RESUMO -Objetivou-se avaliar o comportamento de espécies forrageiras (Brachiaria decumbens cv. Basilisk, Brachiaria brizantha cv. Marandu, Panicum maximum cvs. Tanzânia, Aruana e Mombaça, Hemarthria altissima cv.Florida; Paspalum notatum cv. Pensacola, Axonopus catharinensis, Cynodon sp. híbrido Tifton-85; Arachis pintoi cvs.Alqueire e Amarillo) submetidas a diferentes níveis de luminosidade produzidos por árvores de Pinus taeda (céu aberto; 9 m entre linhas e 3 m entre árvores; e 15 m entre linhas e 3 m entre árvores). Avaliaram-se a produção de MS, a relação lâmina foliar:colmo (L:C), o nível de florescimento das plantas, os teores de PB e FDN e as variáveis meteorológicas e do solo, na projeção da copa e no meio da entrelinha de árvores, de cada parcela. A produção de MS foi afetada negativamente pelo sombreamento, por outro lado, o teor de PB foi maior nas parcelas sombreadas em relação ao pleno sol. Além da menor radiação, a velocidade do vento e a temperatura do solo nas parcelas sombreadas foram menores naquelas a sol pleno. O teor de FDN não diferiu significativamente entre os níveis de luminosidade, embora a relação L:C tenha sido maior na entrelinha do 9 × 3 em relação àquela a céu aberto. As espécies forrageiras mais produtivas e com maior potencial para utilização em ambiente Key Words: forage production, shading, silvipastoral system IntroduçãoOs sistemas silvipastoris têm sido amplamente estudados e aplicados na agropecuária tropical e subtropical visando otimizar a utilização das áreas. Há possibilidade de adaptação de várias espécies forrageiras ao cultivo em consórcio com espécies arbóreas e diferenças no comportamento das pastagens, especialmente em virtude das condições microclimáticas e da competição entre os componentes vegetais pelos recursos naturais disponíveis.

The spatial and temporal variability of crop parameters are fundamental in precision agriculture. Remote sensing of crop canopy can provide important indications on the growth variability and help understand the complex factors influencing crop yield. Plant biomass is considered an important parameter for crop management and yield estimation, especially for grassland and cover crops. A recent approach introduced to model crop biomass consists in the use of RGB (red, green, blue) stereo images acquired from unmanned aerial vehicles (UAV) coupled with photogrammetric softwares to predict biomass through plant height (PHT) information. In this study, we generated prediction models for fresh (FBM) and dry biomass (DBM) of black oat crop based on multi-temporal UAV RGB imaging. Flight missions were carried during the growing season to obtain crop surface models (CSMs), with an additional flight before sowing to generate a digital terrain model (DTM). During each mission, 30 plots with a size of 0.25 m² were distributed across the field to carry ground measurements of PHT and biomass. Furthermore, estimation models were established based on PHT derived from CSMs and field measurements, which were later used to build prediction maps of FBM and DBM. The study demonstrates that UAV RGB imaging can precisely estimate canopy height (R2 = 0.68–0.92, RMSE = 0.019–0.037 m) during the growing period. FBM and DBM models using PHT derived from UAV imaging yielded R2 values between 0.69 and 0.94 when analyzing each mission individually, with best results during the flowering stage (R2 = 0.92–0.94). Robust models using datasets from different growth stages were built and tested using cross-validation, resulting in R2 values of 0.52 for FBM and 0.84 for DBM. Prediction maps of FBM and DBM yield were obtained using calibrated models applied to CSMs, resulting in a feasible way to illustrate the spatial and temporal variability of biomass. Altogether the results of the study demonstrate that UAV RGB imaging can be a useful tool to predict and explore the spatial and temporal variability of black oat biomass, with potential use in precision farming.

