ABSTRACT Analyses of fertilizer are essential to ensuring that fertilizer sold to final users presents chemical and physical qualities in the range determined by law. As regards the sampling of fertilizers, the official method currently used in Brazil for sampling preparation is to reduce the size of the sample (from ~ 3 kg to ~ 0.25 kg) by quartering, followed by grinding (so as to pass through a 0.85 sieve) and nutrient quantification. Herein, we propose an alternative method of sampling preparation by grinding the total sample (~ 3 kg) before quartering to improve accuracy and reduce segregation during quartering. Six formulations of fertilizers (basal samples) were weighed (0.01 kg precision) and sampled according to the two methods (official and alternative), followed by the quantification of nutrient concentration in duplicate. Results showed that both methods presented similar nutrient concentrations for most formulations compared to the basal samples. However, the alternative method presented higher precision (less variation between replicates) and accuracy (versus the basal samples) than the official method. Consequently, the alternative method can be used for sampling preparation fertilizers with high accuracy and precision in determining nutrient concentration. law from 025 0 25 0.2 so 085 85 0.8 sieve Herein ( samples 0.01 001 01 (0.0 alternative, , alternative) duplicate However less replicates versus Consequently 02 2 0. 08 8 0.0 00 (0. (0

ABSTRACT From 1913 onwards, the global situation changed from a scenario of nitrogen (N) scarcity to an abundance of ammonia (NH3) produced synthetically via the Haber-Bosch process. Several N compounds have been synthesized since then, with urea becoming the main source of N, accounting for 55 % of current N consumption. However, N efficiency in agroecosystems is low and, normally, N recovery in cultivated plants is less than 50 %. This occurs because a large amount of reactive N is lost to the environment, inducing various forms of pollution, threatening human and environmental health, in addition to causing a negative economic impact on the farmer. The main processes responsible for low N efficiency are NH3 volatilization, leaching, and N denitrification. Considering global NH3 volatilization losses of 14 %, it can be assumed that up to 8.6 million Mg of urea are lost every year in the form of NH3. For each ton of NH3 produced, 1.9 to 3.8 Mg of CO2 is emitted into the atmosphere. Therefore, increasing N use efficiency (NUE) without compromising yield is a necessity and a challenge for crop improvement programs and current management systems, in addition to reducing greenhouse gas emissions. In this context, enhanced efficiency fertilizers (EEFs), which contain technologies that minimize the potential for nutrient losses compared to conventional sources, are an alternative to increasing the efficiency of nitrogen fertilization. Currently, EEFs are classified into three categories: stabilized, slow-release, and controlled-release. This study aims to understand the technologies used to produce EEFs and the factors that govern their availability to plants. This review covers the following topics: the discovery of N, N dynamics in the soil-atmosphere system, N assimilation in plants, strategies to increase NUE in agrosystems, NH3 synthesis, NH3 volatilization losses, N fertilizer technologies, the importance of characterization of EEFs, conventional nitrate or ammonium-based fertilizers to reduce gaseous losses of NH3 and future prospects for the use of N fertilizers in agriculture. 191 onwards (N NH (NH3 HaberBosch Haber Bosch process then 5 consumption However normally environment pollution health farmer leaching denitrification 1 86 8 6 8. 19 9 1. 38 3 3. CO atmosphere Therefore (NUE systems emissions context , (EEFs) sources fertilization Currently categories stabilized slowrelease, slowrelease slow release, release slow-release controlledrelease. controlledrelease controlled release. controlled-release topics soilatmosphere soil system agrosystems synthesis ammoniumbased ammonium based agriculture (NH (EEFs

