Avaliação agronômica de variedades de cana-de-açúcar inoculadas com bactérias diazotróficas e adubadas com nitrogênio

Abstract

Resumo -O objetivo deste trabalho foi avaliar a eficiência da inoculação de bactérias diazotróficas e da adubação nitrogenada, em duas variedades de cana-de-açúcar, cultivadas nas mesmas condições edafoclimáticas. O experimento foi conduzido durante os anos agrícolas de 2006/2007 e 2008/2009, em delineamento experimental de blocos ao acaso, com quatro repetições, instalado em março de 2006 em área de cultivo comercial, no Município de Campos dos Goytacazes, RJ. Os tratamentos foram: inoculação com bactérias diazotróficas, adubação com 120 kg ha -1 de N, e o controle sem inoculação e sem adubação com nitrogênio. As variedades de cana-de-açúcar avaliadas foram RB72454 e RB867515. O inoculante continha estirpes de cinco espécies de bactérias diazotróficas. Foram feitas avaliações quanto à produtividade de colmos frescos, ao acúmulo de matéria seca total, ao N total da parte aérea e quanto à abundância natural de 15 N do N disponível no solo e na cana-de-açúcar. As variedades apresentaram comportamentos distintos com os tratamentos, em que a RB867515 foi responsiva e a RB72454 não responsiva à inoculação e à adubação nitrogenada. Na variedade RB867515, o crescimento e o acúmulo de N total na parte aérea das plantas, promovidos pela inoculação, foram similares aos do tratamento com adubação nitrogenada.Termos para indexação: Saccharum, fixação biológica de nitrogênio, interação planta-bactéria. Agronomic evaluation of varieties of sugar cane inoculated with diazotrophic bacteria and fertilized with nitrogenAbstract -The objective of this work was to evaluate the efficiency of inoculation with diazotrophic bacteria and nitrogen fertilization, in two varieties of sugarcane grown under the same edaphic and climatic conditions. The experiment was carried out during the agricultural years 2006/2007 and 2008/2009, in a randomized block design with four replicates, installed in March 2006 in an area of commercial cultivation in Campos dos Goytacazes city, in Rio de Janeiro state, Brazil. The treatments were: inoculation with diazotrophic bacteria, fertilization with 120 kg ha -1 N, and a control without inoculation and without nitrogen fertilization. The sugarcane varieties evaluated were RB72454 and RB867515. The inoculant was composed of five strains of diazotrophic bacteria. Evaluations were done for fresh stalk yield, total dry matter accumulation, total N of shoots, and 15 N natural abundance from available N in the soil and in sugarcane. The varieties performed differently to treatments, in which RB867515 was responsive and RB72454 unresponsive to inoculation and nitrogen fertilization. In the variety RB867515, growth and accumulation of total N in the shoots, promoted by inoculation, were similar to the ones in the treatment with N fertilization.

Inoculation of sugarcane with diazotrophic bacteria

“…The reduction in inoculation efficiency with successive harvests may be associated with N depletion in the soil, because some studies showed that inoculation has no influence on BNF in sugarcane (Schultz et al, 2012) and the yield increases after inoculation may be associated with the growthpromoting effects on the plant root system (Sevilla et al, 2001;Saravanan et al, 2007;Videira et al, 2012). In this case, if the benefit of inoculation is related to the increased use efficiency of plant-available soil N and the soil stock of available N decreases as the crops are being harvested, the efficiency of inoculation may decline over the years.…”

“…The seedlings for planting (cuttings with three buds) were originated from a trial planted from micropropagated plantlets of two varieties, laboratoryinoculated by the method of Reis et al (1999), reinoculated in a greenhouse (nursery) and reinoculated again in the field at planting, according to the method described by Schultz et al (2012).…”

“…These five strains were previously tested and selected by Oliveira et al (2003Oliveira et al ( , 2006, in inoculation studies using the method described by Reis et al (1999). To obtain the inoculum, the bacteria (with initials BR) were obtained from the collection of diazotrophic bacteria at Embrapa Agrobiologia and grown in liquid DYGS culture medium (Silva et al, 2012). Subsequently, 75 mL of DYGS culture medium with a population of 10 9 cells mL -1 of each strain was mixed in 175 mL of carboxymethyl cellulose polymer and starch (60 and 40 %, respectively).…”

“…Field studies showed the efficiency of the inoculant in increasing stalk and dry matter yield of different sugarcane varieties (Oliveira et al, 2003;Silva et al, 2009;Schultz et al, 2012). The benefits of inoculation with diazotrophic bacteria for the crop are not yet fully understood , however there are reports that the plantbacteria association may increase the contribution of atmospheric N 2 by biological fixation in plants, according to the cultivar and environmental conditions (Oliveira et al, 2003;Baldani et al, 2009).…”

Efeitos da fertirrigação sobre a ocorrência e danos de Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) em cana-de-açúcar

“…Com sua rápida adaptação, o Brasil atingiu o patamar de maior produtor mundial da cultura, desempenhando papel importante na economia do país (Schultz et al, 2012).…”