Root system distribution of sugar cane as related to nitrogen fertilization, evaluated by two methods: monolith and probes

Abstract

SUMMARYFew studies on sugar cane have evaluated the root system of the crop, in spite of its importance. This is mainly due to the difficulty of evaluation and high variability of results. The objective of this study was to develop an evaluation method of the cane root system by means of probes so as to evaluate the mass, distribution and metabolically active roots related to N fertilization at planting. For this purpose, an experiment was conducted in an Arenic Kandiustults with medium texture in Jaboticabal/SP, in a randomized block design with four replications and four treatments: control (without N) and 40, 80 and 120 kg ha -1 of N applied in the form of urea in the planting furrow of the cane variety SP81 3250. One week before harvest, a urea-15 N solution was applied at the cane stalk base to detect active metabolism in the root system. Trenches of 1.5 m length and 0.6 m depth were opened between two sugar cane rows for root sampling by two methods: monoliths (0.3, 0.2 and 0.15 m wide, deep and long respectively) taken from the trench wall and by probe (internal diameter 0.055 m). For each method, 15 samples per plot were collected. The roots were separated from the soil in a sieve (2 mm mesh), oven-dried (at 65 °C) and the dry matter was measured. Root sampling by probes resulted in root mass that did not differ from the evaluation in monoliths, indicating that this evaluation method may be used for sugar cane root mass, although neither the root distribution in the soil profile nor the rhizome mass were efficiently evaluated, due to the small sample volume. Nitrogen fertilization at planting did not result in a greater root accumulation in the sugar cane plant, but caused changes in the distribution of the root system in the soil. The absence of N fertilization led to a better root distribution in the soil profile, with 50, 34 and 16 % in the 0-0.2, 0.2-0.4 and 0.4-0.6 m layers, respectively; in the fertilized treatments the roots were concentrated in the surface layer, with on average 70, 17 and 13 % for the same layers. The metabolically active roots were concentrated in the center of the cane stool, amounting to 40 % of the total root mass, regardless of N fertilization (application of 120 kg ha -1 N or without N).Index terms: active roots, root sampling methods. RESUMO: DISTRIBUIÇÃO DO SISTEMA RADICULAR DA CANA-DE-AÇÚCAR, EM FUNÇÃO DA ADUBAÇÃO NITROGENADA, AVALIADOS POR DOIS MÉTODOS: MONÓLITO E SONDAPoucos estudos com cana-de-açúcar avaliaram o sistema radicular da cultura, apesar de sua importância. Esse fato é devido, em grande parte, à dificuldade de avaliação e à elevada variabilidade dos resultados. Objetivou-se com este trabalho avaliar um método de avaliação do sistema radicular da cana, por meio de sondagem, a fim de avaliar a massa, a distribuição e as raízes metabolicamente ativas em função da adubação nitrogenada de plantio. Para isso, foi conduzido experimento em um Latossolo Vermelho distrófico típico textura média, em Jaboticabal/SP, no esquema de blocos ao acaso com quatro repetições...

Root growth and distribution in sugarcane cultivars fertigated by a subsurface drip system

“…Otto et al (2009) have also found 65% of root mass in the first 0.2 m soil layer when evaluating the cultivar SP81-3250. Similar results were reported by Vasconcelos et al (2003), with 52% of root mass in the superficial soil layer.…”

“…Although Azevedo et al (2011), Laclau & Laclau (2009), Otto et al (2009 and Vasconcelos et al (2003) have studied sugarcane root system, they used other methods, which difficult the comparison based on the value itself. However, all of them reported large variability for root evaluations such as root mass and length.…”

“…In Brazil, there are few studies about sugarcane root system (Otto et al, 2009;Vasconcelos et al, 2003). When considering samplings along the crop cycle, the data is even scarcer.…”

Manejo da adubação potássica na cultura da cana-de-açúcar

“…Para a dose de 150 kg ha -1 de K 2 O a produtividade foi semelhante entre a aplicação única ou parcelada, indicando que, mesmo perdendo parte dessa quantidade por lixiviação quando o fertilizante foi aplicado totalmente no sulco, a quantidade que restou na zona de absorção radicular foi suficiente para fornecer o nutriente às plantas. Ademais, o parcelamento da adubação, com aplicação superficial após seis meses do plantio, provavelmente promoveu maior absorção de K pela cana-de-açúcar, tendo em vista que a maior parte das raízes responsáveis pela absorção dos nutrientes localiza-se na camada superficial do solo (Inforzato & Alvarez, 1957;Faroni, 2004;Otto, 2009). …”

Contribution of nitrogen from sugarcane harvest residues and urea for crop nutrition

“…Samples were also used to measure soil bulk density as described in Basanta et al (2003) and Gava et al (2005). These distances and depths were adopted since they comprise more than 80 % of the sugarcane root system, according to Otto et al (2009). A specific probe for root sampling (0.055 m in diameter) was used for the 0-0.30 m soil layer while for the 0.30-0.60 m depth a conventional soil probe (0.03 m) was employed pursuing to increase the detection ability of 15 N.…”