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Copyright of Ecosistemas y Recursos Agropecuarios is the property of Universidad Juarez Autonoma de Tabasco and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Water erosion is a process that combines natural and anthropic factors, with effects on systemic productivity and the quality of natural resources. The objective of this work was to make estimates of potential (EP) and current (EA) losses of soil in production systems (SP) with different coverage and topographic characteristics, within the limits of the Ludueña stream basin (Santa Fe, Argentina), using the Universal Soil Loss Equation and the EROSION 6.0 program. For twelve SP, 10 years of rotations under no-tillage were modeled: continuous agriculture with a predominance of soybeans (AC), continuous intensive agriculture with a high proportion of grasses (ACi) and agricultural-livestock rotations with different proportions of pastures (AG 40:60 and AG 30:70). The estimated EP would affect systemic stability since it exceeds 18 tn.ha-1.year-1 in all cases. The EA was 18, 30 and 53% higher in AG 70:30, ACi and AC compared to AG 60:40, with maximum and minimum rates for the total simulations of 7.2 and 1.0 tn.ha-1.year-1. The characteristics of the relief showed that above the value of 0.131 of the LS factor (length and slope gradient), the AC would not be sustainable due to the high rates of EA and because these SP are associated with runoff routes that can facilitate transport of agrochemicals towards lower sectors. The information generated at the farm scale would allow progress in the study of the dynamics of the erosion process and its impact at the basin level. [ABSTRACT FROM AUTHOR]

Soil total (COT) and particulate (COP) organic carbon (C) contents decrease over the years under cropping. Its variation affects many soil processes that determine soil productivity (e.g. nitrogen (N) supply). COT and COP changes depend on the balance between C input and loss. For mollisols of the southeastern region of Buenos Aires province, it was hypothesized that: 1) COT and COP content decrease in the arable layer and vary as a function of the crop sequence regardless of the tillage system (SL), ii) COP content depends on the immediate preceding crop residue characteristics, and iii) changes in COT and COP are related to the soil N supplying capacity, regardless of the SL and crop sequence. Total organic C and COP were determined in soil samples taken annually at 0-5 cm and 5-20 cm depths in a long-term experiment in Balcarce between 2005 and 2011. The experiment comprised two SL (conventional (LC) and no-till (SD) and three crop sequences (with three alternatives (Series) for each one), including corn (M), wheat (T) and soybean (S): MMT, MST y SST. Corn and T were fertilized with N (FN). There were differential decreases in COT and COP among SL (no decrease under SD and decreases of 0.34 and 0.39 Mg ha-1 yr-1 under LC, respectively) only at the 0-5 cm layer. In the whole arable layer COT and COP decreased over the years under cropping (0.30 and 0.26 Mg ha-1 yr-1, respectively), regardless of the SL. No differential COT nor COP decrease was detected related to crop sequences, regardless of the SL. Neither was there an effect of the immediately preceeding crop residue characteristics on COP content. Likewise, COT and COP showed similar dynamics than reported for NAN. Relationships between NAN and COT and NAN and COP were significant although with low R2 (0.55 and 0.57 (0-5 cm), 0.09 and 0.10 (5-20 cm), 0.18 and 0.17 (0-20 cm), respectively). Frequency and rate of FN may have masked the expected effects of the amount of residue C input on COT and COP and, besides, on the relationship of these two variables and NAN. Nitrogen fertilization affects organic material decomposition and transformation dynamics. The experimentally obtained evidences did not support the posed hypotheses. [ABSTRACT FROM AUTHOR]

Cover crops appear as an option to improve the balance of carbon (C) and its quality. The aim of this study was to study the effect of wheat as a cover crop on the dynamics of organic matter and the availability of some macro and micro nutrients under different crop rotations. This work was carried out in a long-term experiment under non-tillage system. Treatments were: soybean-soybean (S-S), soybean-cover crop-soybean (S-CC-S), corn-soybean-wheat/soybean (C-S-W/S) and corncover crop-soybean-wheat/soybean (C-CC-S-W/S). As principal results, it was observed that the fraction of organic carbon between 53 and 105 mm (COPf) was significantly increased when CC were added to soybean monoculture. The carbon fraction of less than 53 mm (COa), was higher when cover crop were incorporated to the rotations. Soybean monoculture had a value of total organic carbon (COPg + COPf) of 11.1 g kg-1, being the lowest value of all treatments and significantly lower than S-CC-S (17 g kg-1). Soil macronutrients concentration had no differences between treatments. Rotations with grasses and legumes (M-S-T/S) determined in general a greater accumulation of zinc (Zn) and manganese (Mn) (2.2 and 63 mg kg-1 respectively) than soybean monoculture (1.4 and 50 mg kg-1) in the depth of 0-5 cm. The concentration of these micronutrients was positively correlated with organic matter content. In this year of study, the CC did not seem to have affected the concentration of micronutrients, thus successive analysis should be performed in order to study the effect of CC in micronutrients dynamics in time. [ABSTRACT FROM AUTHOR]

