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Fertilizer recommendations must be improved to optimize N use efficiency (NUE) for bioenergy crops. A study was conducted to test the hypothesis that sites varying in historical usage of by-product differ in soil N-supplying power and sugarcane (Saccharum spp.) responsiveness to N fertilization. Our aim was to quantify soil N availability and N fertilizer rates, sources, and application timings for their effects on sugarcane yield and NUE. Three N response trials, each involving 0 to 200 kg N ha-1 , were conducted in the state of São Paulo, Brazil, at sites varying historically in the usage of vinasse. Before fertilizer application and at harvest, soil inorganic N content was quantified and potential N mineralization estimated by the Illinois Soil Nitrogen Test (ISNT); stalk yield and sugar content were measured at harvest and used to estimate NUE. Sugarcane showed significant response to N fertilization only at the sites with no history of vinasse usage. Reducing the N rate from 120 to 80 kg N ha-1 showed limited potential for lowering yield (~ 1 %), while increasing the NUE by 54 %, which was far better than the 14 % increase achieved by modifying the N source or application timing. Monitoring inorganic N and ISNT levels over time to estimate soil N-supplying power has potential for predicting the responsiveness of sugarcane to N fertilization; however, ISNT interpretations must consider factors that impede mineralization or crop N utilization, such as soil acidity or a limitation on the availability of Ca or P. Soil N testing can help optimize NUE for sustainable bioenergy production.

Energy cane (Saccharum spp.) is an alternative for biomass production to meet demands for high yield and fiber content feedstock for bioenergy production. However, there is limited research data and information available for this crop that was recently introduced in Brazil. The focus of this study was to evaluate the biomass production and mineral composition of energy cane genotypes to understand their productivity and define nutrient management practices according to nutrient removal. The experiment was conducted in northeastern Brazil during plant cane and first ratoon crop cycles and evaluated six energy cane and one sugarcane (cultivar most grown in the region) genotype. Depending on genotype and crop cycle, energy cane dry biomass production ranged from 43 to 63 Mg ha−1 and was greater than that of sugarcane, ranging from 25 to 51 Mg ha−1. Energy cane allocated a greater amount of dry biomass in dry leaves and tops than sugarcane. Overall, 1 Mg of fresh energy cane required 1.5 kg of N, 0.32 kg of P, 5.1 kg of K, 0.6 kg of Mg, 0.5 kg of S, 5.7 g of B, 1.4 g of Cu, 6.3 g of Mn, and 4.7 g of Zn. Macronutrient removal by some energy cane genotypes was higher than that by sugarcane due to greater biomass production. Energy cane has the potential for greater dry biomass production than sugarcane, but it also removes a larger amount of nutrients. The recommendation of an amount of nutrients needed for energy cane production is a key issue for the establishment of this crop as a raw material for bioenergy production in Brazil.

A single application of polymer-sulfur coated urea (PSCU) and conventional urea (U) is expected to ensure nitrogen (N) throughout the maize (Zea mays L.) growth cycle being U the likely main N-fertilizer supplier at the beginning and PSCU during the maize growth cycle. This research aimed to evaluate N fertilization management (split, incorporated, and broadcast application) and fertilizer blends (30%PSCU + 70%U and 70%PSCU + 30%U) on volatilization of ammonia (AV) and soil N mineral content (NM); plant N uptake (NU) and 15N-fertilizer recovery (NR); and yield (GY). Field experiments were conducted for two growing seasons (2017–2018 and 2019–2020) in Rhodic Eutrustox soil. U was treated with NBPT (N-(n-butyl) thiophosphoric triamide). N rate was 180 kg ha−1. AV reached 12% of the applied N (broadcast-applied 70%PSCU + 30%U, 2017–2018). The 30%PSCU + 70%U application resulted in higher NM at 40–60 cm depth in vegetative and reproductive stages in both seasons. The 70%PSCU + 30%U application resulted in the highest GY in 2017–2018, and the N treatments did not affect GY in 2019–2020. NR was 3% on average at vegetative leaf stage 4 (V4), and PSCU, the main N-fertilizer supplier applying 70%PSCU + 30%U. After V4, the main N-fertilizer supplier is PSCU for 70%PSCU + 30%U and U for 30%PSCU + 70%U application. These blends (incorporated, broadcast, and split application) can ensure N during the maize growth cycle, with NR of 72.5% at maturity (R6) being 47.9% in the grain.

Tabela 2.4-Efeito do manejo do N-fertilizante e dos ciclos de soqueiras da cana-de-açúcar e sua interação, no acúmulo de biomassa seca do colmo, ponteiro, folha seca, parte aérea e colmos subterrâneos (C.S.) da cana-de-açúcar, nos locais 1 e 2