Daniel E. Buschiazzo

Tillage effects on soil properties and crop production in the subhumid and semiarid Argentinean Pampas

Crops have been grown in the subhumid and semiarid Argentinean Pampas for over 50 years using tillage methods (intensive plowing) introduced from more humid regions. As a result, soil degradation due to erosion by wind and water has been moderate to severe. Experiments to control erosion through use of conservation systems were initiated at six semiarid and subhumid sites in the Argentinean Pampas between 1976 and 1990 and conducted for 5 to 11 years. In this paper, we summarize the effect of conventional and conservation tillage treatments on some soil properties and crop yields. Most soil physical, chemical, and biological properties were improved by conservation systems, but the rate of change differed due to climatic and soil differences among sites, with the difference due to tillage generally being greater at the more humid sites with loamy soils than at the drier sites with sandier soils. Crops with a large N requirement yielded less with conservation than with conventional tillage systems. Use of conservation tillage can improve or stabilize soil conditions in the region, but crop nutrient requirements must be met to achieve optimum crop yields when conservation tillage is used. Research regarding the plant nutrient requirements under conservation tillage is being conducted. Also, conservation tillage is gaining acceptance in the Argentinean Pampas region.

Soil organic matter particle size fractions in soils of the semiarid Argentinian pampas

Because the level of organic matter in soils can reflect the intensity of soil utilization, the present study was carried out with the aim of elucidating the precise effects of different soil management practices on total organic matter and its particle size fractions in soils of the semiarid pampa region. Surface samples of 52 entic Haplustolls under three different uses (24 under continuous cropping, 18 under rotation with grass leys and 10 virgin soils) were analyzed in terms of clay, total organic matter content and organic matter particle size fractions. The obtained data show that organic matter fractions differ according to particle size distribution and the prevailing soil management system. Stable organic matter content ( 100 μm) is strongly influenced by the type of soil management utilized.

Organic matter in size fractions of soils of the semiarid Argentina. Effects of climate, soil texture and management

Soil organic matter contents (SOM) of soils of the Semiarid Pampas of Argentina (SAP), mostly Entic Haplustolls, increase with the amount of silt+clay, but it is still not known how soil texture affects its qualitative composition in interaction with climatic and management conditions. Because of that the organic matter content of the following aggregate size fractions were determined: <2000 μm (SOM), 100–2000 μm (YOM), <100 μm (HOM), water floatable organic matter (FOM), and the E4/E6 quotient. These fractions were studied in the 20-cm topsoils of seven REFERENCE (virgin Caldenal savanna-like soils), and 10 CULTIVATED soils (under continuous conventional tillage since more than 50 years). Results showed that SOM of both REFERENCE and CULTIVATED soils was mainly composed by YOM (57%), and to a lesser extent by HOM (37%) and FOM (5%). Silt+clay conditioned positively the contents of SOM, YOM and HOM of both REFERENCE (R2=0.18, R2=0.21, R2=0.21, respectively, n=21, p<0.05) and CULTIVATED soils (R2=0.62, R2=0.44, R2=0.52, respectively, n=30, p<0.001). The positive relationship existing between silt+clay and both SOM and YOM seems to be not longer valid in sites with mean annual temperatures (MAT) higher than 17 °C. YOM and HOM accumulation were positively affected by precipitation and negatively by temperature in combination with silt+clay. This effect was more pronounced for HOM. The slopes of the regressions between SOM, HOM and YOM with silt+clay were more pronounced for REFERENCE soils than for CULTIVATED soils, indicating the largest absolute losses of these organic matter fractions in fine- rather than in coarse-textured soils. E4/E6 quotients were lower than 5 in all studied soils indicating that humic rather than fulvic acids exist in the well humified organic fraction of the studied soils. Contents of FOM and E4/E6 values did not correlated with the climatic conditions nor with soil texture or management. Potential SOM losses can be larger in fine-textured soils (up to 54.3 Mg C ha−1) than in coarse-textured (up to 35.7 Mg C ha−1). Probable changes of soil texture by wind erosion will modify absolute contents of SOM, YOM and HOM, while modifications of temperature or rains regimes will affect HOM more.

