Ricardo Carmona

Problemática e manejo de bancos de sementes de invasoras em solos agrícolas

The problematic of weed seed banks in the soil is discussed in terms of its importance, the mechanisms that guarantee the maintenance of large seed numbers in the soil and the dynamics of weed seed banks. The management of weed seed banks in the soil is also discussed with emphasis in the practices of soil tillage and the application of germination stimulants.

Fitomassa e cobertura do solo de culturas de sucessão ao milho na Região do Cerrado

The objective of this study was to evaluate the biomass production and soil cover by different crops after maize cultivated in conventional tillage and no-tillage, in Cerrado conditions. The biomass of black oat, sunnhep, canavalia, pigeonpea, mucuna, sunflower and millet was obtained when they showed 50% of flowering. Soil coverage was evalluated at 30 and 60 days after sequential crops sowing, in August (during dry season), in October (at the beginning of the rainy season) and after 15 and 45 days of maize crop sowing. Mucuna showed the highest soil coverage rate during its growing. The biomass produced by sunflower had no efficiency for soil coverage. No-tillage showed the highest productions of biomass by sequential crops, compared to the conventional tillage system.

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.

Banco de sementes e estabelecimento de plantas daninhas em agroecossistemas

Em novembro/92 o banco de sementes no solo foi estimado, a 0-10 cm de profundidade, em alguns agroecossistemas: area de rotacao de culturas, varzea, pomar de citrus e pastagem de Brachiaria brizantha, no Distrito Federal, Brasil. Esta estimativa foi realizada atraves da observacao da emergencia de plântulas em amostras de solo incubadas, com e sem lavagem atraves de peneira e presenca ou ausencia de nitrato de potassio. A lavagem do solo para reducao de volume, seguida de utilizacao de nitrato de potassio, mostrou-se desvantajosa para a determinacao dos bancos de sementes viaveis detectadas nas amostras. A quantidade media de sementes por metro quadrado foi de 22313 na varzea, 6768 na area de rotacao, 3595 nas coroas do pomar e 529 na pastagem. Verificou-se que as plantas infestantes estabelecidas em maio/93 nos agroecossistemas, representavam, em relacao a quantidade inicial de sementes: 0,34% na pastagem, 0,71% na varzea, 1,48% nas coroas do pomar e 1,56% na area de rotacao de culturas. Estas plantas seriam aquelas que supostamente mais contribuiram para a manutencao dos bancos de sementes no solo. Houve uma correlacao direta do banco de sementes com o numero de especies e individuos presentes nos agroecossistemas. As especies predominantes nas areas anualmente perturbadas foram Ageratum conyzoides, Bidens pilosa, Cenchrus echinatus, Commelina benghalensis, Emilia sonchifolia, Euphorbia heterophylla e Richardia brasiliensis. Brachiaria spp predominou nas entrelinhas do pomar, enquanto na pastagem as poucas plantas daninhas presentes eram especies de cerrado. A similaridade entre agroecossistemas, com relacao as plantas daninhas foi maior entre as areas mais perturbadas, como areas de rotacao de culturas, varzea e coroas do pomar.The seed bank in the soil was estimated in November/92 at 0-10 cm depth in some agro-ecosystems: arable land, meadow land, citrus orchard and a Brachiaria brizantha pasture in Distrito Federal, Brazil. These estimates were carried out by the evaluation of seedling emergence in incubated soil samples, with and without pre-washing through sieve (0,297 mm mesh). The pre-washed samples were incubated with potassium nitrate, while water was added to the others. The pre-washing plus potassium nitrate reduced the amount of seedlings in all samples, and thus is not recommended. The average numbers of viable seeds per square meter in the non-washed samples were: 22313 in the marsh land, 6 768 in the arable land, 3 595 in the projection of the plants in the orchard and 529 in the pasture. The established plants in the field were evaluated once in May/93, on normal crop conditions. They represented, in relation to the initial seed bank: 0.34% in the pasture, 0,71% in the meadow land, 1,48% in the orchard and 1.56% in the arable land. These plants would contribute to the maintenance of the seed bank in the soil. There was a direct correlation between the plant population and the number of species with the size of seed bank. The species that predominated in the disturbed areas were: Ageratum conyzoides, Bidens pilosa, Cenchrus echinatus, Commelina benhhalensis, Emilia sonchifolia, Euphorbia heterophylla and Richardia brasiliensis. Brachiaria spp predominated between the plants in the orchard, while the few weeds that occurred in the pasture belonged to the natural cerrado vegetation of the region. The similarity of agro-ecosystems was higher in disturbed areas, such as arable land, meadow land and orchard.

