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.

Resumo: O objetivo deste trabalho foi avaliar o efeito da aplicação de cloreto de amônio como fonte de nitrogênio para cana-de-açúcar (Saccharum sp.) no desenvolvimento da parte aérea e radicular da cultura durante dois ciclos consecutivos. O experimento foi conduzido em Latossolo Vermelho distrófico típico nos ciclos de primeira e segunda soqueira. Os tratamentos consistiram de quatro doses de N (50, 100, 150 e 200 kg ha-1) aplicadas na forma de cloreto de amônio (NH4Cl), além do controle, sem aplicação de N. O aumento da dose de NH4Cl elevou em até três vezes a condutividade elétrica do solo na camada de 0,0-0,2 m, com consequente aumento na concentração de cloro nas folhas. No segundo ciclo, os teores de cloro aumentaram em 1.900 mg kg-1 na folha com a aplicação de 200 mg kg-1 de NH4Cl, em comparação ao controle. No primeiro ciclo, a aplicação de doses de NH4Cl acima de 200 kg ha-1 de N promoveu queda na produtividade de colmos. Em ambos os ciclos, não houve efeito das doses de NH4Cl na fitomassa seca de raízes. Elevadas doses de NH4Cl, em ciclos consecutivos da cana-de-açúcar, resultam em decréscimos na produtividade de colmos industrializáveis.

Abstract: The objective of this work was to evaluate the effect of the application of ammonium chloride as a nitrogen source for sugarcane (Saccharum sp.) on the development of the crop’s shoot and roots during two consecutive cycles. The experiment was conducted on a Typic Hapludox in the first and second sugarcane ratoons. The treatments consisted of four N doses (50, 100, 150, and 200 kg ha-1) applied as ammonium chloride (NH4Cl), besides a control, without the application of N. The increase in the NH4Cl dose increased in up to three times soil electrical conductivity in the layer of 0.0-0.2 m, with a consequent increase in the concentration of chlorine in leaves. In the second cycle, the contents of chlorine increased in 1,900 mg kg-1 in the leaf with the application of 200 mg kg-1 NH4Cl, when compared with the control. In the first cycle, the application of NH4Cl doses above 200 kg ha-1 N promoted a decrease in shoot productivity. In both cycles, there was no effect of the NH4Cl doses on root dry matter. High doses of NH4Cl, in consecutive sugarcane cycles, result in a decrease in the productivity of stalks for processing.

ABSTRACT Retaining the mineral N in the form of NH4+ in the soil for a lengthy period is desirable for reducing losses. Furthermore, there is evidence that sugarcane prefers NH4+-N in place of NO3−-N. This study aimed firstly, to evaluate the potential of root extracts of Bracchiaria humidicola andSaccharum spontaneum, in contrast with the DCD (Dicyandiamide) inhibitor, to increase absorption of N by plants fertilized with ammonium sulfate, and secondly, to quantify the emission of N2O fluxes with the use of this inhibitor. The experiment was developed in a glasshouse in an entirely randomized design where four treatments were applied: AS) ammonium sulfate (control); AS+DCD) ammonium sulfate associated with dicyandiamide; AS+BCH) ammonium sulfate associated with root extracts ofBrachiaria humidicola; and AS+SCS) ammonium sulfate associated with root extracts of Saccharum spontaneum. Differences were observed in biomass production in plants 45 and 60 days after fertilization (DAF) and 15 and 60 days in biomass accumulation of roots. The application of AS associated with DCD synthetic inhibitor kept NO3−-N values low throughout the evaluation period, while in other treatments the concentration increased right up to the second evaluation 15 DAF. Sugarcane plants did not benefit from the increased presence of ammoniacal N promoted by DCD. The use of DCD reduced the average flux of N2O during the evaluation period compared to plants receiving AS treatments only, which was not observed when root extracts of B. humidicola and S. spontaneum were used.

