The aim of this study is to analyze the response of exogenous abscisic acid (ABA) application in plants grown under field conditions in semiarid zones in order to increase maize production. For this, it is necessary to understand the factors, such as the size and capacity of transport system involved in the mobilization and distribution of assimilates. The vascular transport capacity of ABA-treated and control plants was compared in terms of number of vascular bundles, phloem area per bundle, and the proportion of phloem in the ear peduncle of female inflorescences. This study showed that the application of exogenous ABA in field-grown maize under moderate drought allows a greater amount of maize production, an increase in the level of photosynthetic pigments, the carbohydrates remobilization to grain, and the capacity of this transport by an increase in the number of vascular bundles and the phloem area in peduncle. Evidence obtained in this study suggests that ABA could help improve agricultural production in rain-fed crops in which irrigation is not possible. This will allow us to follow a new technological strategy to increase the effective filling of organs during crops in unfavorable water conditions.

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The density of sowing (D) is one of the main management practices that influences the yield (Y) of corn. There exists a density value in which the yield is maximum (OPD), depending on the environment, the genotype and its interaction. The objectives of this project were: i-To determine the OPD for two corn genotypes in different productive environments; ii- Analyze the relationship between the number of kernel fixed per plant (KNP) and its plant growing rate (PGR) to different environments and genotypes iii- Determine the KNP that is related to the OPD for two corn genotypes. Three experiments were carried out in different locations (L) of Córdoba (Argentina) during 2013/14, comparing 2 genotypes (G) in 2 management zones (MZ). The statistical design was random blocks, with a factorial arrangement of subdivided plots, with L, MZ and G being the primary, secondary and tertiary factors, respectively. In addition, 5 D were planted to obtain the relationships that estimate OPD, PGR, KNP and Y. The results indicate that OPD was affected by L; the relationship between PGR and KNP was not modified by the environment, but by G. The PGR coincident with the OPD was modified by the G interaction: L. The OPD the PGR was between 2.74 to 4.81 g d -1 , which were associated with the NGP that varied only between 509 and 603 grains p-1 .

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This study reports the effect of topography, stubble grazing, tillage and the addition of fertilizer on the organic carbon content and structural stability of a typic Hapludoll topsoil under mixed agricultural production. The organic carbon content was significantly higher in the lower area of the slope when harvest residues were not grazed and when conservation tillage was performed. The interaction tillage x residue showed the highest carbon content to be attained with reduced tillage and no stubble grazing, and the lowest to be attained with conventional tillage with stubble grazing. Comparisons with minimally altered soil showed the loss of organic carbon to oscillate between 80% with conventional tillage when residues were grazed and 77% when conservation tillage systems were used. With respect to quantities of water-stable aggregates available (four diameter ranges), minimal alteration led to the highest percentages of the most coarse aggregates, while with the different treatments the finest and most coarse aggregates showed the highest percentages. The exception was under direct seeding where the distribution was similar to that for minimal soil alteration, though the percentage of the most coarse aggregates was lower. A linear, positive relationship was found between organic carbon and macroaggregate content. These results may help in the choice of technologies that can improve soil quality.Key words: organic residue, aggregates, topographic position, technologies, alteration, fertilization ResumenEfecto de la topografía, las labranzas y el pastoreo de los rastrojos sobre el carbono orgánico y la estructura del suelo Se estudió el efecto de la topografía, pastoreo de rastrojos, labranzas y fertilización sobre el contenido de carbono orgánico y la estabilidad estructural del horizonte superficial de un Hapludoll típico bajo producción mixta, y se comparó con el mismo suelo con mínima alteración. El contenido de carbono orgánico fue significativamente más elevado en la posición más baja de la pendiente, cuando no se pastorearon los residuos de cosecha y se usaron labranzas conservacionistas. La interacción labranza x residuo indicó que el mayor contenido de carbono se observa en labranza reducida no pastoreada y el menor en labranza convencional con pastoreo de rastrojos. La comparación con la situación de mínima alteración indicó que la pérdida de carbono orgánico oscila entre el 80% en labranza convencional cuando se pastorean los rastrojos y el 77% en labranzas conservacionistas. En cuanto a la cantidad de agregados estables al agua de cuatro rangos de diámetros, se observó que en la situación de mínima alteración los porcentajes más elevados se encontraron en los agregados más gruesos, mientras que en los tratamientos estudiados la distribución fue bimodal, con porcentajes más elevados en los agregados más finos y más gruesos, excepto en siembra directa, que tuvo una distribución semejante a mínima alteración, aunque con valores inferiores de agregados más gruesos. Se encontró relación lineal ...