ABSTRACT The use of nitrification inhibitors (NIs; dicyandiamide - DCD) is an alternative to reduce oxidation of ammonium (NH4+-N) to nitrate (NO3–-N) in the soil, reducing NO3–-N losses from fertilization practices. Based on the hypothesis that DCD reduces conversion of NH4+-N to NO3–-N in tropical soils and inhibits ammonia oxidizing microorganisms (AOM) abundance, soils from the Piracicaba region, São Paulo, with different textures (sand, loam and clay) were incubated with ammonium sulphate (AS) and DCD. Contents of NH4+-N, NO3–-N, soil pH, and AOM abundance were quantified periodically. Ammonium sulphate increased AOM abundance in all soils, but AS+DCD presented AOM abundances similar to the control. During 90 days of incubation, the effectiveness of DCD in reducing NO3–-N production was 1.8, 86.4, and 145.6 mg kg–1, while the effectiveness of DCD in reducing AOM abundance was 1.2, 3.0 and 2.3 × 10–3 g soil–1 for sandy, loamy, and clayey soils, respectively. DCD effectiveness was greater in loamy and clayey soils due to the naturally low nitrification in sandy soils. Application of AS treated with DCD showed potential not only to reduce NO3–-N production in loamy and clayey soils, but also to decrease the soil nitrification rate. Overall, DCD was effective in reducing AOM abundance and conversion of NH4+-N to NO3–-N in loamy and clay soils evaluated here. The increase in clay content directly influences DCD effectiveness in reducing conversion of NH4+-N to NO3–-N.

ABSTRACT: Integrating plant density and nitrogen (N) management is a strategy for improving corn yields, especially for off-season corn production in the tropics. This study tested the hypothesis that increasing plant densities and N rates promotes yield gains for off-season corn production in high-yielding environments. The aim of the study was to investigate the yield performances of two hybrid versions (DKB PRO and DKB PRO3) submitted to three plant densities (55,000; 65,000 and 75,000 plants ha−1) and four N rates (control, 60, 120 and 180 kg ha−1 N). Field trials were undertaken at Uberlândia-MG (site1 and 2) and Pedro Afonso-TO (site 3), Brazil from which data on corn yield parameters were collected and analyzed. Multivariate analysis separated the three trial areas into two groups, presenting high (sites 1 and 2) and low yields (site 3), which were related to weather conditions. There was no influence of a hybrid version or plant densities on crop yields at site 1 or 2. In contrast, there was a positive response to increasing plant densities and the use of DKB PRO3 at site 3. A significant response to N was observed at sites 2 and 3, following a plateau model. Our results suggest that N application rates and plant densities do have the potential to increase off-season corn yields in low yielding environments.

Resumo: O maracujá-amarelo conquistou significativa posição no agronegócio de frutas tropicais, com isso, produtores despertaram interesse para expandir seus pomares, sendo necessárias informações técnicas que garantam a alta produtividade das lavouras. No intuito de observar fatores relacionados ao material propagativo visando a qualidade e a maximização do potencial genético objetivou-se avaliar a germinação e a emergência de sementes de maracujá coletadas em três posições nos frutos e submetidas a métodos de retirada da mucilagem (arilo). Os frutos de maracujá foram seccionados em três partes: distal, mediana e proximal. Cada um destes conteúdos foi submetido aos métodos mecânico e de fermentação para remoção do arilo. Podendo concluir que a posição da semente no fruto do maracujazeiro não interfere na germinação e o método de remoção do arilo por extração mecânica prejudica a germinação e a emergência de plântulas.

Abstract: Yellow passion fruit has conquered a significant position in the agribusiness of tropical fruits; therefore, farmers have been interested in expanding their groves, and technical information that guarantees the high yield of the farmings is needed. Aiming to observe factors related to the propagative material targeted at quality and maximization of the genetic potential, the objective of the study consisted in assessing germination and emergence of passion fruit seeds collected in three positions in the fruits and submitted to different methods of mucilage removal (aryl). The passion fruits were split in three parts: distal, medial and proximal and the contents of each part was divided in two. The content of each part of the fruit was submitted to mechanical and by fermentation methods for removal of aryl. It is concluded that the seed position in the fruit does not interferes with the germination. The aryl removal method by mechanical extraction affects the germination and seedling emergence.

O uso de modelos matemáticos pode ser útil para o entendimento das alterações do uso e manejo do solo e fornecem subsídios para testar cenários futuros, possibilitando desenvolver estratégias de manejo menos impactantes ao meio ambiente. Os objetivos deste trabalho foram: (a) usar o modelo Century v4.5 para simular os efeitos dos usos e manejos sobre os estoques de carbono e nitrogênio do solo em diferentes compartimentos, (b) comparar os estoques medidos e simulados pelo Century, e (c) testar impacto de cenários futuros até o ano de 2100. Os tratamentos avaliados foram Pinus, plantio direto e plantio convencional, com histórico das áreas até o momento da coleta de solo (2004). Para o Pinus foram testados três cenários futuros, um deles simulando o mesmo manejo adotado até o momento da coleta de solo, outro reduzindo os eventos de fogo, além do uso sem preparo do solo para o replantio. Para o plantio direto e plantio convencional, simularam-se dois cenários futuros, um com rotação milho/soja e outro com monocultura de milho. O modelo Century foi sensível às mudanças de manejo adotadas, os compartimentos mais lábeis apresentam maior sensibilidade (ativo e lento), do que o mais estável (passivo). Em relação ao estoque de C, o modelo simulou estoques próximos aos medidos no campo, com um erro mínimo de 0,36%. Para os estoques de N, os valores simulados apresentaram erro de 5,71% para os compartimentos mais lábeis. Os cenários futuros mostraram a importância de se evitar queimadas no Pinus e o uso de monocultivo.

The use of mathematical models can be useful for understanding the changes in the use and management of soil and provide aid in testing future scenarios, making it possible to develop management strategies which have less impact on the environment. The objectives of this study were: (a) to apply the Century Model v4.5 in order to simulate the effects of usages and managements on carbon stocks and soil nitrogen in different compartments; (b) compare both the observed stocks and those simulated by the Century Model; (c) to test the impact of future scenarios until the year 2100. The treatments evaluated were of Pine, under both no-tillage and conventional tillage, using historical data from the areas up until when the soil was sampled (2004). For the pine, three future scenarios were tested, one by simulating the management adopted up to the time the soil was sampled, another by reducing the fire events, as well as by soil usage without any preparation when replanting. For both no-tillage and conventional tillage, two future scenarios were simulated: one with corn and soybean rotation, and the other with a monoculture of corn. The Century model was sensitive to the changes in management which were adopted, the more labile compartments showing greater sensitivity (the active and the slow) than the most stable (passive). In relation to stocks of C, the model simulated values close to those measured in the field, with a minimum error of 0.36%. For stocks of N, the simulated values showed an error of 5.71% for the more labile compartments. For pine, the future scenarios demonstrated the importance of preventing fires, and the use of monocultures.