M. E. Conti

The effect of moisture on nitrous oxide emissions from soil and the N2O/(N2O+N2) ratio under laboratory conditions

Nitrous oxide (N2O) contributes to greenhouse effect; however, little information on the consequences of different moisture levels on N2O/(N2O+N2) ratio is available. The aim of this work was to analyze the influence of different soil moisture values and thus of redox conditions on absolute and relative emissions of N2O and N2 at intact soil cores from a Vertic Argiudoll. For this reason, the effect of water-filled porosity space (WFPS) values of soil cores of 40, 80,100, and 120% (the last one with a 2-cm surface water layer) was investigated. The greatest N2O emission occurred at 80% WFPS treatment where conditions were not reductive enough to allow the complete reduction to N2. The N2O/(N2O+N2) ratio was lowest (0–0.051) under 120% WFPS and increased with decreasing soil moisture content. N2O/(N2O+N2) ratio values significantly correlated with soil Eh; redox conditions seemed to control the proportion of N gases emitted as N2O. N2O emissions did not correlate satisfactorily with N2O/(N2O+N2) ratio values, whereas they were significantly explained by the amount of total N2O+N2 emissions.

Influence of organic amendments on soil quality potential indicators in an urban horticultural system

The short-term response of some soil physical, chemical and biological properties, and the growth of beet, to the application of vermicompost-compost mix and/or bone meal at different doses in an organic system was evaluated in the present work. Fractions of soil organic matter after amendment application were also evaluated. Though no differences were found in oxidizable carbon, the particulate organic carbon was incremented in treatments with the application of vermicompost-compost mix (VC) and the combination of compost and bone meal (VC-BM). When analyzing the fulvic, humic and humin fractions, the highest fulvic acids were found in vermi-compost and bone meal mix, at the higher dose (VC2-BM2). In general, the addition of compost and/or bone meal stimulated microbial respiration. The treatments produced a slight but significant increase in electrical conductivity, thought it was still far from limits that involve risk of salinization. An increment in extractable P was found in all the treatments with amendment application with the exception of bone meal applied at the lower dose (1kgm(-2)). The cation exchange capacity showed a significant increment in VC2-BM2. A single application of VC at dose of 2kgm(-2) was enough to significantly reduce bulk density. An increment in kg dry matter m(-2) of beet was observed in all the treatments, but it only was significant in VC2-BM2. However, the highest N and P concentration was found in beet aerial tissues from the treatments with the higher dose of the compost-vermicompost mix (VC2 and VC2-BM2). Particulate organic carbon, fulvic acid fraction, C from respiration, and bulk density were the soil properties that showed a positive change after amendment application. Treatment combining vermicompost-compost and bone meal (VC2-BM2) seemed to be the best option to achieve an improvement both in soil and crop production and quality.

Nitrous oxide emissions from soil during soybean [(Glycine max (L.) Merrill] crop phenological stages and stubbles decomposition period

The purpose of this study was to evaluate, during the phenological stages of inoculated soybean crop [Glycine max (L.) Merrill], the effect of different N fertilization levels and inoculation with Bradyrhizobium japonicum on N2O emissions from the soil. Gas emissions were evaluated at field conditions by the static-chamber method. Nitrogen fertilization increased N2O emissions significantly (P < 0.05). The variable that best explained cumulative N2O emissions during the whole soybean growing season was the soil nitrate level (r2 = 0.1899; P = 0.0231). Soil moisture presented a greater control on N2O emissions between the grain-filling period and the crop commercial maturity (r2 = 0.5361; P < 0.0001), which coincided with a positive balance of the available soil N, as a consequence of the decrease in crop requirements and root and nodular decomposition. Only soil soluble carbon (r2 = 0.29; P = 0.019) and moisture (r2 = 0.24; P = 0.039) were correlated with N2O emissions during the residue decomposition period. The relationship between soil variables and N2O emissions depended on crop phenological or stubbles decomposition stages.

Chemical and biochemical properties as potential indicators of disturbances.

Abstract The response of a series of soil microbial, chemical, and enzymatic chacacteristics to two different tillage systems (conventional and no-tillage) and two crop rotations (continuous corn and soybean–corn) was evaluated in a long-term field experiment in the Rolling Pampas Region, Marcos Juárez, Córdoba, Argentina. The parameters studied included: oxidizable, soluble and respiration C, total and hydrolyzable N, microbial activity, ammonifiers, nitrifiers, cellulolytic and total microflora, protease and urease activities. After 15 years, oxidizable C, total N and hydrolyzable N showed no differences regarding no-tillage systems. However, differences were found regarding control soil. While soluble C did not exhibit any significant differences, respiration C and microbial activity were indicators sensitive to different treatments. Enzymatic activities, protease in particular, did reflect changes due to management. Fluctuation in microbial population counts were more related to plant residues than to tillage systems.

Relationship of soil carbon light fraction, microbial activity, humic acid production and nitrogen fertilization in the decaying process of corn stubble

Abstract The variation in stubble decomposition due to fertilizer incorporation was determined in a typical Argiudoll of the Argentinian rolling pampas. The experiment was conducted for 15 years, which included a no till system under maize (Zea mays L.) and a soybean rotation (Glycine max) with 0 and 45kg N ha–1 nitrogen fertilization treatments, called NFS and FS, respectively. A higher proportion of residues with a high N content was found in the FS plots. The different substrate quality proved to be the regulating factor for mineralization. This activity was indicated by the increase in soil microbial activity and soil carbon light fraction in FS compared to NFS. This carbon light fraction mineralizes rapidly but does not contribute to the most stable components, which are related to synthesis and polymerization of humic acids. No significant differences in humic acid content were found.

