Robert L. Mikkelsen

Struvite precipitation in anaerobic swine lagoon liquid: effect of pH and Mg:P ratio and determination of rate constant

Because of increased concern about surface water eutrophication from nutrient-enriched agricultural runoff, many swine producers are encouraged to decrease application rates of waste-based P. Precipitation and subsequent removal of magnesium ammonium phosphate (MgNH(4)PO(4) x 6H(2)O), commonly known as struvite, is a promising mechanism for N and P removal from anaerobic swine lagoon effluent. The objectives of this research were to (i) quantify the effects of adjusting pH and Mg:P ratio on struvite precipitation and (ii) determine the rate constant pH effect for struvite precipitation in anaerobic swine lagoon liquid. Concentrations of PO(4)-P in liquid from two anaerobic swine lagoons were determined after 24 h of equilibration for a pH range of 7.5-9.5 and Mg:P ratios between 1:1 and 1.6:1. Struvite formation reduced the PO(4)-P concentration in the effluents to as low as 2 mgl(-1). Minimum concentrations of PO(4)-P occurred between pH 8.9 and 9.25 at all Mg:P ratios. Struvite precipitation decreased PO(4)-P concentrations by 85% within 20 min at pH 9.0 for an initial Mg:P ratio of 1.2:1. The rate of PO(4)-P decrease was described by a first-order kinetic model, with rate constants of 3.7, 7.9, and 12.3 h(-1) at pH 8.4, 8.7 and 9.0 respectively. Our results indicate that induced struvite formation is a technically feasible method to remove N and P from swine lagoon liquid and it may allow swine producers to recover nutrients for off-farm sale.

Controlled-release fertilizers to increase efficiency of nutrient use and minimize environmental degradation. A review.

Total world consumption of fertilizer N, P2O5, and K2O in 1990/1991 was 78, 37, and 26 million tons per annum, respectively, with a projected yearly increase of demand of about 2 to 3%. Trends in crop production (maize and wheat) in the last four decades show that N application rates increased about 15 times whereas its accumulation in grain increased only 3 to 4 times. At the same time nutrient recovery by crops remained relatively low (e.g. about 50% for N). This represents a potentially alarming situation from environmental, economic and resource conservation points of view and indicates an urgent need for improving efficiency of fertilizer use.Anticipated benefits from slow/controlled release fertilizers (SRF/CRF) are addressed through two main processes: a. nutrient availability in the plant-soil system as affected by the interaction/competition between: plant roots, soil microorganisms, chemical reactions and pathways for loss; and b. matching nutrient release with plant demand. The various aspects of fertilization and environmental hazards associated with SRF/CRF and factors affecting nutrient use efficiency (NUE) are discussed in the light of these controlling processes. Environmental aspects include: pollution by nitrate, phosphate, and emission/volatilization of N2O or NH3; quality of food and fibers; and factors affecting soil degradation. Agronomic or physiologic aspects include: reduced losses of nutrients, labour saving, reduction of specific stress or toxicity, increased availability of nutrients and induction of synergistic effects between specific chemical forms of nutrients (e.g. interaction of mixed NH4/NO3 nutrition with K, effects of physiological acidification of the rhizosphere on P and Fe availability etc.).Despite the environmental and agronomic benefits offered by SRF/CRF their practical use in agriculture is still very limited. Possible measures which may encourage their use in practice are: a better assessment of expected benefits; attainment of improved technologies or concepts for producing more efficient and less expensive SRF/CRF; optimal design of fertilizer compositions to induce synergistic effects; better understanding of the mechanisms which control nutrient release; construction of conceptual and mathematical models for predicting release rates and patterns under both laboratory and field conditions, for supporting the technologist, farmer and environmentalist in their decision making.

Using hydrophilic polymers to control nutrient release

Using diverse technological approaches, many types of delivery devices have been used to supply plant nutrients at a controlled rate in the soil. One new approach is the use of hydrophilic polymers as carriers of plant nutrients. These polymers may be generally classified as 1) natural polymers derived from polysaccharides, 2) semi-synthetic polymers (primarily cellulose derivatives), and 3) synthetic polymers. By controlling the reaction conditions when forming the polymers, various degrees of cross-linking, anionic charge, and cationic charge can be added, thereby changing their effectiveness as fertilizer carriers.When fertilizer-containing solutions are mixed with hydrophilic polymers to form a “gel” prior to application in the soil, the release of soluble nutrients can be substantially delayed compared with soluble fertilizer alone. The effectiveness of a specific controlled-release polymeric system is determined in part by its specific chemical and physical properties, its biodegradation rate, and the fertilizer source used. Addition of some polymers with nutrients has been shown to reduce N and K leaching from well-drained soils and to increase the plant recovery of added N, P, Fe, and Mn in some circumstances