ABSTRACT Fertilization with boron (B) is a crucial aspect in the management of tropical soils to achieve high yield and wood quality in forest species. However, studies are still needed for a better understanding of the effects of B on the anatomy and physiology of African mahogany to improve borate fertilization programs in terms of doses and sources of B. The objective was to characterize the morphology and anatomy of African mahogany leaves subjected to doses and sources of B, as well as to investigate leaf lesions caused by excess B. In a 3 × 3 factorial scheme, a randomized block design was used with four replications, resulting in a total of 36 experimental units. The treatments consisted of three sources of B: borax (sodium tetraborate), ulexite, and colemanite, and three doses of B: 0, 1.5, and 3 mg dm –3 . After 120 days of transplanting, leaf samples with and without toxicity lesions were collected for morphological and anatomical evaluations. Following the collection, the samples were photographed and fixed in Karnovsky’s solution. The plants cultivated in the control treatment did not exhibit any symptoms of B deficiency in the leaf tissue. Borax and ulexite sources, and higher doses of B resulted in greater lesions, accompanied by the accumulation of phenols in the necrotic region. In contrast, the source of lower solubility (colemanite) and lower dose of B demonstrated the highest accumulation of starch. African mahogany is sensitive to applying high doses (3 mg dm –3 ) and high solubility sources of Boron (borax). Excessive B levels cause necrosis and structural disorganization of African mahogany leaf tissues. (B species However scheme replications units sodium tetraborate, tetraborate , tetraborate) colemanite 0 15 1 5 1.5 – 12 transplanting evaluations collection Karnovskys Karnovsky s solution tissue region contrast (colemanite starch ( borax. (borax) tissues 1. (borax

Resumo O objetivo deste trabalho foi avaliar a eficiência de fontes e doses de magnésio solúvel (MnSO4.H2O) e insolúvel (MnCO3) nos processos de absorção, transporte e redistribuição deste nutriente na soja (Glycine max), bem como na produtividade da cultura, em solo de Cerrado. O delineamento experimental foi em blocos ao acaso, em arranjo fatorial 4×2 – quatro doses (150, 250, 350 e 450 g ha−1) × duas fontes (MnSO4.H2O e MnCO3) de Mn –, com quatro repetições. Nas safras de 2015/2016 e 2016/2017, realizaram-se adubações foliares no terceiro trifólio e avaliaram-se os conteúdos de Mn e a produtividade da soja. Em ambas as safras, a fertilização foliar com Mn aumentou os teores do nutriente nas folhas, nos caules e nos grãos, mas não afetou o rendimento de grãos e a produção de matéria seca. Os teores máximos de Mn nas folhas foram obtidos com doses entre 150 e 450 g ha−1. A aplicação de MnSO4.H2O aumentou a absorção, o transporte e a redistribuição de Mn na planta, com desempenho superior ao de MnCO3. A fertilização foliar com MnSO4.H2O em soja, em solo de Cerrado, aumenta os teores de Mn nas folhas, mas não a produtividade e a produção de matéria seca.

Abstract The objective of this work was to evaluate the efficiency of sources and rates of soluble (MnSO4.H2O) and insoluble (MnCO3) manganese on the processes of uptake, transport, and redistribution of this nutrient in soybean, as well as on crop yield, in Cerrado soil. The experimental design was randomized complete blocks in a 4×2 factorial arrangement – four rates (150, 250, 350, and 450 g ha−1) × two sources (MnSO4.H2O and MnCO3) of Mn –, with four replicates. In the 2015/2016 and 2016/2017 crop seasons, foliar fertilizations were carried out on the third trifoliate leaflet, and Mn content and soybean yield were evaluated. In both crop seasons, Mn foliar fertilization increased the contents of the nutrient in leaves, stems, and grains, but did not affect grain yield and dry matter production. The maximum Mn contents in leaves were obtained with rates between 150 and 450 g ha−1. The fertilization with MnSO4.H2O increased Mn uptake, transport, and redistribution in the plant, with a performance superior to that of MnCO3. Foliar fertilization with MnSO4.H2O in soybean, in a Cerrado soil, increases Mn contents in the leaves but not yield and dry matter production.

ABSTRACT New apps have changed the traditional way of learning and teaching; they are also applied as a quickly executed and effective method in agriculture. Soil-app is a web application with a friendly click-point interface built through packages lodged in R software. The app is an advanced model of an open-source platform to support teaching and learning activities in soil analyses and fertilizer recommendations. Soil-app includes soil test interpretation, soil amendment calculations (lime and gypsum), the fertilizer rate for the most important crops in Brazil, an NPK blend calculator, and NPK blend evaluation. It also includes experimental statistical analysis as applied to soil science. Soil-app is a user-friendly and high-performance tool, garnering fast adoption by both students and professionals. It is available for network use through the following link: http://www.genetica.esalq.usp.br/alogamas/R.html

