ABSTRACT The use of remote sensing in agriculture presents some practical applications in crop production forecast. In this context, studies with remote sensing are scarce for crops such as white oats, which may indicate the capacity of using this technique in the crop. The aim of this study was to evaluate the accuracy in validation of white oat biomass and grain yield estimates by spectral models previously calibrated using two vegetation indices (NDVI and IRVI) at three phenological stages. The mean values of NDVI and IRVI were correlated with the grain and biomass yield of white oats to obtain regression equations. The accuracy was verified by the determination coefficient (R2), root mean square error (RMSE) and mean bias error (MBE). The models were calibrated using data from a field experiment carried out in 2017 and validated with data from the same experiment, but conducted in 2018. The models had good generalization capacity for estimating yield of white oats, especially for biomass yield. Parametrized models in more advanced phenological stages, showed lower error of estimation. Models calibrated with the vegetation index IRVI had lower error of estimation than when calibrated with NDVI.

ABSTRACT Knowledge on nitrogen absorption rate by crops can indicate important managements, especially the definition of rates of this nutrient and the best time for topdressing application. This study aimed to evaluate and compare the accumulation of biomass and nitrogen in white oat cultivated under severe, moderate and no water deficit. Treatments consisted of levels of irrigation, with four repetitions. The treatments under severe water deficit (L1), moderate deficit (L3) and no deficit (L5) received 11%, 60% and 100% of the water volume evapotranspired by the crop (ETc). For each treatment, six plants were collected in each replicate. After collection, plants were separated into leaves, culm and reproductive structures (panicle + grains). Second and third order regressions were tested to model the behavior of biomass and nitrogen accumulation in white oat leaves, culms, reproductive structures and total over time. The maximum total nitrogen accumulation in white oat plants in the treatments L1, L3 and L5 was 50 kg ha-1, 163 kg ha-1 and 246 kg ha-1, respectively. Severe water deficit drastically reduced biomass and nitrogen accumulation in white oat. Severe water deficit causes earlier peak of biomass and nitrogen accumulation, reduces nitrogen accumulation rate and shortens cycle of white oats.

RESUMO Técnicas de sensoriamento remoto têm sido consideradas uma nova tecnologia na agricultura mundial para o diagnóstico da demanda nutricional das plantas. A eficiência no manejo de fertilizantes é uma meta a ser alcançada, e ferramentas modernas baseadas em sensoriamento remoto são promissoras para monitorar as necessidades das culturas. Objetivou-se avaliar o desempenho agronômico e o retorno econômico relativo de aveia-branca sob doses de nitrogênio, bem como verificar se o índice de vegetação por diferença normalizada (NDVI) e o índice de clorofila foliar (ICF) podem ser utilizados para o manejo da adubação nitrogenada em cobertura, em aveia-branca. Os tratamentos consistiram de cinco estratégias de manejo de adubação nitrogenada em cobertura: T1 - 160 kg ha-1 (dose referência); T2 - 90 kg ha-1 (dose recomendada); T3 - 60 kg ha-1 (dose econômica); T4 - 30 kg ha-1 (quando NDVI < 90 % de T1); e T5 - 30 kg ha-1 (quando LCI < 90 % de T1). A aveia-branca não respondeu à adubação nitrogenada em cobertura. O seu monitoramento temporal por meio de índices espectrais permitiu dispensar a adubação nitrogenada em cobertura sem reduzir a produtividade de grãos e de biomassa e o teor de nitrogênio foliar, em relação ao manejo recomendado (90 kg ha-1 de N em cobertura), não existindo diferenças entre os índices espectrais avaliados. Assim, os índices espectrais NDVI e LCI são ferramentas promissoras para o manejo da fertilização nitrogenada em cobertura na cultura da aveia-branca.

