Carlos Alberto Domingues da Silva

Soil management under no-tillage systems in the tropics with special reference to Brazil

Because of cost reductions and soil erosion control, no-tillage is being rapidly adopted by farmers in the Americas, particularly in the humid and sub-humid tropics. Compared to conventional tillage (tillage operations resulting in <30% cover of plant residue remaining on the surface), no-tillage combined with crop rotation involving cover crops increases soil organic matter content, whilst improving soil fertility. This was mostly evident at 0–5 cm depth. Further successful adoption by farmers, including smallholder farmers from different regions, depends on improvements of various aspects, from edaphological constraints (e.g. in Brazil) to social and infrastructural limitations (e.g. in West and Central Africa). Special emphasis is given to the effects of no-tillage on soil organic matter and the consequences on some chemical (e.g. subsoil acidity, fertilizer management) and physical properties of soils (e.g. soil compaction, aggregate stability). Research imperatives for regional improvement or adaptation of such a conservation tillage are emphasized together with social and economical aspects for its adoption.

Estoques de carbono e nitrogênio e distribuição de frações orgânicas de latossolo do cerrado sob diferentes sistemas de cultivo

This study was carried out to evaluate the effect of cultivation systems on soil carbon and nitrogen contents and on the distribution of light and heavy fractions of soil organic matter (SOM). Density and particle-size fractionations were used to isolate free light fraction (FLF), intra-aggregate light fraction (ILF) and heavy fractions (HF) of a Red-Yellow Latosol from a field experiment at Embrapa Rice and Beans in Goias, Brazil. Treatments consisted of a combination of soil tillage and crop rotation. Soil tillage systems utilized were no-tillage (NT) and conventional tillage (mouldboard ploughing followed by light disc harrowings - CT), under two crop rotations: fallow/rice - fallow/soybean and sunhemp/rice - millet/soybean. As a reference, soil samples were collected from a non-cultivated area nearby the field experiment. All samples were analyzed at Embrapa Soils between January and August 2000. Compared to the forest site, soil cultivation led to a decrease of 50 % in the C and N contents, under both tillage systems. Decreased C and N storages in the cultivated soils were less for ploughed soils than soils under no-tillage. The largest proportion (60-90 %) of C and N was associated with the finest soil particles, with ploughing increasing this tendency. The C content of light fractions decreased due to the replacement of the Cerrado vegetation by cropping systems. Light fraction of the soil organic matter was a sensitive indicator of changes in SOM content caused by cropping systems.

Predation rate of Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae with and without defense by Podisus nigrispinus (Heteroptera: Pentatomidae)

Objetivou-se determinar o efeito da defesa da presa Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) na taxa de predacao por femeas de Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae). Podisus nigrispinus, predou 1,0; 1,4; 1,2; 3,8; 3,0 lagartas de terceiro estadio de S. frugiperda com defesa, respectivamente, nas densidades de uma, duas, quatro, seis e oito lagartas, enquanto esses valores foram de 0,4; 0,8; 1,6; 2,8; 3,2 lagartas sem defesa, respectivamente, nessas densidades. A taxa de ataque (a) e o tempo de manipulacao (Th) foram, respectivamente, de 0,67 ± 0,39-h e 6,72 ± 2,88 horas para femeas de P. nigrispinus alimentadas com lagartas com defesa e de 2,51 ± 0,16-h e 0,51 ± 0,77 horas para aquelas sem defesa. A resposta funcional do predador P. nigrispinus varia com a defesa e a densidade da presa S. frugiperda, com maior consumo de presas sem defesa em altas densidades.

Estimativa da acidez potencial pelo pH SMP em solos do semi-árido do Nordeste brasileiro

In this study the relationship between the pH SMP and H + Al concentrations was evaluated, in order to establish an equation for estimating the potential acidity of soils from Northeastern Brazil. The H + Al concentration (calcium acetate 0.5 mol L-1, pH 7.0) and pH SMP were analyzed in 81 soil samples. Soil carbon content ranged from 1.8 to 35.6 g kg-1, and clay content varied from 60 to 590 g kg-1. The equation H + Al = 31.521(pH SMP)2 -451.61 pH SMP + 1625.3 (R2 = 0.87**), with H + Al in mmolc dm-3, provides a good estimation of potential acidity by using the pH SMP.

