Lourival Vilela

Chemical fractionation of phosphorus, sulphur, and molybdenum in Brazilian savannah Oxisols under different land use

In soils, P, S, and Mo occur organically bound or as oxyanions. In Oxisols, oxyanions may be strongly sorbed due to the high positive surface charge. The objective of this work was to compare chemical fractions of P, S, and Mo in differently used Oxisols with similar properties in an on-farm experiment. Soil samples (0–0.15 m) were taken from three replicate plots of each of conventional tillage (CT) and no-till (NT) maize–soybean and conventional tillage sugarcane (SC) cropping systems, degraded (DP) and productive pastures (PP), Eucalyptus (EU) and Pinus reforestations (PI), and native savannah (CE). The samples were sequentially extracted with (1) 0.5 M NaHCO3, (2) 0.1 M NaOH, (3) 1 M HCl, (4) hot concentrated HCl, and (5) concentrated HClO4/HNO3. In the extracts, inorganic (Pi) and total P, S, and Mo were determined. Organic P (Po) was calculated as total P−Pi. Total concentrations were 333–567 mg P kg−1, 231–284 mg S kg−1, and 3.2–3.9 mg Mo kg−1. The most important fractions in all studied systems were the NaOH fraction for P (38–49% of total P), the HClO4/HNO3 fraction for S (27–35% of total S) and the concentrated HCl fraction for Mo (86–90% of total Mo). The proportion of the more easily extracted NaHCO3+NaOH fractions decreased along the line S>P>Mo. Fertilisation increased plant-available P and S fractions in CT and NT whereas recalcitrant fraction (concentrated HCl and HClO4/HNO3) remained unchanged. The Pi/Po ratios in NT and CT were higher than in CE because fertiliser P mainly accumulated in inorganic P fractions. The pasture soil had lower P concentrations indicating export by grazing. Thus, 12–20 years of land use had marked effects on P, smaller ones on S, and almost none on Mo concentrations and chemical fractions.

Aggregation studied by laser diffraction in relation to plowing and liming in the Cerrado region in Brazil

In the Cerrado savanna region in Brazil, the effects of different land use on Oxisol aggregation were studied using laser diffraction grain size analyses. The topsoil of plowed systems had significantly lower amount of macroaggregates (2000–194 μm) and a significantly higher amount of soil in the microaggregate size and primary particle fraction (<76 μm) compared to pastures and the native Cerrado. In plowed systems low in soil organic carbon (SOC), lime had a negative effect on aggregate stability. Lime addition had no effect on topsoil aggregation in land use systems that were not plowed regularly and generally had a higher SOC content. For all the studied topsoils, pHKCl was positively correlated with the amount of clay dispersed after 3 h of shaking in water. SOC did not influence clay dispersion in the range of soils studied. In continuous cropping systems in the Cerrado region, with a combination of mechanical stress and low SOC, liming will cause an increase in small aggregates and primary particles and hence contribute to a destabilization of the soil structure.

Sistemas de integração lavoura-pecuária na região do Cerrado

O objetivo deste trabalho foi analisar os beneficios e as perspectivas potenciais de sistemas de integracao lavoura-pecuaria no processo de intensificacao de uso das areas em exploracao com lavoura de graos e pastagens no Cerrado, e apontar as principais lacunas de informacao sobre o sistema. Os principais beneficios da integracao lavoura-pecuaria sao: melhoria das propriedades quimicas, fisicas e biologicas do solo; reducao da ocorrencia de doencas, insetos-pragas e plantas daninhas; maior produtividade das plantas e dos animais; e reducao de riscos pela diversificacao de atividades. No entanto, a adocao do sistema de integracao lavoura-pecuaria ainda e pequena, provavelmente em virtude da maior complexidade desse sistema. Concentrar esforcos nos fatores que limitam a adocao desse sistema no Cerrado parece ser um ponto estrategico para novos estudos. A busca por melhoria na qualidade de cobertura de solo para o sistema plantio direto, por meio de gramineas forrageiras, pode auxiliar na adocao da integracao lavoura-pecuaria no Cerrado. A expectativa e de que a adocao de sistemas de integracao lavoura-pecuaria resulte em melhorias significativas na sustentabilidade socioeconomica e ambiental das propriedades e da sua regiao de influencia.

