RESUMO

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.(AU)

Assuntos

RESUMO

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.

Assuntos

RESUMO

Nitrogen can mitigate damages caused by leaf area reduction due to its influence on cell division. This work was carried out aiming to evaluate the efficiency of side-dressing different rates of nitrogen as a management strategy to maize stem defoliation at different growth stages. The experiment was set in Lages, during the 2008/2009 and 2009/2010 growing seasons. The experimental design was a randomized block with split plots. Three defoliation times were tested in the main plot: eight expanded leaves (V8), fifteen expanded leaves (V15) and tasseling (VT), plus a control without defoliation. Four nitrogen rates were assessed in the split-plots: 0, 50, 100 and 200 kg ha-1 of N. Nitrogen was side-dressed at the defoliation day of each growth stage and at V8 in the control. Defoliations performed at V8 did not reduce grain yield, in comparison to the control, regardless of N rate. Side-dressing N rates at V15 increased grain yield, mitigating damages caused by defoliation. Defoliation carried out at VT promoted great grain yield reduction that could not be alleviated with subsequent nitrogen fertilization. The success of nitrogen side-dress as a strategy to minimize maize grain yield losses caused by defoliation depends on the growth stage leaf area reduction occurs.(AU)

O nitrogênio pode mitigar os danos ocasionados pela redução de área foliar por influenciar a divisão celular. Este trabalho teve como objetivo avaliar a eficiência da aplicação de doses de nitrogênio em cobertura como estratégia de manejo da desfolha do colmo em diferentes estádios fenológicos do milho. O experimento foi instalado em Lages, SC, nos anos agrícolas de 2008/2009 e 2009/2010. O delineamento experimental utilizado foi o de blocos ao acaso dispostos em parcelas subdivididas. Na parcela principal testaram-se as épocas de desfolha: sem desfolha; desfolha em V8 (oito folhas expandidas); desfolha em V15(quinze folhas expandidas) e desfolha em VT (pendoamento). Nas subparcelas avaliaram-se quatro doses de nitrogênio: 0, 50, 100 e 200 kg ha-1, aplicadas no dia da desfolha em cada estádio fenológico e em V8 na testemunha não desfolhada. A desfolha realizada em V8 não reduziu o rendimento de grãos do milho, em relação à testemunha não desfolhada, independentemente da dose de N aplicada. A aplicação de nitrogênio em V15 aumentou o rendimento de grãos, reduzindo os prejuízos ocasionados pela desfolha. As desfolhas realizadas em VT causaram grandes prejuízos à produtividade do milho, onde não houve recuperação pela aplicação subseqüente de nitrogênio em cobertura. O sucesso da aplicação de N como estratégia para atenuar os prejuízos ocasionados pela desfolha depende do estádio em que a perda de área foliar ocorre e da dose de N aplicada.(AU)

Assuntos

Assuntos

Assuntos

RESUMO

Nitrogen can mitigate damages caused by leaf area reduction due to its influence on cell division. This work was carried out aiming to evaluate the efficiency of side-dressing different rates of nitrogen as a management strategy to maize stem defoliation at different growth stages. The experiment was set in Lages, during the 2008/2009 and 2009/2010 growing seasons. The experimental design was a randomized block with split plots. Three defoliation times were tested in the main plot: eight expanded leaves (V8), fifteen expanded leaves (V15) and tasseling (VT), plus a control without defoliation. Four nitrogen rates were assessed in the split-plots: 0, 50, 100 and 200 kg ha-1 of N. Nitrogen was side-dressed at the defoliation day of each growth stage and at V8 in the control. Defoliations performed at V8 did not reduce grain yield, in comparison to the control, regardless of N rate. Side-dressing N rates at V15 increased grain yield, mitigating damages caused by defoliation. Defoliation carried out at VT promoted great grain yield reduction that could not be alleviated with subsequent nitrogen fertilization. The success of nitrogen side-dress as a strategy to minimize maize grain yield losses caused by defoliation depends on the growth stage leaf area reduction occurs.