Kaolin spraying protects cotton plants against damages by boll weevil Anthonomus grandis Boheman (Coleoptera: Curculionidae)

The high cost of insecticides, the emergence of insecticide resistance in populations of a number of insect species and other problems arising from their continuous use, such as biological imbalance, cotton fiber waste, and environmental pollution, have prompted the development of new technologies aiming the control of Anthonomus grandis Boheman in cotton crops. This study evaluated the level of protection conferred by kaolin clay foliar spraying to cotton plants against boll weevil damage. Treatment-tested spraying kaolin or endosulfan on cotton plants. The highest percentage of oviposition-punctured squares were observed in the control, and the lowest percentages in the treatments sprayed with endosulfan and kaolin in a systematic manner and where the boll weevil reached the economic threshold at all assessments. The greatest numbers of non-attacked bolls by weevils and cotton-seed yield were observed under the endosulfan treatments, followed by the treatments of kaolin spraying. The smallest number of bolls and lowest cotton-seed yield were observed for the control plots. These finding are of practical significance because they may reduce the cotton production cost and environmental impacts of chemical pesticides and make possible the production of organic cotton with the presence of boll weevils.

Disponibilidade de nitrato em solos brasileiros sob efeito da calagem e de fontes e doses de nitrogênio

The aim of this work was to evaluate the effect of liming and sources and doses of nitrogen on nitrate availability in Brazilian soils. Two experiments were carried out:xa0one with five soils from Bahia State and the other with five soils from Minas Gerais State. Soil samples were previously moistened and incubated at 26°C in order to activate the microorganism population. Soil samples from Bahia State were incubated with 50, 100, 150 e 200xa0mg of N per kg of soil as ammonium sulfate or urea and in the Minas Gerais soils it was evaluated the effect of liming on nitrification. Soil samples were incubated at 26°C during 15 days. Urea nitrified faster than ammonium sulfate. The sandy soil did not exhibit net nitrification following ammonium application, but nitrification in this soil was significantly higher under urea. The nitrate availability increases with the liming of Minas Gerais soils. Nitrification rate showed to be highly correlated with base saturation whereas urea hydrolysis was correlated with organic matter content.

Feeding of fall armyworm, Spodoptera frugiperda, on Bt transgenic cotton and its isoline

Studies on insect food intake and utilization are important for determining the degree of insect/plant association and host species’ resistance, and also for helping design pest management programs by providing estimates of potential economic losses, techniques for mass breeding of insects, and identifying physiological differences between species. We studied the feeding and development of fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), on transgenic (Bt) and non‐transgenic (non‐Bt) cotton. The larvae of S. frugiperda fed on Bt cotton had a longer development period (23.0u2003days) than those fed on non‐Bt cotton (20.2u2003days). Survivorship of S. frugiperda larvae fed on Bt cotton (74.1%) was lower than that of larvae fed on non‐Bt cotton (96.7%). Pupal weight of larvae fed on Bt cotton (0.042u2003g) was lower than that of larvae fed on non‐Bt cotton (0.061u2003g). The cotton cultivar significantly affected food intake, feces production, metabolization, and food assimilation by S. frugiperda larvae. However, it did not affect their weight gain. Intake of Bt‐cotton leaf (0.53u2003g dry weight) per S. frugiperda larva was lower than the intake of non‐Bt‐cotton leaf (0.61u2003g dry weight). Larvae fed on Bt‐cotton leaves produced less feces (0.25u2003g dry weight) than those fed on non‐Bt‐cotton leaves (0.37u2003g dry weight). Weight gain per S. frugiperda larva fed on Bt‐cotton leaves (0.058u2003g dry weight) was similar to the weight gain for larvae fed on non‐Bt‐cotton leaves (0.056u2003g dry weight). The cotton cultivar significantly affected the relative growth, consumption, and metabolic rates, as well as other nutritional indices: the figures were lower for larvae fed on Bt‐cotton leaves than for larvae fed on non‐transgenic cotton leaves.

