Helvécio De-Polli

Spatial heterogeneity of soil respiration and related properties at the plant scale

Geostatistical techniques were used to quantify the scale and degree of soil heterogeneity in 2 m2 plots around 9-year-old poplar trees and within a wheat field. Samples were taken during two years, on an unaligned grid, for analysis of soil respiration, C and N content, available P, gravimetric moisture, pH, nitrification potential, and root biomass. Kriged maps of soil respiration, moisture, and C content showed strong spatial structure associated with poplar trees but not with wheat rows. All soil properties showed higher autocorrelation in June than in April. Isopleth patchiness for all variates was less in June. This was associated with lower respiration rates due to lower litter decomposition. From the degree and scale of heterogeneity seen in this study, we conclude that the main causes of soil heterogeneity at this scale (2 m2) are likely to be found at micro scales controlled in part by plant root and plant residue patterns. These must be understood in the evaluation of ecosystem processes.

Confirmation of nitrogen fixation in two tropical grasses by 15N2 incorporation

Intact soil cores containing plants of Paspalum notatum or Digitaria decumbens were selected with the acetylene reduction method, and then exposed to 15N15 to confirm nitrogen fixation in tropical grass-bacteria associations. In a preliminary experiment with P. notatum15N2 incorporation was slow but progressive during 24 h in roots but translocation to rhizomes and leaves ceased after 17h. With improved assay chambers, enrichments of 0.151 and 0.563 15N atom % excess were obtained in roots of D. decumbens cv transvala and P. notatum systems respectively, after 3 days. Enrichments in rhizomes were similar to those of roots; however in the leaves only 8% of root enrichment was observed. The addition of sucrose to the soil doubled N2-fixation in roots in both grass species studied, but did not result in increased incorporation into the leaves of P. notatum.

Perennial herbaceous legumes as live soil mulches and their effects on C, N and P of the microbial biomass

The use of living mulch with legumes is increasing but the impact of this management technique on the soil microbial pool is not well known. In this work, the effect of different live mulches was evaluated in relation to the C, N and P pools of the microbial biomass, in a Typic Alfisol of Seropedica, RJ, Brazil. The field experiment was divided in two parts: the first, consisted of treatments set in a 2 x 2 x 4 factorial combination of the following factors: live mulch species (Arachis pintoi and Macroptilium atropurpureum), vegetation management after cutting (leaving residue as a mulch or residue remotion from the plots) and four soil depths. The second part had treatments set in a 4 x 2 x 2 factorial combination of the following factors: absence of live mulch, A. pintoi, Pueraria phaseoloides, and M. atropurpureum, P levels (0 and 88 kg ha-1) and vegetation management after cutting. Variation of microbial C was not observed in relation to soil depth. However, the amount of microbial P and N, water soluble C, available C, and mineralizable C decreased with soil depth. Among the tested legumes, Arachis pintoi promoted an increase of microbial C and available C content of the soil, when compared to the other legume species (Pueraria phaseoloides and Macroptilium atropurpureum). Keeping the shoot as a mulch promoted an increase on soil content of microbial C and N, total organic C and N, and organic C fractions, indicating the importance of this practice to improve soil fertility.

Plantio direto de alface adubada com cama de aviário sobre coberturas vivas de grama e amendoim forrageiro