ABSTRACTThe low effectiveness of nitrogen fertilizer (N) is a substantial concern that threatens global sugarcane production. The aim of the research reported in this paper was to assess the residual effect of N-fertilizer applied at sugarcane planting over four crop seasons in relation to sugarcane crop yield. Toward this end three field experiments were established in the state of São Paulo, Brazil, during February of 2005 and July of 2009, in a randomized block design with four treatments: 0, 40, 80 and 120 kg ha−1 of N applied as urea during sugarcane planting. Within each plot, a microplot was established to which 15N-labeled urea was applied. The application of N at planting increased plant cane yield in two of the three sites and sucrose content at the other, whereas the only residual effect was higher sucrose content in one of the following ratoons. The combined effect was an increase in sugar yield for three of the 11 crop seasons evaluated. Over the crop cycle of a plant cane and three ratoon crops, only 35 % of the applied N was recovered, split 75, 13, 7 and 5 % in the plant cane, first, second and third ratoons, respectively. These findings document the low efficiency of N recovery by sugarcane, which increases the risk that excessive N fertilization will reduce profitability and have an adverse effect on the environment.

A caracterização do destino do N proveniente do fertilizante em um sistema é uma ferramenta essencial para a melhoria de práticas de manejo que visem a máxima utilização do nutriente pela cultura e o mínimo de perdas. A erosão do solo ocasiona perda de nutrientes, como o N, causando impactos negativos na qualidade das águas de mananciais superficiais e subterrâneas, além da queda de produtividade agrícola em razão do empobrecimento do solo. Estudos que correlacionam o percentual de N proveniente do fertilizante com as taxas de erosão do solo, bem como os fatores intervenientes nesse processo, são escassos. Nesse sentido, foram quantificadas as perdas de solo e N provenientes do fertilizante por erosão hídrica em solo mobilizado pelo preparo convencional e solo sem mobilização, sob diferentes intensidades de chuva, identificando os fatores que interferem no aumento dessa perda. O experimento foi conduzido em parcelas experimentais de 3,5 m de largura e 11 m de comprimento, com dois tratamentos e três repetições, sob chuva simulada. Os tratamentos utilizados foram solos com mobilização e sem mobilização. Foram aplicadas três chuvas sucessivas, com intervalo de 24 h entre elas, com intensidades de 30 mm/h, 30 mm/h e 70 mm/h. O fertilizante nitrogenado utilizado foi marcado isotopicamente (15N) e incorporado ao solo em linha transversal ao comprimento das parcelas. A ausência de preparo do solo condiciona as maiores perdas de solo por erosão e maiores perdas de nitrogênio total (NT) ao longo das chuvas aplicadas. As perdas do nitrogênio proveniente do fertilizante (NPF) seguiram padrão distinto; as maiores perdas de NPF foram verificados nas parcelas com mobilização do solo, mesmo que tenham apresentado as menores perdas de solo e NT; ou seja, quanto menor a quantidade de sedimentos erodidos maior o percentual de NPF associado a esses. As chuvas de maior intensidade não influenciaram a perda de NPF; as maiores perdas ocorreram em decorrência das chuvas de menor intensidade nos dois tratamentos utilizados.

The description of the fate of fertilizer-derived nitrogen (N) in agricultural systems is an essential tool to enhance management practices that maximize nutrient use by crops and minimize losses. Soil erosion causes loss of nutrients such as N, causing negative effects on surface and ground water quality, aside from losses in agricultural productivity by soil depletion. Studies correlating the percentage of fertilizer-derived N (FDN) with soil erosion rates and the factors involved in this process are scarce. The losses of soil and fertilizer-derived N by water erosion in soil under conventional tillage and no tillage under different rainfall intensities were quantified, identifying the intervening factors that increase loss. The experiment was carried out on plots (3.5 × 11 m) with two treatments and three replications, under simulated rainfall. The treatments consisted of soil with and soil without tillage. Three successive rainfalls were applied in intervals of 24 h, at intensities of 30 mm/h, 30 mm/h and 70 mm/h. The applied N fertilizer was isotopically labeled (15N) and incorporated into the soil in a line perpendicular to the plot length. Tillage absence resulted in higher soil losses and higher total nitrogen losses (TN) by erosion induced by the rainfalls. The FDN losses followed another pattern, since FDN contributions were highest from tilled plots, even when soil and TN losses were lowest, i.e., the smaller the amount of eroded sediment, the greater the percentage of FDN associated with these. Rain intensity did not affect the FDN loss, and losses were greatest after less intense rainfalls in both treatments.

