The purpose of this study was to represent the soil moisture in the profile corresponding to the root zone from TDR sensors in a preserved area of the Caatinga biome and analyze the spatialized moisture adjustment equations under different layers of the soil profile. For that, we analyzed three classes of soil (red yellow Ultisol; Hypochromic Luvisol; Udorthent) in the Aiuaba Experimental Watershed, located in the semiarid zone of northeastern Brazil. The hydro-physical parameters representing the soil water retention (field capacity, wilting point and residual moisture) were collected in four campaigns, in six points and in the profiles corresponding to the effective root depth, totaling 216 samples. For the evaluation of the regression models, we used the coefficient of determination, the Pearson correlation and the performance index. The results indicate that the analyzed parameters are homogeneous for the studied soil profiles. The Pearson correlation coefficient indicates a moderate performance for all regression equations. However, the confidence index was determined as very bad for the Red-Yellow Ultisol, passable for the Hypochromic Luvisol and bad for the Udorthent, for the rainy season, and very bad for all classes, for the dry season. Therefore, the use of the regression models is more indicated for periods of higher soil moisture

A produção de biomassa em uma pastagem pode ser incrementada com o uso de fertilizantes, principalmente os nitrogenados. Diante disso, objetivou-se, com este trabalho, avaliar o fluxo de biomassa do capim-massai, durante o estabelecimento e a rebrotação, em casa de vegetação, sob cinco doses de nitrogênio (0; 150; 300; 450 e 600 mg de N dm-3 de solo), em delineamento inteiramente casualizado, com medidas repetidas no tempo, e cinco repetições. A taxa de alongamento foliar foi incrementada pelas doses de nitrogênio (N) e o crescimento de estabelecimento apresentou maior valor, em relação ao das rebrotações. A taxa de alongamento das hastes não foi influenciada pelas doses de N. O crescimento de estabelecimento apresentou maior valor para esta variável, em relação ao das rebrotações. A taxa de senescência foliar anterior não sofreu influência das doses de N, porém, foi alterada entre os ciclos de crescimento. O número de folhas vivas por perfilho foi superior, para as maiores doses e no estabelecimento, o inverso ocorrendo para o filocrono. A dose aplicada de 600 mg dm-3 de N proporcionou um incremento de 448%, na taxa de produção de forragem, e de 455%, na taxa de acúmulo de forragem, em relação àquelas do manejo sem N. A adubação nitrogenada proporciona respostas positivas nas variáveis do fluxo de biomassa do capim-massai. [Response of biomass flow in Massai grass to nitrogen fertilization during the establishment and regrowth]. The use of fertilizers, especially nitrogen, can increase significantly the biomass production of a pasture. The objective of this study was to evaluate the biomass flow of Massai grass produced in greenhouse during the establishment and regrowth under five nitrogen fertilization levels. The experiment was arranged in a completely randomized split-plot design with five nitrogen levels (0; 150; 300; 450 e 600 mg de N dm-3 of soil) and five replications (plots) .The leaf elongation rate was increased with the nitrogen fertilization levels and the establishment growth presented higher values in relation to the regrowth. The culm elongation rate was not influenced by N levels. The establishment growth presented higher values than regrowth. The leaf senescence rate before the cut was not influenced by the nitrogen fertilization, however it was altered by the growth cycles. The number of living leaves per tiller was superior on plants fertilized with highest N levels and at establishment growth, however an opposite effect was observed to the phylochron. The fertilization level 600 mg de N dm-3 of soil lead to an increase of 448% on herbage growth, and of 455% on herbage accumulation rates in relation to the 0 mg de N dm-3 of soil. The nitrogen fertilization provides positive responses to the biomass flow of Massai grass.201

Recent researches have shown promising results for the use of orbital data using the Normalized Difference Vegetation Index (NDVI) to monitor and predict soybean grain yield. The objective of this work was to evaluate propositions of multiple linear regression models to predict soybean grain yield using NDVI. The research was carried out at the Celeiro Farm, in Monte Alegre do Piauí, PI, Brazil, in an area of 200 ha. Five images were collected during the soybean crop cycle: one from the Landsat 8 and four from the Sentinel 2. Regression analyses were carried out between grain yield data (predicted variable) extracted from harvest maps and spectral data (predictor variables) from NDVI of soybean crops at different developmental stages. The promising models were selected by the Akaike Information Criterion (AIC). The models were validated using Root Mean Square Error (RMSE) and Normalized Root Mean Square Error (nRMSE), considering the mean of soybean yield of the plot. The linear regression models developed with NDVI for the V5-V6 and R2 developmental stages showed promising results for the prediction of soybean grain yield, with mean error of predictions of 153.9 kg ha-1, representing 4.2% when compared to the data from field measures.

The Brazilian semiarid region strongly depends on superficial reservoirs (one every 5 km ${}^2$ ) and hence is subject to the deleterious effects of siltation, which reduces water availability. This research proposed a method, simplified bathymetric surveying using remote sensing, for updating the morphological parameters of reservoirs. The study area was the Pentecoste reservoir (360 hm ${}^3$ ) in northeastern Brazil. The results were compared to the conventional bathymetric survey method, which demands more sampling points (235 compared to 1) and was assumed as reference. Siltation assessed through the proposed method was nearly twice as high as that observed through conventional surveys. The morphological parameters derived by both methods were used to assess the long-term water balance of the reservoir. The results show that the outflow diverged 30%, while the evaporated discharge and water availability diverged 10% between the methods. Therefore, in the conditions of the Brazilian semiarid region, the simplified method suffices to assess the water availability of reservoirs affected by silting.

Soil is an important water compartment into a watershed scale, mainly due to its role in providing water to plants and to the influence of antecedent moisture on the runoff initiation. The aim of this research is to assess the permanence of water effectiveness in the soil under preserved-vegetation constraints in the Caatinga biome, in the semiarid northeastern Brazil. For this purpose, hourly soil moisture measurements were collected with TDR and analyzed between 2003 and 2010 for three soil-vegetation associations in the Aiuaba Experimental Basin. The results showed that in nine months per year soil moisture was below wilting point for two associations, whose soils are Chromic Luvisol and Haplic Lixisol (Abruptic). In the third association, where the shallow soil Lithic Leptosol prevails, water was found non-effective four months per year. A possible reason for the high water permanence in the shallowest soil is the percolation process, generating sub-surface flow, which barely occurs in the deeper soils. In situ observations indicates that the long period of soil moisture below the wilting point was not enough to avoid the blooming season of the Caatinga vegetation during the rainy periods. Indeed, after the beginning of each rainy season, there is a growth of dense green vegetation, regardless of the long period under water shortage.

To evaluate biomass components of Massai grass under five doses of N (0, 150, 300, 450 and 600 mg N/dm3 soil) during three cycles of growth (establishment, regrowth 1 and regrowth 2) this study was carried out. The experiment was carried out in a greenhouse, in a completely randomized design with measures repeted over time and five replications. In the three cycles, nitrogen doses had increasing linear effect on green herbage dry matter (GHDM), green leaf dry matter (GLDM), on the tiller population density (TPD) and on forage density. Canopy height and foliage height were the highest ones in establishment of regrowth 2, respectively, and they decreased at the highest doses of nitrogen. Irrigation depth was the greatest at the highest doses and in regrowth 1. Water use efficiency responded positively to the doses, being the regrowth 2 the highest values were obtained at the highest doses of nitrogen. Nitrogen use efficiency by Massai grass is influenced by fertilizantion as well as by the cycles. Nitrogen fertilization has positive effects on the components of Massai grass biomass.201