Santiago Mahimairaja

Influence of low-molecular-weight organic acids on the solubilization of phosphates

A range of low-molecular-weight organic acids were identified in rhizosphere soil, leaf litter, and poultry manure compost. Laboratory and greenhouse experiments were carried out to examine the effects of seven low-molecular-weight organic acids on phosphate adsorption by soils, and the solubilization and plant uptake of P from soil pre-incubated with monocalcium phosphate and North Carolina phosphate rock. Acetic, formic, lactic (monocarboxylic), malic, tartaric, oxalic (dicarboxylic), and citric (tricarboxylic) acids were used in the study. The addition of organic acids decreased the adsorption of P by soils in the order tricarboxylic acid>dicarboxylic acid>monocarboxylic acid. The decreases in P adsorption with organic acid addition increased with an increase in the stability constant of the organic acid for Al (logKAl). Organic acids extracted greater amounts of P from soils meubated with both monocalcium phosphate and phosphate rock than water did. Although more phosphate was extracted by the organic acids from monocalcium phosphate — than from phosphate rock — treated soils in absolute terms, when the results were expressed as a percentage of dissolved phosphate there was little difference between the two fertilizers. The amount of P extracted by the organic acids from both fertilizers increased with an increase in logKAl values. The addition of oxalic and citric acids increased the dry matter yield of ryegrass and the uptake of P in soils treated with both fertilizers. The agronomic effectiveness of both fertilizers increased in the presence of organic acids and the increase was greater with the phosphate rock than with the monocalcium phosphate. The results indicated that organic acids increase the availability of P in soils mainly through both decreased adsorption of P and increased solubilization of P compounds.

Losses and transformation of nitrogen during composting of poultry manure with different amendments : an incubation experiment

The transformation of nitrogen (N) and its subsequent loss during aerobic and anaerobic composting of poultry manure with different amendments were investigated through laboratory incubation experiments. The amendments included: four carbon (C) rich bedding materials (woodchip, paper waste, cereal straw and peat), one acidifying material (elemental sulphur, S0) and two adsorbents (zeolite and soil). The loss of N through ammonia (NH3) volatilization from aerobic condition was about 17% of total manure N which was reduced by 90–95% under anaerobic condition. Under aerobic incubation systems, amongst the bedding materials examined, wheat straw and peat were found to be superior in reducing the NH3 loss by 33·5 and 25·8%, respectively. Loss of NH3 was reduced by 60% in manure amended with S0. Zeolite was a more effective NH3 (or NH44) adsorbent than soil and reduced NH3 loss by 60%. The amount of 2 m KCl extractable NH4+ -N was almost 1000 times higher than of nitrate (NO3− -N) in all composting mixtures suggesting little oxidation of NH4+ to NO3− (nitrification) occurred. The measurement of total N in the compost at the end of the experiment showed a total loss of about 50 and 26% of manure N during aerobic and anaerobic incubations, respectively, as against only about 17 and <1% losses measured through NH3 volatilization. This suggested that the N loss through denitrification could be considerably higher than that occurred through NH3 volatilization.

Phosphorus–arsenic interactions in variable-charge soils in relation to arsenic mobility and bioavailability

Phosphorus (P) influences arsenic (As) mobility and bioavailability which depends on the charge components of soil. The objective of this study was to examine P-As interaction in variable-charge allophanic soils in relation to P-induced As mobilization and bioavailability. In this work, the effect of P on arsenate [As(V)] adsorption and desorption was examined using a number of allophanic and non-allophanic soils which vary in their anion adsorption capacity. The effect of P on As uptake by Indian mustard (Brassica juncea L.) plants was examined using a solution culture, and a soil plant growth experiment involving two As-spiked allophanic and non-allophanic soils which vary in their anion adsorption capacity, and a field As-contaminated sheep dip soil. Arsenate adsorption increased with an increase in the anion adsorption capacity of soils. The addition of P resulted in an increase in As desorption, and the effect was more pronounced in the case of allophanic soil. In the case of both As-spiked soils and field contaminated sheep-dip soil, application of P increased the desorption of As, thereby increasing its bioavailability. The effect of P on As uptake was more pronounced in the high anion adsorbing allophanic than low adsorbing non-allophanic soil. In the case of solution culture, As phytoavailability decreased with increasing concentration of P which is attributed to the competition of P for As uptake by roots. While increasing P concentration in solution decreased the uptake of As, it facilitated the translocation of As from root to shoot. The net effect of P on As phytoavailability in soils depends on the extent of P-induced As mobilization in soils and P-induced competition for As uptake by roots. The P-induced mobilization of As could be employed in the phytoremediation of As-contaminated sites. However, care must be taken to minimize the leaching of As mobilized through the P-induced desorption, thereby resulting in groundwater and off site contamination.

