Resumo -A palhada das plantas de cobertura, mantida sobre o solo no plantio direto, representa uma reserva de nutrientes para cultivos subseqüentes. O objetivo deste trabalho foi avaliar a decomposição e a liberação de macronutrientes de resíduos de nabo forrageiro. O experimento foi realizado no campo, durante o ano de 1998, no Município de Marechal Cândido Rondon, PR. O nabo forrageiro foi dessecado e manejado com rolo-faca 30 dias após a emergência. Avaliaram-se a persistência de palhada e a liberação de nutrientes dos resíduos aos 0, 13, 35 e 53 dias após o manejo. O delineamento experimental foi de blocos casualizados, com quatro repetições. O nabo forrageiro produziu, até o estádio de pré-florescimento, elevada quantidade de massa seca da parte aérea em cultivo de inverno (2.938 kg ha -1 ), acumulando 57,2, 15,3, 85,7, 37,4, 12,5 e 14,0 kg ha -1 , respectivamente, de N, P, K, Ca, Mg e S. O manejo do nabo forrageiro no estádio de pré-florescimento apresenta rápida degradação da palhada, acarretando liberação de quantidades significativas de macronutrientes. Os nutrientes disponibilizados em maior quantidade e velocidade para a cultura subseqüente, são o K e o N. A maior velocidade de liberação de macronutrientes pelo nabo forrageiro ocorre no período compreendido entre 10 e 20 dias após o manejo da fitomassa.Termos para indexação: Raphanus sativus, resíduo vegetal, degradação de fitomassa, reciclagem de nutrientes, taxa de decomposição. Persistence and nutrients release of forage turnip straw utilized as mulching in no-tillage crop systemAbstract -Straw of covering plants kept on soil surface in no-tillage system is an important source of nutrients for subsequent tillage. The objective of this work was to evaluate decomposition and macronutrients release from forage turnip residues. The experiment was set under field conditions during 1998 in Marechal Cândido Rondon, PR, Brazil. Forage turnip plants were desiccated and lodged 30 days after emergence. Straw persistence and nutrient release were evaluated at 0, 13, 35 and 53 days after management. The experimental design was a randomized block with four replications. Until pre-flowering stage, the forage turnip showed a great dry matter yield (2,938 kg ha -1 ) during winter growing and 57.2, 15.3, 85.7, 37.4, 12.5 and 14.0 kg ha -1 of N, P, K, Ca, Mg and S were respectively accumulated. Forage turnip management at pre-flowering stage cause a quick straw degradation and macronutrients release. Potassium and nitrogen were released in the highest amounts and in the shortest time to the subsequent tillage. Quickest liberation of nutrients occurred between 10 to 20 days after plant management.

Agriculture and livestock integration is a sustainable practice that improves both crop yield and pasture recuperation/formation. However, to achieve success it is important to identify crop cultivars more adapted to intercropping with grasses. Th erefore, the objective was to evaluate nutrient concentration and grain yield of soybean [Glycine max (L.) Merr.] cultivars with diff erent life cycles as aff ected by palisadegrass [Brachiaria brizantha (Hochst. ex A. Rich) Stapf] intercropped in the same furrow at diff erent depths, in a no-till system, as well as dry matter production and protein concentration of palisadegrass pasture. Experiments were performed during two growing seasons, on a Typic Haplorthox, at Botucatu, São Paulo State, Brazil. Th e experimental design was a randomized block, arranged in a 2 × 4 factorial scheme, with six replications. Treatments consisted of two cropping systems (sole cropped soybean; soybean and palisadegrass intercropped) and four soybean cultivars (super-early cycle [Monsoy 6101], early cycle [Embrapa 48], normal cycle [BRS 133], and late cycle [Emgopa 313]). Life cycle duration of the soybean had a marked eff ect, and only early cycle soybean were successful intercrops. Intercropping palisadegrass with super-early or early soybean cultivars were viable options to crop-livestock integration, because they did not aff ect both soybean or palisadegrass yield. In addition, with these cultivars, it was possible to cultivate grain and then aft erward more time for cattle (Bos taurus and Bos indicus) grazing in the same area, providing greater revenue compared to sole soybean cropped or in the intercropping with longer cycle cultivars.

