Avi Shaviv

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.

Fourier Transform Infrared—Attenuated Total Reflection Nitrate Determination of Soil Pastes Using Principal Component Regression, Partial Least Squares, and Cross-Correlation

This paper investigates the use of Fourier transform infrared (FT-IR) attenuated total reflectance (ATR) spectroscopy as a fast and simple way for direct determination of nitrate concentration in soil pastes, which would assist precision fertilizer placement and reduce nitrate pollution. Eight types of soils are investigated, with nitrate concentrations ranging from 0 to 1000 ppm-N. The spectral region around the nitrate band (1300–1550 cm−1) is analyzed by (1) principal component regression (PCR), (2) partial least squares (PLS), and (3) cross-correlation with reference libraries that include spectra of pure ions and/or soils. The main obstacle to accurate nitrate measurement appears to be an interfering band present in calcareous soils. This band, which may be due to carbonate, is located around 1450 cm−1 and overlaps with the nitrate band centered around 1370 cm−1. For non-calcareous soils, and in particular for light sandy agricultural soils, PLS and cross-correlation with a reference library containing only spectra of ions in water give similar results (about 8 ppm-N on dry soil basis), while PCR leads to slightly poorer results. When calcareous soils are included in the analysis, the prediction errors are about twice as large. In this case, the best results are obtained using PLS, followed by PCR, while cross-correlation with reference libraries leads to poorer results.

Characterization of Soils Using Photoacoustic Mid-Infrared Spectroscopy

This study investigates the use of photoacoustic spectroscopy (PAS) for rapid soil analysis. Photoacoustic spectroscopy requires very minimal sample preparation (air-drying), which is a major advantage compared to the more traditional transmittance technique, which requires time-consuming preparation of pellets. The amount of information contained in the PAS spectra appears to be similar to that contained in transmittance spectra, and the PAS spectra exhibit a large number of bands that can be associated with various soil constituents such as quartz, calcium carbonate, and various types of clay. Comparison with attenuated total reflection (ATR) spectra of saturated soil pastes shows that the PAS spectra provide much more information than the ATR spectra due to the strong water bands present in the latter. PAS quantitative analysis of clay, calcium carbonate, and organic matter is presented, with respective determination errors of ∼12% clay, ∼5% CaCO3, and ∼0.2% organic matter.

Method for the Analysis of Oxygen Isotopic Composition of Soil Phosphate Fractions

The isotopic signature of oxygen in phosphate (δ(18)O(P)) of various soil fractions may shed light on P transformations, including phosphorus (P) recycling by soil microorganisms, uptake by plants and P adsorption, precipitation and release by oxides and minerals, thus increasing our understanding on P cycling and lability in soils. We developed and tested a protocol to extract and purify inorganic phosphate (Pi) from different soil fractions distinguished by binding strength and precipitate it as silver phosphate (Ag(3)PO(4)) for δ(18)O(P) analysis. Soil P is extracted sequentially using water, NaHCO(3), NaOH and HCl and Pi in each solution is purified and precipitated as Ag(3)PO(4). The unique characteristics and possible interferences of the soil solution extracts are addressed. Two agricultural soil samples receiving reclaimed wastewater or fresh water were analyzed, and results indicate that all soil fractions analyzed have been impacted to some degree by biologically enzyme mediated cycling of P in the soil.

Wetting mechanisms of gel-based controlled-release fertilizers

The release mechanism of gel-based controlled release fertilizers (CRFs) involves water penetration into dry mixtures of fertilizers and gel forming polymers. Water penetration provides an upper limit to the whole release process. Where wetting prediction is often based on models that describe the flow of the liquid phase, vapor motion may become significant when a sharp wetting front exists. In this study we examine the role of vapor and fluid flows in the wetting process of CRFs consisting of urea or KNO(3) mixed with polyacrylamide (PAM). Vapor adsorption isotherms were obtained for typical fertilizer-PAM mixtures. Wetting and release experiments were conducted by dividing the CRFs into regions alternately filled with a pure fertilizer and mixtures of PAM and fertilizer. The experiments were designed in such a way that when the wetting front reaches a mixtures interface, its motion depends on the gradient imposed by the difference in osmotic potential (OP). The coupled equations of vapor and liquid flow in initially dry conditions were solved numerically to demonstrate the conceptual understanding gained by the experiments. The results show that wetting front motion is affected by transport and adsorption of vapor. It was also shown that the release rate is different when wetting is governed by vapor flow or by liquid flow. The release pattern from a multi-regions device was consistent with the wetting pattern, demonstrating the possibility to tailor the release according to periods of peak demand.