The objective of this study was to identify parasitic nematodes associated with the tomato crop in Leon and Chinandega western region of Nicaragua. During the period of 2010-2011, five tomato fields were sampled in both Leon and Chinandega; these samples included soil and roots, the total sampled area was of 2.5 ha. Eight samples were collected from each of the ten tomato plantations studied, for a total of 80 samples. Soil and root samples were taken 10 m from each other in a zig-zag pattern. Soil nematode extraction was conducted using the Modified Baermann funnel technique and maceration and sieving method was used for root nematodes. The data obtained was correlated with predisposing factors that have been reported to influence nematodes such as soil type, crop rotation and precipitation. Similarly, the population growth of the main nematode genera was described through mathematical models. The greatest densities of nematodes were isolated from soil samples; the most common nematodes in 100 grams of soil were Meloidogyne with 739, Pratylenchus with 555, Tylenchorhynchus with 386 and Helicotylenchus with 252. It was proven that precipitation had no significant effect on the parasitic nematode population. Finally, it was determined that the increasing number of Meloidogyne and Pratylenchus in the tomato crop fit a linear mathematical model (R2=0,98 for both nematodes), showing an existing positive and linear correlation between the phenological stages of the tomato and the increment of the nematodes in the soil. [ABSTRACT FROM AUTHOR]

Soil organic carbon (CO) content determines many soil functions in the agroecosystem, including nitrogen (N) supply to crops. The level and distribution of organic carbon fractions and mineralizable N in the soil depends on management practices. The aim of this work was to analyze total organic carbon content (COT) associated with the mineral (COA) and particulate (COP) fraction and mineralizable N (through N release during anaerobic incubation, NAN) in whole soil and in macro- and microaggregates under different cropping systems (pastures and cropping with conventional tillage (LC) and with no-tillage (SD)) and N fertilization (0 and 120 kg N ha-1). Soil samples were taken from a long-term crop rotation and tillage system trial at Balcarce, Buenos Aires province. Macro- and microaggregates were separated by dry sieving and COT, COA, POC, and NAN content were determined in whole soil and in each aggregate fraction. The soils under pasture showed the highest CO fraction and NAN content both in whole soil and in each of the aggregate fractions. The longer the period under cropping and LC, the lower the variables compared with the SD regime. Although the proportion of macro- and microaggregates did not vary among treatments, a significant correlation was found between COT and POC content in macroaggregates and their stability when soil was less disturbed (pastures and SD). Under LC, aggregate stability was lower and there was no correlation with CO content. Under cropping there was a significant correlation between NAN in whole soil and NAN in the macroaggregates. A higher expression of N mineralization potential can therefore be expected in soils under management techniques that tend to break up macroaggregates or where these are less stable. However, the lack of significant differences in aggregation and in NAN and CO fractions under cropping suggests that careful tilling can help N mineralization largely without affecting its properties and that the inclusion of pastures in the rotation would reverse the effect of cropping. [ABSTRACT FROM AUTHOR]

The aim of this work was to determine the taxonomic composition and relative abundance of the soil meso and macrofauna and their different trophic groups as affected by soil management practices. Four cropping systems were evaluated: LC50 [(50% pasture - 50% cropping under conventional tillage (LC)], SD50 [(50% pasture - 50% cropping under no-tillage (SD)], LC75 (25% pasture - 75% cropping under LC), SD75 (25% pasture - 75% cropping under SD). In the year 2000, a pasture (P) was sown on LC50 and SD50 and in 2001 it was one year old. On LC75 and SD75, corn was planted in 2000 and soybean was planted in 2001. Most of the individuals observed in 2000 within the mesofauna were enchytraeids and their abundance was not different between LC and SD, whereas in 2001 the highest abundance of enchytraeids was observed under the 15-year-old P. Within the macrofauna, earthworms, isopods and miriapods predominated, but isopods and miriapods were dominant under P in both years. In the first year, the meso and macrofauna densities were not significantly different (p>0.003) among cropping systems, although they tended to be greater under SD. In the second year, such densities were significantly higher (p<0.003) under P. In both years, density interactions between cropping systems and fertilization rates were not significant (p>0.003) for detritivours, herbivours, predators and omnivous. Despite the lack of significant differences (p>0.003) among systems during the first year, all four trophic groups were more abundant under P and SD than under LC. In the second year, detritivours, predators, and omnivours were significantly more abundant under P than under soybean. Our results confirm that the cropping systems affected the taxonomic composition of the soil meso and macrofauna and their trophic groups. On the other hand, the abundance of both communities increased under P throughout the experiment. [ABSTRACT FROM AUTHOR]

The effect of preceding crop residue characteristics on N availability for wheat (Triticum aestivum L.) may mask the changes in soil capability to provide N due to management. Preceding crop effects should be taken into account to diagnose N fertility. The aims of this work were to evaluate i) wheat relative (to the maximum obtained in the corresponding experiment and year) yields (RR) and aboveground dry matter (MSR) and N accumulation (NR) in time after different preceding crops, and ii) the relationship between RR, MSR and NR variation and soil organic matter content changes. In two long term crop rotation experiments at Balcarce (on a complex of Typic Argiudoll and Petrocalcic Paleudoll) the variation of RR, MSR and NR along years under cropping with conventional tillage, was analyzed. The preceding crops were potato (Solanum tuberosum L.), soybean (Glycine max L. Merr.), wheat, sunflower (Helianthus annuus L.) and maize (Zea mays L.). All three variables showed a decrease along cropping years, but up to different levels according to which had been the preceding crop. Residue characteristics and/or the way they had been managed before wheat seeding made that RR, MSR and NR after soybean, potato and wheat were higher. On the other hand, wheat RR, MSR, NR after maize were the lowest. These effects were associated with the role of residues on N mineralization-immobilization cycle. In general, the variation in wheat RR, MSR and NR along cropping years was not associated with changes in soil organic matter due to soil management under cropping. The short term effect of preceding crop residues and of its management on N dynamics defined the amount and timing of the availability of N for wheat. This was independently of the effect of the rotation on the capability of the soil to mineralize N due to how the residues intervene on the cycle mineralization-immobilization. [ABSTRACT FROM AUTHOR]