Dinâmica e contribuição da micorriza arbuscular em sistemas de produção com rotação de culturas

Rotacao de culturas e variacoes sazonais podem promover alteracoes quantitativas e qualitativas na comunidade de fungos micorrizicos arbusculares nativos e na formacao da micorriza arbuscular. Essa dinâmica foi avaliada, em campo, num Latossolo Vermelho, em relacao ao tempo de cultivo e variacao sazonal, em sistemas de rotacao de culturas. Em casa de vegetacao, avaliou-se, em solo proveniente da area experimental, a contribuicao da micorriza arbuscular no crescimento de soja e capim-andropogon utilizados na rotacao. O numero de esporos dos fungos aumentou no solo cultivado. O numero de esporos e o porcentual de colonizacao radicular, inicialmente maiores sob pastagem, variaram de acordo com o tempo de cultivo, as estacoes seca e chuvosa, a cultura e o sistema de rotacao utilizados. O numero de generos e especies aumentou com o tempo de cultivo e manejo de culturas e foi maior sob culturas anuais em rotacao. A presenca dos fungos no solo contribuiu no crescimento da soja e do capim-andropogon em 53% e 95%, respectivamente. A cultura e o sistema de cultivo sao fatores determinantes para o enriquecimento do sistema com micorriza arbuscular.

Manejo da adubação nitrogenada de tensões hídricas sobre a produção de matéria seca e índice de área foliar de Tifton 85 cultivado no Cerrado

This work was carried out to evaluate the influence of water tensions (35, 60, 100 and 500 kPa) and nitrogen levels (0 - Control, 45, 90, 180, 360 kg/ha) on the dry matter (DM) yield, the dry matter yield rate (DMYR) and the leaf area index (LAI) of Cynodon spp. cv. Tifton 85 bermudagrass. A randomized blocks design in a split splot scheme with three replications was used, split plots were represented by the water tensions were and the plots, by the nitrogen (N) levels. The dry matter yield was influenced by the nitrogen levels for all tensions, where the highest productivity (41.8 t/ha) was obtained at 35 kPa the tension and the maximum N level (360 kg/ha of N), while the smallest productivity (17.3 t/ha), at 100 kPa the tension without N addition. At the tensions of 60, 100 and 500 kPa there was limitation in the use of N at the highest doses, due to the deficit water. Higher DMAR were observed from 09/21 to 11/29, and the averages ranged from 73.4 to 194.6 kg/ha/day of DM, while from 05/26 to 08/09 the smallest averages were observed, that ranged from 44.9 to 55.2 kg/ha/day of DM. No effect of N levels was observed from 03/16 to 08/09. In the other periods, DMYR increased as N levels increased. There was no effect of the different water tensions on DMYR. LAI increased as N levels increased, from 09/21 to 01/10, with averages from 3.07 to 9.64. In the periods with low temperatures, N levels and did not affect LAI. Water tension did not affect LAI in all evaluated periods.

Adsorção de nitrato em solos de cerrado do Distrito Federal

This work aimed to assess the rate of nitrate adsorption and identify the soil properties that most affect it, in a Dark-Red Latosol, with 56% clay content, in Planaltina, DF, Brazil. Soil samples were collected from areas with four different management systems, at depths of 0-20, 20-40, 40-80 and 80-100†cm. Three of the areas were obtained from an on-going five-year experiment, i.e., native grass savannah land and two areas cultivated with soybeans and maize that received different amounts of liming, sulphate and other nutrients and whose soils had inverted charges in depth. The fourth area was a woody savannah land, with negative net electric charge in depth. The relationship between nitrate adsorbed and nitrate in solution, was described by Freundlich equation, and the relationship between nitrate adsorbed and some soil physical-chemical properties was studied by multiple regression. Ni- trate adsorption increased with soil depth in all treatments. Nitrate adsorption was higher in the native grass and woody savannah than in the other treatments. The DpH as an index of net electric charge did not affect nitrate adsorption. There was a negative correlation between nitrate adsorption, organic matter and extractable sulphate. Nitrate adsorption increased with organic matter reduction in the deep layers of the soil and with decrease in extractable sulphate.

Banco de sementes no solo em sistemas de cultivo lavoura-pastagem

The objective of this study was to evaluate the effects of cultivation and tillage systems, and fertilization level, on soil seedbanks of areas submitted to: three cultivation systems - continuous crop (L), crop-pasturecrop (LPL), pasture-crop-pasture (PLP); two tillage systems - tillage (C) and no-tillage (D); two fertilization levels - maintenance (1) and gradual corrective (2); and a continuous pasture area under tillage and gradual corrective fertilization. Seed density of crop-pasture cultivation systems, was lower than in continuous crop, and higher compared to continuous pasture system, except for LPLC1 and LPLC2 cultivated areas. The seedbanks in continuous cropping areas was lower in no-tillage than in tillage system areas, but in PLP areas with gradual corrective fertilization, there was no difference between tillage systems. The fertilization level caused a reduction in seed density only in LPLC and PLPC cultivated areas. Integrated crop-pasture system with no-tillage adoption can be useful in weed management of grains crop areas.