Wind erosion in loess soils of the semiarid Argentinian pampas

This study is the first effort to measure wind erosion in the field in South America. Wind erosion of two bare soils, a loamy sand surface Typic Ustipsamment and a sandy loam surface Entic Haplustoll of the Semiarid Argentinian Pampas, were measured in the field during wind storms that started on June 16 (mean wind speed = 14 km/h; storm duration 103 h) and June 30 (mean wind speed = 21.4 km/h; storm duration 25 h) of 1995. Measurements were made with dust samplers placed at heights of 0.135, 0.54, and 1.47 m within a 1-ha field. Mass flux (amount of eroded material within a given time) was larger in the Ustipsamment soils than in the Haplustoll soils in both storms. A maximum amount of transported dust was found within the limits of the studied field (100 x 100 m 2 ) during the June 16 wind storm and outside the studied field during the June 30 wind storm. This was attributed to the variation in wind direction on June 16. The total amount of material eroded from the field during each storm reached 1.82 mt ha -1 in the Ustipsamment and 0.29 mt ha -1 in the Haplustoll on June 16 and 0.98 mt ha -1 in the Ustipsamment and 0.75 mt ha -1 in the Haplustoll on June 30. Wind velocity was high enough to erode the loosened Ustipsamment but not the better structured Haplustoll on June 16. On June 30, wind velocity was high enough to erode both soils, but a shorter storm duration did not allow the erosion of large amounts of soil.

Management discriminant properties in semiarid soils

The physical properties of coarse-textured soils in semiarid regions often deteriorate with use. We hypothesized that the changes in the physical properties of the soil were related to the cropping systems employed. Surface samples of 52 Entic Haplustolls under three different uses (24 under continuous cultivation (C), 18 under rotation with grass leys (R), and 10 virgin soils (V)) were analyzed for clay, silt, organic matter and water content, bulk density, compaction and aggregate stability. Data were analyzed statistically using principal components, canonical variables, and discriminant functions. A satisfactory segregation of the soils according to discriminant properties (coarse organic matter, aggregate stability, and susceptibility to compaction) was obtained. The model developed satisfactorily classified the soils under different uses (100% R, 83% C and 88% V). Principal component analysis also showed that bulk density, compaction, and wet aggregate stability are related to organic matter content. We conclude that, in the studied region, the lower the ratio of organic matter to clay + silt content, the more severe the physical deterioration of the soils.

Safflower productivity as related to soil water storage and management practices in semiarid regions

In semiarid regions the availability of water has an important influence on dryland crop productivity. Water availability is closely related to soil organic matter (SOM) content, texture and soil thickness. Safflower (Carthamus tinctorius L.) is an important winter crop in some semiarid regions due to its deep roots and drought tolerance. However, its adaptation to different soil conditions is still not well known. The objective of this study was the evaluation of safflower productivity, in relation to soil properties, across 30 grower fields of the semiarid Pampas region of Argentina. The soils were Entic and Aridic Haplustolls under continuous row-cropping (CC) or pasture–row crop rotations (PC). Grain yields varied between 0 and 1600 kg ha−1, and were positively correlated with the maximum soil water retention (SWR) of the top layer (0–20 cm) and the soil use management (SUM, r=0.93, p<0.01). Oil yield and plant growth was also positively correlated with SWR and SUM. This trend was explained on the basis of better water and nutrient supply to the plants in finer textured soils during the pronounced moisture deficiency that occurred at the flowering stage of the crop. In soils with similar textures, safflower production was highest in sites that included PC, had high SOM levels, and in which indurate sub-surface layers were absent. Highly productive dryland safflower crops in coarse textured soils from semiarid regions can be achieved by using cultural practices that increase SOM levels (pasture–arable crop rotation) and loosen compacted layers.

Dynamics of volcanic ash remobilisation by wind through the Patagonian steppe after the eruption of Cordón Caulle, 2011

Wind erosion of freshly-deposited volcanic ash causes persistent storms, strongly affecting ecosystems and human activity. Wind erosion of the volcanic ash was measured up to 17 months after the ash deposition, at 7 sites located within the ash-deposition area. The mass flux was measured up to 1.5 m above ground level. Mass transport rates were over 125 times the soil wind-erosion rates observed before the ash deposition, reaching up to 6.3 kg m−1 day−1. Total mass transport of ash during the 17 months ranged between 113.6 and 969.9 kg m−1 depending on topographic location and wind exposure. The vertical distribution of the mass flux at sites with higher vegetation cover was generally inverted as compared to sites with lower vegetation cover. This situation lasted 7 months and then a shift towards a more uniform vertical distribution was observed, in coincidence with the beginning of the decline of the mass transport rates. Decay rates differed between sites. Despite changes over time, an inverse linear correlation between the mass transports and the mass-flux gradients was found. Both the mass-flux gradients and the average mass-transport rates were not linked with shear-stress partition parameters, but with the ratio: ash-fall thickness to total vegetation cover.

