Volumen 21, Número 2 (Diciembre, 2003)

Earthworms are important components of soil fauna and their activity contributes to soil health. The aims of this work were to determine: a) the relationship between seasonal earthworm density (PD) – biomass (PB) in different production systems, and b) the relationship between vertical distribution of earthworms and environmental and edaphic properties. This work was carried out in southeast Buenos Aires province in four management conditions: natural (N), organic livestock (GO), intensive livestock (GF) and conventional agriculture (AC) from spring 1998 to summer 1999. The comparative study of adults earthworm populations showed significant interaction between site and season (p menor que 0.05) in density and biomass. GO and N systems supported an earthworm PD intermediate between PD of agroecosystems under intensive fertilization (GF) and that of conventional agriculture (AC). GO and N averaged 32 to 275 ind m-2 (individues per m-2) in during sampling seasons. PD values in GF were 506 ind m-2 spring 1998, 562 ind m-2 for fall and 446 ind m-2 for winter 1999. For AC were 80 ind m- 2 for spring 1998 and 28 for fall 1999. PB was highest in GF during fall and winter 1999 13.15 and 15.66 g m-2 respectively. Earthworms occur at 30 cm depth with a clear concentration in the top 10 cm on the basis of organic matter and soil moisture contents. Vertical distribution was also influenced seasonality as worms migrated deeper in the dry season.

Nitrogen fertilization of potato can reduce tuber yield and quality in soils with high organic matter content. Three potato cultivars (Asterix, Kennebec and Spunta) were grown with four nitrogen fertilization rates: OOO = control; NOO = 80 kg N ha-1 at planting; NNO (160 kg N ha-1) = 80 kg N ha-1 at planting + 80 kg N ha-1 at tuber initiation; NNN (240 kg N ha-1) = 80 kg N ha-1 at planting + 80 kg N ha-1 at tuber initiation + 80 kg N ha-1 at tuber bulking. Shoot biomass, tubers fresh and dry matter (DM), and petiole N-NO3 – concentration were quantified periodically during the growing season. respectively). Petiole N-NO3 – concentration, up to 45 days after emergence (DAE), was located in the Nitrogen fertilization during crop cycle did not increase yields of all cultivars (13, 9, 7 Mg DM ha-1, excess N-NO3 – levels (average 20 to 25 g kg-1) in the three cultivars. Tubers dry matter concentration diminished linearly with increasing N-NO3 – concentration (R2 = 0.54). Nitrogen fertilization at the end of the growing cycle diminished tuber growth rate, harvest index and gross margin. At harvest, the concentration of available soil nitrogen was significantly higher in plots with 240 kg N ha-1. In this experience, nitrogen fertilization during crop cycle did not increase crop yields, decreasing farmer incomes.

In the southeast of the Buenos Aires Province (Argentina) agricultural soils have been intensively used and wheat productivity increased in the last two decades. Therefore, nitrogen and phosphorus fertilization is an usual practice in wheat production. However, some micronutrients like zinc (Zn) or copper (Cu) considered not restrictive can be limiting for wheat under more intensive management practices. The objective of this work was to evaluate wheat yield response to Zn and Cu fertilization during two years (2000-2001) in 19 farmer fields. In each field a randomized completely block design with three replications was carried out. Experiments were conducted without deficiencies of nitrogen (N), phosphorus (P) and sulfur (S). In 2000, treatments were: NPS and NPS plus 7.2 kg ha-1 of Zn and 7.0 kg ha-1 of Cu (NPS+Zn+Cu). In 2001, treatments were: NPS, NPS plus 7.2 kg ha- 1 of Zn (NPS+Zn) and NPS plus 7.0 kg ha-1 of Cu (NPS+Cu) and NPS plus 7.2 kg ha-1 of Zn and 7.0 kg ha-1 of Cu (NPS+Zn+Cu). Wheat grain yield responses to micronutrient addition were positive in only 4 sites (between 246 and 890 kg ha-1), and negative in one site. In both years, a significant and linear relationship between yield response to micronutrient and soil Zn concentration (Melhich-3) determined at sowing (ZnMh-3) was observed (y= 899.2 – 157.8 x ZnMh-3; r 2 = 0.39). No relationship was found between yield response and soil Cu content (Melhich-3) at sowing. Therefore, the Zn availability would have limited wheat grain yield. When soil pH was included as a variable to ZnMh- 3, grain yield response was better explained (y= -977.7 – 158.1 x ZnMh-3 + 313.9 x pH; r2= 0.51). The results indicate that Zn availability and soil pH must be used like diagnostics to estimate wheat Zn fertilization needs in soils of southeast Buenos Aires.