ABSTRACT The use of nitrification inhibitors (NIs; dicyandiamide - DCD) is an alternative to reduce oxidation of ammonium (NH4+-N) to nitrate (NO3–-N) in the soil, reducing NO3–-N losses from fertilization practices. Based on the hypothesis that DCD reduces conversion of NH4+-N to NO3–-N in tropical soils and inhibits ammonia oxidizing microorganisms (AOM) abundance, soils from the Piracicaba region, São Paulo, with different textures (sand, loam and clay) were incubated with ammonium sulphate (AS) and DCD. Contents of NH4+-N, NO3–-N, soil pH, and AOM abundance were quantified periodically. Ammonium sulphate increased AOM abundance in all soils, but AS+DCD presented AOM abundances similar to the control. During 90 days of incubation, the effectiveness of DCD in reducing NO3–-N production was 1.8, 86.4, and 145.6 mg kg–1, while the effectiveness of DCD in reducing AOM abundance was 1.2, 3.0 and 2.3 × 10–3 g soil–1 for sandy, loamy, and clayey soils, respectively. DCD effectiveness was greater in loamy and clayey soils due to the naturally low nitrification in sandy soils. Application of AS treated with DCD showed potential not only to reduce NO3–-N production in loamy and clayey soils, but also to decrease the soil nitrification rate. Overall, DCD was effective in reducing AOM abundance and conversion of NH4+-N to NO3–-N in loamy and clay soils evaluated here. The increase in clay content directly influences DCD effectiveness in reducing conversion of NH4+-N to NO3–-N.

RESUMO Adubações com fósforo (P) apresentam baixa eficiência devido à adsorção de P na superfície da argila em solos tropicais. O superfosfato complexado com ácido húmico (SSP+HA) é apresentado como uma alternativa para melhorar a eficiência do uso do P e a produtividade das culturas. Nesse sentido, o objetivo deste estudo foi investigar o desempenho do SSP+HA na produção de cana-de-açúcar com incrementos da matéria seca (MS) e conteúdo de P nas plantas. O experimento foi conduzido com duas fontes de P (superfosfato simples-SSP; SSP+HA) e cinco doses (0; 45; 90; 135 e 180 kg ha-1 de P2O5). A dose de 135 kg ha-1 foi usada para explicar o efeito residual do P, coletando solo na cana-planta e primeiro corte. Amostras de caules, ponteiras e raízes foram coletadas para determinar MS e conteúdo de P; ambas variáveis foram usadas para calcular a eficiência de assimilação de fósforo (EaP). Os resultados mostraram que a aplicação de SSP aumentou MS e conteúdo de P nas plantas, com desempenho superior ao SSP+HA. A EaP foi maior no SSP+HA, indicando que o P foi metabolizado de forma mais eficiente, mas não refletiu no aumento de MS. As doses de P aumentaram a produtividade da cana-planta, mas não houve efeito do P aplicado em soqueira, devido ao efeito residual do P aplicado no plantio. O SSP apresentou desempenho superior ao SSP+SH no plantio da cana-de-açúcar. Mais pesquisas são necessárias para melhor ilustrar o efeito do SSP+HA na absorção e translocação do P.

ABSTRACT In tropical soils, the efficiency of phosphorus (P) fertilization is low, due to P adsorption on the surface of the clay. Superphosphate complexed with humic acid (SSP+HA) is presented as an alternative for improving P use efficiency and crop yields. The aim of this study was to investigate SSP+HA performance in sugarcane production including increases in plant dry matter (DM) and P content. The experiment was conducted with two sources of P (simple superphosphate - SSP, SSP+HA) and five doses (0, 45, 90, 135 and 180 kg ha-1 P2O5). The dose of 135 kg ha-1 P2O5 was used to explain the residual effect of P, collecting soil samples from the plant cane and first ratoon. Stalk, top and root samples were collected to determine DM and P content; both variables were used to calculate the P assimilation efficiency (PaE). Results showed that the application of SSP increased the DM and P content of the plants, with superior performance compared to SSP+HA. PaE was greater under SSP+HA, indicating that P was metabolized more efficiently; however this did not reflect in an increase in DM. AThe P rates increased the sugarcane yield in cane plant, but there was no effect of P applied in the first ratoon due to the residual effect of P applied in planting. SSP presented superior performance compared to SSP + SH in sugarcane planting. Further research is needed to better demonstrate the effect of SSP+HA on the absorption and translocation of P.