Airborne Horizontal Mass Flux Calculated With Different Equations

The quantification of airborne material passing by a vertical plane as a function of height, the horizontal mass flux (HMF), is essential in measuring field wind erosion. Two commonly used equations to calculate HMF are : Q = a Z-b [1], where Q is the amount of dust collected, Z the height, and a and b are regression coefficients: and Q = fo(1 + (Z/ ¥o) i©©¬ [2] where fo = is the movement of the soil at the soil surface, ¥o and ©¬ are regression coefficients. Since the integration of the eroded material as a function of height can be performed from 0 (surface) with equation [2] but not with equation [1], an evaluation of these equations is needed because different HMF estimates often occur among equations. Calculations were made for 28 storms using dust samplers placed at heights of a) 13.5, 50 and 150 cm (Q3) and b) 0.15, 0.7, 1.5, 7, 12, 22.5, 13.5, 50 and 150 cm (Q9). HMF calculated with equations [1] and [2] correlated well but HMF of equation [1] were 40 to 55% lower than those of equation [2]. The averaged fitting of the amount of transported material with height was lower and more variable when using equation [1] than when using equation [2]. These results showed that HFM obtained with equation [1] are highly dependent on sampling height, and need to be corrected on the basis of data obtained closer to the surface before they can be used to test wind erosion prediction models, unlike HMF obtained using equation [2].

Contents and weathering state of volcanic ashes and their effects on phosphate sorption in soils of the semiarid pampa of Argentina

Eolian parent materials of soils of the semiarid Argentinean Pampas show high volcanic ash contents. Weathering products of volcanic ashes can sorb anions in many soils. The objective of this study was to analyze the volcanic ash distribution in soils of the semiarid Pampas, its weathering state, and the influence of its weathering products on phosphate sorption. Sixteen soils, classified as Entic Hapludolls and Entic Haplus‐tolls, were studied at different landscape positions of five sites placed in a SW‐NE‐oriented climosequence within the semiarid Pampa. Results showed that volcanic ashes accumulated more in the subsoil of SW‐placed profiles and in the topsoil of NE‐placed profiles. Topsoil accumulated ashes of NE‐placed profiles were deposited by the eruption of Quizapu volcano in 1932. Subsoil accumulated ashes of SW‐placed profiles were deposited by older volcanic eruptions. Acid oxalate soluble Al (Alo), an index of the degree of volcanic ash weathering, was higher in the subsoil of profiles placed...

Temporal variations of organic matter fractions of different lability in an Entic Haplustoll

Stable and labile soil organic compounds play different roles in the soil. It is a question of how far soil organic matter (SOM) fractions with different labilities vary as a function of climatic and management conditions. In order to answer this question stable (organic C -C-, total N -N-, organic P -Po-), and labile SOM fractions (total carbohydrates -CHt- and hot water soluble carbohydrates -CHw-) were measured monthly for two years in the 10-cm soil top-layer of an Entic Haplustoll, under conventional tillage (CT), vertical tillage (VT) and no-till (NT). Results showed that contents of all analyzed organic fractions were higher in NT than in VT and CT in almost all sampling dates. All organic compounds were less variable with time in NT and VT than in CT, in agreement with the smaller soil disturbance of NT and VT compared to CT. The more labile fractions varied as a function of short term changes in the climatic conditions, mainly temperature. Under soil disturbing tillage systems, the most stable fractions tended to decrease and the more labile to increase with time. This was attributed to the transformation of the more stable into the more labile fractions, possibly due to the disruption of aggregates produced by tillage that favored SOM mineralization. Po was the less variable compound, even under the most disturbing tillage conditions. The quotients C/N, CHt/C and CHw/C evolved similarly in all tillage systems, indicating that that tillage systems change the amount but not the quality of SOM.