O nitrogênio é requerido em grandes quantidades pelas plantas e sua dinâmica no consórcio entre milho e forrageiras tropicais perenes é pouco conhecida. Objetivou-se avaliar a eficiência de utilização da adubação nitrogenada (15NH4NO3) no capim-marandu (Brachiaria brizantha cv. Marandu), proveniente de duas épocas de consórcios com o milho, realizadas após a colheita da cultura granífera, bem como o efeito residual no milho cultivado em sucessão. O experimento foi conduzido na Faculdade de Ciências Agronômicas da UNESP em Botucatu, SP, em Nitossolo Vermelho sob sistema plantio direto. O delineamento experimental foi em blocos casualizados em parcelas subdivididas. As parcelas foram constituídas pelas épocas de consórcio: milho e capim-marandu semeados simultaneamente; e capim-marandu semeado na adubação de cobertura do milho. As subparcelas foram compostas pelas doses de 30, 60 e 120 kg ha-1 de N, aplicadas no capim-marandu após a colheita da cultura do milho. Nas subparcelas, foram alocadas microparcelas para aplicação de nitrato de amônio enriquecido (15NH4NO3) nessas mesmas doses. A época de implantação do consórcio influenciou a produção de massa de matéria seca da forrageira, a quantidade de N na planta proveniente do fertilizante e a eficiência de utilização do N pelas plantas forrageiras. A aplicação de N no outono no capim-marandu, implantado por meio do consórcio com o milho, tanto na semeadura quanto na adubação nitrogenada de cobertura, proporcionou aumento de produtividade da forrageira até a dose de 60 kg ha-1. Os maiores acúmulos de N e a eficiência de utilização do fertilizante pelo capim-marandu, oriundo de ambas as épocas de consórcio, ocorreram aos 160 dias após a fertilização, independentemente das doses de N. O residual das doses de N, aplicadas no capim-marandu, não interferiu na nutrição nitrogenada do milho em sucessão, porém incrementou a produtividade de grãos nas doses de 60 e 120 kg ha-1 de N, quando o cereal foi cultivado sobre palhada proveniente do consórcio implantado na adubação de cobertura do milho. Com base nos resultados, pode-se inferir que a implantação antecipada do consórcio proporciona maior produtividade de massa de matéria seca da forrageira, enquanto quando implantado mais tarde propicia maior produtividade de grãos do milho em sucessão à forrageira adubada com N.

Nitrogen is required in large amounts by plants and their dinamics in corn and perennial forages intercropped is little known. This study analyzed the efficiency of nitrogen fertilization (15NH4NO3) applied after corn grain harvest to palisadegrass (Brachiaria brizantha cv. Marandu) in intercrops sown at two times, as well as the N residual effect on the subsequent corn crop. The field experiment was performed in Botucatu, São Paulo State, in southeastern Brazil, on a structured Alfisol under no-tillage. The experiment was arranged in a randomized block design in a split plot scheme with four replications. The main plots consisted of two intercropping systems (corn and palisadegrass sown together and palisadegrass sown later, at corn top-dressing fertilization). The subplots consisted of four N rates (0, 30, 60, and 120 kg ha-1 N). The subplots contained microplots, in which enriched ammonium nitrate (15NH4NO3) was applied at the same rates. The time of intercrop sowing affected forage dry matter production, the amount of fertilizer-derived N in and the N use efficiency by the forage plants. Nitrogen applied in autumn to palisadegrass intercropped with corn, planted either at corn sowing or at N top-dressing fertilization, increased the forage yield up to a rate of 60 kg ha-1. The amount of fertilizer-derived N by the forage plants and the fertilizer use efficiency by palisadegrass were highest 160 days after fertilization for both intercrop sowing times, regardless of N rates. Residual N did not affect the N nutrition of corn plants grown in succession to palisadegrass, but increased grain yield at rates of 60 and 120 kg ha-1 N, when corn was grown on palisadegrass straw from the intercrop installed at corn fertilization (top-dressing). Our results indicated that the earlier intercropping allowed higher forage dry matter production. On the other hand, the later intercrop allowed a higher corn grain yield in succession to N-fertilized palisadegrass.

