Diego Cosentino

Influence of tillage systems on biological properties of a Typic Argiudoll soil under continuous maize in central Argentina

Abstract Farmers are increasingly using zero tillage in Central Argentina to replace other tillage systems. Intensive tillage decreases soil organic matter content and causes physical degradation. The objective of this work was to evaluate changes in some soil biological properties induced by different tillage systems. A 6 year experiment in which continuous maize ( Zea mays L.) was grown using three tillage systems (conventional tillage, reduced tillage and zero tillage) was carried out at Cordoba Province, Argentina, on a Typic Argiudoll. Variations in total organic C content, microbial biomass C, metabolic quotient (qCO 2 ) and the proportion of the organic C present in the microbial biomass were evaluated at two sampling depths (0–5 and 5–15 cm). Additional samples from a nearby site (undisturbed grassland) were also taken and considered as a control. Concentrations of soil organic C and microbial biomass C were higher under zero tillage as compared with conventional tillage, at the 0–5 cm soil depth. Differences were not evident among tillage systems at the 5–15 cm soil depth. An analysis of the microbial biomass C content, in relation to the organic C, revealed higher values at the 0–5 cm soil depth only for those systems which provoke less disturbance of the soil (i.e. reduced tillage and zero tillage). Significantly greater amounts of CO 2 C were released from zero tillage and reduced tillage soils than from conventionally tilled soils. This release was positively correlated with microbial biomass C. qCO 2 values were not significantly different between tillage systems. Zero tillage proved to be more efficient in the conservation of organic C and microbial biomass C. The tillage systems impact on respiration was due to its effect on the microbial biomass.

Null Creation Of Air-filled Structural Pores By Soil Cracking And Shrinkage In Silty Loamy Soils

Information about abiotic regeneration of air-filled porosity in silty soils is scarce. It could be a key mechanism to explain their low physical resilience. In the present work, we aim at evaluating whether changes in intrinsic soil properties (e.g., soil organic carbon, clay content, and clay mineralogy) caused by degradation affected soil volume response to wetting-drying cycles. Volume and size distribution of cracks and clod shrinkage curves were determined in silty loamy soils (Typic Argiudoll) of Argentina under nearby conventionally tilled (CT), eroded CT, and Pasture management. Crack volume increased from 1000 cm3 in CT and Pasture soils to 6000 cm3 in the more clayey and swelling eroded CT soil. Crack size distribution was similar in all studied soils with large cracks (first and second size order) prevailing over small ones (fourth and fifth size order). Clod shrinkage curves had no S-shape, thus showing the lack of structural shrinkage in all studied soil management regimens. Air content in structural pores was as low as 0.03 to 0.10 cm3 g−1 at the air entry point. This little air entry during drying agreed with the lack of small cracks and can be related to the prevalence of plasma (i.e., silt and clay) over sand. Results showed that key intrinsic properties did not drive soil volume changes in the studied silty loamy soils. They change their volume during drying, but the creation of air-filled structural pores is little or null.ABBREVIATIONS: ACr: area of the crack calculated from its width and length; AE: air entry; Airp: air content of the plasma; Airstr (AE): air content of structural porosity at the air entry transition point; Airstr (SAT): air content of structural porosity at saturation; CT: conventionally tilled; Cter: eroded conventionally tilled; DCr: depth of the crack; Id: density of cracks; KBs: slope of the basic shrinkage; KR: slope of the residual shrinkage; KStr: slope of the structural shrinkage; LCr: length of the crack; ML: macroporosity limit; MS: aximum swelling; PD: particle density; S: surface of the pot; SC: swelling capacity of the soil from saturation to the shrinkage limit transition point; ShC: shrinkage curve of the soil; SL: shrinkage limit; Subang Bk: subangular blocks; V: bulk specific volume; VAE: specific volume at the air entry transition point; VCr: specific volume of the crack calculated from its area and depth; VML: specific volume at the macropore limit transition point; VMS: specific volume at the maximum swelling transition point; VP(AE): plasma porosity at the air entry transition point; Vp(ML): plasma porosity at the macropore limit transition point; Vp(MS): plasma porosity at the maximum swelling transition point; Vp(SL): plasma porosity at the shrinkage limit transition point; VSL: specific volume at the shrinkage limit transition point; Vstr(AE): structural porosity at the air entry transition point; Vstr(ML): structural porosity at the macropore limit transition point; Vstr(MS): structural porosity at the maximum swelling transition point; Vstr(SL): structural porosity at the shrinkage limit transition point; W: gravimetric water content; WAE: gravimetric water content at the air entry transition point; WCr: width of the crack; W/D cycles: soil wetting and drying cycles; WML: gravimetric water content at the macropore limit transition point; WMS: gravimetric water content at the maximum swelling transition point; Wp: water content in the plasma porosity; W range (SAT-SL): gravimetric water content range from saturation to the shrinkage limit transition point; WSL: gravimetric water content at the shrinkage limit transition point; WStr: water content in the structural porosity; &phgr;ML: bulk density at the macropore limit transition point; &phgr;MS: bulk density at the maximum swelling transition point; &phgr;SAT: bulk density at saturation; &phgr;SL: bulk density at the shrinkage limit transition point.