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Year-round PoultrY litter decomPosition and n, P, K and ca release summarY Poultry litter is an important nutrient source in agriculture, although little information is available regarding its decomposition rate and nutrient release. to evaluate these processes, poultry litter (Pl) was applied to the soil to supply 100, 200 and 300 kg ha -1 n contained in 4,953, 9,907 and 14,860 kg ha -1 Pl, respectively. the litter bag technique was used to monitor the process of decomposition and nutrient release from the litter. these bags were left on the soil surface and collected periodically (after 15, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, and 365 days). the dry matter (dm) loss was highest (35 %) after the first 30 days of field incubation. the highest nutrient release occurred in the first 60 days on the field, when 40, 34, 91, and 39 %, respectively, of n, P, K, and ca of the initial Pl dry matter (4,860 kg ha -1 ) was already released to the soil. in absolute terms, these percentages represent 40, 23, 134, and 69 kg ha -1 of n, P, K, and ca and these values doubled and tripled as the Pl fertilization rates increased to 9,907 and 14,860 kg ha -1 , respectively. after one year of field incubation, the residual contents in the litter were 27, 15, 18 and 30 % of the initial dm , and n, P and ca, respectively. the release rate of K was the fastest and 91 % of the K had been released from the Pl after 30 days of field incubation. index terms: litter bag, filed incubation, organic fertilizer, residual contents.

Plants have developed different mechanisms to absorb and solubilize phosphorus (P) in the soil, especially in environments with low P availability. This study evaluated the effects of different winter cover crops on soil P availability in a clayey subtropical (Hapludox) soil receiving soluble P fertilizer and a rock phosphate applied to the summer crop, under no-tillage. The experiment was carried out over 3 yrs (2009)(2010)(2011) with five different cover crop species: common vetch, fodder radish, ryegrass, black oat, white clover and fallow as control. The soil was sampled after the third year of cover crop cultivation and analysed for inorganic and organic P forms according to the well-established Hedley fractionation procedure. Phosphate fertilizers promoted accumulation of both labile and nonlabile P pools in soil in the near surface layer, especially under rock phosphate. Fertilizer applications were not able to change P fractions in deeper layers, emphasizing that the Brazilian clayey soils are a sink of P from fertilizer and its mobility is almost nil. Although the cover crops recycled a great amount of P in tissue, in a short-term evaluation (3 yrs) they only changed the content of moderately labile P in soil, indicating that long-term studies are needed for more conclusive results.

Core Ideas Phosphorus recycling by cover crops in a typical Brazilian cropping system. Maize response to phosphate sources under no‐till management. Residual effects of phosphate sources in tropical weathered soils. Rock phosphate was more effective than soluble phosphate in supplying P for maize over time. This research evaluated the potential benefits of winter cover crops on the utilization and cycling of P in Brazilian tropical cropping systems. The effect of P fertilizer [none, rock phosphate (RP), and soluble phosphate (single superphosphate, SSP)] in combination with cover crop residues (common vetch [Vicia sativa L.], white lupin [Lupinus albus L.], forage radish [Raphanus sativus L.], ryegrass [Lolium multiflorum Lam], black oat [Avena strigosa Schreb.], red clover [Trifolium pratense L.], and fallow) were evaluated on maize (Zea mays L.) yield and P use efficiency over three maize cropping seasons under no‐tillage, from 2009 to 2012. Cover crop yields and P uptake were higher under phosphate fertilizers than nil‐P across all seasons evaluated. The highest amounts of P recycled in cover crops over the period were under white lupin, followed by radish and ryegrass, but without any significant cover crop effect on maize yield. The largest response and greatest P use efficiency (30 kg grain per kg P applied) was obtained in the third year of evaluation, when maize yield was restricted by low rainfall. In this year, RP promoted greater maize yield than SSP and the nil‐P. Soil available P at the end of the experiment was higher under RP than SSP. It is concluded that RP solubility is higher than currently predicted (9% P2O5 in citric acid). Cover crops were not able to affect maize yield after 3 yr of leaving the residues on the surface, however they can reduce the soil loss by erosion and runoff.

