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A definição dos critérios para seleção de materiais é especialmente importante para o cultivo do pinhão-manso (Jatropha curcas L.), pois subsidia a caracterização dos ideótipos mais adequados para o plantio

Leaf area is an important parameter in agronomic and physiological studies; thereby, the techniques used for its determination should be simple, fast and accurate. The objective of this study was to evaluate the efficiency of an equation for the indirect determination of leaf area in 'Conilon' (Coffea canephora) genotypes cultivated in the Western Amazon. The experiment was carried out in Porto Velho, Rondônia, in August and September 2011. It was arranged in a completely randomized 2 × 15 factorial design combining two methods of determining leaf area (estimated and actual) and fifteen 'Conilon' coffee genotypes, with 64replicates. The estimated leaf area was determined by the equation LA = 0.3064 × Age -0.0556 × LMR -2.0133 (R 2 =0.98), developed by Partelli et al. (2006), while the actual leaf area was obtained from images of leaves scanned into digital format using an image scanner. The genotypes belong to the Coffee Breeding Program at Embrapa Rondônia. The efficiency of the equation for determining leaf area of 'Conilon' coffee varies according to the genotype evaluated; therefore, the equation must not be used without prior calibration. As the species is a perennial crop and the number of commercial genotypes widely accepted by farmers is restricted, the validation of the equation or the development of new equations capable of estimating the leaf area of the cultivated genotypes can help in the management of coffee plantationsn.

RESUMOA melhoria da qualidade estrutural do solo pelo uso continuado do sistema semeadura direta ocorre junto com o processo de sua (re)acidificação. Em algumas circunstâncias, ocorre também compactação superficial devido ao tráfego de máquinas, que necessita ser corrigida pela mobilização do solo. Assim, em experimento conduzido há 12 anos sob diferentes sistemas de manejo do solo, avaliou-se o tempo necessário para o solo readquirir os atributos físicos iniciais, alterados no processo de revolvimento do solo, por ocasião da reaplicação de calcário. O experimento foi realizado na Estação Experimental Agronômica da UFRGS, em Eldorado do Sul -RS, em um Argissolo Vermelho distrófico típico. Os sistemas de manejo avaliados foram: (a) preparo convencional durante 12 anos, (b) sistema semeadura direta com revolvimento do solo para incorporar calcário a cada quatro anos, (c) sistema semeadura direta durante oito anos e (d) sistema semeadura direta durante 12 anos. Determinaram-se, imediatamente antes e 6, 12, 24, 36 e 48 meses depois da terceira reaplicação de calcário, a densidade, a porosidade total, a macroporosidade, a microporosidade, a estabilidade de agregados e o teor de C orgânico em três camadas (0,0-2,5; 2,5-7,5 e 7,5-15,0 cm) de solo. O revolvimento do solo para incorporação do calcário no sistema semeadura direta de quatro anos propiciou condições mais favoráveis de densidade e porosidade do solo, mas diminuiu a estabilidade de agregados. Houve necessidade de um período de quatro anos de cultivo do solo no sistema semeadura direta para o retorno da estabilidade de agregados à condição original. Os atributos físicos do solo foram mais uniformes no perfil no preparo convencional, porém com menor estabilidade de agregados na camada superficial, que foi relacionada ao teor de C orgânico.Termos de indexação: mobilização do solo, agregação, densidade, porosidade.

RESUMO -O sistema plantio direto é uma estratégia sustentável de produção que preconiza a manutenção da cobertura vegetal como prática conservacionista do solo. Objetivou-se avaliar o efeito de plantas de cobertura sobre atributos fisiológicos e agronômicos do milho na região sudoeste da Amazônia. Foram avaliadas 15 estratégias de sucessões de culturas com o milho e a influência sobre o rendimento de biomassa, de grãos, altura de plantas e inserção da espiga, índice de espiga, massa de 100 grãos, teor foliar de nitrogênio e clorofilas total, a e b em plantas de milho.Observou-se efeito das plantas de cobertura sobre o rendimento de grãos, de biomassa fresca e seca, na massa de grãos e nos teores de clorofila. Os efeitos sobre os teores de clorofila foram mais pronunciados na clorofila b e nos estádios fenológicos finais da cultura. O feijão-de-porco promoveu as maiores produtividades de grãos (7.539,3 kg ha -1 ) e potencial de silagem (16,2 Mg ha -1 de biomassa seca). A adequada escolha das espécies que compõe um sistema de plantio direto é preponderante para o apropriado desempenho agronômico do milho na região sudoeste da Amazônia. Palavras-chave:Zea mays, intensificação ecológica, sustentabilidade, integração lavoura-pecuária, plantio direto. CROPPING SYSTEMS ON THE PERFORMANCE OF CORN PLANTS IN THE SOUTHWESTERN AMAZONABSTRACT-A sustainable strategy for agricultural systems is the use of cover crops in no-tillage systems, as a conservationist soil practice. This paper aimed to evaluate the short-term effects of different cover crops on some physiological and agronomic attributes of corn crop in the Southwestern Amazon region. The effects of 15 cover plants on the biomass and grains yield, plant height, ear insertion height, ear index, mass of 100 grains, leaf nitrogen content and a, b and total chlorophyll levels of corn plants were evaluated. A randomized complete block design was used with four replications. Grain yield, fresh and dry biomass yield, mass of 100 grains and chlorophyll content were affected by some cover crops. Jack bean promoted the highest grain yield (7,539.3 kg ha -1 ) and biomass yield (16.2 Mg ha -1 dry matter) among the options assessed. Cover crops provided different levels of total, a and b chlorophyll levels, on the corn plants. Some cover crops presented the potential to improve the agronomic performance of the succeeding corn crop in the Southwestern Amazon region. The proper agronomic performance of corn in a no-till system depends on the adequate choice of cover plants to compose the system. Sorgo, v.15, n.3, p. 531-542, 2016 RESUMO -O sistema plantio direto é uma estratégia sustentável de produção que preconiza a manutenção da cobertura vegetal como prática conservacionista do solo. Objetivou-se avaliar o efeito de plantas de cobertura sobre atributos fisiológicos e agronômicos do milho na região sudoeste da Amazônia. Foram avaliadas 15 estratégias de sucessões de culturas com o milho e a influência sobre o rendimento de biomassa, de grãos, altura de plantas e inserção da e...