Sugarcane (Saccharum spp.) harvested without burning provides a substantial amount of remains (trash) on soil profiles which can be decomposed and release nutrients contributing to reduce fertilizer needs. The contribution of nitrogen (N) from sugarcane plant residues and fertilizer in sugarcane nutrition was assessed. Plant cane treatments were micro plots of 15N-labeled urea, sugarcane trash and root system; the last two to simulate the previous crop residues incorporated into the soil after crop renewal. For ratoons, N-ammonium nitrate (N-AN) micro plots, 150 kg ha-1 of N-AN and control (0 kg ha-1) were set up to evaluate the contribution of trash in N supply and quantify the effects of N-fertilizer on N-trash mineralization. The N balances derived from each 15N source were calculated after four crops and resulted in: 15N-urea applied at planting, 31 % was recovered by plant cane, 12 % by the following ratoons, 20 % remained in the soil and 37 % was not found in the soil-system (NOC). For crop residues 15N-trash + roots 26 % was recovered by sugarcane, 51 % remained in soil, and 23 % was NOC. N-fertilizer applied to ratoons nearly doubled the amount of N from green harvest residues recovered by sugarcane; 17 vs. 31 %. Water balances and crop evapotranspiration were correlated with 15N-sources recoveries and cumulative N recovery presented a positive correlation with evapotranspiration (2005 to 2009). The 15N balances indicated that crop residues are supplementary sources of N for sugarcane and may contribute to reduce N fertilizer needs since trash is annually added to the soil.

The area under mechanized sugarcane (Saccharum spp.) harvesting is expanding in Brazil, increasing the return of trash to the soil. The main questions regarding this management are: (i) after adopting unburned mechanical harvesting, how long will it take to observe decreases in fertilizer requirements, (ii) what will be the magnitude of this decrease and, (iii) the impact in the short run of removing trash for energy purposes in the nutrient cycling? This study aimed to build an N prediction model for long term assessment of the contribution of sugarcane crop residues to sugarcane nutrition and to evaluate the cycling of other nutrients derived from crop residues. Keeping crop residues over the soil will increase soil N stock and N recovery by sugarcane, reaching equilibrium after 40 years with recovery of approximately 40 kg ha-1 year-1 of N. Removing trash for energy production will decrease the potential reduction in N fertilizer requirement. Of the total nutrients in the trash, 75 % of the K2O (81 kg ha-1 year-1) and 50 % of the N (31 kg ha-1 year-1) are in the tops, indicating the importance of maintaining tops in the soil to sustain soil fertility. Because the input data employed in the simulations are representative of the conditions in Southeast Brazil, these results might not be definitive for situations not represented in the experiments used in the study, but the model produced is useful to forecast changes that occur in the soil under different trash management.

Sugarcane (Saccharum spp.) crops provide carbon (C) for soil through straw and root system decomposition. Recently, however, sugarcane producers are considering straw to be removed for electricity or second generation ethanol production. To elucidate the role of straw and root system on the carbon supply into the soil, the biomass inputs from sugarcane straw (tops and dry leaves) and from root system (rhizomes and roots) were quantified, and its contribution to provide C to the soil was estimated. Three trials were carried out in the State of Sao Paulo, Brazil, from 2006 to 2009. All sites were cultivated with the variety SP81 3250 under the green sugarcane harvest. Yearly, post-harvest sugarcane residues (tops, dry leaves, roots and rhizomes) were sampled; weighted and dried for the dry mass (DM) production to be estimated. On average, DM root system production was 4.6 Mg ha-1 year-1 (1.5 Mg C ha-1 year-1) and 11.5 Mg ha-1 year-1 (5.1 Mg C ha-1 year-1) of straw. In plant cane, 35 % of the total sugarcane DM was allocated into the root system, declining to 20 % in the third ratoon. The estimate of potential allocation of sugarcane residues to soil organic C was 1.1 t ha-1 year-1; out of which 33 % was from root system and 67 % from straw. The participation of root system should be higher if soil layer is evaluated, a deeper soil layer, if root exudates are accounted and if the period of higher production of roots is considered.

