Marcos A.V. Ligo

Measurements of CO2 exchange over a woodland savanna (Cerrado Sensu stricto) in southeast Brasil

A tecnica de correlacao dos vortices turbulentos (eddy correlation) foi utilizada para se estimar a produtividade liquida do ecossistema (PLE) em uma area de Cerrado Sensu stricto, no sitio experimental da Gleba Pe de Gigante, no sudeste do Brasil. O conjunto de dados coletados incluiu tambem medidas de variaveis climatologicas e de respiracao do solo com câmaras estaticas, no periodo de 10 de Outubro de 1999 a 30 de Marco de 2002. A respiracao do solo media anual foi de 4.8 molCO2m-2s-1, com diferencas sazonais que variaram entre 2 a 8 molCO2 m-2s-1 durante a estacao seca (Abril a Agosto) e na estacao chuvosa, respectivamente, por um padrao de sensivel correlacao com a temperatura (Q10=4.9) e umidade do solo. Com base nos fluxos atmosfericos de CO2, a PLE mostrou uma variabilidade no ciclo diurno grandemente controlada pela radiacao solar, umidade e temperatura do ar. Na escala sazonal, a umidade do solo foi uma variavel de alta correlacao com a PLE, que aparentemente induziu a queda de folhedo, reducao da atividade fotossintetica e da respiracao do solo. O sinal da PLE foi negativo (sumidouro) na estacao chuvosa e no inicio da estacao seca, com taxas de -25 kgCha-1dia-1, e maximos de ate 40 kgCha-1dia-1. Na estacao seca o sinal foi positivo (emissao), o que foi revertido logo no inicio das chuvas. No fim da estacao seca, em dias de grande estresse hidrico, ainda observou-se a resposta da fotossintese na escala do ecossistema, mesmo tendo sido positiva a PLE. Paralelamente ao decorrer da estacao seca, a PLE progressivamente aumentou de 5 ate 50 kgCha-1dia-1. A soma annual da PLE mostrou-se aproximadamente balanceada, tendo sido no entanto, sob um vies de maior precisao, um pequeno mas significativo sumidouro de 0.1 0.3 tCha-1ano-1. Consideramos a hipotese de um pequeno sumidouro como possivelmente realista, dadas as restringentes correcoes impostas no calculo dos fluxos turbulentos, e algumas hipoteses favoraveis de sucessao de estagios do Cerrado, fertilizacao de CO2 atmosferico e variabilidade climatica.

Soil organisms in organic and conventional cropping systems

Despite the recent interest in organic agriculture, little research has been carried out in this area. Thus, the objective of this study was to compare, in a dystrophic Ultisol, the effects of organic and conventional agricultures on soil organism populations, for the tomato (Lycopersicum esculentum) and corn (Zea mays) crops. In general, it was found that fungus, bacterium and actinomycet populations counted by the number of colonies in the media, were similar for the two cropping systems. CO2 evolution during the cropping season was higher, up to the double for the organic agriculture system as compared to the conventional. The number of earthworms was about ten times higher in the organic system. There was no difference in the decomposition rate of organic matter of the two systems. In general, the number of microartropods was always higher in the organic plots in relation to the conventional ones, reflectining on the Shannon index diversity. The higher insect population belonged to the Collembola order, and in the case of mites, to the superfamily Oribatuloidea. Individuals of the groups Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura and Symphyla were occasionally collected in similar number in both cropping systems.

Water use in a sugarcane plantation

The evapotranspiration (E) from a sugarcane plantation in the southeast Brazil was measured by the eddy‐covariance method during two consecutive cycles. These represented the second (393 days) and third year (374 days) re‐growth (ratoon). The total E in the first cycle was 829 mm, accounting for 69% of rainfall, whereas in the second cycle, it was 690 mm, despite the total rainfall (1353 mm) being 13% greater. The ratio of E to available energy, the evaporative fraction, exhibited a smaller variation between the first and second cycles: 0.58 and 0.51, respectively. The estimated interception losses were 88 and 90 mm, respectively, accounting for approximately 7% of the total rainfall. The sugarcane yield in the second cycle (61.5 ± 4.0 t ha−1) was 26% lower than the first cycle, as well as lower than the regional average for the third ratoon (76 t ha−1). The below average yield was associated with less available soil water at the beginning of the cycle, with the amount of rainfall recorded during the first 120 days of re‐growth in the second cycle being 16% of that recorded in the first (203 mm).

Organic matter decomposition and microarthropod community structure in corn fields under low input and intensive management in Guaíra (SP)

The rate of organic matter decomposition and the structure of the communities of microarthropods were compared between two corn fields receiving contrasting agricultural management practices (low input and intensive farming). The rate of decomposition tended to be higher in the intensively managed field in the beginning of the growing season, but decreased to a level significantly lower than the observed in the low input field by the end of the growing season. This suggested that the biological community associated with the decomposition process could be negatively influenced in the intensively managed field. Analyses of the structure of microarthropod communities indicated differences between the two areas. The microarthropod populations present in the intensively managed field suffered abrupt decrease in numbers as the season progressed.

VARIABILIDADE DAS MEDIDAS DE FLUXOS DE CO2 DO SOLO OBTIDAS PELO MÉTODO DA CORRELAÇÃO DE VÓRTICES

Variabilidade das medidas de fluxos de CO2 do solo obtidaspelo metodo da correlacao de vortices

AVALIAÇÃO DO MÉTODO DE MULTIPLE IMPUTATION NO PREENCHIMENTO DE FALHAS DE FLUXOS DE ENERGIA SOBRE UMA ÁREA DE CANA-DE-AÇÚCAR

Avaliacao do metodo de Multiple Imputation nopreenchimento de falhas de fluxos de energia sobre umaarea de cana-de-acucar