major Land Resource Areas (MLRAs) in West Virginia with large proportions of pasture land were collected in cooperation with state soil scientists. Standard procedures for the determination of lime requirements by the Mehlich Buffer (MB), Adams-Evans Buffer (AEB) and Shoemaker-McLean-Pratt Single Buffer (SMPB) methods were used. Statistically significant improvements in lime recommendations for target pH 6.5 and 5.5 were achieved by accounting for soil order. Mehlich single buffer recommendations were better for Alfisols and Ultisols than for Entisols to achieve pH 6.5. Lime correlations were developed for all three chemical buffers by multiple regression where the independent variables were target pH and soil-buffer pH. The Adam-Evans buffer predicted lime rates better for target pH 5.5. Equation-based lime correlations were also developed for all three chemical buffers by multiple regressions where the independent variables are target pH and soil-buffer pH. The second experiment was conducted to quantify the critical growth factors such as water potential, pH, nitrogen, and phosphorus and their interactions to deduce a comprehensive prescription of site-specific management techniques to forage production in acidified hill land pastures of West Virginia. In order to achieve this objective, a pot experiment was set up with two water potentials, five pH levels, five N and P fertilizer rates were imposed on bluegrass (sole) and bluegrass + white clover mixture. The estimation of overall effects of these four factors showed that levels of water potential, pH, N fertilizer doses as well as their interactions significantly affected the bluegrass (sole) production (p\u3c0.05). In case of bluegrass and white clover mixture cropping system, all four factors (water potential, pH, N and P levels) and their interactions exhibited significant influence on dry matter yield as well as nutrient concentration in shoot tissue. Nutrient concentrations also showed a synergistic relationship among each other as well as with dry matter yield in both bluegrass and bluegrass + white clover mixture. Response yield function was determined using significant factors and their interactions for blue grass (sole) and blue grass and white clover mixture

Phosphorous dynamics in soils under contrasting long-term agricultural management practices in the KwaZulu-Natal midlands.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.Little is known regarding the effects of land use on soil organic matter and P status of South African soils. For that reason, the effects of the main agricultural land uses in the midlands region of KwaZulu-Natal [maize (Zea mays), sugarcane (Saccharum spp), annual ryegrass pasture (Lolium multiflorum), permanent kikuyu pasture (Pennisetum clandestnum), gum (Eucalyptus grandis) and pine (Pinus patula)] on soil organic matter content, microbial biomass C and P and inorganic and organic P pools derived from a modified Hedley P fractionation was investigated on two sites where the longterm history of land management was known. In comparison with undisturbed native grassland, permanent kikuyu pasture resulted in an increase in organic C, organic P and microbial biomass C and P. Maize and sugarcane production resulted in a decrease in organic C, organic P and microbial C and P. Under annual pasture, gum and pine forests, organic matter and microbial biomass concentrations remained similar to those under native grassland. Under native grassland, extractable organic P accounted for 50% or more of the total P content of soils but under agricultural management with regular applications of fertilizer P, there was an increase in the percentage of total P present as inorganic P. Agricultural management greatly affected the distribution of P among the various inorganic and organic P fractions. Resin-Pi and NaHC03-Pi (the potentially-available forms of Pi) showed similar trends with land use being greatly elevated under kikuyu pasture at both sites and sugarcane and maize at one site. This accumulated Pi was thought to have originated from recent fertilizer applications and possibly recently mineralized organic P. Trends for NaOH-Pi with land use differed greatly from those of the Resin- and NaHC03Pi fractions. Concentrations were notably high under maize and sugarcane production. Of the pools of soil organic P, the NaHC03-Po fraction was most greatly affected by land use, being elevated under kikuyu and decreased under maize and sugarcane. This supports the assertion that it is the NaHC03-Po fraction that is the most labile soil organic P pool. It was concluded that land use greatly affects soil organic C and P status, soil microbial biomass C and P contents, soil inorganic P concentrations and the distribution of P among the various P fractions. A short-term (8 weeks) laboratory incubation experiment was carried out to compare the effects of inorganic (KH2P04) and organic (cattle manure, poultry manure and maize crop residues) sources of P, applied at a rate equivalent to 30 kg P ha-1 , on soil inorganic and organic P fractions and the potential availability of soil P. Additional treatments consisted of lime [Ca(OHhl at 5 ton ha-1 and lime plus inorganic P. Applications of lime raised soil pH to a similar extent after 1, 4 and 8 weeks incubation. After 8 weeks, a small increase in soil pH was also noted for the cattle and poultry manure and maize residue treatments. For the inorganic P fractions, substantial treatment effects were observed only for the Resin-Pi fraction. The inorganic P source was more effective than the organic ones at increasing Resin-Pi after 1 and 4 weeks incubation and of the organic sources, cattle and poultry manure were more effective than maize residues. Resin-Pi concentrations generally increased between 1 and 4 weeks incubation but then declined rapidly between 4 and 8 weeks incubation. After 8 weeks incubation, treatment effects on Resin-Pi were small. Concentrations of NaHC03-Pi, dilute HCI-Pi and concentrated HCI-Pi all declined over the incubation period. There was no clear trend with incubation for NaOH-Pi although for the poultry manure and maize treatments, concentrations declined between 4 and 8 weeks incubation. In general, concentrations of NaHC03-Po were greater for organic than inorganic P sources after 8 weeks incubation suggesting microbial immobilization of P in these treatments. There were increases in NaHC03-Po and concentrated HCI-Po over the incubation period suggesting progressive immobilization of P from the Pi fractions that declined in concentration during the incubation. Concentrations of NaOH-Po were not greatly affected by incubation period. The lime treatments, however, had lower NaOH-Po concentrations than the others suggesting that liming may have stimulated microbial mineralization of Po. Residual-P concentrations increased over the incubation period. This was attributed to conversion of extractable Pi fractions into recalcitrant, non-extractable Pi forms and/or immobilization of Pinto intransigent organic forms

