ABSTRACT Corn grain yield, nitrogen (N) fertilizer efficiency and distribution to corn alone and three forms of corn and palisadegrass (Urochloa spp.) intercropping implantation was investigated. A field experiment with 15N labeling fertilizer was performed in randomized block design. No form of palisadegrass intercropping implantation affected corn grain yield, total N accumulation and N use efficiency (NUE), which were 8.7 t ha-1, 205 kg ha-1 and 37% respectively. The palisadegrass produced on average 1.9 t of dry mass, absorbing a maximum of 6 kg ha-1 or 5.5% of N fertilizer during corn growing. Furthermore, the palisadegrass did not affect N fertilizer distribution in soil-plant system, in which 28.2% was recovered in the soil and 40.4% in the plants (corn + palisadegrass). The results show that for the three intercropping implantation methods the palisadegrass did not compete with corn for N fertilizer.

Particle-size fractionation is supported by the concept that soil organic matter (SOM) fractions associated with different mineral particle sizes have different structure and functions, and play different functions in SOM turnover. The objective of this work was to verify the quality of the organic matter fractionation of a Molisol dispersed with water or Na-hexametaphosphate (HMP) and to analyze the C and N distribution and δ13C values of the separated fractions. We compared the mineral fraction distribution of the soil by completely oxidizing SOM through heating with hydrogen peroxide (AGUAOX) versus water dispersion and HMP dispersion. The soil suspension was wet-sieved with 200, 50 and 20 μm-sieves. The >200 μm fraction was suspended in water in order to separate the floating material (light, L) from the heavy one (H) which settles. The accumulated soil mass (98.4- 99.7%), N (87.4-99.4%) and C (91.4- 96.2%) recoveries were high, but water dispersion presented the higher values. HMP presented more variability than water dispersion; but it dispersed the >200 μm aggregates, allowing the recovery of the high amount of N and C accumulated in the smaller fractions, whereas the use of water did not disperse those aggregates appropriately. High N quantity was recovered in <20 μm fraction, while the C was mainly accumulated in the 200-50 μm fraction. The δ13C values in the smallest fraction were near to the original ones for soils developed under C3 and C4 plants mixture (-21.7‰) whereas the coarse light fraction ones were similar to those of C3 plants (-27.7 ‰). Considering these results, we conclude that the HMP dispersion method is suitable for the particle-size fractionation of the analyzed soil.

El fraccionamiento granulométrico de la materia orgánica (MO) se basa en que las fracciones asociadas con partículas de diferente tamaño difieren en estructura y funciones y cumplen diferentes roles en el reciclado de la misma. El objetivo del presente trabajo fue comprobar la calidad del fraccionamiento de la MO de un Molisol a través del uso de: a) agua y b) hexametafosfato de sodio (HMP) como dispersantes y analizar la distribución del C y N y los valores de δ13C en las distintas fracciones separadas. Se compararon la distribución de la fracción mineral del suelo con la MO destruida por calentamiento con agua oxigenada vs. dispersión en agua o dispersión con HMP. Las suspensiones de suelo fueron tamizadas por tamices de 200, 50 y 20 μm y la fraccion >200 μm fue separada en liviana y pesada por flotacion en agua. Las recuperaciones acumuladas de la masa de suelo (98,4 - 99,7%), N (87,4 - 99,4%) y C (91,4 - 96,2%) fueron altas en general, si bien el agua produjo mayores recuperaciones y HMP presentó mayor variabilidad. El HMP dispersó los agregados de la fracción >200 μm, permitiendo comprobar la gran cantidad de N y C que se acumula en las fracciones más finas, mientras que el agua no dispersó adecuadamente estos agregados. Gran cantidad de N quedó en la fracción <20 μm, en cuanto que el C se acumuló en mayor cantidad en la fracción entre 200-50 μm. Los valores de δ13C en las fracciones más finas fueron cercanos a los valores originales para estos suelos desarrollados bajo vegetación mezcla de especies C3 y C4 (-21,7‰) mientras que en las fracciones gruesas fueron semejantes a los de plantas C3 (-27,7‰). En base a los resultados obtenidos se considera que el método de dispersión con HMP es adecuado para el fraccionamiento granulométrico del suelo analizado.

