No abstract

Intercropping of maize (Zea mays L.) with perennial forage, such as palisade grass [Brachiaria brizantha (Hochst. ex A. Rich) Stapf], provides large amounts of biomass that can be used as straw for no-tillage systems or as pasture for animal grazing. In addition, the use of narrow row spacing may increase maize grain yield. However, it is important to evaluate intercrops at different row spacing to avoid reductions in both maize and forage biomass production. The objectives of this field experiment during two growing seasons in Brazil were as follows: (1) to evaluate the influence of intercropping and row spacing on maize yield, leaf nutrient concentration, and plant population and development; and (2) to assess the influence of row spacing on palisade grass herbage mass and leaf nutrient concentration. The experimental design was a randomised complete block design in a 2 × 2 factorial scheme, with eight replications. The treatments comprised two row spacing distances (0.45 and 0.90 m) and two crop management types (maize monoculture and intercropped with palisade grass). The nutrient concentrations in the leaves of the maize plants were in the ideal range for this crop under all conditions studied. Plant height, height of first ear, and number of grains per ear were higher with the narrow row spacing. Maize grain yield was similar in both crop management types (10 301 and 9745 kg ha–1 for monoculture maize and intercropped, respectively). However, maize grain yield at the narrow row spacing was higher than that obtained with the wide row spacing (9948 v. 8905 kg ha–1). In contrast, row spacing did not affect the nutrient level or quality (crude protein concentration) of palisade grass. The amount of dry matter (DM) from palisade grass was lower at maize harvesting (4.7 Mg ha–1) and 90 days after harvesting (6.9 Mg ha–1) under narrow spacing. However, the amount of DM was similar at both row spacings at 120 days after maize harvesting (9.2 Mg ha–1). When there is no problem with water and nutrient availability, the use of maize and palisade grass intercropping under both row spacing conditions (0.45 and 0.90 m) provides an option for the production of forage DM without reducing the maize grain yield.

Agricultural intensification offers potential to grow more food while reducing the conversion of native ecosystems to croplands. However, intensification also risks environmental degradation through emissions of the greenhouse gas nitrous oxide (N2O) and nitrate leaching to ground and surface waters. Intensively-managed croplands and nitrogen (N) fertilizer use are expanding rapidly in tropical regions. We quantified fertilizer responses of maize yield, N2O emissions, and N leaching in an Amazon soybean-maize double-cropping system on deep, highly-weathered soils in Mato Grosso, Brazil. Application of N fertilizer above 80 kg N ha−1 yr−1 increased maize yield and N2O emissions only slightly. Unlike experiences in temperate regions, leached nitrate accumulated in deep soils with increased fertilizer and conversion to cropping at N fertilization rates >80 kg N ha−1, which exceeded maize demand. This raises new questions about the capacity of tropical agricultural soils to store nitrogen, which may determine when and how much nitrogen impacts surface waters.

Intercropping sorghum [Sorghum bicolor (L.) Moench] with tropical perennial grasses and using the appropriate rate of sidedress N application can maximize grain yield (GY) and revenue and can improve land-use effi ciency (LUE). Th e eff ects of monocropped sorghum (MS) or sorghum intercropped with palisadegrass (Urochloa brizantha cv. Marandu; SPG) or guineagrass (Panicum maximum cv. Mombaça; SGG) and sidedress N application rates of 0, 50, 100, and 200 kg ha -1 on leaf nutrient concentration, sorghum GY, revenue, and LUE were investigated during three growing seasons at Botucatu, SP, Brazil, on a clay, kaolinitic, thermic Typic Haplorthox. Th e SGG treatment had lower leaf N, P, and K concentrations and lower 1000-grain weight, shoot dry matter, and GY than MS and SPG at all sidedress N rates; MS and SPG at 200 kg ha -1 of sidedress N resulted in greater sorghum GYs (3.80 and 3.81 Mg ha -1 , respectively). Th e forage dry matter production (FDMP) and crude protein of tropical perennial grasses were higher as a function of the sidedress N rate. Th e SGG treatment resulted in negative net profi ts for all sidedress N rates. Th e MS and SPG treatments (independent of sidedress N rates) resulted in similar net profi ts (approximately US$85 and $60 ha -1 , respectively). Th e SPG treatment using 200 kg ha -1 of sidedress N resulted in a higher land equivalent ratio and relative N yield (1.27 and 123%, respectively) than SGG (0.96 and 107%, respectively). Th e SPG treatment with 200 kg ha -1 of sidedress N is the best option for increasing sorghum GY, revenue, and FDMP from autumn to part of the spring and for improving LUE.

PALAVRAS CHAVES ADICIONAISIntegração agricultura-pecuária. Milho. Plantio direto. Forrageiras. ADDITIONAL KEYWORDSAgriculture-pasture integration. No tillage systems. Forage. RESUMOEm regiões caracterizadas com temperaturas altas e ocorrência de chuvas em grande intensidade no verão, porém com inverno seco, as maiores limitações para a sustentabilidade do plantio direto são a baixa produção de palha no período de outono-primavera, aliada a rápida decomposição durante a estação das chuvas. Para tentar solucionar o problema, o cultivo consorciado de culturas produtoras de grãos com espécies forrageiras tem apresentado resultados promissores, dando sustentabilidade ao plantio direto, podendo fornecer forragem no período de maior escassez nas regiões caracterizadas com inverno seco. Contudo, por ser uma tecnologia recente, há necessidade de estudos nas várias áreas abrangidas por esse sistema de produção. Em função do exposto, o projeto de pesquisa teve o seguinte objetivo: 1) avaliar a produção da cultura de milho em diferentes épocas de consorciação com Brachiaria brizantha e Panicum maximum em plantio direto, e 2) o desempenho das forrageiras consorciadas em diferentes épocas e a resposta à adubação nitrogenada aplicada após a colheita do milho, quanto à produtividade de massa e qualidade bromatológica. O experimento foi instalado na Fazenda Experimental Lageado, da Faculdade de Ciências Agronômicas -Campus de Botucatu, em Nitossolo Vermelho Estruturado. O delineamento experimental foi o de blocos casualizados, com quatro repetições. Os tratamentos foram compostos por quatro sistemas de cultivo do milho: 1) cultivo do milho solteiro; 2) cultivo do milho com Brachiaria brizantha cv. Marandu, consorciada na semeadura; 3) cultivo do milho com Brachiaria brizantha cv. Marandu consorciada na adubação de cobertura; 4) cultivo do milho com Panicum maximum cv. Mombaça consorciado na semeadura e 5) cultivo do milho com Panicum maximum cv. Mombaça consorciado na adubação de cobertura. Após a colheita do milho, foi aplicado nitrato de amônio em cobertura nas quantidades equivalentes em nitrogênio (N) nas doses de 0, 30, 60 e 120 kg ha -1 , determinando a produtividade de massa das forrageiras e a qualidade bromatológica. O cultivo simultâneo de milho com P. maximum cv. Mombaça na semeadura compromete a produtividade de grãos. Quando semeada em consórcio, a B. brizantha apresenta redução no teor de fibra e maior teor de NDT com o decorrer do período de outono-inverno. Tendo em vista os benefícios do cultivo consorciado visando à utilização em sistemas de produção