Controle de Acacia farnesiana e de Mimosa pteridofita em pastagem

Control of Acacia farnesiana and of Mimosa pteridofita in pastures Abstract†n†An experiment was carried out to study the efficacy of herbicide treatments in controlling two serious pasture weeds: Acacia farnesiana and Mimosa pteridofita. The following herbicides were applied to the stump, after cutting: diesel oil, used engine lubricant oil, 2,4-D†+ picloram diluted in water or diesel oil and a control treatment without herbicide. All†herbicide treatments were tested on two sizes of the plants and two heights of cutting, except the lubricant†oil. The shrub control and sprouting vigor were evaluated in all treatments. The results showed that cutting of plants is effective only when it is carried out at the soil surface level and followed by a specific herbicide treatment, such as 2,4-D†+ picloram. Diesel†oil controlled 100% of the younger plants of both species, at lower costs. There is an antagonistic effect between diesel oil and 2,4-D†+ picloram to control both species. The lubricant oil did not show any herbicide effects on these species.

Germinação de sementes de cenoura osmoticamente condicionadas e peletizadas com diversos ingredientes

Germination of carrot seed primed and pelleted with several ingredients Carrot seeds are small and the distribution in the field by seeders is generally very difficult. Seed pelleting has been used to improve sowing and consequently the stand establishment. Pelleted seeds generally present lower germination rate than raw seeds from the same seed lot. Seed priming has been used to increase germination rate of several species. Various binder materials for seed pelleting were evaluated and the relation between the osmoconditioning and germination of pellet seeds verified, using ‘Alvorada’ carrot cultivar. The pellet was obtained through a mixture of equal parts of microcelulose and sand as filling materials; five binder materials were also evaluated: bentonite, methocel, opadry, rhoximat and arabic gum. Part of the pelleted seeds received an external coat treatment (iriodin). Raw seeds were included as control. In another study, seeds were primed in an aerated solution of polyethylene glycol, dried and then pelleted. Rhoximat and opadry showed better characteristics as binder materials presenting pellets with smooth surface, uniform and excellent external appearance. In general, seed pellets showed a slight decrease of the germination rate and total germination compared to raw seeds, with greather differences for pellets finished with iriodin. Priming enhanced the germination rate of pelleted carrot seeds.

Dormancy and storage potential of Melinis minutiflora seeds

The African grass species, Melinis minutiflora, which was an important forage species in the Brazilian Cerrado region for around two centuries, is nowadays considered an important weed in this region. The present study aimed to evaluate seed dormancy and viability during storage, aspects that could affect species dissemination. Seeds of the cultivars Roxo and Cabelo-de-Negro stored under laboratory conditions in Brasilia-DF, Brazil, were tested periodically, both at alternating temperatures of 20-30 oC (16/8 hours), with white fluorescent light during the highest temperature, plus potassium nitrate at 0.5%, and at 25 oC in darkness and in water. Recently-harvested seeds of both cultivars showed approximately 100% viability and a high primary dormancy level. Seed viability remained high for around three years (at least 90%), and even after eight years of storage under these conditions some seeds remained viable. At alternating temperatures, the average germination period is 4.3 days for the Roxo cultivar and 4.4 days for Cabelo-de-Negro. Seed dormancy was completely overcome after 3.8 years of storage. The high seed viability, dormancy and germination speed observed in this study help to explain the success of this species in colonizing new areas.