The agronomic viability of no-tillage system for lettuce was evaluated, using grass and legume as cover crop under organic management. A randomized complete block design with split plot arrangement was used. Plot treatments were conventional soil tillage (control), bahia grass and perennial peanut cultivated for living cover crops on no-tillage system. Split-plot treatments were doses of poultry manure (0; 7; 14 and 28 t ha-1) in three application periods. Lettuce cv. Vera yield was not affected by tillage system neither by cover crop. The quadratic model was the most appropriate to describe the variation of yield. The greatest yield estimated by regression models was 348 g plant-1 with 23 t ha-1 of poultry manure bed. On the no tillage system, using bahia grass or perennial peanut, the estimated yield by regression models was similar to the conventional soil tillage system, with a yield of 55,99 t ha-1 using 23,4 t ha-1 of poultry manure bed.A viabilidade agronomica do plantio direto de alface cv. Vera foi avaliada sobre coberturas vivas perenes de graminea e leguminosa em sistema de manejo orgânico. Empregou-se o delineamento de blocos casualizados, dispostos em parcelas sub-divididas. Os tratamentos nas parcelas constaram de plantio em sistema de preparo convencional do solo (controle), plantio direto sobre cobertura viva de grama batatais e plantio direto sobre cobertura viva de amendoim forrageiro. Os tratamentos nas subparcelas constaram de adubacao com doses de cama de aviario aplicada em cobertura (0; 7; 14 e 28 t ha-1), parceladas em tres epocas. Observou-se que a producao de cabeca de alface nao foi influenciada pelo modo de plantio e nem pela especie de cobertura viva sobre a qual foi realizado o plantio direto. Modelo quadratico mostrou-se adequado para descrever a variacao observada dos valores de producao de cabeca de alface em relacao a doses. O rendimento maximo estimado pelo modelo de regressao para a massa fresca media de alface foi de 348 g planta-1 para a dose de 23 t ha-1 de cama de aviario. O plantio direto de alface sobre cobertura viva de grama batatais e amendoim forrageiro acarretou desempenho semelhante ao desta hortalica, em sistema de preparo convencional do solo, com nivel maximo de produtividade de 55,99 t ha-1 de massa fresca estimado pelo modelo de regressao.

Physiology of nitrogen fixation in Azospirillum lipoferum Br 17 (ATCC 29 709)

Changes of cellular activities during batch cultures with Azospirillum lipoferum strain Br 17 (ATCC 29 709) were observed within the growth cycle, at optimal pO2 (0.002–0.003 atm). The relative growth rate for cells growing with N2 as sole nitrogen source during log phase was μ=0.13 h-1 and the doubling time was 5.3 h. Nitrogenase activity was not accompanied by hydrogen evolution at any growth stage, and a very active uptake hydrogenase was demonstrated. The hydrogenase activity increased towards the end of the growth period when glucose became limiting and N2 fixation reached its maximal specific activity. Oxygen consumption and oxygen tolerance at the various growth stages, increased simultaneously with the uptake hydrogenase activity indicating a possible role of this enzyme in an oxygen protection mechanism of A. lipoferum nitrogenase. The efficiency of nitrogen fixation expressed as mg total nitrogen fixed in cells and supernatant per g glucose consumed, was 20 at the early log phase and increased to 48 at the late log phase. About 25% of the total fixed nitrogen was recovered in the culture supernatant.

Cyperus rotundus control by solarization

ABSTRACT Soil solarization by means of polyethylene cover sheets was tested for the control of Cyperus rotundus weed infestation. Following solarization, which lasted for a period of approximately three months, the field was cultivated with carrots and dwarf green beans. Solarization was shown to provide a highly significant reduction of the weed population and to increase carrot yield. As for green beans, soil treatment was less effective and yield was not affected. In the solarized plots no weeding was needed during the vegetable crops cycle whereas the untreated plots required hand weeding within the first month from sowing. Soil solarization significantly reduced ant and earthworm numbers but had no effect on millipede population. Soil microbial biomass carbon (SMBC) was affected by solarization. However, actinomycete and bacterial populations, including nitrogen- fixing bacteria, showed no obvious pattern related to soil solarization.

Feijão-vagem semeado sobre cobertura viva perene de gramínea e leguminosa e em solo mobilizado, com adubação orgânica

O objetivo deste trabalho foi avaliar o desempenho agronomico do feijao-vagem, cv. Alessa, cultivado sobre cobertura viva perene de grama-batatais (Paspalum notatum Flugge) e de amendoim forrageiro (Arachis pintoi Krapov & Gregory), e em solo convencionalmente preparado, como controle. Diferentes doses de cama de aviario (0, 7, 14 e 28 t ha-1) foram fornecidas, parceladamente, em um Planossolo, em Seropedica, RJ, de agosto a outubro de 2002. O delineamento adotado foi o de blocos ao acaso, dispostos em parcelas subdivididas, com quatro repeticoes, utilizando-se modelo quadratico para analise dos resultados. A produtividade de vagens foi semelhante nos tres sistemas de cultivo sem efeito competitivo das especies de cobertura viva, sobre as quais foi realizada a semeadura direta da cultura, com enxada. A produtividade maxima estimada pelo modelo de regressao foi 20,3 t ha-1 de vagens. Esse valor foi obtido com a dose de 26 t ha-1 de cama de aviario, aplicada de forma parcelada. A semeadura direta de feijao-vagem sobre cobertura viva perene de grama-batatais e de amendoim forrageiro e viavel, com resultados preliminares positivos.