Solute diffusion coefficient in the internal medium of a new gel based controlled release fertilizer

Abstract The diffusion of solutes in a new controlled release device was investigated and in situ measurements of constant and variable diffusion coefficients were obtained. The new controlled release device consists of a dry mixture of fertilizer and gel forming thickener contained in a nonpermeable coating having at least one opening. Water penetrates into the device through the opening, forms a gel and dissolves the fertilizer, which is then released by Fickian or non-Fickian diffusion mechanisms. Based on measurements of the penetration of water and the dissolution of fertilizer, the pseudo-steady state transport equation was solved and the solute diffusion coefficient was calculated. The computation of the diffusion coefficient was possible solely because a dual boundary condition exists at the dissolution front. An analytical solution was developed assuming a constant diffusion coefficient. A numerical solution was obtained for the case where the diffusion coefficient is concentration dependent. Two thickeners were tested: sodium carboxymethylcellulose (Na-CMC) and sodium polyacrylamide (Na-PAM). It was found that the solute diffusion mechanism in Na-CMC gels is Fickian-like and can be approximated by a constant diffusion coefficient. The solute diffusion in Na-PAM gels showed non-Fickian behavior and was estimated numerically using the variable diffusion coefficient. For comparison with the theoretical solutions, a dialysis cell was used to simulate the conditions in the gel formed inside the device and to evaluate the effects of thickener concentration on the diffusion coefficient. Reasonable agreement was found between the pseudo-steady state solutions and the dialysis cell experimental results.

Control of nitrification rate by increasing ammonium concentration

Lysimeter experiments with maize and incubation experiments showed that increased ammonium concentrations in soil reduced nitrification rates. A modified Lees and Quastel kinetic model was proposed for predicting the relation between initial ammonium concentration in soil and nitrification rate. A term Mi strongly dependent on initial ammonium concentration ([NH40]) was introduced into the model which took the form: dy/dt = R(A − y)(Mi + y), where R is a rate constant, y represents the concentration of formed nitrate and A is an asymptotic value of initial ammonium concentration. Mi was obtained by a curve fitting procedure applied to experimental data. An exponential decay of Mi with [NH4]0 was formulated. The modified model thus obtained provides an effective tool for predicting nitrification rates related to a wide range of ammonium concentrations.

The effect of CO2 concentration on a nitrifying chalk reactor

The effect of CO2 concentration on nitrification rate was studied in a fluidized bed reactor using chalk (solid calcium carbonate) as the biomass carrier and buffering agent. Using one chalk type and uniform particle size, carbon dioxide was found to limit the nitrification rate in the reactor at concentrations up to 0.3 mmol l(-1). At this concentration the nitrification rate was about 2.5-2.7g NH4+-Nl reactor(-1) d(-1). The pH established in the reactor varied between 4.5 and 5.5, remarkably with lower pH obtained remarked at higher nitrification rates. Kinetic parameters for nitrification rate with CO2 as the rate limiting substrate were determined: a Michaelis-Menten constant, Km, of 0.013 mmol l(-1) CO2 and a maximum ammonium oxidation rate of 2.33g NH4+-Nl reactor(-1) d(-1).

Interaction of ammonium and nitrate nutrition with potassium in wheat

A greenhouse experiment with wheat in 3L pots filled with a sandy loam soil in a factorial design was conducted to determine the effect of potassium on nitrogen utilization. Nitrogen was applied in three NH4-N/NO3-N ratios, 0/100, 25/75 and 50/50, at three levels: 0.75, 1.50 and 3.00gN/pot, and potassium was applied at three levels: 0, 0.5 and 1.0gK/pot. The higher levels of nitrate nitrogen with or without potassium reduced dry matter yields drastically, while the same levels of a NH4-N/NO3-N mixture of 50/50 with applied potassium reduced yields only slightly. Highest grain yield and total yield were obtained with a 25/75 mixture of ammonium/nitrate nitrogen with added potassium. Potassium addition to soil increased the utilization of nitrogen fertilizers, particularly when the ratio of ammonium to nitrate was increased. The highest uptake of reduced nitrogen was at the highest level of the ammonium to nitrate nitrogen ratio (50/50) when potassium was applied. Tillering was enhanced by an increased ammonium ratio in the nitrogen mixture, and by potassium.

Determination of Soil Nitrate and Water Content Using Attenuated Total Reflectance Spectroscopy

Direct determination of nitrate and soil moisture can significantly improve N-application management and thus reduce N-derived environmental pollution related to agriculture. Several studies have shown that Fourier transform infrared attenuated total reflectance (FT-IR/ATR) spectroscopy could be used to estimate the nitrate content of standardized soil pastes. Paste standardization appeared to be the main obstacle to in situ application of this approach, and the present study shows how FT-IR/ATR can be used to estimate both water content and nitrate concentration of field soil samples. Water content and nitrate concentration are determined sequentially using two subsamples of the initial soil sample. An a priori determined amount of highly concentrated nitrate solution is added to the first subsample and the ATR spectrum of this paste is used to estimate the sample water content. It is then possible to calculate the amount of water that should be added to the second subsample so that the resulting paste is very close to the ideal standard paste. Nitrate concentration, mg [N]/kg [dry soil], is estimated using the FT-IR/ATR spectrum of this second paste. Results are presented for a laboratory experiment with four agricultural soils, as well as for a field trial with a calcareous soil. For water content, the determination errors range from 0.01 to 0.02 g [water]/g [dry soil]. For nitrate concentration, the errors for three of the soils range from 5.9 to 8.4 mg [N]/kg [dry soil], while for the fourth, calcareous clay soil, the determination error is 13.6 mg [N]/kg [dry soil]. The determination errors obtained for the field trial are similar to the ones obtained for a similar soil under laboratory conditions, which shows the potential usefulness of the approach for improving N-application management and reducing environmental pollution.