Mini sensor Irrigas® na determinação da curva de retenção de água em substratos para hortaliças Mini Irrigas® sensor in determining the curve of water retention in substrates for vegetables

No Brasil, ainda não existe um método padrão, confiável, para a determinação da curva de retenção de água em todos os tipos de substratos existentes para o cultivo de hortaliças, principalmente para substratos à base de fibras longas e curtas, como é o caso do substrato de coco verde. Assim, neste trabalho, o objetivo foi obter a curva de retenção de água em substratos para o cultivo de hortaliças, utilizando-se um mini sensor Irrigas®. Foram utilizados os substratos de coco verde, sem compostagem, compostado durante 45; 90; 135 e 180 dias e o substrato Plantmax®, utilizado como controle. O delineamento experimental foi de blocos ao acaso no esquema fatorial 6 x 11 (substrato x tensão) com três repetições. Para o substrato S0; S45; S90; S135 e S180 as médias obtidas foram porosidade total: 85%; espaço de aeração: 72%; água facilmente disponível: 4%; água disponível: 9%; água tamponante: 5% e, água remanescente: 4%. O espaço de aeração (72%), foi indicativo de que é conveniente melhorar a distribuição do tamanho de partículas desse substrato, de modo a reduzir o espaço de aeração e aumentar a capacidade de retenção de água. O aumento da tensão de água foi obtido de forma natural, pela evaporação da água das amostras. A utilização do sensor Irrigas® permitiu rapidez na obtenção dos resultados e possibilitou a medição da tensão da água, de maneira contínua e paralela, entre tensões de 0 e 11 kPa, simultaneamente, em três amostras de substrato. Estes resultados tornaram evidente a possibilidade de uso do mini sensor Irrigas® na determinação de curvas de retenção de água em substratos para hortaliças, gerando inclusive perspectivas para a realização de estudos futuros de comparação com outros métodos.<br>In Brazil, no reliable standard method exists to determine the water retention curve in all available types of substrates for the cultivation of vegetables, mainly for substrates with long and short fibers, such as those of green coconut shell. In this work, the objective was to obtain the substrate water retention curve for the cultivation of vegetables, using a mini Irrigas® sensor. Green coconut substrate was used without composting and with composting during 45; 90; 135 and 180 days while the Plantmax® substrate was used as control in a complete block experimental design with 6 substrates, 11 water tension levels and three replications. For the substrates S0, S45, S90, S135 and S180 the obtained average were: total porosity; 85%; aeration space: 72%; easily available water: 4%; available water: 9%; buffering water: 5% and remaining water: 4%. The aeration space (72%) was indicative that it is convenient to improve the particle size distribution of this substrate, in order to reduce the aeration space to gain water retention capacity. Water tension in the samples was slowly increased by evaporation as the substrate air interface and mini Irrigas® sensors enabled the required water tension measurements, continuously, in three parallel substrate samples for water tensions ranging from zero to 11 kPa. These results make evident the possibility of using the mini Irrigas® sensor for the determination of water retention curves in substrates for growing vegetables, and also opens the possibility of future studies, aiming at comparative tests for other methods

Calibration of Passive UHF RFID Tags Using Neural Networks to Measure Soil Moisture

This paper presents a system to monitor soil moisture using standard UHF RFID tags buried on the soil. An autonomous mobile robot is also presented, which is capable to navigate on the field and automatically read the sensors, even if they are completely buried on the soil. Thus, passive RFID tags are buried on the soil, allowing wireless moisture measurement without the need of batteries for long periods. The system dispenses external cables and antennas and may be composed of a single RFID tag buried on the soil or by several RFID tags buried at different depths on the soil. An antenna coupled to a RFID reader can be pointed to the place of installation of these tags, and by measuring the received signal strength indicator (RSSI) and other parameters, it allows to estimate the amount of water on the soil. The estimation of volumetric water content (VWC) on the soil was successfully obtained and calibrated with R2>0.9 using neural networks trained with experimental data from a reference capacitive soil moisture sensor. In addition to the simplified installation procedure, the system allows manual or automatic reading through irrigation systems or other systems to control irrigation systems. The system has been evaluated in several experiments, and nine tags were buried on the field, being used for at least three years. Experimental results show that it is possible to read tags at 40 cm deep in the soil with the RFID reader antenna 10 cm far from the soil surface