Perda de amônia por volatilização em pastagem de capim-tanzânia adubada com uréia no verão

Parte do nitrogenio (N) do fertilizante aplicado a pastagem pode ser perdida do sistema e, em pastagens tropicais, a volatilizacao de amonia (NH3) e uma das principais vias de perda. Objetivou-se, com o presente estudo, estimar a perda de N-NH3 por volatilizacao em pastagem de Panicum maximum cv. Tanzânia adubada com ureia durante o verao. Adotou-se um delineamento inteiramente casualizado, com medidas repetidas no tempo e tres repeticoes. Nas parcelas, encontravam-se as doses de N-ureia (40, 80 e 120 kg/ha de N-ureia) e, nas subparcelas, o periodo depois da adubacao nitrogenada (1, 5 e 9 dias). A interacao entre o nivel de adubacao e o periodo depois da aplicacao de ureia foi significativa para as variaveis volatilizacao acumulada de N-NH3 e taxa diaria de volatilizacao de N-NH3. A combinacao de elevada umidade do solo, ausencia de chuvas durante o primeiro dia depois da adubacao e alta temperatura elevada determinaram elevadas perdas de amonia por volatilizacao. A perda acumulada de N-NH3 no periodo representou 48%, 41% e 42% do N aplicado nas adubacoes com 40, 80 e 120 kg/ha de N-ureia, respectivamente. A volatilizacao acumulada de N-NH3 (kg/ha) aumentou, enquanto a taxa diaria de volatilizacao de N-NH3 diminuiu com o aumento do tempo depois da adubacao.

Effect of no-tillage and conventional tillage systems on the chemical composition of soil solid phase and soil solution of Brazilian savanna Oxisols

No-tillage (NT) cropping systems are becoming increasingly important in the Brazilian savanna. To evaluate their sustainability we compared soil chemical properties in 1- to 3-year-old NT systems following 9 to 11 years of conventional tillage (CT) with systems where CT was continuously in place for 12 years. In the rainy season 1997/98, NT was cropped with soybean and CT with corn while in the rainy season 1998/99 both systems were cropped with soybean. Soil solid phase samples were taken from the 0-0.15, 0.15-0.3, 0.3-0.8, 0.8-1.2, and 1.2-2 m layers on three spatially separated plots under each of NT and CT. Soil solution samples were collected weekly at 0.15, 0.3, 0.8, 1.2, and 2 m soil depth during two rainy seasons (14 October to 28 April 1997/98 and 1998/99). We determined soil moisture contents, pH, the concentrations of exchangeable cations, the electrical conductivity (EC) of the soil solution, and the concentrations of Al, C, Ca, Cl - , K, Mg, Mn, Na, NH 4 + , NO 3 - , P, S, and Zn in solid soil and soil solution samples. Differences in soil solid phase properties and moisture content between NT and CT were small, few were significant. Under NT, the average solution pH was significantly lower (5.5), Al (26 tag 1 -1 ), Mn (17 μg 1 -1 ) and total organic C concentrations (TOC, 6.5 mg 1 -1 ) were higher than under CT (pH: 6.0, Al: 14μg 1 -1 , Mn: 14μg 1 -1 , TOC: 5.5 mg 1 -1 ). Irrespective of the different crops in the first rainy season, under NT, the EC (205 μS cm -1 ), Ca (17 mg 1 -1 ), and Mg (2.9 mg 1 -1 ) concentrations at 0-0.3 m depth were lower than under CT (EC: 224 μS cm -1 , Ca: 25 mg 1 -1 , Mg: 5.6 mg 1 -1 ). At 1.2-2 m depth, the reverse order was observed (EC: 124 μS cm -1 under NT and 84 μS cm -1 under CT, Ca: 11 mg 1 -1 under NT and 7.5 mg 1 -1 under CT, Mg: 3.1 mg 1 -1 under NT and 1.8 mg 1 -1 under CT). Our results indicate that enhanced soil acidification because of higher rates of organic matter mineralization and a more pronounced nutrient leaching because of increased pore continuity may limit the sustainability of NT.

Banco de sementes em cerrado sensu stricto sob queimada e sistemas de cultivo

The objective of this work was to evaluate the burning and cultivation effects on soil seedbanks originally under cerrado vegetation. Two areas under cerrado sensu stricto were sampled, one burned and the other one not burned, as well as areas under tilled crop and pasture. There was no reduction on seedbank, although lower number of species and families and diversity index (Shannon and Simpson) with burning were observed. There was also greater importance value index (IVI) and number of native species, in the non burned area, and of weeds in the burned one. It was observed that the crop area had higher seed density than the pasture and cerrado areas. The species with the highest IVI in the areas were those considered as weeds and forages. The crop area presented lower IVI of native species than the pasture and cerrado areas; besides, it presented diversity indexes (Shannon and Simpson) and native species percentage lower than pasture and cerrado. The cultivation with crop cause higher disturbance in the areas than burning.