ABSTRACT: The utilization of insoluble sources of micronutrients as concentrated suspensions (CSs) is increasing in Brazilian agriculture; however, much information regarding the physicochemical characterization of these products is required to demonstrate the absorption behavior by plant leaves. This study aimed to characterize the CSs available on the Brazilian market to support their potential use as foliar fertilizers. We selected five CSs containing Mn, five CSs containing Zn and three CSs containing Cu from five different companies. In each product, the mean particle size was evaluated by dynamic light scattering (DLS), the particle shape and size were evaluated by scanning electron microscopy (SEM), the aggregation degree was determined by the zeta potential and the heavy metal contents were determined by acid digestion followed by reading on ICP-OES. The mean hydrodynamic diameter of fertilizers containing Cu, Mn and Zn was 315 ± 55, 378 ± 184 and 435 ± 107 nm, respectively. The zeta potential varied from –20 to –30 mV, indicating potential particle aggregation and formation of higher structures. SEM images indicated great variation in the size and shape of the particles in each product. All products exhibited concentrations of toxic elements within the legislation thresholds. The average particle size of CSs currently marketable in Brazil does not allow their classification as nanomaterials (< 100 nm). Therefore, their foliar absorption is unlikely, once the particle size is higher than the exclusion limit observed for stomata and cuticle pathways, as well as the nutrient content as ions is low according to the solubility constant.

ABSTRACT: Integrating plant density and nitrogen (N) management is a strategy for improving corn yields, especially for off-season corn production in the tropics. This study tested the hypothesis that increasing plant densities and N rates promotes yield gains for off-season corn production in high-yielding environments. The aim of the study was to investigate the yield performances of two hybrid versions (DKB PRO and DKB PRO3) submitted to three plant densities (55,000; 65,000 and 75,000 plants ha−1) and four N rates (control, 60, 120 and 180 kg ha−1 N). Field trials were undertaken at Uberlândia-MG (site1 and 2) and Pedro Afonso-TO (site 3), Brazil from which data on corn yield parameters were collected and analyzed. Multivariate analysis separated the three trial areas into two groups, presenting high (sites 1 and 2) and low yields (site 3), which were related to weather conditions. There was no influence of a hybrid version or plant densities on crop yields at site 1 or 2. In contrast, there was a positive response to increasing plant densities and the use of DKB PRO3 at site 3. A significant response to N was observed at sites 2 and 3, following a plateau model. Our results suggest that N application rates and plant densities do have the potential to increase off-season corn yields in low yielding environments.

ABSTRACT: N 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.

ABSTRACT Intercropping corn and palisade grass is a technique to increase straw production, soil C contents, nutrient cycling and crop yield. However, concerns arise from nitrogen (N) uptake by the intercropping crop causing reduction in the yield of the corn. Our objective was to evaluate N recovery efficiency (NRE), and the N dynamics in the soil-plant system in corn intercropped with palisade grass. A field trial was carried out in Bahia, Brazil, evaluating two cropping systems: corn (monoculture) and corn intercropped with palisade grass sowed between rows on the same day as the corn crop, with four replicates in a completely randomized block design. Nitrogen (150 kg∙ha–1of 15N-urea) was applied at sowing to determine NRE, which means the amounts of N-fertilizer uptake in corn and palisade grass, the amounts of N-fertilizer in soil and the 15N-fertilizer balance. Neither the NRE (63.3% in monoculture and 57.2% in intercropping) nor corn grain yield (9,800 kg∙ha–1 in monoculture and 9,671 kg∙ha–1 in intercropping) was affected by intercropping, which accumulated only 2.1 kg∙ha–1 of N-fertilizer or 1.4% N rate. In addition, palisade grass yielded 2,265 kg∙ha–1 of dry matter. The balance indicated that 82.4% of N-fertilizer was recovered in the monoculture and 86.9% in the intercropping. Intercropping palisade grass does not affect grain yield or N corn nutrition and has the potential to increase straw production contributing to maintenance of no-till.