Considerar a mineralização do nitrogênio (N) da matéria orgânica do solo é questão fundamental para o manejo eficiente dos fertilizantes nitrogenados nos sistemas agrícolas. A incubação aeróbia de longa duração é o método de referência para estudos que envolvem a calibração de métodos químicos de extração, a fim de estimar o N potencialmente mineralizável do solo. Contudo, a técnica é laboriosa e de alto consumo de tempo e custo. Os objetivos deste trabalho foram determinar o N mineralizável do solo na profundidade de 0-60 cm e avaliar a possibilidade de adotar a incubação anaeróbia de curta duração no lugar da aeróbia de longa duração, para estimar a mineralização líquida de N em solos cultivados com cana-de-açúcar. Utilizaram-se cinco solos, coletados nas camadas de 0-20, 20-40 e 40-60 cm, em locais que não receberam fertilização prévia com N. As amostras de solo foram incubadas aerobiamente a 35 ºC, durante 32 semanas, e anaerobiamente (saturadas com água) a 40 ºC, por sete dias, para determinar a mineralização líquida de N do solo. Os teores de areia, silte e argila apresentaram alta correlação com os índices usados para predizer o N mineralizável. O N mineralizável do solo foi mais bem estimado na profundidade de 0-40 cm, enquanto a camada de 40-60 cm apresentou baixa mineralização líquida de N em ambos os procedimentos de incubação. Na incubação anaeróbia, estimou-se adequadamente o N mineralizável do solo, correlacionando-se com o N mineralizado acumulado e o N potencialmente mineralizável do solo, ambos obtidos por meio da incubação aeróbia. A manutenção do N-NH4+ preexistente da amostra melhorou a estimativa do N mineralizável por meio da incubação anaeróbia.

Considering nitrogen mineralization (N) of soil organic matter is a key aspect for the efficient management of N fertilizers in agricultural systems. Long-term aerobic incubation is the standard technique for calibrating the chemical extraction methods used to estimate the potentially mineralizable N in soil. However, the technique is laborious, expensive and time-consuming. In this context, the aims of this study were to determine the amount of soil mineralizable N in the 0-60 cm layer and to evaluate the use of short-term anaerobic incubation instead of long-term aerobic incubation for the estimation of net N mineralization rates in soils under sugarcane. Five soils from areas without previous N fertilization were used in the layers 0-20, 20-40 and 40-60 cm. Soil samples were aerobically incubated at 35 ºC for 32 weeks or anaerobically incubated (waterlogged) at 40 ºC for seven days to determine the net soil N mineralization. The sand, silt and clay contents were highly correlated with the indexes used for predicting mineralizable N. The 0-40 cm layer was the best sampling depth for the estimation of soil mineralizable N, while in the 40-60 cm layer net N mineralization was low in both incubation procedures. Anaerobic incubation provided reliable estimates of mineralizable N in the soil that correlated well with the indexes obtained using aerobic incubation. The inclusion of the pre-existing NH4+-N content improved the reliability of the estimate of mineralizable N obtained using anaerobic incubation.