Fertilizantes de leguminosas como fontes alternativas de nitrogênio para produção orgânica de alface

O objetivo deste trabalho foi avaliar o potencial de dois fertilizantes de leguminosas - produtos derivados do corte, desidratacao e moagem da biomassa aerea das leguminosas mucuna-cinza (Mucuna pruriens) e gliricidia (Gliricidia sepium) - como fontes alternativas de nitrogenio (N) para a producao orgânica de alface (Lactuca sativa cv. Vera), e a influencia dessas adubacoes sobre a vida util pos-colheita da hortalica, em condicoes de laboratorio. Esses fertilizantes foram empregados em cobertura e comparados com cama-de-aviario industrial, assegurando-se doses equivalentes de N total. O delineamento experimental foi o de blocos ao acaso, com cinco tratamentos e quatro repeticoes: T1: adubacao pre-plantio, com termofosfato silico-magnesiano + sulfato de potassio; T2: T1 + esterco bovino, em pre-plantio; T3: T2 + fertilizante de mucuna-cinza, em cobertura; T4: T2 + fertilizante de gliricidia, em cobertura; T5: T2 + cama-de-aviario em cobertura. Nao houve diferenca entre os fertilizantes de ambas as especies de leguminosas e a cama-de-aviario, quanto a produtividade, teor de N, padrao comercial e periodo de vida util pos-colheita das alfaces, o que indica potencial de uso desses fertilizantes como fontes de N para sistemas orgânicos de producao de hortalicas.

Response of soil mites to organic cultivation in an ultisol in southeast Brazil

Soil-dwelling mites of four plots under organic management were investigated in April and December 1998 and in December 1999. Their populations were compared with mite populations in a pasture and forest in the vicinity. It was observed that there was always an initial reduction in the populations of soil mites and in the activity of the epigeic forms whenever a plot was opened up and disturbed mechanically in preparation for cultivation, irrespective of previous organic inputs. With time, the densities and activities of mites recovered under organic management. The uropodine and oribatid mites in particular benefited more from organic management than gamasine and actinedid mites. Uropodine mites increased tremendously under banana where there was fresh cow dung manure. Oribatid mite species Nothrus seropedicalensis and Archegozetes magnus were dominant in organic plots where the soil was moist and temperatures were lower than the ambient. Protoribates rioensis was dominant in organic plots where the soil was drier and temperatures were higher than the ambient. Galumna was the most active oribatid taxon on the floor of all plots, with the highest activity recorded under maracuja and in pasture plots. The results suggest that while densities and activities of soil mites increased in the organic plots, the community structure and recruitment period of oribatid mites were altered. Oribatid mite diversity was higher in the organic plots than in the pasture but lower than in the forest, where Belba sp. and many Eremobelboid brachypiline genera were present, but absent in the organic plots and pasture.

Sucessão entre cultivos orgânicos de milho e couve consorciados com leguminosas em plantio direto

Organic crop succession of maize and collard greens intercropped with legumes in no-tillage system New farming practices have been developed to reduce the application of fertilizer and pesticides and minimize the aggression to the environment, producing healthy foods and environmentally correct. We evaluated the performance of the succession of collard greens (Brassica oleracea L. var. acephala) and corn (Zea mays L.) intercropped with green manure legumes under no-tillage organic system. The study was conducted in Seropedica, Rio de Janeiro State, during two years. We utilized dwarf velvet bean (Mucuna deeringiana) and showy crotalaria (Crotalaria spectabilis) as green manure intercropped with collard greens and in succession sunn hemp (Crotalaria juncea) and velvet bean (Mucuna pruriens) intercropped with corn. As a control, there was a single crop system of corn and collard greens. The experimental design was of randomized complete blocks, a factorial 3 (crop system) x 2 (doses of poultry bed manure), with four replications, in plots of 20 m 2 . For the collard greens we applied 0 and 5.4 t ha -1 of poultry bed manure (2.7 t ha -1