ABSTRACT: Determining nutrient uptake and accumulation rates by cotton crops is important to define management strategies, especially for transgenic varieties, which are cultivated using high-technology approaches that require substantial investment to maximize yield. Currently in Brazil, the states of Bahia and Mato Grosso are responsible for 84.4 % of the total cotton growing area. In the present study, two trials were conducted in 2013, one that involved planting FM 940 GLT, FM 980 GLT, and FM 913 GLT varieties in the state of Bahia and the other which involved FM 940 GLT and FM 980 GLT varieties in the state of Mato Grosso. The aim of the two trials was to represent the two regions that currently encompass the largest areas of cotton cultivation. Tissue samples, consisting of leaves, stems, and reproductive components, were collected eleven times during the crop cycle for determination of nutrient content and shoot dry matter. After weighing, plant tissue samples were dried and ground to determine nutrient contents. Because there were no overall differences in nutrient contents and biomass accumulation of the varieties during the crop cycle, we undertook joint analysis of the data from all varieties at each site. Favorable climatic conditions in Bahia promoted plant biomass production that was twice as much as plants grown in Mato Grosso, with cotton yields of 6.2 and 3.8 t ha−1 of lint and seed, respectively. The maximum nutrient accumulation occurred between 137-150 days after emergence (DAE) for N; 143-148 for P; 172-185 for K; 100 for Ca; 144-149 for Mg; and 153-158 for S. Maximum uptake ranged from 218-362 kg ha−1 N; 26-53 kg ha−1 P; 233-506 kg ha−1 K; 91-202 kg ha−1 Ca; 28-44 kg ha−1 Mg; and 19-61 kg ha−1 S. On average, the sites revealed nutrient export of 14, 2, 23, 3, 2, and 2 kg t−1 of lint and seed for N, P, K, Ca, Mg, and S, respectively, with little variation among sites. Extraction of nutrients per area by cotton vary among sites, but nutritional requirement of cotton per unit of lint and seeds is similar independently of yield potential.

Resumo: O objetivo deste trabalho foi avaliar o efeito da aplicação foliar de magnésio no desempenho produtivo de soja (Glycine max) e milho (Zea mays) em solo com níveis adequados de saturação por base e conteúdo de magnésio, no Brasil. Os experimentos foram desenvolvidos em Latossolo Vermelho-Amarelo distrófico cultivado com soja e milho nas safras 2013/14 e 2014/15, respectivamente. Os tratamentos consistiram de aplicação foliar de doses de Mg (50, 100, 250, 500, 1.000 e 1.500 g ha-1 e controle sem Mg) nos estádios fenológicos V4, R1 e R5.1 (soja) ou V4 e R2 (milho), na forma de sulfato de magnésio heptahidratado (MgSO4∙7H2O). Avaliaram-se o índice SPAD, teor foliar de Mg, produtividade de grãos e massa de 100 grãos. A aplicação foliar de Mg aumentou o índice SPAD na cultura da soja e o teor foliar de Mg na cultura do milho. As doses de Mg de 540 e 890 g ha-1 proporcionaram incrementos de 325 e 737 kg ha-1 na produtividade da soja e do milho, respectivamente, independentemente do estádio fenológico. A aplicação foliar de Mg no estádio reprodutivo aumentou em 2% a massa de 100 grãos de ambas culturas. A pulverização foliar de Mg melhora os parâmetros produtivos das culturas de soja e milho.

Abstract: The objective of this work was to evaluate the effect of magnesium foliar spray on yield performance of soybean (Glycine max) and corn (Zea mays) cultivated in soil with adequate levels of base saturation and magnesium content in Brazil. The field trials were conducted on a Typic Hapludox cultivated with soybean and corn in the 2013/2014 and 2014/2015 crop seasons, respectively. Treatments consisted of Mg rates (50, 100, 250, 500, 1,000 and 1,500 g ha-1 and a control without Mg) applied during the V4, R1, and R5.1 (soybean) or V4 and R2 (corn) phenological growth stages as magnesium sulfate heptahydrate (MgSO4∙7H2O). The SPAD index, leaf Mg content, grain yield, and 100-grain weight were evaluated. The Mg foliar spray increased the SPAD index in soybean and the leaf Mg content in corn. The Mg rates of 540 and 890 g ha-1 increased in 325 and 737 kg ha-1 the yield performance of soybean and corn, respectively, regardless of the phenological growth stages. The Mg application during the reproductive stages increased in 2% the 100-grain weight for both crops. Foliar spraying of Mg improves the yield performance in soybean and corn crops.

