ABSTRACT Through the use of remote sensing, the productivity and the nutritional state of the plants can be estimated in relation to the nitrogen doses due to the modification of the canopy reflectance. In this study, values of the normalized difference vegetation index (NDVI) obtained by a terrestrial optical sensor were correlated with productivity and contents of nitrogen (N) and of foliar crude protein (CP) of Brachiaria brizantha cv. Marandu, fertigated with doses of sewage treatment effluent (STE) The NDVI average rates of the forage were obtained by the active terrestrial sensor (GreenSeeker) before the harvests that were realized every 28 days in 2014. Five fertigated treatments with the following fractions of STE in water were evaluated: E5 = 1.0; E4 = 0.87; E3 = 0.60; E2 = 0.31; and E1 = 0.11. During the 12 months of experiment, the treatment E5 received 1,132 kg ha-1 of N and the others received quantities proportional according to the application fractions defined in each treatment. The increasing application doses of STE resulted in higher yields of dry biomass and better leaf qualities in N and crude protein (CP). The productivity, the foliar N content and the NDVI index were increasing due to the gradual application of applied STE. There was a high linear correlation among the NDVI indexes and the productivity (r>0.9256) and with the N content (r>0.9570) and also for CP (r>0.8421) and leaf N (r>0.8339), demonstrating that the method can be used to estimate forage productivity and quality.

RESUMO Os erros de posicionamento pelo GNSS são inevitáveis, independentemente do tipo de posicionamento adotado. Na agricultura esses erros podem representar maior ou menor taxa de sobreposição entre as passadas dos conjuntos mecanizados, o que afeta, consequentemente, a qualidade da operação. Objetivou-se, neste sentido, avaliar os principais erros ocasionados durante a operação de semeadura de amendoim utilizando direcionamento automático com sinal RTX, por meio da análise do Controle Estatístico de Processo. Foram avaliados o erro de deslocamento do trator, o erro de execução do projeto, em quatro passadas, além do erro de paralelismo entre as passadas do conjunto trator-semeadora. O erro médio de execução ficou, em todas as passadas, dentro do estipulado pelo fornecedor do sinal, com valores menores que 3,8 cm. O erro médio do conjunto trator-semeadora encontrou-se no limite do aceitável. Já para o deslocamento lateral do trator, pela análise das cartas de controle, houve interferência da declividade na ocorrência de erros acima do estipulado. Com base na análise das cartas de controle constata-se que houve precisão para o erro de execução de projeto e que é possível utilizar o sinal RTX em operações agrícolas que requerem precisão menor que 3,8 cm, como a semeadura de amendoim.

ABSTRACT GNSS positioning errors are certain, regardless of the adopted positioning method. In agriculture, these errors may represent higher or lower overlapping rates between passes of a mechanical assembly, affecting operation quality. Therefore, this study evaluated the main errors arising from peanut sowing operation performed with an auto-steer guidance system by an RTX signal, using the Statistical Process Control techniques. The errors evaluated were: in tractor lateral displacement, project execution, and parallelism between passes of tractor-seeder set. The average errors of project execution in all passes were within the range specified by the manufacturer, i.e. lower than 3.8 cm. The average error of tractor-seeder set was also within the accepted range. However, as shown in control charts, lateral tractor displacement had interference of terrain slope, causing average errors higher than the accepted range. Based on the control charts, project execution accuracy was satisfactory, and it is possible to use the RTX signal in agricultural operations that require accuracy lower than 3.8 cm, such as peanut sowing.

ABSTRACT The mechanical resistance to penetration when related to the water content is an indicator often used of soil compaction, the use of positioning methods for greater accuracy of this review is important. In this context, this study aimed to determine the variability of positioning methods provided by GPS receivers to determine the spatial behavior of physical attributes related to soil compaction. The study area is located in the municipality of Jaboticabal, around the latitude 21º15’22”S and longitude 48º18’58”W, being characterized with a clayey Oxisol. The variables used as parameters of soil physical properties were the mechanical resistance to penetration and water content, using a sampling grid of 20 x 20 m, totaling 60 points. We used six models of GPS receivers: Garmin Etrex Vista, Garmin Etrex 30, Ashtech MM6, Trimble Nomad, Garmin Map 62 and Trimble R6, with all georeferenced points in the regular grid intersections. The georeferencing using GPS receivers (single point positioning and post-processed differential correction) interfered in characterizing the spatial variability of soil resistance to penetration, differently for some receivers to the water content attribute. Positioning methods with post-processed differential correction, using R6 and MM6 models, better define the management zones of soil resistance to penetration.