O objetivo deste trabalho foi avaliar a eficiência agronômica das fontes nitrogenadas ureia (U), nitrato de amônio (NA), sulfato de amônio (SA) e cloreto de amônio (CA) em soqueira de cana-de-açúcar colhida sem queima, bem como determinar o efeito residual dessas fontes sobre a produtividade da cultura no ano agrícola subsequente. Utilizou-se o delineamento experimental de blocos ao acaso, com quatro repetições. Os tratamentos consistiram da aplicação de 120 kg ha-1 de N a um Latossolo Vermelho distrófico, coberto por palhada resultante da colheita sem queima da primeira soqueira. Incluiu-se um tratamento de controle sem adição de N fertilizante. Para avaliar o efeito residual dos adubos nitrogenados, aplicaram-se 450 kg ha-1 do formulado 20-5-19 após o corte da cana-soca. A maior produção de colmos e de açúcar na safra 2006/2007 foi obtida com a fonte SA. Na safra 2007/2008, não foi verificado efeito residual da adubação nitrogenada e houve queda de produtividade do tratamento CA em comparação ao controle. A fonte CA, à dose de 120 kg ha-1 de N em adubação de soqueira de segundo corte, é agronomicamente tão eficiente quanto as demais fontes de N utilizadas, mas tem menor eficiência no ano agrícola subsequente.

The objective of this work was to evaluate the agronomic efficiency of the nitrogen sources urea (U), ammonium nitrate (AN), ammonium sulfate (AS), and ammonium chloride (AC) on green harvesting sugarcane ratoon, as well as the residual effect of these sources on crop productivity in the subsequent crop year. A randomized block design was used with four replicates. Treatments consisted of applying 120 kg ha-1 of N fertilizer on a Typic Hapludox covered by straw residues resulting from the harvest without burning of the first ratoon. A control treatment was included with no N fertilizer. To evaluate the residual effect of the nitrogen fertilizers, 450 kg ha-1 of a 20-5-19 formulation was applied to soil after sugarcane ratoon harvest. The highest production of stalks and sugar, in the 2006/2007 season, was obtained with the source AS. In the 2007/2008 harvest season, no residual effect of N fertilization was observed and there was a productivity decrease in the AC treatment in comparison to the control. The AC source, at a dose of 120 kg ha-1 N in the fertilization of the second ratoon, is agronomically as efficient as the other N sources used, but shows less efficiency in the subsequent crop year.

A quantificação das perdas de amônia (NH3) proveniente da aplicação de ureia sobre a palhada de cana-de-açúcar pode ser realizada com uso de coletores, que recuperam o NH3 em absorvedores acidificados. Desse modo, o uso de coletor aberto com absorvedor envolto em película de politetrafluoroetileno (PTFE) torna-se uma opção interessante, pois apresenta baixo custo, fácil manuseio, além de não interferir nas condições microclimáticas. O objetivo deste estudo foi avaliar a eficiência de um coletor aberto na quantificação do N-NH3 volatilizado da ureia aplicada sobre solo coberto com restos vegetais de cana-de-açúcar. O experimento foi desenvolvido em área de cana-de-açúcar localizada na região de Piracicaba, Estado de São Paulo, Brasil. As perdas de N-NH3 foram estimadas pelo coletor semi-aberto estático calibrado com 15N (método de referência) e coletor aberto com absorvedor envolto em película de PTFE. A ureia foi aplicada sobre a superfície do solo, em tratamentos que corresponderam às doses de 50, 100, 150 e 200 kg ha-1 de N. A aplicação de ureia fertilizante sobre a palhada da cana-de-açúcar resultou em perdas de N-NH3 de até 24 % da dose aplicada. O coletor aberto não alterou a quantidade de N-NH3 volatilizada em relação ao coletor semi-aberto estático. A eficiência do sistema coletor variou de forma não linear, com valor médio de 58,4 % na faixa de 100 a 200 kg ha-1 de N-ureia. O coletor aberto apresentou expressivo potencial de uso, porém novas pesquisas são necessárias visando à adequação do método proposto.