Sorption of organic phosphorus compounds in Atlantic Coastal Plain soils

Organic phosphorus (P) can comprise a significant amount of the total P in animal wastes, yet there is little information on the potential for organic P to be transferred from soils to watercourses. We examined the adsorption of organic P compounds to soils typical of the southeastern United States, i.e., Blanton Sand (loamy, siliceous, thermic, Grossarenic Paleudult), Cecil sandy clay loam (fine, kaolinitic, thermic, Typic Kanhapludult), and a Belhaven sandy loam (loamy, mixed, dysic, thermic, Terric Medisaprist). The behavior of four organic P compounds was studied: adenosine 5′-triphosphate (ATP), adenosine 5′-diphosphate (ADP), adenosine 5′-monophosphate (AMP), and inositol hexaphosphate (IHP); while KH2PO4 (ortho-P) was used as an inorganic reference. Laboratory studies were conducted to determine the effects of concentration (0–130 μg P mL−1), pH (4.6–7.6), and soil properties on P adsorption. All the organic P compounds had greater adsorption than KH2PO4 on the Blanton and Cecil soils at all concentrations and ranges of pH. In the Belhaven soil, IHP had the greatest sorption followed by KH2PO4 and the nucleotides (ATP, ADP, and AMP, respectively). Adsorption of organic P was positively correlated with soil organic matter and Fe and Al contents. The greater sorption of some organic P compounds over that of ortho-P suggests that these compounds may pose less of a threat to water quality, although this preferential sorption may increase soluble P in situations where there is displacement of ortho-P by organic P added in manures.

Nitrogen leaching and plant uptake from controlled-release fertilizers

Controlled-release N fertilizers are commonly used in the production of container-grown ornamental crops, yet the relative effects of various nutrient sources on N leaching are not well known. A 27-week experiment was conducted to evaluate N leaching loss and plant growth following two applications of six controlled-release N fertilizers and one soluble N fertilizer to container-grownEuonymus patens Rehd. The controlled-release fertilizers evaluated were (noncoated) isobutylidene diurea, oxamide, urea formaldehyde, and (coated) Osmocote, Prokote Plus, and sulfur-coated urea. Of the fertilizers tested, the coated fertilizers generally out-performed the noncoated fertilizers in reducing N leaching losses, stimulating plant growth, and increasing tissue N concentrations. Low N concentrations in the leachate of some treatments indicated efficient nutrient use by the plant. In other treatments, low N concentrations in the leachate merely reflected incomplete N release from the fertilizer. A daily application of NH4NO3 resulted in a constant rate of N loss but was not the most effective in promoting growth. Plant growth, tissue N concentrations, and N leaching losses were all increased by doubling the fertilizer application rate from 1 kg N m−3 to 2 kg N m−3.

Optimization of sample pH and temperature for phosphorus-31 nuclear magnetic resonance spectroscopy of poultry manure extracts.

Abstract Organic phosphorus (P) compounds can be characterized using nuclear magnetic resonance (NMR) spectroscopy provided conditions are suitable for detecting the NMR signal. The objective of the research was to optimize pH and temperature conditions for turkey manure extracts prior to analysis of organic P compounds using NMR. Samples of turkey manure were extracted with 0.25 MNaOH + 0.05 MEDTA. The extracts were lyophilized and resolubilized in distilled H2O before analysis on a General Electric GN500 NMR spectrometer. Initial 31P NMR experiments were run to determine the optimal instrumental parameters for 31P studies. Samples were titrated to seventeen pH values ranging from 4.0 to 13.2. Samples adjusted to pH 10.0 had the greatest spectral resolution. A seven‐by‐three factorial experiment was used to investigate the effect of seven temperatures (5,10,20,30,40,50, and 60°C) on three separate samples at pH 6.5,9.0, or 10.0. Spectra resolution was greatest at pH 10.0 and 20°C.

Addition of gel-forming hydrophilic polymers to nitrogen fertilizer solutions

Environmental and economic concerns are causing a search for more effective fertilizer products and improved methods for managing existing fertilizers. This laboratory and greenhouse study was conducted to determine if the addition of gel-forming, hydrophilic polymers to N fertilizer solutions could reduce N leaching loss and increase plant uptake of N. In the first experiment, a solution of urea ammonium nitrate (UAN, 32% N) was mixed with a variety of polymers at three concentrations, band applied to a sandy soil, and leached weekly for six weeks. Nitrogen leaching losses were reduced from 0 to 45% during the first four weeks due to polymer addition, compared with UAN alone. A second experiment examined the addition of various guar (Cyamopsis psoralides DC.)-derived polymers to UAN as a means of reducing N loss and increasing plant growth. Leaching losses were reduced an average of 26, 16, 7, and 7% for the first four weeks following fertilizer application with the addition of polymer. When UAN was applied with some polymers, growth of fescue (Festuca arundinacea L.) was increased as much as 40% and N accumulation increased as much as 50% as contrasted with UAN alone. These experiments indicate that under highly leached conditions, N leaching loss may be temporarily reduced and plant recovery of N increased through use of some gel-forming, hydrophilic polymers.