Soil volumetric changes in natric soils caused by air entrapment following seasonal ponding and water table rises

Soil volumetric changes have been seldom studied in seasonally ponded soils subjected to periodic water table rises. In the Flooding Pampa of Argentina the topsoils develop significant swelling and shrinkage, despite their low percentages of total and expansible clay. We tested the hypothesis that: (a) the swelling of a Natraquoll and a Natraqualf of this region is caused by the wide change in water contents during ponding–drying cycles; and (b) soil swelling is accentuated by the effect of air entrapment ahead of the advance of soil wetting fronts. The relationship between the reciprocal of bulk density (i.e. soil specific volume), ν, and water content, θ, was determined in the laboratory (clod shrinkage curves) and in the field (repeated core sampling). Soil clods behaved in accordance to their inherent soil properties, with zero and residual shrinkage (slope n=δν/δθ<1) in both top horizons, and normal shrinkage (slope n=δν/δθ≈1) throughout the water content range of Bt horizons. Unlike the clods, in the field the slope, n, was as high as 1.47–1.48 in top horizons, and 1.93–1.98 in both Bt horizons, showing the occurrence of abnormal soil swelling processes. Taking into account the narrow volumetric water content range found in the field (i.e. 0.25 v/v in both Bt horizons), this rejects our first proposed hypothesis. Soil air became trapped ahead of the advance of two field wetting fronts: (a) water table rises from depth and (b) surface ponded water. As a result, pore air volume increased during soil wetting, and was as high as 0.24–0.34 v/v, and 0.35 v/v at the maximum swelling limit of top and Bt horizons, respectively. Results show that air entrapment caused the swelling or “inflation” of soils, which agrees with our second hypothesis. However, the influence of air entrapment was more pronounced than a simple accentuation of swelling in Bt horizons. Air entrapment caused the whole soil to a depth of about 0.4 m to expand.

Aggregation agents and structural stability in soils with different texture and organic carbon contents

The flat pampas in the state of Santa Fe in Argentina have soils with high silt content, variable carbon content, and diverse degrees of structural degradation. Aggregate stability has been used as an indicator of the structural condition of the soil. This study aimed to quantify the effect of the addition of crop residues and root activity on the agents of aggregation and mechanisms of aggregate breakdown in soils with different carbon contents and textures cultivated under no-till. An experimental trial was conducted on a loamy soil (Typic Hapludoll, Santa Isabel series) and a silty soil (Typic Argiudoll, Esperanza series) under controlled conditions for 112 days with the following treatments: (i) with and without wheat plant growth and (ii) with and without addition of wheat residues. Soil structural stability by a method allowing for differentiation of aggregate breakdown by slaking, mechanical effect and microcracking, total organic carbon content, particulate organic carbon, glomalin and carbohydrate fractions was assessed. In general, the addition of residues and the presence of plant with active roots increased the presence of all aggregation agents and decreased aggregate breakdown processes in both soils. Soluble carbohydrates and proteins related to glomalin were the most important aggregating agents and their function was to reduce the magnitude of breakdown mechanisms, slaking and microcracking, evidencing a greater impact on the silty soil.

La textura del suelo como factor regulador de la adsorción de Escherichia coli en una cuenca de la Pampa Ondulada (Argentina)

Resumen es: El aumento de la carga animal vacuna en la Pampa Ondulada asociado a areas fragiles supone un importante riesgo de contaminacion biologica. Dicha contami...

The effect of different soil management procedures on carbon cycle components in an Entic Hapludoll

Abstract Sampling on different plots of a field located in Pehuajo, Buenos Aires Province, Argentina, on an Entic Hapludoll, was conducted to determine the: effect of different soil management procedures on carbon cycle components. The plots studied were: A) eight years of mixed pasture followed by oat (Avena saliva L.) crop, B) five years of mixed pasture followed by maize (Zea mays L.) with direct drilling, and C) five years of mixed pasture followed by maize crop with conventional tillage. The sampling was done during the month of June 1994. By that time, plot A was in oat production and plots B and C were in fallow. Microbial biomass carbon (MBC) values differed significantly between the three plots, whereas no differences were found in the organic carbon (OC) content. Plots B and C differed both in respiration and qCO2 (the ratio between C‐CO2 released by respioration and the microbial biomass C). For the latter, no differences had been found as a function of the tillage system in a previous work tha...

Adsorption and affinity of Escherichia coli to different aggregate sizes of a silty clay soil

The sediments produced by water erosion are the main source of pollution of agricultural origin of surface water bodies. These sediments may be associated to bacteria, compromising the quality of nearby water bodies. Therefore, to understand this biological contamination, it is necessary to find out the adsorption capacity and bacterial affinity to aggregate sizes that may result in a differential sedimentation. To this end, in the present work, the distribution, adsorption capacity and affinity to different aggregate sizes of two strains of Escherichia coli in two liquid media of contrasting ionic strength were evaluated in a silty clay soil. The 2 μm, the 20–50 μm fraction was the one that showed the highest bacterial adsorption in both liquid media (37.9%). On the other hand, the highest values of bacterial affinity were found in the 20 to 50 μm fraction (coarse silt) in the low ionic strength media and 20–50 and >50 μm in the high ionic strength media. However, the bacterial strains used revealed only some trends in the modification of these variables. This work contributes to the development and implementation of strategies to mitigate pollution, such as control of sediment generation and its subsequent capture in filter strips.

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 ...