Dissolution of phosphate rock during the composting of poultry manure: an incubation experiment

Dissolution of phosphate rocks (PRs) during composting with poultry manure was examined using a radioactive32P labelled synthetic francolite and North Carolina phosphate rock (NCPR) through laboratory incubation experiments. Francolite or NCPR was mixed with different poultry manure composts at a rate equivalent to 5 mg P g−1 and the dissolution was measured after 60 and 120 days incubation by a sequential phosphorus (P) fractionation procedure.The use of32P labelled francolite showed that in manure systems, PR dissolution can be measured more accurately from the increases in NaOH extractable P (ΔNaOH-P) than from the decreases in HCl extractable P (ΔHCl-P) in the PR treated manure over the control. The dissolution measurements showed that approximately 8 to 20% of francolite and 27% of NCPR dissolved during incubation with poultry manure composts in the presence of various amendments. Addition of elemental sulphur (S°) to the compost enhanced the dissolution of PRs. The results provide no evidence for the beneficial effect of protons (H+), produced during the nitrification of NH4+ in manure composts, on PR dissolution. The low level of dissolution of PR in poultry manure composts was attributed mainly to the high concentration (4.8 × 10−2 mol L−1) of calcium (Ca2+) in manure solution.

Agronomic effectiveness of poultry manure composts

Abstract Two field experiments were conducted to examine the agronomic value of poultry manure composted in the presence of both phosphate rock (PR) and elemental sulphur (S°) (sulphocompost) and PR alone (phosphocompost). Winter cabbage and summer maize were used as test crops. For the first seasons winter cabbage, the phosphocompost and sulphocompost were approximately 12% and 60% as effective as urea and both composts were equally effective as urea for the second seasons maize crop. The greater agronomic effectiveness of sulphocompost could be attributed to the improved nitrogen (N)‐use efficiency increased PR dissolution and improved S nutrition. Distribution of nitrate‐nitrogen (NO3‐N) in the soil profile of field plots indicated greater potential for winter leaching of N from urea than poultry manure which could be the reason for the improved residual value of the manure reflected in summer maize yields. The results from the field experiments indicated that composting poultry manure with S° and PR...

Sorption–bioavailability nexus of arsenic and cadmium in variable-charge soils

In this work, the nexus between sorption and bioavailability of arsenic (As) and cadmium (Cd) as affected by soil type, soil pH, ageing, and mobilizing agents were examined. The adsorption of As and Cd was examined using a number of allophanic and non-allophanic soils which vary in their charge components. The effect of pH and ageing on the bioavailability of As and Cd was examined using spiked soils in a plant growth experiment. The effect of phosphate (P)-induced mobility of As on its bioavailability was examined using a naturally contaminated sheep dip soil. The results indicated that the adsorption of both As and Cd varied amongst the soils, and the difference in Cd adsorption is attributed to the difference in surface charge. An increase in soil pH increased net negative charge by an average of 45.7 mmol/kg/pH thereby increasing cation (Cd) adsorption; whereas, the effect of pH on anion (As) adsorption was inconsistent. The bioavailability of As and Cd decreased by 3.31- and 2.30-fold, respectively, with ageing which may be attributed to increased immobilization. Phosphate addition increased the mobility and bioavailability of As by 4.34- and 3.35-fold, respectively, in the sheep dip soil. However, the net effect of P on As phytoavailability depends on the extent of P-induced As mobilization in soils and P-induced competition for As uptake by roots. The results demonstrate the nexus between sorption and bioavailability of As and Cd in soils, indicating that the effects of various factors on bioavailability are mediated through their effects on sorption reactions.

Evaluation of methods of measurement of nitrogen in poultry and animal manures

Kjeldahl nitrogen (N), total N and forms of inorganic N (ammoniacal (NH4)-N, nitrate (NO3)-N and nitrite (NO2)-N) were measured in a range of animal manures. The manures include fresh samples of poultry manure, sheep manure, horse manure, dairy slurry and pig slurry and composted poultry manure. Kjeldahl N was measured by standard micro-Kjeldahl digestion. For total N measurements, NO3-N and NO2-N were recovered during Kjeldahl digestion by pretreatments with various oxidizing and reducing agents. Inorganic forms of N were measured by extraction with 2M KCl solution.Kjeldahl digestion alone allowed measurement only of organic N and NH4-N. Amongst various modifications to the Kjeldahl, pretreatment with either acidified (H2SO4) Zn-CrK(SO4)2 or acidified (H2SO4) reduced Fe achieved complete recovery of NO3-N. Nitrite N was only recovered by first oxidising the NO2- to NO3- with KMnO4 followed by reduction to NH4-N with acidified (H2SO4) reduced Fe.More than 95% of the total N in fresh animal manure was present as organic N and NH4-N which were recovered by the standard Kjeldahl digestion. In the case of fresh manures there was no difference between the amount of total N measured by the Kjeldahl digestion and its modified methods. However composting of poultry manure or drying of poultry manure, pig slurry and dairy slurry resulted in an increase in NO3-N which was not recovered during Kjeldahl digestion alone. Under these conditions the total N could be measured by pretreating the samples with KMnO4 and reduced Fe prior to Kjeldahl digestion.Drying of animal manures caused a decrease in organic N and NH4-N, especially in poultry, pig and dairy manures. There was a slight increase in NO3-N; but most of the decrease in N content with drying was attributed to the volatilization loss of ammonia (NH3). Amongst various drying methods examined air drying caused maximum loss of N as NH3 whereas freeze drying caused minimum loss of N. This suggests that fresh animal manures can be freeze dried for analysis of N which causes minimum loss of N.

