RESUMO: O cultivo de soja e milho safrinha avança em condições edafoclimáticas restritivas, como nos PLINTOSSOLOS PÈTRICOS, que apresentam proporções consideráveis de cascalho no seu perfil e são deficientes em cobre (Cu) e zinco (Zn). Não se sabe os efeitos de doses de Cu e Zn na nutrição da soja cultivada em PLINTOSSOLO PÉTRICO, nem se os níveis considerados adequados para outros solos são suficientes para solos cascalhentos, ou ainda, se altas doses de Cu e Zn podem causar toxidez nas plantas de soja. O objetivo foi comparar a resposta a doses de Cu e Zn em soja cultivada em PLINTOSSOLO PÉTRICO e em LATOSSOLO, a fim de identificar alterações provocadas pelo solo com cascalho, e adicionalmente, avaliar o efeito residual da adubação feita na soja para o milho safrinha cultivado no LATOSSOLO. Quatro experimentos foram desenvolvidos com doses de Cu e Zn aplicadas via solo na cultura da soja em LATOSSOLO e em PLINTOSSOLO PÉTRICO. Houve a mesma taxa de incremento na concentração de Zn no tecido foliar da soja nos dois solos estudados, para cada kg ha-1 de Zn aplicado, o incremento foi de 0,7 mg·kg-1 demonstrando que não há diferença de um solo com ou sem cascalho para os efeitos da adubação. As doses de oxissulfato de Zn e Cu aplicadas via solo não causaram efeito residual no milho safrinha. As maiores doses de Cu e Zn não causaram efeito tóxico nas plantas. Os principais critérios de interpretação de Cu e Zn em análise do solo se aplicam para soja cultivada em PLINTOSSOLO PÉTRICO.

ABSTRACT: Cultivation of soybean and off-season corn is advancing in areas under restricted edaphoclimatic conditions, such as petric plinthosols, which have significant proportions of gravel and are deficiency in micro-nutrients such as copper (Cu) and zinc (Zn). The effects of Cu and Zn concentrations on soybean nutrition cultivated in petric plinthosol are unclear, and it is unknown whether the levels considered adequate for other soils are sufficient for gravely soils, or even if higher Cu and Zn rates can cause a toxic effect in soybean. The objective was to compare the response of soybean grown in petric plinthosol and ferralsol to Cu and Zn doses for identifying the changes induced by gravel soils and to evaluate the residual effect on off-season corn grown in ferralsol. Four experiments were carried out with Cu and Zn doses applied to soil with the soybean crop in ferralsol and plinthosol. The leaf tissues of soybean crops in the two soils showed the same rate of increase in Zn concentrations, for each kg·ha-1 of Zn applied, the increase in Zn was 0.7 mg·kg-1, suggesting no difference in the effect of Zn fertilization between soils with and without gravel. The dosages of Zn and Cu Oxysulfate applied to soil did not cause residual effects in the off-season corn. The highest doses of Cu and Zn did not have any toxic effects on the plants. The main criteria for interpreting Cu and Zn in soil analysis are thus also applicable to soybean crops grown in petric plinthosol.

ABSTRACT: Soybean [Glycine max (L.) Merr.] grain yield is closely associated with the level of optimal nitrogen (N) supply, especially during the reproductive stages. Foliar fertilization with low rates of N have been considered as a strategy for furnishing additional N and enhancing grain yields. Field studies using 15N tracer were conducted over two growing seasons to investigate the impact of foliar N fertilization on grain yield, plant N content, the amount of N derived from fertilizer (NDFF) and N recovery efficiency (NRE). Four foliar N rates (0, 1300, 2600 and 3900 g ha−1) were supplied by two equal split applications at the R1 and R3 stages. Foliar N fertilization of soybean canopies did not affect grain yield, grain N content, shoot N content nor plant N content. Total NDFF was increased from 0.7 to 2.0 kg ha−1 across the N rates. Nonetheless, NRE was unaffected by foliar N fertilization, which averaged 53 %. Soybean plants allocated the same amount of N fertilizer to both grains and shoots. No significant effects of low rate foliar N fertilization were registered on soybean grain yield nor plant N content, despite considerable N fertilizer recovery by plant organs.