RESUMO A manutenção da palha na superfície do solo dificulta a incorporação mecânica dos fertilizantes nitrogenados no solo. A aplicação de ureia na superfície nestas condições favorece as perdas de N-NH3 por volatilização, tornando necessário o uso de inibidores de urease ou fontes menos sujeitas à volatilização. Avaliou-se a volatilização de NH3 de fontes de N aplicadas sobre palhada de cana-de-açúcar. O experimento foi realizado em Nitossolo Vermelho eutrófico no município de Iracemápolis-SP em junho de 2014. O delineamento experimental foi em blocos aleatorizados, com sete tratamentos e quatro repetições. Os tratamentos foram controle [CO], nitrato de amônio [NA], NS30TM (fusão entre nitrato de amônio-75% e sulfato de amônio-25%) [NS30TM], mistura física de sulfato de amônio (75%) e nitrato de amônio (25%) [NA-SA], ureia [UR], ureia recoberta com 0,4% Cu e 0,15% B [UR-CuB] e ureia tratada com 530 mg NBPT kg-1 [UR-NBPT]. Todos os tratamentos (exceto controle) foram aplicados na dose de 100 kg ha-1 de N. As perdas de N-NH3 foram avaliadas até 30 dias após adubação (DAA). As máximas perdas de N-NH3 ocorreram aos 16 DAA para UR e UR-CuB e aos 20 DAA para UR-NBPT. As perdas acumuladas de N-NH3 foram 20, 17 e 14% para UR, UR-CuB e UR-NBPT, respectivamente; para as fontes não amídicas as perdas foram inferiores a 1% do N aplicado. A adição de inibidores de urease tem potencial em reduzir perdas por volatilização da ureia mesmo em condições de elevada quantidade de palha sobre o solo.

ABSTRACT Maintenance of crop residues over soil surface under conservational systems limits incorporation of nitrogen fertilizers into the soil. Application of urea over crop residues enhance N-NH3 volatilization losses, justifying the usage of urease inhibitors or N sources less susceptible to volatilization under such conditions. This study aimed to evaluate volatilization losses from N sources applied over sugarcane straw. A field trial was carried out in a sugarcane field in Iracemapolis, Sao Paulo on a Typic Kandiudox in June 2014. We used a complete block experimental design, with seven treatments and four replications. Treatments included Control [CO], ammonium nitrate [AN], NS30TM (ammonium nitrate-75% and ammonium sulfate-25% fused mixture) [NS30TM], ammonium nitrate plus ammonium sulfate (ammonium nitrate-75% and ammonium sulfate-25% physical mixture) [AN-AS], urea [UR], urea treated with 0.4% Cu and 0.15% B [UR-CuB], urea treated with 530 mg kg-1 of NBPT [UR-NBPT]. Treatments were applied at rate of 100 kg ha-1 N (except CO). Volatilization losses were quantified up to 30 days after fertilization (DAF). Maximum N-NH3 occurred 16 DAF for UR and UR-CuB and 20 DAF for UR-NBPT. Accumulated N-NH3 losses ranged from 20% (UR), 17% (UR-CuB), and 14% (UR-NBPT) of applied N; non-amidic sources showed losses lower than 1%. Adding urease inhibitor to urea shows potential in reducing volatilization losses even under application over large amounts of straw.

ABSTRACT When the harvesting of sugarcane involves a mechanized process, plant residues remain on the soil surface, which makes proximal and remote sensing difficult to monitor. This study aimed to evaluate, under laboratory conditions, differences in the soil spectral behavior of surface layers Quartzipsamment and Hapludox soil classes due to increasing levels of sugarcane’s dry (DL) and green (GL) leaf cover on the soil. Soil cover was quantified by supervised classification of the digital images (photography) taken of the treatments. The spectral reflectance of the samples was obtained using the FieldSpec Pro (350 to 2500 nm). TM-Landsat bands were simulated and the Normalized Difference Vegetation Index (NDVI) and soil line were also determined. Soil cover ranged from 0 to 89 % for DL and 0 to 80 % for GL. Dry leaf covering affected the features of the following soil constituents: iron oxides (480, 530 and 900 nm) and kaolinite (2200 nm). Water absorption (1400 and 1900 nm) and chlorophyll (670 nm) were determinant in differentiating between bare soil and GL covering. Bands 3 and 4 and NDVI showed pronounced variations as regards differences in soil cover percentage for both DL and GL. The soil line allowed for discrimination of the bare soil from the covered soil (DL and GL). High resolution sensors from about 50 % of the DL or GL covering are expected to reveal differences in soil spectral behavior. Above this coverage percentage, soil assessment by remote sensing is impaired.