M. B. Rodriguez

Heavy metals in soils of Argentina: Comparison between urban and agricultural soils

Abstract Trace metals, including heavy metals, can be harmful to the biota and human beings. This leads to study the accumulation of those elements in soils. In the Pampean region (Argentina) this knowledge is scarce. Our objectives were to (i) determine the trace metal concentration in soils of Buenos Aires City and agricultural areas, (ii) start to establish the soil trace metals baseline concentration, and (iii) find relationships between soil properties and those elements Topsoil samples were taken in Buenos Aires City and on farms along an arc 50 to 250 km away from the metropolis. All studied soils were Mollisols. Soil samples were analyzed for their cadmium (Cd), copper (Cu), zinc (Zn), chromium (Cr), cobalt (Co), lead (Pb), and nickel (Ni) contents by acid extraction. Soil properties were determined using standard methods. The soils of Buenos Aires City show the highest average concentrations of Cd, Cu, Pb, and Zn. The further the sampling sites were from Buenos Aires, the lower the metal concentr...

Perception of sweetness and bitterness in different vehicles

In the present study, we investigated taste-taste, taste-vehicle, and simultaneous taste-vehicle-taste mixtures. Subjects made estimates of the sweetness and bitterness of 27 stimuli. Sucrose (292, 585, and 1170 mM), caffeine (13, 26, and 52 mM), and binary mixtures of low (292-13 mM), middle (585-26 mM), and high (1170-52 mM) levels of both components were dispersed in water, carboxymethylcellulose (CMC) 1% w/v, and gelatin 6% w/v. The sweetness and bitterness of the sucrose-vehicle-caffeine combinations were significantly weaker than the respective sucrose-vehicle and caffeine-vehicle combinations. The emerged mutual suppressive effects were asymmetrical and persisted when both tastants were presented in CMC and gelatin. Moreover, the increase in vehicle consistency and the simultaneous addition of another taste reduced the perceived intensity of a taste either presented alone or dissolved in water. For both sweetness and bitterness, the total taste suppression observed was always significant.

Soil Acidity Changes in Bulk Soil and Maize Rhizosphere in Response to Nitrogen Fertilization

The capacity of nitrogen (N) fertilizers to acidify the soil is regulated principally by the rate and N source. Nitrogen fertilizers undergo hydrolysis and nitrification in soil, resulting in the release of free hydrogen (H+) ions. Simultaneously, ammonium (NH4 +) absorption by roots strongly acidifies the rhizosphere, whereas absorption of nitrate (NO3 −) slightly alkalinizes it. The rhizosphere effects on soil acidity and plant growth in conjunction with N rate are not clearly known. To assess the impact of these multiple factors, changes in the acidity of a Typic Argiudol soil, fertilized with two N sources (urea and UAN) at two rates (equivalent to 100 and 200 kg N ha−1), were studied in a greenhouse experiment using maize as the experimental plant. Soil pH (measured in a soil–water slurry), total acidity, exchangeable acidity, and exchangeable aluminum (Al) were measured in rhizospheric and bulk soil. Plant biomass and foliar area (FA) were also measured at the V6 stage. Nitrogen fertilization significantly reduce the pH in the bulk soil by 0.3 and 0.5 units for low and high rates respectively. Changes in the rhizosphere (the “rhizospheric effect”) resulted in a significant increase in soil pH, from 5.9 to 6.2. The rhizospheric effect × N source interaction significantly increased exchangeable acidity in the rhizosphere relative to bulk soil, particularly when UAN was added at a low rate. Only total acidity was significantly increased by the fertilizer application rate. In spite of the bulk soil acidification, no significant differences in exchangeable aluminum were detected. Aerial biomass and FA were significantly increased by the higher N rate, but N source had no effect on them. Although changes in acidity were observed, root biomass was not significantly affected.

