ABSTRACT Digital aerial images obtained by cameras embedded in remotely piloted aircraft (RPA) have been used to detect and monitor abiotic stresses in soybeans, such as water and nutritional deficiencies. This study aimed to evaluate the ability of vegetation indexes (VIs) from RPA images to remotely detect water and nutritional status in two soybean cultivars for nitrogen. The soybean cultivars BONUS and BRS-8980 were evaluated at the phenological stages R5 and R3 (beginning of seed enlargement), respectively. To do so, plants were subjected to two water regimes (100% ETc and 50% ETc) and two nitrogen (N) supplementation levels (with and without). Thirty-five VIs from multispectral aerial images were evaluated and correlated with stomatal conductance (gs) and leaf N content (NF) measurements. Near-infrared (NIR) spectral band, enhanced vegetation index (EVI), soil-adjusted vegetation index (SAVI), and renormalized difference vegetation index (RDVI) showed linear correlation (p<0.001) with gs, standing out as promising indexes for detection of soybean water status. In turn, simplified canopy chlorophyll content index (SCCCI), red-edge chlorophyll index (RECI), green ratio vegetation index (GRVI), and chlorophyll vegetation index (CVI) were correlated with NF (p<0.001), thus being considered promising for the detection of leaf N content in soybeans.

RESUMO Objetivou-se, neste estudo, avaliar a produtividade de colmos de dez cultivares de cana-de-açúcar (RB962962, RB 931011, RB931530, RB98710, RB92579, RB867515, RB863129, SP791011, RB72454 e VAT90212) submetida aos regimes hídricos de deficiência, irrigação plena e excedente hídrico, por gotejamento subsuperficial, durante três ciclos de cultivo (2011-2014). O ensaio foi conduzido no Campo Experimental da Embrapa Meio-Norte, Teresina, PI, em Argissolo Vermelho-Amarelo Distrófico. As cultivares RB962962 (162,3 Mg ha-1) e RB867515 (158,5 Mg ha-1) apresentam melhor produtividade de colmos em comparação às demais cultivares, em todos os regimes hídricos e ciclos de cultivo.

ABSTRACT This study aimed to evaluate the stalk yield of ten sugarcane cultivars (RB962962, RB931011, RB931530, RB98710, RB92579, RB867515, RB863129, SP791011, RB72545 and VAT90212) subjected to water deficit, full irrigation and water surplus by subsurface drip irrigation, during three cropping seasons (2011-2014). The experiment was conducted at the Experimental Field of Embrapa Meio-Norte, Teresina, Piauí State, Brazil, in dystrophic Red Yellow Argisol. The cultivars RB962962 (162.3 Mg ha-1) and RB867515 (158.5 Mg ha-1) have better stalk yield compared with other cultivars in all water regimes and cropping seasons.

O efeito da aplicação de nitrogênio em fertirrigação foi avaliado sobre o rendimento e os componentes de produção de melancia, cultivar Crimson Sweet. Conduziu-se essa pesquisa na área experimental da Embrapa Meio-Norte, localizada no município de Parnaíba, PI, no período de setembro a novembro de 2004. O delineamento experimental utilizado foi o de blocos inteiramente casualizados com 4 repetições. Os tratamentos consistiram de 5 níveis de nitrogênio aplicados via fertirrigação (0, 40, 80, 120 e 160 kg ha-1 de N). Os resultados mostraram que a qualidade dos frutos de melancia não foi afetada significativamente pelos níveis de nitrogênio. A produção comercial dos frutos aumentou com a adubação nitrogenada aplicada até 97,61 kg ha-1 e foi de 60,17 Mg ha-1.

To evaluate the effect of nitrogen application under fertigation on yield and production components of watermelon, a study was carried out in an experimental area of Embrapa Meio-Norte in Parnaíba, in the State of Piauí, Brazil, 02º 54' S, 41º 47' W and 46 m altitude) from September to November. The experimental design was in randomized blocks, with four replications. The treatments were composed of five doses of nitrogen (0, 40, 80, 120 e 160 kg ha-1 of N). Results showed that the quality of watermelon fruits was not significantly affected by nitrogen doses. The marketable fruit yield increased up to a nitrogen dose of 97.61 kg ha-1 of N and corresponded to 60.17 Mg ha-1.