Urea and sugarcane straw nitrogen balance in a soil-sugarcane crop system

Abstract

-The objectives of this study were to evaluate nitrogen utilization by sugarcane ratoon from two sources, applied urea and sugarcane straw covering soil surface (trash blanket), besides the recovery of N from both sources in the soil-plant system. The following treatments were established in a randomized block design with four replicates: T1, vinasse-urea (100 kg ha -1 of urea-N) mixture applied on the total area of the soil covered with cane trash labeled with 15 N; T2, vinasse-urea mixture (urea labeled with 15 N; 100 kg ha -1 of urea-N) applied on the total area of the soil covered with non-labeled sugarcane trash; and T3, urea-15 N (100 kg ha -1 of urea-N) applied in furrows at both sides of cane rows, with previous surface application of vinasse, onto soil without trash covering. The vinasse was applied at a rate of 100 m 3 ha -1 in all treatments. The experiment was carried out on a Yellow Red Podzolic soil (Paleudalf), from October 1997 to August 1998, in Piracicaba, SP, Brazil. The nitrogen use efficiency of urea by the sugarcane ratoon was 21%, while that of the sugarcane straw was 9%. The main contributions of N from sugarcane trash, during one cycle, are the preservation and increase of the organic N in soil. The tendency for a lower accumulation of urea-N in the sugarcane plant, in the soil surface covered with sugarcane residue, was compensated by the assimilation of N from trash mineralization. Nitrogen derived from cane trash was more available to plants in the second half of the ratoon cycle.

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

“…The N recoveries observed for the first ratoon (2007) in treatments with and without N reached 8 % and 11 %, respectively (Table 3). Results were consistent with the findings of Chapman et al (1992) and Gava et al (2005) who obtained 5 % to 9 % of N-trash recoveries by sugarcane after one year. However, at the end of three crops (2007 to 2009), the N recovery by sugarcane almost doubled due to N-fertilizer application (17 against 31 % of the total N of the green harvest residues, respectively, 0 and 150 kg ha -1 of N).…”

“…As aforementioned, the low degradability of sugarcane trash is also related to its high C:N ratio, varying from 70:1 to 120:1 (Gava et al, 2005;Meier et al, 2006;Oliveira et al, 2002;Robertson and Thorburn, 2007ab) while Spain and Hodgen (1994) reported 170:1, one of the highest values in literature. Therein, lower rates of net mineralization of green harvest residues are expected in short-term, although the N supplied by fertilization LSD = least significant difference; CV % = coefficient of variation.…”

“…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).…”

“…This composition affords intense N immobilization by the soil microbial biomass and a slow net mineralization of C and N. Likewise, the recovery rates of N from crop residues incorporated into the soil varied from 2 % to 15 % of the total N contained in such residues (Ambrosano et al, 2005;Basanta et al, 2003;Chapman et al, 1992;Gava et al, 2005;Meier et al, 2006;Ng Kee Kwong et al, 1987;Trivelin et al, 2002;Vitti et al, 2010).…”

Soil and crop residue CO2-C emission under tillage systems in sugarcane-producing areas of southern Brazil

“…This harvesting procedure has provided the return of large amounts of sugarcane crop residues on soil surface and favored soil organic matter accumulation, compared to the burn system where the sugarcane is burned in the fi eld a few days before harvesting. The crop residues (15 Mg ha -1 , dry mass) had high C:N ratios (close to 125:1 in location A; Gava et al, 2005, and close to 99:1 in location B). Tillage operations were applied every six years with chisel plows and ratoon remover.…”