Nitrogênio mineral na soja integrada com a pecuária em solo arenoso

Abstract

Resumo:No Brasil, a soja tem sido introduzida em regiões que apresentam solos arenosos e clima tropical, sendo muitas vezes integrada com a pecuária. A demanda da oleaginosa por nitrogênio(N) é suprida pela mineralização da matéria orgânica do solo e pela fixação biológica do N. No entanto, há questionamentos quanto ao efeito da adubação nitrogenada na cultura da soja cultivada em solos arenosos, com alta quantidade de palha de gramíneas. Objetivou-se com este trabalho avaliar o desempenho de duas cultivares de soja, em solo arenoso, após dois anos com pastagem de Urochloa brizantha, submetidas a diferentes doses (20 e 45 kg de N ha -1 ) e épocas de aplicação (semeadura, no início do florescimento e no início do enchimento dos grãos) de N em solo com elevada quantidade de palha de U. brizantha. Foram conduzidos dois experimentos no Noroeste do Paraná, Brasil, um com a cultivar BMX Potência RR e outro com a cultivar BRS 360 RR, em um solo muito arenoso (11% de argila). Ao todo, foram testados sete tratamentos (fatores combinados e a testemunha), arranjados em delineamento de blocos casualizados, com quatro repetições. Em solo arenoso, com alta quantidade de palha de pastagem de U. brizantha, a adubação nitrogenada, aplicada em diferentes doses e estádios de desenvolvimento da soja, cultivares BMX Potência RR e BRS 360 RR, não influencia a partição de fotoassimilados entre folhas e caules, o teor de N nas folhas, a produtividade, os componentes de rendimento e os teores de óleo e proteína nos grãos. Palavras-chave:Composição. Glycine Max L.Merril. Integração Lavoura-Pecuária. Plantio Direto. Produtividade. Abstract:In Brazil, soybean has been introduced in areas with sandy soil and tropical climate, often under crop-livestock system. The use of nitrogen (N) for this crop is supplied by the soil organic matter mineralization and the biological N fixation. However, there are questions about the effect of nitrogen fertilization in soybean crop under sandy soils with a high amount of straw. The aim of this study was to evaluate the agronomic performance of two soybean cultivars in different doses (20 and 45 kg N ha -1 ) and application times (sowing, at flowering or early grain filling) of N in sandy soil with high amount of Urochloa brizantha straw. Two experiments were conducted in Northwest of Paraná state, Brazil, the first experiment with the BMX Potência RR cultivar and the second one with the BRS 360 RR cultivar, in a sandy soil (11% clay). The experiment were composed by seven treatments (interaction between factors and the control), settled in a randomized block design with four replications. In sandy soil, with high amount of U. brizantha straw, the nitrogen fertilizer applied at different doses and at soybean development stages, cultivars BMX Potência RR and BRS 360 RR, does not influence the photoassimilates partition between stem and leaves, foliar N concentration, yield, yield components, and the oil and protein content in the grains.

Soybean growth and nitrogen accumulation by soybeans in response to desiccation times of Urochloa brizantha pasture and nitrogen fertilization

“…The same was observed at R4 in the experiment without N application and with 150 kg ha -1 of N. For the experiment treated with 300 kg ha -1 of N, there was effect of desiccation times on LAI and plant dry mass at R4, when earlier desiccation before sowing increased these variables. Thus, these effects on soybean growth and N accumulation disappeared with later on the crop cycle, corroborating previous results from Franchini et al (2015a), Balbinot et al (2016b).…”

“…In the non-N-fertilized pasture, N supply to soybean may have been counterbalanced by greater biological N fixation (Balbinot et al, 2016a). In a study of Balbinot et al (2016b), no significant differences for N concentration and shoot biomass were found either in response to different rates (20 and 45 kg ha -1 of N) or N application times (sowing, R1, and R5.2) after two years of U. brizantha pasture. In a study of Franchini et al (2015b), the application of 30 kg ha -1 of N at soybean sowing did not change the canopy cover and the final plant stand either.…”

Assessing Nitrogen Limitation in Inoculated Soybean in Southern Brazil

“…Soybean yield response to small N amounts should be expected only in N‐deficient soils (Dadson and Acquaah, 1984), which is not the case of soils from the Center‐South region of Paraná, southern Brazil with high SOM (SOM > 41 g kg −1 ; Table 1) (Fontoura and Bayer, 2009). Lack of yield response to starter N is consistent with previous studies in Brazil (Jendiroba and Câmara, 1994; Mendes et al, 2003; Hungria et al, 2006; Aratani et al, 2008; Balbinot Junior et al, 2016) and around the world (Herridge and Brockwell, 1988; Mrkovački et al, 2008; Josipović et al, 2011; Kamara et al, 2012; Janagard and Ebadi‐Segherloo, 2016) with diverse soil and weather conditions.…”

“…The rationale behind this practice is to supply low amounts of N early in the season when nodules are not completely formed and N 2 fixation is not active (Abendroth et al, 2006) as well as when N derived from mineralization can be scarce under low temperatures and/or low levels of SOM (Dadson and Acquaah, 1984). Results of those studies are contradictory, showing either yield increases (e.g., Osborne and Riedell, 2006; Boroomandan et al, 2009; Gai et al, 2017) or lack of yield response to N (e.g., Hungria et al, 2006; Mrkovački et al, 2008; Josipović et al, 2011; Kamara et al, 2012; Balbinot Junior et al, 2016).…”

Brachiaria and Panicum maximum in an integrated crop–livestock system and a second-crop maize system in succession with soybean

“…Mulch biomass also provides physical benefits such as increased aeration and uncompacted soil (Flávio Neto et al ., 2015). Mulch biomass also provides biological benefits such as increased microbial decomposition activity and excretion of animal faeces and decreased amounts of weeds and pesticide applications, improving soybean plant establishment (Balbinot Junior et al ., 2016).…”