Biologia e exigências térmicas do ácaro-vermelho (Tetranychus ludeni Zacher) em folhas de algodoeiro

O objetivo deste trabalho foi estudar a biologia e as exigencias termicas de Tetranychus ludeni Zacher (Acari: Tetranychidae) em folhas de algodoeiro (Gossypium hirsutumxa0L. r.xa0latifolium (Hutch)). Foram utilizadas câmaras climatizadas, ajustadas nas temperaturas de 20, 23, 25, 28 e 30oC, umidade relativa de 70% e fotofase de 12xa0horas. Osxa0periodos de desenvolvimento de ovo a adulto variaram de 20,77 (20oC) a 8,50xa0dias (30oC), em femeas, e de 18,83 (20oC) a 7,75xa0dias (30oC), em machos. Asxa0temperaturasbase, estimadas pelo metodo da interseccao de X, para os periodos de desenvolvimento de ovoadulto, foram de 14,05oC para femeas e 13,91oC para machos, enquanto os valores da constante termica estimados de acordo com a lei de Reamur foram de 138,34xa0grausdia, para femeas e 130,91xa0grausdia, para machos. Naxa0temperatura de 30oC foram observados os maiores valores de razao intrinseca de crescimento (0,418), numero de ovos de femeas/dia (3,47), fecundidade (61,29) e taxa liquida de reproducao (48,00) e o menor valor para o tempo medio de uma geracaoxa0(9,27).

Carbono, nitrogênio e enxofre em frações granulométricas de dois latossolos submetidos à calagem e adubação fosfatada

The amount and distribution of carbon, nitrogen, and sulfur in whole soil and in particle-size fractions were analyzed in two clayey Dark Red Latosols (LE1 and LE2). LE1 (forest as natural vegetation), from Cordeiropolis, Sao Paulo, cultivated with citrus since 1982 receiving two lime treatments, control and 18 t ha-1 applied twice in 1983 and 1994. Since 1976, LE2 (cerrado as natural vegetation) from Planaltina, Federal District (cerrado region), was cultivated with different crops (wheat, soybean, rice and sorghum) sown for 14 years with pasture grass (Andropogon gayanus L.), with and without the addition of 1.660 kg ha-1 of P2O5 as triple superphosphate. For reference purposes, additional samples were collected from uncropped soils in both LE1 and LE2 sites. Carbon, nitrogen and sulfur contents were determined in whole soils and in their particle-size fractions. The drastic reduction of carbon, nitrogen and sulfur contents in the cultivated areas of LE1 was followed by an intensive depletion in CEC at limed and control plots, stressing the importance of management and conservation of organic matter in this soil. In the LE2 soil, the reduction of C, N and S contents with cultivation was less intense and associated with a higher decomposition of organic compounds linked to the intermediate fraction. Liming resulted in a higher preservation of soil organic matter, although phosphorus addition did not affect carbon and nitrogen contents in the LE2 cultivated areas. Fine fraction plays a crucial role in the stabilization of soil organic matter, since the largest reservoirs of carbon, nitrogen and sulfur were associated to this particle-size. The distribution of carbon, nitrogen and sulfur between particle-size fractions is characterized by a depletion of organic materials associated to coarse, intermediate and fine fractions and a shift towards fine fraction associated materials.

The introduced tree Prosopis juliflora is a serious threat to native species of the Brazilian Caatinga vegetation

Despite its economic importance in the rural context, the Prosopis juliflora tree species has already invaded millions of hectares globally (particularly rangelands), threatening native biodiversity and rural sustainability. Here we examine seedling growth (leaf area, stem diameter, plant height) and seedling mortality across five native plant species of the Caatinga vegetation in response to competition with P. juliflora. Two sowing treatments with 10 replications were adopted within a factorial 2 × 5 randomized block design. Treatments consisted of P. juliflora seeds sowed with seeds of Caesalpinia ferrea, Caesalpinia microphylla, Erythrina velutina, Mimosa bimucronata and Mimosa tenuiflora (one single native species per treatment), while seeds of native species sowed without P. juliflora were adopted as controls. Overall, our results suggest that P. juliflora can reduce seedling growth by half and cause increased seedling mortality among woody plant species. Moreover, native species exhibit different levels of susceptibility to competition with P. juliflora, particularly in terms of plant growth. Such a superior competitive ability apparently permits P. juliflora to establish monospecific stands of adult trees, locally displacing native species or limiting their recruitment. The use of less sensitive species, such as C. ferrea and M. tenuiflora, to restore native vegetation before intensive colonization by P. juliflora should be investigated as an effective approach for avoiding its continuous spread across the Caatinga region.