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There is a growing interest in employing sub-soil sensing systems to support precision agriculture. This thesis presents the design of an RFID sub-soil sensing system which is based on integrating passive RFID technology and sub-soil sensing technology. The proposed RFID sub-soil system comprises of an above-ground RFID reader and a number of RFID sub-soil sensor nodes. The key feature of the system is that the sensor nodes do not require an on-board battery, as they are capable of harvesting energy from the ElectroMagnetic (EM) field generated by the RFID reader. The sensor nodes then transmit sensor measurements to the reader wirelessly through soil. With the proposed RFID sub-soil system, the high path loss of the sub-soil wireless channel is a significant problem which leads to the challenge for the system to achieve an acceptable Quality of Service (QoS). In this project, the path loss in soil has been characterised through CST simulations. In the simulations, the effect of the soil on the sensor node antenna has also been investigated. This thesis also presents the design and implementation of a programmable RFID reader platform and an embedded RFID sensor node prototype. The RFID reader platform is implemented using a National Instruments (NI) PXI system, and it is configured and controlled by NI LabVIEW software. The sensor node prototype is capable of harvesting RF energy and transmitting sensor measurements from a temperature sensor through backscatter communication. A series of sub-soil experiments have been carried out to evaluate the performance of the RFID sensor node prototype using the PXI-based RFID reader platform. The experimental results are presented and analysed in this thesis. Additionally, this work has explored trade-offs in the system design, and these design trade-offs are summarised and described.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Among the benefits of gypsum can cite, improving subsoil, generated by higher Ca, m % and reduction of depth of root crops. This study was conducted on an Oxisol in the city of Boa Vista do Padlock northwestern region of Rio Grande do Sul experiment in a completely randomized design with 5 replications. The treatments used in the study were different doses of gypsum (CaSO4.2H2O) at doses of 0,0; 2,0; 4;0 and 8,0 Mg ha-1 applied to the surface of the soils under different management as irrigation with the aid of center pivot. Each soil sample was stratified in 5 depths, these layers were 0-0.05, 0.05-0.10, 0.10-0.20, 0.20-0.40 and 0.40-0,60 m depth. The soil samples were taken at time zero (initial characterization), after 10 months and 18 months of application of the plaster surface. The soil nutrients evaluated were pH, P, K, Ca, Mg, Al, S and saturation in CTC. Also granulometric content of the soil such as clay as well as yield of corn and soybean compared using the Tukey test at 5% probability (p = 0.05). The results obtained in the study show that the aluminum saturation, Ca, Ca/CTC, Ca/Mg, CTC, S and base saturation were influenced by the addition of gypsum applied to surface. The contents of Al, Ca, Ca/CTC, Mg, Mg/CTC, Ca/Mg, S, pH, P and base saturation were influenced as to irrigation management and the time with the exception of Al the productivity of corn and soybean were not affected significantly by treatments, possibly shortly after application. The gypsum applied superficially, was an effective alternative for improving the chemical quality of the subsurface layer of an Oxisol managed under no-tillage system. / Entre os benefícios do gesso agrícola, pode-se citar, o melhoramento do solo em subsuperfície, gerado pela elevação dos teores de Ca, redução da m% e aprofundamento do sistema radicular das culturas. O presente estudo foi realizado em um latossolo vermelho distrófico localizado no município de Boa Vista do Cadeado, região do noroeste do Rio Grande do Sul. O delineamento experimental em blocos inteiramente casualizados com 5 repetições. Os tratamentos utilizados no estudo foram diferentes doses de gesso agrícola (CaSO4.2H2O), nas doses de 0,0; 2,0; 4;0 e 8,0 Mg ha-1 aplicados na superfície do solo sob condições de manejo diferenciado quanto à irrigação com auxílio de pivô central. Cada amostra de solo foi estratificada em 5 profundidades, estas camadas foram de 0-0,05; 0,05-0,10; 0,10-0,20; 0,20-0,40 e 0,40-0,60 m de profundidade. As amostragens de solo foram realizadas no tempo zero (caracterização inicial), após 10 meses e 18 meses de aplicação do gesso em superfície. Os nutrientes de solo avaliados foram pH, P, K, Ca, Mg, Al, S e a saturação na CTC. Também teores granulométricos do solo como a argila além da produtividade das culturas do milho e da soja comparadas utilizando o teste de Tukey a 5% de probabilidade (p=0,05). Os resultados obtidos no estudo, demonstram que a saturação por alumínio, Ca, Ca/CTC, Ca/Mg, CTC, S e saturação por bases foram influenciados pela adição de gesso agrícola aplicado em superfície, Os teores de Al, Ca, Ca/CTC, Mg, Mg/CTC, Ca/Mg, S, pH, P e saturação por bases foram influenciados quanto ao manejo da irrigação e para o tempo com exceção do Al. A produtividade das culturas do milho e da soja não foram influenciadas significativamente pelos tratamentos, possivelmente pelo pouco tempo após aplicação. O gesso agrícola aplicado superficialmente, foi uma eficiente alternativa para a melhoria da qualidade química da camada sub superficial de um Latossolo vermelho manejado sob sistema plantio direto.