Silicon has beneficial effects on many crops, mainly under biotic and abiotic stresses. Silicon can affect biochemical, physiological, and photosynthetic processes and, consequently, alleviates drought stress. However, the effects of Si on potato (Solanum tuberosum L.) plants under drought stress are still unknown. The objective of this study was to evaluate the effect of Si supply on some biochemical characteristics and yield of potato tubers, either exposed or not exposed to drought stress. The experiment was conducted in pots containing 50 dm3 of a Typic Acrortox soil (33% clay, 4% silt, and 63% sand). The treatments consisted of the absence or presence of Si application (0 and 284.4 mg dm−3), through soil amelioration with dolomitic lime and Ca and Mg silicate, and in the absence or presence of water deficit (−0.020 MPa and −0.050 MPa soil water potential, respectively), with eight replications. Silicon application and water deficit resulted in the greatest Si concentration in potato leaves. Proline concentrations increased under lower water availability and higher Si availability in the soil, which indicates that Si may be associated with plant osmotic adjustment. Water deficit and Si application decreased total sugars and soluble proteins concentrations in the leaves. Silicon application reduced stalk lodging and increased mean tuber weight and, consequently, tuber yield, especially in the absence of water stress.

Intercropping corn (Zea mays L.) with forages, such as palisadegrass {Urochloa brizantha (Hochst. ex A. Rich.) R. D. Webster [syn. Brachiaria brizantha (Hochst. ex A. Rich.) Stapf]} or guineagrass [Megathyrsus maximus (Jacq.) B. K. Simon & S. W. L. Jacobs (syn. Panicum maximum Jacq.)], provides large amounts of biomass for use as straw in no‐tillage systems or as pasture. However, it is important to evaluate what time these forages have to be sown into corn systems to avoid reductions in both corn and forage production. This study, conducted for three growing seasons at Botucatu, Brazil, evaluated nutrient concentration and yield of corn as affected by time of forage intercropped as well as forage's dry matter production. Our data showed that intercropping systems did not reduce leaf nutrient concentrations and grain yield of corn in relation to sole corn. The simultaneous intercropping of corn and guineagrass resulted in the lowest plant population (51,200 plant ha−1), number of ears per plant (1.0), and, consequently, the lowest corn grain yield (9801 kg ha−1). Guineagrass seeded at the time of corn fertilizer topdressing resulted in the highest plant population (59,400 plants ha−1), number of ears per plant (1.2), and corn grain yield (12,077 kg ha−1). Forage production was highest when intercrop was done simultaneously. Palisadegrass could be intercropped with corn both simultaneously or at topdressing fertilization stage. In contrast, it is recommended that guineagrass should only be intercropped with corn at topdressing fertilization.

Resumo -O objetivo deste trabalho foi avaliar a influência, sobre a produtividade de grãos, da modalidade de consorciação da Brachiaria brizantha cultivar Marandu com a cultura do milho, em dois espaçamentos de semeadura, em sistema plantio direto. O experimento foi instalado em campo, em e 2003, Botucatu, SP. O delineamento experimental foi o de blocos ao acaso, em esquema fatorial simples 2x4, com quatro repetições. Os tratamentos foram dois espaçamentos entre linhas de milho (0,45 e 0,90 m) e quatro modalidades de cultivo: milho solteiro; milho com braquiária na linha de semeadura; milho com braquiária na entrelinha; e milho com braquiária simultaneamente na linha e na entrelinha. A modalidade de consórcio e o espaçamento utilizado não comprometem a absorção de nitrogênio, nem pelo milho nem pela forrageira. A produtividade de grãos de milho, no espaçamento de 0,45 m, é menor com o consórcio da braquiária na linha e entrelinha simultaneamente. Conforme o ano agrícola, a produtividade de grãos é maior no espaçamento reduzido, quando consorciado com braquiária, independentemente da modalidade.Termos para indexação: Zea mays, sistema de cultivo, integração lavoura-pecuária, consórcio. Corn yield, spacing and intercropping modalities with Brachiaria brizantha in no-tillage systemAbstract -The objective of this research was to evaluate the effects on corn yield of different modes of corn intercropping with Brachiaria brizantha cv. Marandu. The experiment was carried out in field conditions, in , in Botucatu, SP, Brazil. The experimental design was the randomized complete block, as a factorial 2x4, with four replications. The treatments were two row spacings of corn (0.45 and 0.90 m) and four intercropping modalities: single corn; corn intercropped with B. brizantha in the row of sowing; corn intercropped with B. brizantha in space between two rows; and corn intercropped simultaneously with B. brizantha in the row and in the inter-row. The consortium modalities and the spacing used did not damage nitrogen absorption, neither for the corn nor the forage. Corn grains productivity in 0.45 m row spacing was lower with the row and inter-row Brachiaria consortium. Depending on agricultural year, grain yield is greater in the reduced row spacing, when intercropping with Brachiaria, independently of the modality.

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