The quantification of ammonia (NH3) losses from sugarcane straw fertilized with urea can be performed with collectors that recover the NH3 in acid-treated absorbers. Thus, the use of an open NH3 collector with a polytetrafluoroethylene (PTFE)-wrapped absorber is an interesting option since its cost is low, handling easy and microclimatic conditions irrelevant. The aim of this study was to evaluate the efficiency of an open collector for quantifying NH3-N volatilized from urea applied over the sugarcane straw. The experiment was carried out in a sugarcane field located near Piracicaba, São Paulo, Brazil. The NH3-N losses were estimated using a semi-open static collector calibrated with 15N (reference method) and an open collector with an absorber wrapped in PTFE film. Urea was applied to the soil surface in treatments corresponding to rates of 50, 100, 150 and 200 kg ha-1 N. Applying urea-N fertilizer on sugarcane straw resulted in losses NH3-N up to 24 % of the applied rate. The amount of volatile NH3-N measured in the open and the semi-open static collector did not differ. The effectiveness of the collection system varied non-linearly, with an average value of 58.4 % for the range of 100 to 200 kg ha-1 of urea-N. The open collector showed significant potential for use; however, further research is needed to verify the suitability of the proposed method.

O objetivo deste trabalho foi estudar a transferência do nitrogênio de adubos verdes para alface em cultivo consorciado, através da técnica da abundância natural de 15N. Os tratamentos foram: alface em monocultivo (testemunha), alface consorciado com aveia-preta, com feijão-caupi e com tremoço-branco, em duas épocas de semeadura dos adubos verdes: 60 dias antes e no transplante das mudas de alface. Observou-se que a alface consorciada com adubos verdes adquiriu a mesma massa fresca das alfaces solteiras quando a semeadura do adubo verde foi simultânea com o plantio da mesma; no entanto quando os adubos verdes foram semeados com 60 dias de antecedência as alfaces solteiras obtiveram maior massa fresca ; independentemente da época de semeadura as alfaces solteiras alcançaram maior massa seca; o tremoço-branco e o caupi transferiram maior quantidade de N para a alface, independentemente de sua época de semeadura; a relação C:N do feijão-caupi e tremoço-branco foram menores que a da aveia-preta; o cultivo consorciado de tremoço-branco, caupi e a aveia-preta transferiram 18%, 17% e 7% de N para a alface; e que em cultivo consorciado há transferência de N proveniente da fixação biológica do nitrogênio (FBN) dos adubos verdes tremoço-branco e caupi para a alface.

The aim of this work was to evaluate the transfer of N via biological nitrogen fixation from green manures to intercropped lettuce using the 15N abundance method. The treatments consisted of lettuce with black oats, lettuce with cowpea, lettuce with white lupin and monocropped lettuce (control). Green manures were sown at two different times including the following: 60 days before transplanting of lettuce seedlings and simultaneous to transplanting of lettuce seedlings. N transfer was estimated using the natural 15N abundance method. It was observed that lettuce intercropped with green manures reached the same fresh mass of monocropped lettuce when the green manures were sown at the same time as the vegetables were planted. However, when the green manures were sown previously, the fresh mass of the monocropped lettuce was higher, and independent of the sowing time of green manures, the monocropped lettuce reached a higher dry mass. White lupin and cowpea transferred higher amounts of N regardless of sowing time, and the C:N ratio of white lupin to cowpea was lower compared to black oats. Intercropping with white lupin, cowpea and black oat transferred 18%, 17% and 7% of N, respectively, to lettuce.

Leguminosas, como adubo verde, são fontes alternativas de nitrogênio para as culturas e podem complementar ou mesmo substituir a adubação mineral nitrogenada, devido ao seu potencial de fixação biológica de nitrogênio (FBN). A utilização do nitrogênio pela cana-de-açúcar (Saccharum spp.) fertilizada com crotalária (Crotalaria juncea L.) e sulfato de amônio (SA) foi avaliada utilizando a técnica de traçador 15N. As quantidades equivalentes a 196 e 70 kg de N por hectare foram adicionados como adubo verde crotalária júncea (CJ) e como o sulfato de amônio (SA), respectivamente, nos seguintes tratamentos: (i) controle; (ii) SA15N; (iii) CJ15N + SA; (iv) CJ15N; e (v) SA15N + CJ. A cana-de-açúcar foi cultivada por cinco anos e colhida três vezes. A recuperação do 15N foi avaliada nas duas primeiras colheitas. Na soma das três safras, os maiores rendimentos de colmos foram obtidos com uma combinação de adubos verdes e fertilizantes N inorgânicos, mas, no segundo corte rendimentos superiores foram observados nos tratamentos com CJ em comparação com os observados com SA. A recuperação de N nas primeiras duas safras consecutivas representou 19 a 21% do N aplicado como adubo verde e 46 a 49% do N aplicado como SA. As quantidades de N inorgânico derivado das fontes marcadas, presentes na camada 0-0,4 m do solo na primeira safra após a aplicação do N foram inferiores a 1 kg ha-1.