No-tillage is an agricultural system that is proposed as a sustainable soil management system. This paper aims to evaluate the short-term effects of cover crops on a no-tillage system, by assessing a number of physical and chemical attributes of soil of the Brazilian Amazon region. The experiment was carried out in a typical Ferralsol under a no-tillage system from March to December, 2014. A randomized block design, with four replicates was used. The performance and effects of fourteen cover crops (Cajanus cajan, Canavalia ensiformis, Crotalaria juncea, Crotalaria ochroleuca, Crotalaria spectabilis, Stizolobium aterrima, Stizolobium cinereum, Pennisetum glaucum, Sorghum bicolor, Sorghum sudanense, Urochloa brizanha cv. Xaraés, Urochloa brizantha cv. Piatã and Urochloa ruziziensis and Zea mays) and fallow (control treatment) on the soil quality were assessed. The cover crops were sown in the off season in April 2014, before the summer crop (maize). The levels of P, K, Ca 2+ , Mg 2+ , Al 3+ , H+Al, saturation by aluminum, sum of bases, organic matter, pH and resistance to soil penetration were evaluated following the end of the cover crops growth. Some near-surface soil attributes were affected by the cover crops. Urochloa species improved the levels of potassium in the soil at depths up to 5 cm below the surface. The highest penetration resistance was observed in the superficial layer between 12 and 16 cm deep, with penetration resistance values varying between 2472 and 2912 kPa. The Urochloa exhibited satisfactory agronomic performance when grown under a simulated crop livestock integration system. It is concluded that the use of cover crops in a no-till system has the potential to improve the chemical quality of soil in the Southwestern Amazon region.

The objective of this work was to evaluate urease inhibitors for the reduction of ammonia volatilization in Amazonian soils. The work was carried out on a clayey yellow Oxisol, a clayey red Oxisol, and on a light silty Ultisol. Each experiment was conducted in split plots, using standard urea, urea + a benzimidazole-type urease inhibitor (BZI1), urea + a benzoylthiourea-type urease inhibitor (RTB68), urea + N-(n-butyl) triamide thiophosphate (NBPT), or a fertilizer-free control. Volatilized ammonia was collected at 48, 96, 144, 192, 240, 288, 336, and 384 hours after fertilization. Ammonia volatilization reached a maximum at 144 hours in the urea, urea + benzimidazole, and urea + benzoylthiourea treatments. A peak level was reached at 192 and 288 hours in the urea + N-(n-butyl) triamide thiophosphate treatment. In yellow Oxisols, benzimidazole and benzoylthiourea reduced the ammonia losses by 22 and 10%, respectively, in soils without urease inhibitors. However, neither of these agents significantly reduced ammonia volatilization at the rate determined for standard urea in red Oxisols or Ultisols. N-(n-butyl) triamide thiophosphate is the most efficient urease inhibitor for the soils of southwestern Amazonia.

This study presents an evaluation of the viability of using protected urea under different irrigation depths to reduce nitrogen losses caused by the volatilization of ammonia (NH3) under the conditions of the Southwestern Amazon. The study was carried out at the Experimental Station of Embrapa Rondônia, in the municipality of Porto Velho, Rondônia State, Brazil. The experiment was conducted in a Red-Yellow Latosol and arranged in a 5 x 6 factorial design consisting of a combination of five treatments (N sources) with six irrigation depths. The sources of N were as follows: 1) urea (45.5% N); 2) urea (44.3% N) + 0.15% copper and 0.4% boron; 3) urea (45% N) + NBPT; 4) urea (43% N) + sulfur (1%); and 5) control (without N). The irrigation depths were 0, 5, 10, 15, 20, and 25 mm. The results showed that, regardless of the use of urease inhibitors, an irrigation depth of 10 mm is suitable for incorporating urea into the soil and stabilizing N losses from NH3 volatilization. NBPT is the most efficient inhibitor under nonirrigated conditions. All N sources promote increases in the concentrations of nitric and ammonia nitrogen in the soil. In the first 15 days after fertilizer application, the highest concentrations of ammonium were in the 0 - 10 cm and 10 - 20 cm soil layers, and NBPT showed the highest ammonium content compared to that of the other sources in the 0 - 10 cm layer. The nitric nitrogen content in the soil was slightly influenced by the irrigation depth in the first 15 days after fertilizer application. However, the ammonia nitrogen content decreased exponentially with the increase in irrigation depth due to the movement of ammonia in the soil.