ABSTRACT: Integrating plant density and nitrogen (N) management is a strategy for improving corn yields, especially for off-season corn production in the tropics. This study tested the hypothesis that increasing plant densities and N rates promotes yield gains for off-season corn production in high-yielding environments. The aim of the study was to investigate the yield performances of two hybrid versions (DKB PRO and DKB PRO3) submitted to three plant densities (55,000; 65,000 and 75,000 plants ha−1) and four N rates (control, 60, 120 and 180 kg ha−1 N). Field trials were undertaken at Uberlândia-MG (site1 and 2) and Pedro Afonso-TO (site 3), Brazil from which data on corn yield parameters were collected and analyzed. Multivariate analysis separated the three trial areas into two groups, presenting high (sites 1 and 2) and low yields (site 3), which were related to weather conditions. There was no influence of a hybrid version or plant densities on crop yields at site 1 or 2. In contrast, there was a positive response to increasing plant densities and the use of DKB PRO3 at site 3. A significant response to N was observed at sites 2 and 3, following a plateau model. Our results suggest that N application rates and plant densities do have the potential to increase off-season corn yields in low yielding environments.

RESUMO A dinâmica de biomassa e nutrientes do milho pode ser alterada quando consorciado com Brachiaria (syn. Urochloa spp.). Objetivou-se investigar a dinâmica de biomassa, nitrogênio (N), fósforo (P) e potássio (K) para sistemas de produção de milho consorciado com espécies de Brachiaria. Campos experimentais foram conduzidos durante a safra e safrinha, em esquema de parcelas subdivididas. As parcelas principais foram compostas por espécies de braquiária (B. brizantha,B. ruziziensis, e B. Convert) consorciadas com milho, além de monocultivo de milho. As subparcelas consistiram de períodos de amostragem da forragem, variando de 0 a 60 dias após a colheita do milho. O consórcio não afetou a produtividade de grãos, acúmulo e partição de nutrientes no milho. Após a colheita de grãos, B. brizantha obteve a maior taxa de acúmulo de biomassa na safra (69 kg ha-1 dia-1) e safrinha (17 kg ha-1 dia-1). O acúmulo de nutrientes variou amplamente entre as espécies de Brachiaria e estação de cultivo: 0.2-1.2 kg ha-1 dia-1 para N; 0.01-0.07 kg ha-1 dia-1 para P; e 0.13-0.8 kg ha-1 dia-1 para K. Contudo, o maior acúmulo de nutrientes foi registrado para B. brizantha, seguida de B. ruziziensis e B. Convert. A curto prazo, o milho consorciado com Brachiaria na safra obteve maior efeito sobre a ciclagem de nutrientes e produção de biomassa. O consórcio entre milho e B. brizantha na safra foi a melhor opção para aumentar a produção de biomassa e a ciclagem de N, P e K.

ABSTRACT The corn biomass and nutrient dynamics may be altered when it is intercropped with Brachiaria (syn. Urochloa spp.). The present study aimed to investigate the dynamics of biomass, nitrogen (N), phosphorus (P) and potassium (K) for farming systems that produce corn intercropped with Brachiaria species. Field experiments were performed during the season and off-season, in a split-plot design. The main plots were composed of Brachiaria species (B. brizantha,B. ruziziensis and B. Convert) intercropped with corn, in addition to corn monocropping. The subplots consisted of three forage sampling periods, ranging from 0 to 60 days after the corn harvest. The intercropping arrangements did not affect the corn grain yield, nutrient accumulation and partitioning, relatively to the corn monocropping. After the grain harvest, B. brizantha achieved the greater biomass accumulation rate in both the season (69 kg ha-1 day-1) and off-season (17 kg ha-1 day-1). The nutrient accumulation ranged widely between the Brachiaria species and planting seasons: 0.2-1.2 kg ha-1 day-1 for N; 0.01-0.07 kg ha-1 day-1 for P; and 0.13-0.8 kg ha-1 day-1 for K. However, the greatest nutrient accumulation was found for B. brizantha, followed by B. ruziziensis and then B. Convert. In the short-term, corn intercropped with Brachiaria in the season showed the largest effect on the nutrient cycling and biomass yield. The intercropping between corn and B. brizantha in the season was the best way to enhance the biomass yield and the N, P and K cycling.