β‐Glucosidase and Proteases Activities as Affected by Long‐Term Management Practices in a Typic Argiudoll Soil

The objective of the present study was to determine the effect of tillage systems on the activities of enzymes associated with the carbon (C) and nitrogen (N) cycles (β‐glucosidase and protease) on a Typic Argiudoll (Marcos Juárez Series). The experiment was performed in a randomized complete block design with three replications under no till, conventional tillage and native pasture used as control soil. The activities of β‐glucosidase and protease, total N and oxidizable C contents were determined at depths of 0–5 and 5–15 cm. Not only the activities of both enzymes, but also C and N contents were greater in the native soil at both depths, which shows the impact of land use on this soil. The enzymatic activities in the surface of no‐till soil were significantly higher than those for conventional tillage. At the 5–15 cm depth these variables did not present significant differences between tillage systems. The enzymatic activity was more sensitive to tillage systems than oxidizable C content in the first cm of the top layer. These results indicate that β‐glucosidase was a more sensitive index of management effects than protease.

Urease activity in Argentine soils: Field studies and influence of sample treatmenT

Abstract The effects of various treatments and seasonal variation upon urease activity were studied on surface samples of Argentine agricultural soils. Samples were selected to be representative of the zone covering a wide range of chemical and physical soil properties. Five sample treatments were selected: moist fresh; moist stored; air-dried; refrigerated; and frozen. It was shown that storage of soil at 4°C in sealed plastic bags maintained the natural moisture content and resulted in urease values most closely to those obtained at the time of sampling. Three Typic Argiudols under different vegetation covers were selected to elucidate the seasonal variation of urease activity. The highest enzymatic activities were found during the summer, whereas lowest values were encountered during the winter. The gradients of urease activity were different for the two types of vegetation studied (forest and natural grassland). As the values of urease activity also presented differences between soils under the two types of vegetation it may be presumed that the activity of this enzyme is related to the type of vegetation.

Seasonal variations of the light organic fractions in soils under different agricultural management systems

Abstract Annual dynamics of soil organic matter and seasonal evolution of total and light forms of carbon (CL) and nitrogen were studied for three series of soils in the humid Pampa of Argentina. Agricultural practice effects on the organic fraction of soil were also evaluated. Seasonal fluctuations in the light organic fractions of soils were confirmed, presenting each one of them its particular behaviour. In the Typic Argiudoll (Azul) and the Argiaguic Argialboll (Lujan) persistence of CL is related to low temperaure and moisture excess. Diferences between grasses and other crops are of small importance. In the Typic Hapludoll Pehvajo, soil texture and climatological conditions favour rapid mineralization. In this case, is very important that the maintenance of light carbon incorporation be made by pastures.

Factors affecting potassium fixation in Argentine agricultural soils

Potassium (K) fixation in Argentine soils and its effects on fertilizer K dose effectiveness remains an under-researched topic. The effects of K addition doses and clay type and content on the K fixation/release dynamics of added K in four soils, two Argiudols, an Ultisol and an Andisol were studied. Fixation responded to soil type, but not to K doses. From 5 to 24% of the applied K was fixed by the soils ranking from highest to lowest: Aquic Argiudol, Typic Palehumult, Typic Udivitrand and Typic Argiudol. The trend for K fixation relative to clay content was reversed. The soils fixed between 0.23 and 2.38 (cmolc kg−1) (g clay)− 1 in increasing order: Typic Argiudol, Typic Palehumult, Aquic Argiudol and Typic Udivitrand. Potassium fixation by occlusion in clay pores could account for the high activity of the Andisol. The Q/I isotherms results were consistent with those from the fixation experiment. The residuality index, B, ranged from 0.65 (Aquic Argiudol) to 0.95 (Typic Argiudol), a trend consistent with K fixation by these soils. Exchangeable K measured in the fertilized soils and calculated through the residuality index was highly correlated (r=0.95; p < 0.01). This study shows that the B index is a useful tool in quantifying the potential of contrasting soils for net K fixation and in adjusting K rates to accommodate for this process.

Effect of potassium fertilizers on quantity‐intensity parameters in some argentine soils

Abstract The parameters obtained from the quantity‐intensity (Q/I) isotherms have been used by several authors as criteria to estimate the immediate availability of labile potassium (K) in a soil. The aim of this work was to study how these parameters have been modified in four agricultural soils in Argentina by the addition of K (0 to 936 kg K2O ha‐1) in an incubation trial simulating K fertilizers application. In two of the soils, the increase in the labile forms of K was proportional to the amount of added K and the recovery percentages were high. In the other soils, a contrasting behavior was found. This difference might be due to different fixing capacity of the soils, which was related to the clay content and mineralogical composition of this fraction. The slopes of the Q/I curves for each soil indicate that the potential buffer capacity (PBC) was similar for the different treatments over the range of K added. The addition of K produced proportional increases in ARe and ?Ko values. This could be att...