The effect of nitrogen (N) fertilization on the dry-matter (DM) yield and nutritional value of sorghum (Sorghum sp., cv. Jumbo) and black oat (Avena strigosa cv., IPR 61) was investigated in the context of forage and livestock production in southern Brazil. Sorghum was cultivated with 0, 37Á5, 75, 150, 225, 300 and 375 kg N ha À1 during the summer crop seasons of 2010/11 and 2011/12. Black oat received 0, 40, 80, 120, 160, 200 and 240 kg N ha À1 in the winter of 2011. According to the adjusted polynomial regression, sorghum DM yield increased in response to N up to 288 (12Á9 t ha À1 ) and 264 kg ha À1 (5Á6 t ha À1 ) in 2010/11 and 2011/12 respectively. Crude protein (CP) content of sorghum was highest at 349 and 328 kg N ha À1 , but in vitro drymatter digestibility (IVDMD) was highest at 212-207 kg N ha À1 in 2010/11 and 2011/12 respectively. Sorghum neutral detergent fibre (NDF) and acid detergent fibre (ADF) were not affected by N fertilization. In black oat, the maximum DM yield (6Á0 t ha À1 ) was obtained with 187 kg N ha À1 ; the IVDMD, NDF and ADF were not affected by N fertilization, but the CP content increased up to 220 kg N ha À1 . It is concluded that these forage species can improve the year-to-year amount and quality of forage produced but high rates of N fertilizer are required to achieve high yields. Fertilizer N rates of 210-280 kg N ha À1 in sorghum and 180 kg N ha À1 in black oat in the crop rotation provide the greatest responses in DM yield consistent with good nutritional quality for livestock production.

RESUMO -Objetivou-se determinar os possíveis efeitos da restrição de luminosidade, obtida com distintas densidades de árvores de Pinnus taeda, sobre a produção e qualidade de: aveia-preta (Avena strigosa Schreb) cv. Comum, aveia-branca (Avena sativa L.) cv. Fapa 2, azevém (Lolium multiflorum L.) cv. Comum, trigo (Triticum aestivum L.) duplo propósito cv.BRS Tarumã e ervilhaca peluda (Vicia villosa L.). Avaliaram-se três níveis de luminosidade: a sol aberto (sem presença de árvores de Pinnus taeda), 30% de restrição de radiação (usando espaçamento entre árvores de 15 × 3 m, com 222 árvores/ha) e 60% de restrição de radiação (usando espaçamento de 9 × 3 m, com 370 árvores/ha). Foram realizadas avaliações da produção de forragem, da composição química e dos componentes estruturais das plantas, do potencial hídrico das plantas, da umidade do solo, das variáveis microclimáticas e da produção de acículas. O delineamento experimental foi de blocos completos ao acaso, em parcelas subdivididas e três repetições. O azevém foi a espécie mais produtiva em todos os níveis de luminosidade, embora a ervilhaca tenha apresentado a menor redução de produção quando sombreada. Houve maior potencial hídrico nas plantas e maior umidade no solo nos ambientes sombreados, mesmo assim, a produção de forragem reduziu significativamente no sombreamento mais intenso (81%). A composição química e os componentes estruturais de todas as forrageiras estudadas também são afetados pelo aumento da restrição luminosa.Palavras-chave: composição química, matéria seca, sistema silvipastoril, sombreamento Performance of hibernal forages under distinct brightness levelsABSTRACT -Possible effects of brightness restriction, obtained by different Pinnus taeda tree densities, on the production and quality of black oat (Avena strigosa Schreb) cv. Common, white oat (Avena sativa L.) cv. FAPA 2, annual ryegrass (Lolium multiflorum L.) cv. Common, hairy vetch (Vicia villosa), wheat (Triticum aestivum L.) cv. dual purpose BRS Tarumã were studied. It was evaluated three brightness levels: 1 -full sunlight with no trees; 2 -30% of radiation restriction, using 15 × 3 m spacing between trees (222 trees/ha), and; 3 -60% of radiation restriction, using 9 × 3 m between trees (370 trees/ha). It was performed evaluations of forage production, chemical composition and structural component of plants, water potential of the plants, soil moisture, microclimate variables and production of needles. The experimental design was completely randomized blocks, in split-plots and three replicates. Ryegrass was the most productive species at all brightness levels, although hairy vetch showed the lowest reduction on production under shading. There was higher water potential in the plants and higher soil moisture under shading, however, forage production was significantly reduced in the most intense shading (81%). Chemical composition and structural components of all studied forage species are also affected by brightness restriction increase. IntroduçãoO agronegócio, ao longo das cade...