ABSTRACT Remote sensing techniques have been considered a new technology in worldwide agriculture for diagnosing the plant nutritional demand. Fertilizer management efficiency is a goal to be achieved, and modern tools based on remote sensing are promising for monitoring the crop needs. This study aimed to evaluate the agronomic performance and relative economic return of white oat under nitrogen rates, as well as to verify whether the normalized difference vegetation index (NDVI) and leaf chlorophyll index (LCI) could be used for topdressing nitrogen fertilization management, in white oat. Treatments consisted of five topdressing nitrogen fertilization strategies: T1 - 160 kg ha-1 (reference rate); T2 - 90 kg ha-1 (recommended rate); T3 - 60 kg ha-1 (economic rate); T4 - 30 kg ha-1 (when NDVI < 90 % of T1); and T5 - 30 kg ha-1 (when LCI < 90 % of T1). The white oat did not respond to the topdressing nitrogen fertilization. Its temporal monitoring using spectral indices allowed dispensing the topdressing nitrogen fertilization without reducing the grain and biomass yields and the leaf nitrogen content, when compared to the recommended management (90 kg ha-1 of N as topdressing), with no differences between the evaluated spectral indices. Thus, both the NDVI and LCI spectral indices are promising tools for the topdressing nitrogen fertilization management in the white oat crop.

ABSTRACT Prior research on sugarcane showed increment of productivity following molybdenum (Mo) fertilization and some indication of the potential role either on nitrate reductase activity (NRA). However, this increment can depend on sugarcane variety and nitrogen (N) fertilization. This study aimed to evaluate the effect of Mo fertilization on Mo uptake, on NRA, nitrate (NO3--N), and ammonium (NH4+-N) contents in leaves and roots of sugarcane, and the accumulation of N and biomass across two sugarcane varieties (RB 867515 and RB 92579). The varieties were subjected to two rates of N fertilization (without N fertilization and 60 kg ha-1 of N) and two rates of Mo fertilization (without Mo fertilization and 200 g ha-1 of Mo). At 70, 100, 130, 200, and 365 days after planting (DAP), the following parameters were determined: Mo, NO3--N and NH4+-N contents, NRA in the leaves and roots, and the accumulation of N, as well as shoot dry matter (SDM). Molybdenum fertilization increased N accumulation in 36 and 44 % in the varieties RB 867515 and RB 92579, respectively. This increase in N accumulation was associated with NRA stimulation of 13 % in the leaves and 42 % in the roots. The maximum NRA occurred around 100 DAP, and its contents in the leaves and roots of the RB 92579 were 0.83 and 0.46 µmol NO2- g-1 h-1 of fresh matter, respectively, and in RB 867515 these values were 0.61 and 0.43 µmol NO2- g-1 h-1 of fresh matter, respectively. The assimilation of NO3--N was increased with Mo application, both with and without N fertilization, suggesting that Mo fertilization is indicated in nutrition management of sugarcane. This study provides insight into how Mo fertilization interacts with N fertilization and sugarcane varieties, altering N accumulation and dry matter production.

Abstract: The increase of N fertilization in sugarcane can negatively influence the technological quality of the crop for sugar and alcohol production. The use of Mo in fertilization combined with N can reduce this effect and increase agricultural and sugar yield. The objective of this study was to evaluate the levels of Mo in soil, roots and leaves of sugarcane fertilized with N and Mo, to measure agricultural and sugar productivity and to evaluate quality of the technological attributes for production of sugar and alcohol. Two varieties were cultivated (RB867515 and RB92579) under field conditions, submitted to two doses of N (0 and 60 kg ha-1) and two doses of Mo (0 and 200 g ha-1) both applied to the soil. The source of N used was urea and the source of Mo was sodium molybdate. RB867515 was influenced by Mo and agricultural and sugar productivity increased by 21%. N fertilization did not increase agricultural productivity but reduced the technological quality of sugarcane, and Mo did not change this reduction. It is suggested that N fertilization should be reduced in first crop cycle and Mo fertilization should be stimulated.