In the southwesterrn Pampean region, the variability in soil spatial distribution is clearly related to soil landscape position and soil characteristics reflect the geo-pedogenetic evolution. Our hypothesis suggests that the great climatic changes, as those between the Pleistocene and the Holocene, are detected in the soils architecture even in stable landforms. The unstable geomorphic surfaces are more sensitive and the associated soils reflect the small climatic changes occurred in the Holocene. The objectives of this paper were: 1) to correlate soil parent materials to geologic formations, 2) to present the soils’ mineralogy, macro and micromorphology to identify features indicative of polygenesis, 3) to explain the geo-pedogenetic history based in the morphogenesis-pedogenesis balance to interprete the evolutionary trend during the Holocene. The study area is located in Paraje Puente Canesa, in the Aa Napostá Grande basin. A toposequence has been selected and chemical, mineralogical and micromorphological analysis were performed to discuss time and spatial variability of soil forming factors. A buried paleosoil, developed in alluvial sediments underlying the recent aeolian sediments has been identified in the alluvial terraze. This geosol differs from the surface soils in their macro- microcharacteristics and chemical properties, and correspond to a soil-climate episode of the Holocene more humid than present. However, in the soils of the stable landforms, pedofeatures associated to minor climatic oscillations occurred during the Holocene sub-epochs have not been detected. The type, origin and age of parent materials or landscape position have not strongly influence the clay fraction mineralogy. Soil parent materials have been correlated with Saavedra Formation (Muzzi Soil), with Matadero Saldungaray Formation (Canesa Soil 1 and upper section of Canesa Soil 2) and with Agua Blanca Formation-Limo Arenoso Superior member (lower section of Canesa Soil 2). A geo- pedogenetic history related to the different climatic phases of the Holocene sub-epochs has been proposed

Vehicular and foot traffic increase soil compaction in sport and recreational areas, reducing shoot and root growth and overall quality of turfgrasses. Soil enrichment with sands is a common practice to cope with this problem,. Sand-soil mixtures require a high input of fertilizers and water to maintain a high quality surface. These practices may increase contamination of groundwaters. The objective of this work was to evaluate the effect of soil composition , nitrogen fertilization and irrigation on nitrate leaching in turfgrass soils. Plants of Lolium perenne were grown in pot culture in 3 different growing media (topsoil plus 10, 40 or 70% sand v/v) , two nitrogen treatments and two irrigation regimes. Plant biomass and nitrate in the leaching water was measured several times along the growing period (7 months). Increases in nitrate concentration of leaching water was observed right after nitrogen fertilization in high nitrogen treatment pots. These nitrate pulses were not affected by irrigation regime of soil treatments. No significant treatment effects were observed in the other sampling dates. Discussion is given on management strategies to reduce nitrate leaching

Pore size distribution plays an essential role in the diagnosis of soil physical behaviour. The objective of this work was to compare the results obtained using two indirect techniques to analyse soil pore distribution: pore size (relating soil water content with soil matric pressure of a given soil sample) to identify macro, meso and microporosity, and pore origin (using the method of textural bulk density with kerosene) to identify structural and textural porosity. Soil samples were taken from three long term field trials located in Pergamino (Typic Argiudoll) with two tillage systems (chisel plow vs. no tillage). There was a high relationship between the two approaches in both tillage systems. Under chisel ploughing it was more convenient to classify soil porosity by its origin because soil pores have low stability, and hence, they are less disturbed using non polar liquids. The use of the water retention approach was the best method for no tillage systems as it avoided methodological errors related with high soil moisture, characteristic of these samples.

The objectives of this study were to determine the chemical fractions of Fe, Cu, Mn, and Zn in soils of the upper Rio Negro Valley, and to analyze their relationships with some physical and chemical soils properties. Soil samples were taken at 0-25 cm depth in seven (Typic Torrifluvents) and seven (Typic Haplocambids). Through sequential extractions, the following micronutrient forms were quantified: exchangeable, bound to carbonates, adsorbed to organic matter (OM), residual, and total. Results indicated that 90% of the all studied micronutrients were bound to the least available fraction (residual). The increment of organic matter and phosphorus fertilization increased the more labile Zn, Mn, Cu and Fe forms.