Resumo: O objetivo deste trabalho foi avaliar as perdas causadas pelas podridões da base do colmo em híbridos de milho (Zea mays), bem como identificar os principais patógenos causadores da doença, durante a safrinha, no Estado do Tocantins, Brasil. Foram realizados dois ensaios, um com cinco híbridos, em 2015, e outro com quatro, em 2016. Espigas de plantas sadias e doentes foram colhidas em cada parcela, por ocasião da colheita. Foram medidos tamanho de espigas, peso de grãos e espigas, e umidade dos grãos. De cada planta doente, foi retirado um fragmento do colmo com dois a três entrenós, utilizado para identificação e quantificação dos patógenos. Os patógenos mais comuns foram: Fusarium graminearum, Stenocarpella maydis e Macrophomina phaseolina. Todas as variáveis de produtividade foram significativamente menores nas plantas doentes, com perdas médias de 30,6%, em 2015, e de 34,3% em 2016. As maiores perdas são observadas em híbridos com maior relação entre pesos de grãos e espigas.

Abstract: The objective of this work was to assess yield losses due to stalk rot in corn (Zea mays) hybrids, as well as to identify the main pathogenic fungi responsible for the disease during the off-season, in the state of Tocantins, Brazil. Two field experiments were carried out, one with five hybrids, in 2015, and another with four, in 2016. Ears of healthy and stalk rot-infected plants were collected from each plot, at harvest. Ear size, grain and ear weights, and grain moisture content were measured. From each diseased plant, a stalk piece with two to three nodes was removed for pathogen identification and quantification. The most common pathogens were: Fusarium graminearum, Stenocarpella maydis, and Macrophomina phaseolina. All yield parameters were significantly lower in stalk rot-infected plants, with average losses of 30.6%, in 2015, and of 34.3% in 2016. The highest yield losses are observed in hybrids with the highest grain/ear weight ratio.

ABSTRACT Intercropping corn and palisade grass is a technique to increase straw production, soil C contents, nutrient cycling and crop yield. However, concerns arise from nitrogen (N) uptake by the intercropping crop causing reduction in the yield of the corn. Our objective was to evaluate N recovery efficiency (NRE), and the N dynamics in the soil-plant system in corn intercropped with palisade grass. A field trial was carried out in Bahia, Brazil, evaluating two cropping systems: corn (monoculture) and corn intercropped with palisade grass sowed between rows on the same day as the corn crop, with four replicates in a completely randomized block design. Nitrogen (150 kg∙ha–1of 15N-urea) was applied at sowing to determine NRE, which means the amounts of N-fertilizer uptake in corn and palisade grass, the amounts of N-fertilizer in soil and the 15N-fertilizer balance. Neither the NRE (63.3% in monoculture and 57.2% in intercropping) nor corn grain yield (9,800 kg∙ha–1 in monoculture and 9,671 kg∙ha–1 in intercropping) was affected by intercropping, which accumulated only 2.1 kg∙ha–1 of N-fertilizer or 1.4% N rate. In addition, palisade grass yielded 2,265 kg∙ha–1 of dry matter. The balance indicated that 82.4% of N-fertilizer was recovered in the monoculture and 86.9% in the intercropping. Intercropping palisade grass does not affect grain yield or N corn nutrition and has the potential to increase straw production contributing to maintenance of no-till.

