Search

The use of 15N tracers in blends of N-fertilizers contributes to determining the N derived from each N-fertilizer in the plant, improving the recommendation in the field. However, to evaluate the contribution of two 15N-labeled fertilizers to maize nutrition is an expensive process, and it is challenging to manufacture 15N-labeled controlled-release urea (CRU) considering a polymer-sulfur coated urea (PSCU). The objective of this study was to evaluate, in a field experiment, two methods to quantify the N derived from the PSCU (NdfPSCU) in maize plant using two blends (70% PSCU + 30% urea (U) and 30% PSCU + 70% U) applied in three ways (incorporated, broadcast and split application). The first method quantifies the NdfPSCU by subtracting the total N uptake in the N treatment by the sum of the N uptake in the control treatment (without N-fertilizer application) and the N derived from the U (NdfU) in the plant quantified with 15N. The second method quantifies the NdfPSCU using 15N (precise and direct method). Despite the first method is less expensive than the second it underestimated the NdfPSCU in four maize growth stages in Rhodic Eutrustox soil, being necessary the use of 15N in the PSCU to quantify the NdfPSCU with blends of PSCU + U. [ABSTRACT FROM AUTHOR]

Blending polymer-sulfur coated urea (PSCU) and conventional urea (U) for maize (Zea mays L.) fertilization can supply nitrogen (N) during the crop cycle with a single application. Proper placement of PSCU + U (0.15 m below and 0.1 m to the side of seed row) in band application at sowing is necessary to reduce salt stress that can decrease dry weight (DU) and N uptake (NU) of maize plant compromising maize yield. It is not clear the proper N rate in the proper placement for band application of PSCU + U at maize sowing to avoid salt stress. In the current literature, reduction of N rates are being recommended using PSCU + U without consider the probably salt stress provided by high rates of PSCU + U. DW and NU in maize plant as well as soil pH and electrical conductivity (EC) were evaluated in a greenhouse pot trial. N treatments were equivalent to 0, 90, 180, 360 and 540 kg N ha−1 applied incorporated in band in two contrasting soils (Rhodic Eutrustox and Typic Haplustox) using 70%PSCU + 30%U. At V10 (vegetative leaf stage 10), DW and NU of maize aerial part had quadratic behavior in response to increase N rates in the Typic Haplustox soil. In the Rhodic Eutrustox was not observed known behavior for DW and NU in response to increase N rates. Soil pH and EC was higher in the fertilizer row than sowing row. A N rate above of 180 kg N ha−1 using 70%PSCU + 30%U incorporated in bands can reduce DW and NU in early maize plant growth associated with salt concentration of N fertilizer in a Typic Haplustox soil, which could compromise maize yield. [ABSTRACT FROM AUTHOR]

A single application of polymer-sulfur coated urea (PSCU) and conventional urea (U) blends can supply nitrogen (N) throughout the maize (Zea mays L.) cycle but it could become harmful for plants if not properly placed in the soil due to a possible salt stress which would reduce dry weight (DW) and N uptake (NU) in maize. DW and NU in maize plant as well as soil pH and electrical conductive (EC) were evaluated in a greenhouse pot trial. Treatments consisted of different placements (0.05, 0.1 and 0.15 m below and 0, 0.05 and 0.1 m to the side of seed row) of fertilizers (70%PSCU + 30%U, and 100%U) applied at maize sowing in band at a rate equivalent to 180 kg N ha−1 in a Rhodic Eutrustox soil. Control treatment (without N) was also included. At V7 (vegetative leaf stage 7), N fertilizers placed 0.15 m below of seed row provided higher total DW, total NU, EC and pH (in fertilizer row) than 0.05 m and 0.1 m. 70%PSCU + 30%U provided higher total DW and total NU than 100%U in placement 0 m. In addition, 70%PSCU + 30%U placed 0.1 m to the side of seed row provided lower total NU and EC (in fertilizer row) than 0 m. 70%PSCU + 30%U and 100%U placement can negatively interfere maize in vegetative stage when applied incorporated in band at sowing. The proper placement for this condition was 0.15 m below and 0.1 m to the side of seed row. [ABSTRACT FROM AUTHOR]

Urea treated with urease inhibitors (UI) in association with humic substances (HS) is expected to improve urea efficiency by reducing ammonia losses and also provide the benefits of HS such as improve nitrogen (N) recovery by plants. Ammonia volatilization (AV), 15N recovery efficiency in the soil (NRE) and 15N use efficiency (NUE) were evaluated in maize (Zea mays L.) in a greenhouse pot trial. Treatments consisted of 15N-urea treated with UI (0, 0.4% boron (B) +0.15% copper (Cu), 0.64% B, and NBPT (N-(n-butyl) thiophosphoric triamide)) and three levels of HS (0%, 0.6%, and 1.2%). A control treatment (without N) was also included. N treatments were applied at V4 (vegetative leaf stage 4) on soil surface. HS was not efficient on AV reduction, NBPT had the greatest reduction in AV, and B had higher efficiency on AV reduction than Cu. At V8 (vegetative leaf stage 8), NBPT had the greatest NUE followed by B. At VT (tassel fully emerged), NUE from urea treated with NBPT reduced when increased levels of HS, and NBPT had the greatest NRE. UI in association with HS treated-urea does not reduce AV and it does not improve NUE by maize in vegetative stages. [ABSTRACT FROM AUTHOR]

Blends of controlled-release urea (CRU) and conventional urea can be an alternative to conventional fertilization to improve nitrogen use efficiency (NUE) and reduce costs when applied as a single application to agricultural crops. Different indexes of NUE, grain yield, nutrient uptake and partitioning in maize (Zea mays L.) were investigated in field experiments. The treatments consisted of a single rate of 180 kg N ha−1 with different proportions of polymer-sulfur coated urea (PSCU) and conventional urea (U) applied incorporated at sowing (0.05 m below and 0.1 m to the side of the seed row) at two tropical sites (Site 1, Typic Haplustox; Site 2, Rhodic Haplustox) in Brazil. A control treatment (without urea-N) and a treatment with conventional urea management (UCM: 20% of urea-N applied as basal fertilizer and 80% of N applied as top dressing) were also included. This study demonstrates that blends of PSCU and U are efficient in supplying N throughout the maize cycle at a Typic Haplustox site when applied in a single application incorporated at sowing, resulting in high yields and adequate macronutrient uptake. PSCU improved NUE index compared to U and UCM. There was not response for N fertilization in the Rhodic Haplustox site. [ABSTRACT FROM AUTHOR]