Luz e KNO3 na germinação de sementes de Ageratum conyzoides L. sob temperaturas constantes e alternadas

Ageratum conyzoides e uma planta daninha de origem tropical que apresenta presenca expressiva nos bancos de sementes em que ocorre. Considerando-se a importância de conhecer os fatores que afetam a germinacao de sementes no manejo das especies de plantas daninhas, avaliou-se o efeito de luz e KNO3 sob temperatura constante e alternada na germinacao de sementes de A. conyzoides. Quatro subamostras de 75 sementes para cada tratamento foram submetidas a combinacao fatorial de luz (escuro; 12 horas de luz) e KNO3 (0% de KNO3; 0,2% de KNO3) para os ensaios a 25°C constante e a 15oC/35oC por 12h/12h, em delineamento inteiramente casualizado. Efetuou-se a contagem diaria das ocorrencias germinativas durante 21 dias. Em temperatura constante, a presenca de luz aumentou a porcentagem e a velocidade de germinacao e o KNO3 reduziu a porcentagem e a velocidade de germinacao de sementes de A. conyzoides no escuro. Na temperatura constante houve ajuste da curva de germinacao acumulada ao modelo exponencial. Na temperatura alternada, o KNO3 na presenca de luz aumenta a porcentagem e a velocidade de germinacao de sementes de A. conyzoides. Em temperaturas alternadas, houve ajuste da curva de germinacao acumulada ao modelo logistico, demonstrando maior assincronia na germinacao das sementes no tempo do que em temperatura constante.

Influência da quantidade de pólen na produção e qualidade de sementes híbridas de abóbora

The low production of squash hybrid seeds obtained in our conditions is probably due to the inefficient production methods. The amount of pollen transferred naturally or artificially between the two parents may affect not only the hybrid seed production but also the seed quality of squash. In this study, flowers were manually pollinated using five amounts of pollen to pollinate one female flower: 1/4 of pollen from one flower; half of the amount of pollen from one flower; pollen of one flower; pollen of two flowers and pollen of four flowers. The randomized complete block design was adopted, with three replications and eighteen plants per plot. The increasing pollen amount affected significantly seed yield per fruit and seed yield per area, but did not influence significantly seed quality. A lower germination was observed in fruits originated from flowers pollinated with 1/4 of pollen of one flower.

Influência das variacões estacionais e profundidade de sementes no solo na dormência e germinação em Rumex crispus L.

Rumex crispus L. seeds were buried at 1 and 10 cm depth in the soil and retrieved at regular intervals during two years. Retrieved seeds were tested at 10o and 20o in darkness; at 5/25oC (16/8 hours) with 10 mM potassium nitrate and light; and at an alternating temperature regime corresponding to the minimum and maximum soil temperatures (MMTS) at a depth of 1 cm during the six days prior to each retrieval. MMTS treatments were carried out in darkness with either 1 mM potassium nitrate or a cocktail of dormancy relieving chemicals consisting of potassium nitrate, thiourea, ethephon, sodium azide and hydrogen peroxide. There was no appreciable loss of seed viability in the soil during the study period. The seeds showed dormancy cycles in the soil throughout the year, where low soil temperatures relieved primary dormancy and induced secondary dormancy, which in turn was relieved by high temperatures. There was a year-to-year reduction in seed dormancy. The environment at 10 cm favoured loss of dormancy, however the depletion due to in situ germination was faster at 1 cm. The chemical mixture was more effective when dormancy was minimal and the soil temperatures were more promotive, which coincided to the warm period of the year (from spring to autumn). These results are discussed in terms of the interpretation of the ecological behaviour of this species in the field and the adoption of practices of management of seed banks in the soil.