The role of low molecular weight organic acids from decomposing rye in inhibiting root-knot nematode populations in soil

Organic soil amendments have been employed as an alternative to or in combination with, chemical nematicides and cultural practices to control plant-parasitic nematodes. Rye ( Secale cereale L.) has been shown to be effective in minimizing the damage caused by root-knot nematodes (Meloidogyne incognita(Kofoid and White) Chitwood) when grown as a cover crop and then incorporated into the soil prior to planting. It has been suggested that the release of low molecular weight organic acids during the decomposition of rye is the cause of the nematicidal effects. This study was conducted to quantify the concentration and persistence of formic, acetic, propionic, butyric, and valeric acids in soil solution following the incorporation of fresh rye foliage. Formic and acetic acids were detected by means of ion exclusion chromatography, primarily in the first 24 h following addition of rye, and at concentrations <450mmol/l. The effect of the rye treatment on the root-knot nematode population was determined by growing tomato plants (Lycopersicon esculentumMill.) in the rye-amended soil and assessing the nematode damage to the root systems. Despite the low concentrations of organic acids detected, the rye treatment resulted in a significant suppression of root-knot nematode activity. To determine the fate of these acids in soil, an addition of each acid was made to a field soil resulting in a soil water concentration of 1500 mmol/l for each acid. Soil solution samples were collected every 2 h for 10 h and analyzed for the five added organic acids by means of ion exclusion chromatography. The concentration of all acids declined by 54‐97% over the 10 h incubation. Although low molecular weight organic acids may be one of many factors that contribute to restriction in root-knot nematode damage, these acids do not appear to be solely responsible for the nematicidal effect of the rye.

Monitoring phosphorus mineralization from poultry manure using phosphatase assays and phosphorus-31 nuclear magnetic resonance spectroscopy

Phosphatase enzymes are responsible for mineralization of organic-phosphorus (P) compounds in soil where they hydrolyze the organic phosphate esters to inorganic phosphate. One way to monitor the mineralization process in soils receiving poultry manure is by assessing the activity of phosphatase in a soil amended with poultry manure relative to a soil that is not amended. In a laboratory incubation, soil phosphomonoesterase activity and soil phosphodiesterase activity were measured 0, 1, 2, 4, 8, 12, 16, and 20 weeks after soil incorporation of poultry litter. Two soils, both Fine-loamy siliceous, thermic Typic Kandiudults, were used in the study. Both soils differed in their previous management. The first soil was from a conventionally tilled field that received annual poultry litter applications for 18 consecutive years. The second soil was from an adjacent recently cleared woodland that had no history of manure application. In the previously non-manured soil, soil phosphodiesterase activity following poultry litter addition increased from 4 to 66 μg p-nitrophenol g soil−1 hour−1 by the second week. However, in the same soil, after 8 weeks, phosphodiesterase activity resulting from poultry litter applications was not evident. There was a net increase in phosphomonoesterase activity from week 0 to 20 in the previously manured and previously non-manured soils that were amended with poultry litter. A simultaneous study was conducted to measure the relative concentration of organic P forms during the mineralization process using 31P nuclear magnetic resonance. Subsamples from the poultry manure-amended soil were extracted with 0.25 M NaOH+0.05 M EDTA following 0, 1, 2, 4, 8, 12, 16, and 20 weeks after manure addition and incorporation. The concentration of organic P compounds decreased from the time of poultry litter incorporation until week 20 whereas orthophosphate concentration increased during this period.

Runoff Phosphorus Losses as Related to Soil Test Phosphorus and Degree of Phosphorus Saturation on Piedmont Soils Under Conventional and No-Tillage

Abstract Elevated soil phosphorus (P) concentrations on agricultural land from the application of P in fertilizers and animal manures have increased the potential for excessive P losses in runoff to nutrient-sensitive waters. This study was conducted to determine P losses in runoff from agricultural land in the Piedmont region of the southeastern U.S. with varying soil P levels resulting from past applications of broiler litter and inorganic P fertilizers. The correlations between soil P content and P in runoff can be used to validate and develop P loss-assessment tools for Piedmont soils of the southeastern US. Rainfall simulation at rates of 6.35 cm hr−1 were utilized to collect runoff samples from cropland under conventional tillage (CT) and no tillage (NT) with a range of initial P concentrations. Runoff samples were collected at 5-min intervals for 30 min and analyzed for reactive P (RP), algal-available P (AAP), and total P (TP). Concentration of RP in runoff from CT and NT plots was positively correlated with Mehlich-3 extractable P (M3 STP) (r 2 = 0.70 and 0.67, respectively) and oxalate extractable degree of P saturation (DPS) (r 2 = 0.62 and 0.57, respectively). A Mehlich-3 extractable P concentration of 294 mg P kg−1 and a DPS of 65% corresponded to 1 mg RP L−1 in runoff from NT plots. There was a significant linear relationship between M3 STP concentration and DPS on CT and NT plots. Results of this study indicate that both M3 STP concentration and DPS can be used to help predict P losses from a typical Piedmont soil managed with CT and NT cultivation. Overall, these soil tests predicted P concentration in runoff more effectively than P mass losses in runoff.