Legumes as green manure are alternative sources of nitrogen (N) for crops and can supplement or even replace mineral nitrogen fertilization due to their potential for biological nitrogen fixation (BNF). The utilization of nitrogen by sugarcane (Saccharum spp.) fertilized with sunn hemp (Crotalaria juncea L.) and ammonium sulfate (AS) was evaluated using the 15N tracer technique. N was added at the rate of 196 and 70 kg ha-1 as 15Nlabeled sunn hemp green manure (SH) and as ammonium sulfate (AS), respectively. Treatments were: (i) Control; (ii) AS15N; (iii) SH15N + AS; (iv) SH15N; and (v) AS15N + SH. Sugarcane was cultivated for five years and was harvested three times. 15N recovery was evaluated in the two first harvests. In the sum of the three harvests, the highest stalk yields were obtained with a combination of green manure and inorganic N fertilizer; however, in the second cutting the yields were higher where SH was used than in plots with AS. The recovery of N by the first two consecutive harvests accounted for 19 to 21% of the N applied as leguminous green manure and 46 to 49% of the N applied as AS. The amounts of inorganic N, derived from both N sources, present in the 0-0.4 m layer of soil in the first season after N application and were below 1 kg ha-1.

O objetivo deste trabalho foi avaliar a recuperação, pela cana-planta, do nitrogênio (15N) proveniente da ureia e de resíduos culturais da palhada e do sistema radicular da cultura da cana (Saccharum spp.) incorporados ao solo. O experimento foi instalado na safra de 2005/2006, com a cultivar SP81-3250. No plantio, foram instaladas microparcelas de 1,5x2 m, em que aplicaram-se doses equivalentes a 80 kg ha-1 de N (ureia com 5,05% de 15N) e 14 Mg ha-1 de resíduos culturais, dos quais 9 Mg ha-1 de palhada (PA) e 5 Mg ha-1 de sistema radicular (SR), marcados com 15N (1,07 e 0,81% de 15N, respectivamente). Durante o ciclo da cultura, determinou-se o acúmulo total de N da planta. Embora o aproveitamento do N oriundo da mineralização dos resíduos culturais (PA e SR) pela parte aérea tenha aumentado expressivamente com o tempo, esta fonte pouco contribuiu para a nutrição da cultura. A recuperação pela cana-planta de 15N-ureia, 15N-PA e 15N-SR foi de 30,3±3,7%, 13,9±4,5% e 6,4±0,9% respectivamente, o que representa 15,9, 4,7 e 1,4% do nitrogênio total acumulado pela parte aérea da cultura.

The objective of this work was to evaluate the recovery, by plant cane, of the nitrogen (15N) from urea and from sugarcane (Saccharum spp.) crop residues - straw and root system - incorporated into the soil. The experiment was settled in 2005/2006 with the sugarcane cultivar SP81 3250. At planting, microplots of 2 m length and 1.5 m width were installed, and N applications were done with 80 kg ha-1 N (urea with 5.05% in 15N atoms) and 14 Mg ha-1 crop residues - 9 Mg ha-1 of sugarcane straw (SS) and 5 Mg ha-1 of root system (RS), labeled with 15N (1.07 and 0.81% in 15N atoms, respectively). The total N accumulation by plants was determined during the crop cycle. Although the N use by shoot from crop residue mineralization (PA and SR) increased significantly over time, this source hardly contributed to crop nutrition. The recovery of the 15N-urea, 15N-SS and 15N-RS by plant cane was 30.3±3.7%, 13.9±4.5% and 6.4±0.9%, respectively, representing 15.9, 4.7 and 1.4% of total nitrogen uptake by shoot.