A publicação da Lei 10.267, de 28-08-2001, alterou o paradigma do cadastro rural brasileiro, pois essa lei, conhecida como "Lei do Georreferenciamento", criou o Cadastro Nacional de Imóveis Rurais, que unifica, em uma base comum, diferentes cadastros presentes em vários órgãos governamentais, como do Instituto Nacional de Colonização e Reforma Agrária (INCRA), da Secretaria da Receita Federal, do Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais e da Fundação Nacional do Índio. Também, esse novo sistema cadastral tem uma componente gráfica até então inexistente, em que os limites do imóvel rural são georreferenciados ao Sistema Geodésico Brasileiro. Esse novo paradigma teve como consequência uma padronização no levantamento de campo e respectiva representação dos imóveis rurais, conforme a Norma Técnica para Georreferenciamento de Imóveis Rurais, publicada pelo INCRA, em atendimento à nova legislação. Graças ao georreferenciamento, possibilitou-se a criação de um SIG público de acesso gratuito via Internet. Como dificuldades, temos a grande extensão territorial brasileira, necessidade de profissionais especializados e, principalmente, o processo de certificação que o INCRA tem de realizar para cada imóvel georreferenciado. Espera-se que essa última dificuldade seja sanada com a implantação do Sistema de Gestão Fundiária, que permitirá a certificação automatizada e online, tornando o processo mais transparente, ágil e rápido.

The publication of the Law 10,267 of 08/28/2001 changed the paradigm of rural registration in Brazil, because this law known as the "Law of Georeferencing" has created the National Registration of Rural Property, that unifies in a common basis different registrations present in several government agencies, such as the National Institute for Colonization and Agrarian Reform (INCRA), the Secretariat of Federal Revenue, the Brazilian Institute of Environment and Natural Resources, and the National Indian Foundation. Also, this new registration system has a graphical component which has not existed until such date, where the boundaries of rural property are georeferenced to the Brazilian Geodetic System. This new paradigm has resulted in a standardization of the survey and its representation of rural properties according to the Technical Standard for Georeferencing of Rural Properties, published by INCRA in compliance with the new legislation. Due to the georeferencing, the creation of a public GIS of free access on the Internet was possible. Among the difficulties found it may be observed the great Brazilian territory, the need for specialized professionals, and especially the certification process that INCRA has to perform for each georeferenced property. It is hoped that this last difficulty is solved with the implementation of the Land Management System that will allow automated and online certification, making the process more transparent, agile and fast.

A caracterização da variabilidade espacial dos atributos do solo é indispensável para subsidiar práticas agrícolas de maneira sustentável. A utilização da geoestatística para caracterizar a variabilidade espacial desses atributos, como a resistência mecânica do solo à penetração (RP) e a umidade gravimétrica do solo (UG), é, hoje, prática usual na agricultura de precisão. O resultado da análise geoestatística é dependente da densidade amostral e de outros fatores, como o método de georreferencimento utilizado. Desta forma, o presente trabalho teve como objetivo comparar dois métodos de georreferenciamento para a caracterização da variabilidade espacial da RP e da UG, bem como a correlação espacial dessas variáveis. Foi implantada uma malha amostral de 60 pontos, espaçados em 20 m. Para as medições da RP, utilizou-se de penetrógrafo eletrônico e, para a determinação da UG, utilizou-se de trado holandês (profundidade de 0,0-0,1 m). As amostras foram georreferenciadas, utilizando-se do método de Posicionamento por Ponto Simples (PPS), com de (retirar) receptor GPS de navegação, e Posicionamento Relativo Semicinemático, com receptor GPS geodésico L1. Os resultados indicaram que o georreferenciamento realizado pelo PPS não interferiu na caracterização da variabilidade espacial da RP e da UG, assim como na estrutura espacial da relação dos atributos.

The characterization of the spatial variability of soil attributes is essential to support agricultural practices in a sustainable manner. The use of geostatistics to characterize spatial variability of these attributes, such as soil resistance to penetration (RP) and gravimetric soil moisture (GM) is now usual practice in precision agriculture. The result of geostatistical analysis is dependent on the sample density and other factors according to the georeferencing methodology used. Thus, this study aimed to compare two methods of georeferencing to characterize the spatial variability of RP and GM as well as the spatial correlation of these variables. Sampling grid of 60 points spaced 20 m was used. For RP measurements, an electronic penetrometer was used and to determine the GM, a Dutch auger (0.0-0.1 m depth) was used. The samples were georeferenced using a GPS navigation receiver, Simple Point Positioning (SPP) with navigation GPS receiver, and Semi-Kinematic Relative Positioning (SKRP) with an L1 geodetic GPS receiver. The results indicated that the georeferencing conducted by PPS did not affect the characterization of spatial variability of RP or GM, neither the spatial structure relationship of these attributes.