Oxisol Typic Research Articles

Long-term behavior of Cu and Zn in soil and leachate of an intensive no-tillage system under swine wastewater and mineral fertilization

The fertilization of crops with swine wastewater is a common practice and attractive for the reduction of natural resources and environmental pollution control. The feasibility of such use is due to the large volume of waste generated and the amount of nutrients that are easily mineralized when applied in soil. However, copper and zinc, added in high concentrations in swine rations, can accumulate on soil-water-plant system after successive applications. Thus, this study aimed at evaluating the effects of doses of swine wastewater associated with mineral fertilization in the levels of copper and zinc in an intensive no-tillage system (maize, black oats and soybeans) for four years. The experiments were carried out in area with twenty-four lysimeters of drainage, in typical oxisol. Swine wastewater treated in stabilization ponds and biodigester was applied in doses of 0, 100, 200 and 300 m3 ha-1 associated with presence and absence of mineral fertilization, resulting in eight treatments with three repetitions each. Increases of 15.60% copper and 188% zinc in soil were found after four years of swine wastewater application. In the presence of mineral fertilization, zinc was 57% higher than in its absence. Copper and zinc levels detected were within the recommended range of mineral nutrition for maize, black oats and soybeans. Key words: Fertilization, heavy metals, leaching, pig slurry, water reuse.

Microbial activities during the early stage of laboratory decomposition of tropical leaf litters: the effect of interactions between litter quality and exogenous inorganic nitrogen

The comparative decomposition of tropical leaf litters (e.g. Andropogon gayanus, Casuarina equisetifolia, Faidherbia albida) of different qualities was investigated under laboratory conditions during a 60-day incubation period conducted with a typical oxisol. Total CO2-C, soil inorganic N, microbial biomass (fumigation-extraction), β-glucosidase and dehydrogenase activities were determined over the incubation to assess how they responded to the addition of inorganic N (+N). Cumulative CO2-C evolved from the litter-amended soils was higher than that recorded for the unamended control soil. For the unfertilized treatment (0 N), correlation coefficients calculated between initial chemical data and CO2 flux during the first day of incubation were r =0.963 for water soluble-C and 0.869 for soluble carbohydrates (P <0.05). At the end of the incubation, the amounts of CO2-C in the F. albida- and A. gayanus-amended soils were higher than that in the C. equisetifolia-amended treatment. Cumulative net N immobilization increased during the first 30 days of incubation, the amounts being similar for A. gayanus- and C. equisetifolia-amended soil and higher than that recorded in the F. albida-amended treatment. Soil microbial biomass and enzyme activities increased in the litter-amended soils during the first 15 days of incubation and decreased (except for the dehydrogenase activity) thereafter. The addition of inorganic N modified the patterns of CO2-C respiration and net N immobilization. The magnitude of these modifications varied according to the litter quality. The use of an accurate indicator based on several litter components to predict the amplitude of organic material decomposition is discussed.

Influence of phenamiphos on the vesicular-arbuscular mycorrhizal symbiosis in Leucaena leucocephala

Concentrations of phenamiphos ranging from 0 to 40 μrg/g soil were established in a typical Oxisol (Tropeptic Eutrustox), inoculated or uninoculated with Glomus aggregatum. The effect of the nematicide on the development of vesicular-arbuscular mycorrhizal (VAM) symbiosis was evaluated in the greenhouse using Leucaena leucocephala as an indicator host plant. Treatment of soil with phenamiphos did not have a significant influence on the development of mycorrhizal activity measured in terms of subleaflet phosphorus concentrations. Similarly, the nematicide did not have an adverse effect on the level of mycorrhizal colonization or on the P content of shoots, as determined at the time of harvest. However, shoot dry weight was adversely influenced by phenamiphos when the chemical was applied to the uninoculated soil at 20 μg/g soil or higher, and when it was applied to the inoculated soil at 40 μg/g soil. It is concluded that phenamiphos is not likely to influence the growth of Leucaena or its symbiotic association with VAM fungi if the concentrations applied do not exceed levels known to suppress nematodes.

Determining vesicular–arbuscular mycorrhizal effectiveness by monitoring P status of leaf disks

A greenhouse experiment was conducted to monitor the development of symbiotic interaction between the vesicular–arbuscular mycorrhizal (VAM) fungus Glomus aggregatum and Vigna unguiculata grown in a typical Oxisol before and after the soil was subjected to simulated erosion and at various levels of phosphorus in the soil solution. VAM development monitored in terms of P status of cowpea leaf disks revealed that VAM activity was not detected in the eroded soil unless the soil was amended with P. When P was not limiting, VAM activity (effectiveness) was detected as early as 17 days from planting, the activity peaking 5–10 days thereafter. Peak VAM activity was observed at a soil solution P level of 0.026 μg/mL and the peak values were similar in the eroded and uneroded soil samples. Maximum mycorrhizal inoculation effect was also observed at this level of soil solution P. Our results illustrate the usefulness of the leaf-disk technique for monitoring the development of the VAM symbiosis and the significance of soil solution P in regulating host response to VAM inoculation.

Título en español.

En este estudio se presentan datos sobre la humedad disponible en el suelo Catalina arcilloso, un Oxisol, y en el Cialitos arcilloso, un Ultisol. Ambos suelos tienen un contenido de arcilla sumamente alto y uno de materia orgánica bastante alto. El suelo Catalina arcilloso es alto en óxidos de hierro libres alcanzando un nivel de 18.2 por ciento, mientras que en el Cialitos éstos sólo alcanzan un 13 por ciento. Ambos suelos tienen una baja capacidad para suministrar el agua en estado disponible. Sin embargo, cuando se toman en cuenta los agregados individualmente, se observa que los más pequeños retienen un volumen mayor de agua disponible que los más grandes. Esto es así, porque la humedad retenida a tensiones altas decrece cuando disminuye el tamaño de los agregados, mientras que la retenida a tensiones bajas aumenta cuando disminuye el tamaño de los agregados. Los resultados se atribuyen al hecho de que los agregados grandes tienen un volumen mayor de poros pequeños, mientras que entre los agregados pequeños se forman poros más grandes.