RESUMO A fim de obter uma produção ótima e sustentável, os produtores precisam conhecer a taxa de aplicação de potássio (K) e fósforo (P) fertilizante. Objetivou-se determinar o desenvolvimento de arroz, em resposta a taxas combinadas de P e K, em Plintosolos (380-400 g kg-1 de argila), em condições de fertilidade alta e baixa, na planície irrigável tropical do rio Araguaia. Foram instalados três experimentos, sendo que cada um deles consistiu em delineamento fatorial em blocos casualizados, com três repetições. Os tratamentos incluíram a combinação de seis doses de K2O (0 kg ha-1, 30 kg ha-1, 60 kg ha-1, 90 kg ha-1, 120 kg ha-1 e 150 kg ha-1) com seis doses de P2O5 (0 kg ha-1, 30 kg ha-1, 60 kg ha-1, 90 kg ha-1, 120 kg ha-1 e 150 kg ha-1). Não foi observado efeito da interação entre doses de P e K nas variáveis analisadas em nenhum nível de fertilidade/ano. A aplicação de P sob condição de baixa fertilidade, bem como de K sob alta fertilidade, afetam a nutrição da cultura de forma geral, capacidade de perfilhamento, componentes da produtividade e rendimento de grãos de arroz de terras baixas, embora não tenha sido observado efeito da aplicação de P em área de alta fertilidade e K na área de baixa fertilidade. Na condição de alta fertilidade, a taxa de incremento de rendimento de grãos devida à aplicação de K foi de 4,04 kg ha-1, e na condição de baixa fertilidade, como áreas recém-abertas, a produtividade máxima foi de 7.161 kg ha-1, quando aplicados 140 kg ha-1 de P.

ABSTRACT In order to reach an optimum and sustainable production, growers must know the fertilizing potassium (K) and phosphorous (P) application rates. The present study aimed to determine the rice development in response to combined rates of P and K, on Plinthaquults (380-400 g kg-1 of clay), under high and low fertility conditions, in the tropical lowland plain of the Araguaia river, Brazil. Three field experiments were performed, each one consisting of a completely randomized factorial block design, with three replications. Treatments included a combination of six K2O rates (0 kg ha-1, 30 kg ha-1, 60 kg ha-1, 90 kg ha-1, 120 kg ha-1 and 150 kg ha-1) with six P2O5 rates (0 kg ha-1, 30 kg ha-1, 60 kg ha-1, 90 kg ha-1, 120 kg ha-1 and 150 kg ha-1). No interaction effect between P and K rates was observed for the evaluated variables in any fertility level/year. Phosphorous application under low fertility conditions, as well as K under high fertility conditions, affect overall crop nutrition, tillering capacity, yield components and grain yield of lowland rice, though no effects were observed due to the P application in high fertility soils and K in low fertility soils. Under high fertility conditions, the grain yield increment rate due to the K application was 4.04 kg ha-1, whereas in the low fertility areas, such as recently cleared fields, a maximum yield of 7,161 kg ha-1 was achieved by applying 140 kg ha-1 of P.

RESUMO O uso de plantas de cobertura pode alterar atributos do solo e afetar significativamente a nutrição das plantas e produtividade do arroz cultivado em planícies inundáveis. Este trabalho teve como objetivo determinar atributos do solo, nutrição de plantas e produtividade do arroz irrigado tropical em planícies irrigáveis por inundação após o cultivo de plantas de cobertura, no preparo convencional do solo (PC) ou sistema plantio direto (SPD) em baixa e alta adubação com N. O delineamento experimental foi em blocos casualizados, no esquema de parcelas sub-subdivdidas, com quatro repetições. Nas parcelas estavam as coberturas vegetais [Crotalaria juncea, C. spectabilis, mucuna preta (Mucuna aterrina), feijão de porco (Canavalia ensiformis), feijão guandu (Cajanus cajan), nabo forrageiro (Raphanus sativus), feijão caupi (Vigna unguiculata) e pousio], nas subparcelas o sistema de preparo do solo (PC ou SPD) e nas sub-subparcelas a adubação nitrogenada (10 e 45 kg ha-1 N). As plantas de cobertura, com exceção do nabo forrageiro, proporcionam incrementos nos teores de N total e nitrato no solo. C. juncea, C. spectabilis, mucuna preta e feijão caupi proporcionam incrementos nos teores de amônio no solo. O SPD proporciona maiores teores de N total e amônio do que o PC. No âmbito geral, as plantas de cobertura proporcionaram maiores teores de nutrientes nas plantas de arroz no SPD do que no PC. As plantas de cobertura também proporcionaram maior produtividade do arroz em relação ao tratamento pousio. O rendimento do arroz é maior em SPD do que PC, e superior com alto nível de adubação nitrogenada.