O nitrogênio pode mitigar os danos ocasionados pela redução de área foliar por influenciar a divisão celular. Este trabalho teve como objetivo avaliar a eficiência da aplicação de doses de nitrogênio em cobertura como estratégia de manejo da desfolha do colmo em diferentes estádios fenológicos do milho. O experimento foi instalado em Lages, SC, nos anos agrícolas de 2008/2009 e 2009/2010. O delineamento experimental utilizado foi o de blocos ao acaso dispostos em parcelas subdivididas. Na parcela principal testaram-se as épocas de desfolha: sem desfolha; desfolha em V8 (oito folhas expandidas); desfolha em V15(quinze folhas expandidas) e desfolha em VT (pendoamento). Nas subparcelas avaliaram-se quatro doses de nitrogênio: 0, 50, 100 e 200 kg ha-1, aplicadas no dia da desfolha em cada estádio fenológico e em V8 na testemunha não desfolhada. A desfolha realizada em V8 não reduziu o rendimento de grãos do milho, em relação à testemunha não desfolhada, independentemente da dose de N aplicada. A aplicação de nitrogênio em V15 aumentou o rendimento de grãos, reduzindo os prejuízos ocasionados pela desfolha. As desfolhas realizadas em VT causaram grandes prejuízos à produtividade do milho, onde não houve recuperação pela aplicação subseqüente de nitrogênio em cobertura. O sucesso da aplicação de N como estratégia para atenuar os prejuízos ocasionados pela desfolha depende do estádio em que a perda de área foliar ocorre e da dose de N aplicada.

Assuntos

RESUMO

Historicamente, os perfilhos têm sido considerados indesejáveis na cultura do milho, porque não produzem espigas e podem drenar fotoassimilados do colmo principal. Este trabalho foi desenvolvido objetivando avaliar o efeito do estádio de remoção dos perfilhos sobre o rendimento de grãos do milho, em duas épocas de semeadura. O experimento foi conduzido em Lages, SC, durante os anos agrícolas de 2006/07 e 2008/09. Utilizou-se o delineamento experimental em blocos casualizados, dispostos em parcelas subdivididas. Na parcela principal, foram testadas duas épocas de semeadura: segunda quinzena de outubro (recomendada) e segunda quinzena de dezembro (tardia). Nas subparcelas, foram avaliados quatro estádios de remoção dos perfilhos: colmo principal com seis (V6), nove (V9) e quinze folhas expandidas (V15) e testemunha com perfilhos mantidos até a colheita. Testou-se o híbrido P30F53, na densidade de 55.000 plantas ha-1 e espaçamento entrelinhas de 0,7m. A percentagem de plantas perfilhadas e o número de perfilhos por planta foram maiores nas semeaduras de outubro do que nas de dezembro. Não houve diferenças no rendimento de grãos do tratamento em que os perfilhos foram mantidos, em relação àqueles em que eles foram removidos em V6, V9 ou V15, independentemente da época de semeadura. Isso demonstra que os perfilhos não são drenos que comprometam o desempenho agronômico do milho. Além disso, eles podem contribuir para o rendimento de grãos nas semeaduras feitas em outubro.

Historically, tillers have been considered detrimental to maize because they do not produce ears and may act as sinks competing for carbohydrates with the main stem. This work was carried out aiming to evaluate the effect of tiller removal on maize grain yield at different sowing dates. The experiment was set during the 2006/07 and 2008/09 growing seasons. A randomized complete block design disposed in split-plots was used. Two sowing dates were tested in the main plots: second half of October (recommended) and second half of December (late). Four tiller's fates were evaluated in the split-plots: tiller removal when the main stem had six expanded leaves (V6), nine expanded leaves (V9), fifteen expanded leaves (V15) and tiller maintenance until harvesting. Hybrid P30F53 was sowed at 55,000 plants ha-1, with a row spacing of 0.7m. The percentage of plants with tillers and the number of tillers per plant were higher when maize was sown in October than in December. There was no grain yield difference between treatments where tillers were preserved and those where they were removed at V6, V9 or V15, regardless of sowing date. Such behavior demonstrates that tillers are not sinks that compromise maize agronomic performance. Furthermore, tillers may contribute positively to grain yield when maize is sown in October.