ABSTRACT Due to the large extent of degraded areas in the Amazon, the use of conservation systems is very important to contain the advance of the agricultural frontier, and may favor the availability of nutrients such as phosphorus (P). This study evaluated effect of tillage systems on and cover plants distribution of organic P fractions (Po) in oxisol under soybean and grasses in crop successions. The experimental design was completely randomized with four replicates and five treatments: (i) conventional tillage (CT) with annual soil tillage; (ii) no-till (NT) in succession with Urochloa ruziziensis (NT1); (iii) NT in succession with U. brizantha (NT2); (iv) NT in succession with Panicum maximum (NT3); and (v) a control consisting of a fragment of native vegetation (NV). The Po fractions were quantified at depths of 0-5, 5-10, and 10-20 cm, before and after soybean cultivation and the P fractions were analyzed. The samples at a depth 0-5 and 5-10 cm had increased levels of biomass P in the NT1 and NT2. In addition, at depths of 0-5 and 5-10 cm, the treatments in no-tillage systems accumulated the most of the Po labile fractions. These results showed that conservation systems tend to accumulate most of the P fractions in soil through decomposition of organic residues. Thus, no-tillage system was shown to be important for Po supply, where the use of U. brizantha ‘Piatã’ (NT2) favored higher levels of organic P in labile and moderately labile fractions in soil, which was considered the best alternative for Po supply among the species tested.

Com este trabalho, visou-se a identificar, por meio de bioensaio, o efeito dos extratos de caruru (Amaranthus retroflexus L.), capim-marmelada (Brachiaria plantaginea (Link.) Hitchc.), mentrasto (Ageratum conyzoides L.) e de três cultivares de milho (AG1051, C333 e C435) sobre a germinação e crescimento de alface (Lactuca sativa L. cv. Marisa AG216). Os extratos metanólicos foram concentrados sob vácuo e solubilizados em surfactante Tween 80 a 1% (v/v) em água. A seguir, aplicaram-se as soluções obtidas em papel de filtro sobre placa de Petri, onde foi semeada alface. Utilizaram-se água destilada como testemunha e surfactante Tween 80 a 1% como tratamento branco. O extrato de mentrasto, o de caruru e da cultivar de milho AG1051 promoveram redução no índice de velocidade de germinação em relação à testemunha com água destilada. O percentual de germinação foi afetado apenas pelo extrato de mentrasto (82,5% de redução). Todos os extratos e o surfactante Tween 80 provocaram inibição do crescimento de radículas de plântulas de alface, com redução de comprimento de raiz entre 9,53 e 14,83 mm, e de hipocótilo, entre 21,6 a 30,95 mm.

This work aimed at identifying, through bioassay, the effect of organic extracts of pigweed (Amaranthus retroflexus L.), signal grass (Brachiaria plantaginea (Link.) Hitchc.), ageratum (Ageratum conyzoides L.) and three corn cultivars (AG1051, C333 and C435) on lettuce (Lactuca sativa L. cv. Marisa AG216) germination and seedling. Thus, the methanolic extracts of their straws were concentrated under vacuum and dissolved in 1% (v/v) aqueous surfactant Tween 80. Then, the resulting solutions were applied to filter papers contained in Petri dishes, where lettuce was sowed. Distilled water and 1% Tween 80 were used as controls treatment. The corn cultivar extracts AG1051, pigweed and ageratum promoted reduction of the germination index in relation to the control with distilled water. The germination percentage was affected by ageratum extract (82.5% less than the control). All extracts and the surfactant Tween 80 promoted inhibition lettuce seedling growth with reduction of root length between 9.53 and 14.83 mm and hypocotyls between 21.64 to 30.95 mm.

Com esta pesquisa visou-se a testar o efeito de restos culturais da parte aérea de três cultivares de milho sobre o crescimento de plântulas de cafeeiro, cv. Rubi, em condições de casa-de-vegetação, na Universidade Federal de Lavras, Lavras - Minas Gerais. Os tratamentos foram constituídos de 0, 2, 4 e 8 t ha-1 de palhada de milho (cv. AG1051, C333 e C435), incorporada ou em cobertura, em vasos de 8 L de capacidade preenchidos com solo. Avaliaram-se a área foliar, altura e diâmetro de caule das plantas de café aos 60, 120 e 180 dias após o plantio (DAP), o teor de clorofila aos 170 DAP e a biomassa seca de raízes aos 180 DAP. A palhada de milho incorporada ao solo causou redução na área foliar, na altura e no diâmetro de caule até os 60 DAP. A palhada da cultivar AG1051 ocasionou maiores efeitos negativos sobre o crescimento das plantas de cafeeiro, quando incorporada. O uso de palhada de milho em cobertura promoveu aumento de todas as características estudadas, com exceção do teor de clorofila. A palhada da cultivar C435 em cobertura do solo foi a que mais estimulou o crescimento das plantas.

The objective of this research was to verify the effect of three corn cultivars residues, on coffee plants, cv. Rubi, under greenhouse conditions, at Lavras Agricultural University, Lavras, Minas Gerais State, Brazil. The treatments were zero, 2, 4 and 8 t ha-1 of corn residues (cv. AG1051, C333 and C435) either incorporated or on the top of 8 L pots filled with soil. Leaf area, plant height and stem diameter of coffee plants were taken at 60, 120 and 180 days after planting (DAP); at 170 DAP chlorophyll content was determined and at 180 DAP roots were harvested. Incorporated corn residues promoted reduction on leaf area, plant height and stem diameter at 60 DAP. The AG1051 cultivar corn residues showed strongest inhibitory effects on coffee plants when incorporated in soil, while C435 stimulated coffee growth when applied on top of the soil, except for chlorophyll content which was not altered when compared with no corn residues treatment.