Performance of Winter Wheat Varieties with and Without the ALMT1 Gene in Acid Soils

Aluminum (Al) tolerant wheat cultivars are often utilized in the southern Great Plains to damper the yield limiting impacts of Al toxicity in acidic soils. The tolerance is mainly facilitated by Al-activated malate transporter 1 (ALMT1) gene, which increases anion permeability of wheat roots and exudes malate in the presence of Al. However, no study has explored the phenotypic incongruities of those closely related genotypes with ALMT1(+) or without ALMT1(-)]. Moreover, there is currently no quantitative ranking of Al tolerance for newly released winter wheat varieties in forage and grain dual-purpose (DP) management systems. This field scale study consisting of two locations in central Oklahoma was established to determine the Al tolerance of eight parentally related but gene divergent winter wheat varieties [(Duster (+), Lonerider (+), OK14319 (+), Jagger (+), Iba (-), Gallagher (-), Spirit Rider (-), Smith's Gold (-)]. The design structure was a split-plot in a randomized complete block with a two-way treatment (6 x 8). Main plots were amended with alum/hydrated lime to reach the following target soil pH: 4.0, 4.5, 5.0, 5.5, 6.0, and 7.0. Soil samples were collected at two months after planting in order to determine soil pH and Al saturation (Alsat). Each variety was hand clipped during December to determine fall forage yield. Grain was harvested in June to measure grain yield, wheat protein concentration, test weight and wheat moisture content of each variety. Results varied between study years and locations. Significant differences were found between the relative forage yields of ALMT1 (-) and (+) genotypes groups at Stillwater and Chickasha in Year 1 (p = 0.0042 and p = 0.0440, respectively); however, differences were not significant in Year 2 (p = 0.7228 and p = 0.7792, respectively). No significant differences were found between relative grain yields of genotype groups at Chickasha (Alsat ≤ 8%) or Stillwater (Alsat ≤ 38%) in Year 1 (p = 0.9172 and p = 0.2102, respectively) or Year 2 (p = 0.2106 and p = 0.2684, respectively). Notwithstanding genotype group affiliation, significant differences were found among varieties in their response to Al concentration and soil acidity. Similarly, the productivity of genotype groups in this study varied between years and was not wholly dependent on the presence or absence of the ALMT1 gene. Additionally, varieties differed in their yearly and environmental responses despite close parental relationships. Nevertheless, the utilization of acid tolerant winter wheat varieties has the potential to significantly reduce yield loss under acidic soil conditions with high Al concentrations. The findings in this study should equip researchers and producers with the necessary knowledge to reduce yield losses when traditional methods of soil acidity amelioration such as liming are not feasible