Bioavailability and ecotoxicity of arsenic species in solution culture and soil system: implications to remediation

In this work, bioavailability and ecotoxicity of arsenite (As(III)) and arsenate (As(V)) species were compared between solution culture and soil system. Firstly, the adsorption of As(III) and As(V) was compared using a number of non-allophanic and allophanic soils. Secondly, the bioavailability and ecotoxicity were examined using germination, phytoavailability, earthworm, and soil microbial activity tests. Both As-spiked soils and As-contaminated sheep dip soils were used to test bioavailability and ecotoxicity. The sheep dip soil which contained predominantly As(V) species was subject to flooding to reduce As(V) to As(III) and then used along with the control treatment soil to compare the bioavailability between As species. Adsorption of As(V) was much higher than that of As(III), and the difference in adsorption between these two species was more pronounced in the allophanic than non-allophanic soils. In the solution culture, there was no significant difference in bioavailability and ecotoxicity, as measured by germination and phytoavailability tests, between these two As species. Whereas in the As-spiked soils, the bioavailability and ecotoxicity were higher for As(III) than As(V), and the difference was more pronounced in the allophanic than non-allophanic soils. Bioavailability of As increased with the flooding of the sheep dip soils which may be attributed to the reduction of As(V) to As(III) species. The results in this study have demonstrated that while in solution, the bioavailability and ecotoxicity do not vary between As(III) and As(V), in soils, the latter species is less bioavailable than the former species because As(V) is more strongly retained than As(III). Since the bioavailability and ecotoxicity of As depend on the nature of As species present in the environment, risk-based remediation approach should aim at controlling the dynamics of As transformation.

Chapter 27 Manipulating bioavailability to manage remediation of metal-contaminated soils

Publisher Summary This chapter focuses on bioavailability manipulation for managing the remediation of meta-contaminated soils. One of the primary objectives of remediating contaminated sites is to reduce the bioavailability of metals. Therefore, in situ immobilization using soil amendments that are low in heavy metal content may offer a promising option. A major inherent problem associated with immobilization techniques is that although the heavy metals become less bioavailable, their total concentration in soils remains unchanged. The immobilized heavy metal may become plant-available with time through a natural weathering process or through the breakdown of high-molecular-weight organic-metal complexes. Although the formation of soluble metal–organic complexes reduces the phytoavailability of metals, the mobility of the metal may be facilitated greatly in soils receiving alkaline-stabilized biosolid because of the reduction of metal adsorption and increased concentration of soluble metal–organic complex in solution. In the chapter, after a brief introduction of the sources of metal inputs and their dynamics in soils, the role of various inorganic and organic soil amendments in the (im)mobilization of metals in soils in relation to managing their remediation is reviewed. The definition and indicators of bioavailability are presented and soil amendments for metal (im)mobilization are also analyzed in the chapter.

Absorption of Ammonia Released from Poultry Manure to Soil and Bark and the Use of Absorbed Ammonia in Solubilizing Phosphate Rock

Composting systems were designed to utilize ammonia (NH3) released during composting of poultry manure to solubilize phosphate rock (PR). The NH3 released from decomposing manure was allowed to pass through columns containing soil or bark materials mixed with North Carolina phosphate rock (NCPR) at a rate of 1 mg P g−1. After eight weeks of incubation, the columns were dismantled and the forms of P and N in PR/soil or PR/bark mixtures were measured. The dissolution of PR was determined from the increases in the amount of soluble and adsorbed P (resin plus NaOH extractable P) or from the decreases in the residual apatite P (HC1 extractable P).The amounts of NH4+-N in the soil and bark columns increased due to absorption of the NH3 released from poultry manure. No nitrification of absorbed NH3 occurred, however, unless the soil or bark were reinoculated with a fresh soil solution and incubated for further six weeks.In the absence of NH3 absorption, soil and bark materials dissolved approximately 33 percent ...