Nitrogen Availability for Maize from a Rolling Pampa Soil After Addition of Biosolids

Abstract The objective of this paper was to evaluate the influence of different rates of biosolids on the soil nitrogen (N) availability for maize and its residuality. A field experiment was developed in a typic Argiudol located in the NE of the Buenos Aires Province. Maize was sown for two consecutive years 1997–1999. Biosolids from a sewage treatment plant of Buenos Aires outskirts were superficially applied to the soil and incorporated by plowing. There were eight treatments: Check; 8, 16, and 24 Mg of dry biosolid ha−1; 8 and 16 Mg of dry biosolid ha−1 applied one year before, 100 and 150 kg N ha−1 of calcium ammonium nitrate (CAN). The sampling and determinations were done during the second maize cycle. At presowing (PS), sowing (S), 6 expanded leaves (V6), 12 expanded leaves (V12), and Flowering (Fl) composite soil samples from 0–40 cm depth were obtained to determine ammonium and nitrate contents. At Fl maize plants were sampled in order to determine total biomass and N content. The N‐nitrate content in the soil was significantly increased by the biosolids application (p < 0.05), and varied for each increment depending on the biosolids rates and the phenological stage. After 30 days from the incorporation the increases of 1.19, 1.34, and 2.05% were observed for N‐nitrates for 8, 16, and 24 Mg ha−1, respectively. The contribution of mineral N from the biosolids was 2.48, 6.46, and 5.01 kg N Mg−1 when the rates were incremented from 0–8, 8–16, and 16–24 Mg ha−1, respectively. The nitrogen mineralization followed a release pattern with a maximum value of 296 kg N‐nitrate ha−1 at sowing for 24 Mg ha−1. Since then, the release of mineral nitrogen decreased significantly till Fl. The N‐nitrates values variation with the temperature adjusted to polinomic functions. The mineral N released from the biosolids increased as a response to the increment of soil temperature and then decreased due to the maize nitrogen absorption and the potentially mineralized nitrogen exhaustion. The application of 150 kg N ha−1 as CAN incremented significantly the soil N‐nitrate content and equalized 16 and 24 Mg of dry biosolids ha−1 at V6. But, no synchronism between the high nitrate releasing from biosolids and the increment in the nitrogen absorption by maize was observed. This fact generates a surplus of nitrate that incremented the potential of nitrogen loss by lixiviation. We observed a residual effect from the biosolids that were applied the previous year. This contribution represented the 35% of the maize requirements and was similar to the nitrate content observed in Bio 16. The biosolids might be a valuable source of nitrogen for maize crop if the synchronism between the soil supply and maize demand is observed in order to avoid nitrates surplus.

Denitrification in tillage and no tillage pampean soils : relationships among soil water, available carbon, and nitrate and nitrous oxide production

Abstract The interactions among the denitrification (DN) regulating factors under no tillage (NT) and conventional tillage (CT) during the production of a wheat crop were studied. The usefulness of the water field pore space (WFPS) as an indicator of the magnitude of the nitrous oxide (N2O) losses under the two tillage methods was also analyzed. The N2O production, mineralizable carbon (MC), WFPS, and nitrate (NO3) content were measured in a typic argiudol. The NT system increased N2O losses by DN at the 0–10 cm sampling depth because of its action on the MC and WFPS. Denitrification correlated significantly with the WFPS (r = 0.6, p<0.01), MC (r = 0.69, p<0.01), and NO3 content (r = 0.37, p<0.05). The influence of these factors on denitrification explained 55% of the differences between tillage methods, and as a consequence, we would suggest another possible influence of other factors not considered in this investigation. The addition of fertilizer (urea) would result in an increase in DN losses with nei...

Influence of growing plants and nitrogen fertilizer on saturated hydraulic conductivity

Abstract A field experiment was conducted on a sandy loam (typic Hapludoll) to test the effect of maize (Zea mays L.) and nitrogen (N) fertilizers on soil saturated hydraulic conductivity (Ksat). Half of the plots were planted to maize and the other half were kept unplanted. All the plots were fertilized at the rate of 75 kg ha‐1, with two fertilizers differing in their acidity index [calcium ammonium nitrate (CAN)=16 and ammonium sulphate (AS)=111]. Undisturbed topsoil samples were taken at the time of maize harvest to determine soil Ksat in the laboratory. Total organic carbon (TOC) and soluble carbon (SC), pH (1:2.5), and the electrical conductivity (EC) of soil saturated extract were determined in grounded and sieved soil samples. The Ksat reached the highest values under maize fertilized with AS. Most of the variation of soil Ksat was determined by the increment of soil salinity. So, soil permeability improvements were caused by a greater flocculation of soil colloids because of saline effects. Soil ...