O uso do traçador 15N em pesquisas agronômicas que envolvem o ciclo do nitrogênio (N) e o destino do N do fertilizante está bem estabelecido, entretanto, para o caso de experimentação com plantas perenes como citrus, café e seringueira, ainda existem limitações devidas ao porte das plantas, à amostragem, aos níveis de detecção e à interferência no sistema. Este estudo procura contribuir metodologicamente no delineamento experimental e no desenvolvimento desse tipo de experimentação, em condições de campo, fazendo uso, por dois anos, do experimento de uma cultura de café adubada com fertilizante marcado com 15N. O N da planta derivado do fertilizante foi estudado nas diferentes partes da planta de café para determinar sua distribuição dentro dela e a eficiência agronômica da prática de adubação. Um enriquecimento do N do fertilizante da ordem de 2% em abundância de 15N foi suficiente para estudar taxas de absorção de N e estabelecer balanços do N do fertilizante depois de um e dois anos de cultivo. A principal fonte de erros dos valores estimados está na variabilidade agronômica das repetições e não na precisão das medidas de conteúdo de N e de enriquecimento em 15N por espectrometria de massa.

The use of the 15N label for agronomic research involving nitrogen (N) cycling and the fate of fertilizer-N is well established, however, in the case of long term experimentation with perennial crops like citrus, coffee and rubber tree, there are still shortcomings mainly due to large plant size, sampling procedures, detection levels and interferences on the system. This report tries to contribute methodologically to the design and development of 15N labeled fertilizer experiments, using as an example a coffee crop fertilized with 15N labeled ammonium sulfate, which was followed for two years. The N of the plant derived from the fertilizer was studied in the different parts of the coffee plant in order to evaluate its distribution within the plant and the agronomic efficiency of the fertilizer application practice. An enrichment of the fertilizer-N of the order of 2% 15N abundance was sufficient to study N absorption rates and to establish fertilizer-N balances after one and two years of coffee cropping. The main source of errors in the estimated values lies in the inherent variability among field replicates and not in the measurements of N contents and 15N enrichments of plant material by mass-spectrometry.

Estudaram-se os efeitos da aplicação de CO2, via água de irrigação, e da enxertia do tomateiro no transporte de 15N e na produção do tomateiro. Os tratamentos foram arranjados em delineamento inteiramente ao acaso no esquema fatorial 2 x 2 (com e sem CO2 na água de irrigação e tomateiro enxertado e pé-franco). A injeção do CO2 na água iniciou-se aos 34 dias após o transplante das mudas (DAT) e se prolongou em todas as irrigações. A aplicação do sulfato de amônio com abundância em átomos de 15N de 3,13% nas plantas destinadas à análise foi feita aos 45 DAT quando as plantas estavam em plena frutificação. Após 14 dias da aplicação do fertilizante (15N ) as plantas foram colhidas, lavadas, secadas e enviadas ao laboratório, para análise do 15N nos seus tecidos. Os resultados demonstraram que o CO2 e a enxertia não alteraram o transporte de 15N na planta. A produção de frutos comerciais foi maior quando se aplicou CO2 na água.

The effects of CO2 application through irrigation water, and of grafting in transport of 15N and in the tomato production, were studied. These treatments were arranged in a 2 x 2 factorial scheme (with and without CO2 in irrigation water and grafted and non-grafted tomato), in a completely randomized design, with four replications. The injection of CO2 into the water began at 34 days after transplant of seedlings (DAT) and continued for all irrigations. The application of the sulfate of ammonium with abundance in atoms of 15N of 3.13% in plants destined to analysis was done at 45 DAT when the plants were in the middle of fructification. After 14 days of fertilizer (15N ) application the plants were harvested, washed, dried and sent for analysis of 15N in plant tissue. The results demonstrated that CO2 and the grafting did not alter the transport of 15N in the plant. The production of commercial fruits was larger when CO2 was applied in water.