ABSTRACT In flood plains, cover crops are able to alter soil properties and significantly affect rice nutrition and yield. The aims of this study were to determine soil properties, plant nutrition, and yield of tropical rice cultivated on flood plains after cover crop cultivation with conventional tillage (CT) and no-tillage system (NTS) at low and high nitrogen (N) fertilization levels. The experimental design was a randomized block in a split-split-plot scheme with four replications. In the main plots were cover crops [sunhemp (Crotalaria juncea and C. spectabilis), velvet bean (Mucuna aterrima), jackbean (Canavalia ensiformis), pigeon pea (Cajanus cajan), Japanese radish (Raphanus sativus), cowpea (Vigna unguiculata)] and a fallow field. In the subplots were the tillage systems (CT or NTS). The nitrogen fertilization levels in the sub-subplots were (10 kg N ha-1 and 45 kg N ha-1). All cover crops except Japanese radish significantly increased mineral soil nitrogen and nitrate concentrations. Sunhemp, velvet bean, and cowpea significantly increased soil ammonium content. The NTS provides higher mineral nitrogen and ammonium content than that by CT. Overall, cover crops provided higher levels of nutrients to rice plants in NTS than in CT. Cover crops provide greater yield than fallow treatments. Rice yield was higher in NTS than in CT, and greater at a higher rather than lower nitrogen fertilization level.

Resumo: O objetivo deste trabalho foi avaliar métodos de implantação do consórcio milho e espécies forrageiras de Panicum spp. e os efeitos na produtividade do milho e no desenvolvimento das forragens. Dois experimentos com Panicum spp. foram conduzidos, um com 'Tanzania' e outro com 'Massai' em Piracicaba, SP, na safra 2012/2013. Em ambos os experimentos, os tratamentos foram: Panicum spp. semeado a lanço no momento da semeadura do milho; milho com Panicum spp. nas entrelinhas; Panicum spp. semeado com fertilizante; Panicum spp. semeado nas entrelinhas depois do estabelecimento do milho; Panicum spp. semeado a lanço depois do estabelecimento do milho; e milho solteiro. Para o milho, avaliaram-se a concentração de nitrogênio foliar, a altura de espigas e a produtividade de grãos. Para as cultivares de Panicum spp., avaliaram-se altura, massa seca, número de perfilhos e relação folha:colmo. Os métodos de implantação do consórcio avaliados não afetam o crescimento, a produtividade de grãos e a concentração foliar de N do milho. A implantação das cultivares de Panicum spp., quando o milho apresenta quatro folhas expandidas, reduz a massa seca e aumenta a relação folha:colmo das plantas forrageiras. A semeadura a lanço de Panicum spp., depois do estabelecimento do milho, não permite o estabelecimento adequado, com poucas plantas na área.

Abstract: The objective of this work was to evaluate methods of intercropping corn and Panicum spp. forages and their effects on corn yield and forage development. Two experiments with Panicum spp. were conducted, one with 'Tanzania' and other with 'Massai' in the municipality of Piracicaba, in the state of São Paulo, Brazil, in the 2012/2013 growing season. In both experiments, the treatments were: broadcast seeding of Panicum spp. at the same time of corn sowing; corn with Panicum spp. between rows; Panicum spp. sown with fertilizer; Panicum spp. sown between corn rows after corn establishment; broadcast seeding of Panicum spp. after corn establishment; and sole corn sowing. For corn, leaf nitrogen content, ear height, and grain yield were evaluated. For Panicum spp. cultivars, height, dry mass, tiller density, and leaf:stem ratio were evaluated. The intercropping establishment methods used do not affect corn growth, grain yield, and N leaf content. The seeding of both cultivars of Panicum spp. when corn plants had four expanded leaves reduces forage dry mass production and increases the leaf:stem ratio. The Panicum spp. broadcast method, performed after corn was established, does not allow appropriate establishment, with few plants in the area.