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Though researchers have employed various techniques (gravimetric, electromagnetic, neutron scattering, heat pulse, micro-wave and optical remote sensing techniques) for soil moisture measurement, dielectric based techniques (Time Domain Reflectometry, TDR, and capacitance technique, CT) have gained much more popularity, mainly due to revolutionary developments in the field of electronics and data communication systems. However, suitability and relative performance of these techniques for moisture measurement of soils is a point of debate. Hence, in order to address this issue, extensive studies were conducted on the soils of entirely different characteristics, compacted at various compaction states (dry density and water content) by employing TDR and capacitance probes. Subsequently, the dielectric constant of the soil and its bulk electrical conductivity were obtained using these probes and compared against each other and that computed from Topp's equation, which is a well-established relationship between the dielectric constant of the soil and its volumetric moisture content. An attempt was also made to correlate K a values obtained from the dielectric techniques and Topp's equation with that of Time Propagation (TP) mixing model, which incorporates in it the properties of the soil matrix as well. It has been observed that K a-TDR matches well with the K a-Topp and K a-TP , while the best match has been observed between K a-TDR and K a-Topp as compared to the K a-CT . As such, the study demonstrates, clearly, that Topp's equation, which ignores the soil specific parameters, is capable of determining the soil moisture content appropriately. This study proposes an empirical equation which relates dielectric constants obtained from Topp's equation to those obtained from the TDR, capacitance technique and TP mixing model. Such a relationship can be further utilized for estimating the volumetric soil moisture content.

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Background: The Fe toxicity is a perpetual problem of low lying poorly drained acid soils. It also affects the solubility and availability of most of the plant nutrients, by reducing toxic concentrations of iron, aluminum and manganese. To overcome these constraint, application of lime is inevitable but high cost of liming materials necessitate the use of low-cost, internally sourced, environmentally friendly and adoptable organic sources. In present study rice husk ash was used as a soil ameliorant in lieu of liming. Methods: A field experiment was conducted at Rice Research Station, Moncompu during 2017-2018 with nine treatments replicated thrice in RBD using rice variety Uma. A customized formulation with composition of K (8.9 %), Mg (3.2 %), Ca (3.7 %), Zn (2.1 %), Mn (0.23 %), B (3.5 %) and Cu (0.96 %) was developed based on the available nutrient status of the region and crop requirement and used for supplementary foliar nutrition. Result: It was found that treatment comprising of Soil test based RDF + Rice husk ash @ lime (based on pH) + foliar spray of 0.5 % solution of customized formulation @ 5 kg ha-1 as foliar application of 0.5 % solution in two splits at maximum tillering and panicle initiation stage was the best treatment in increasing yield by 23 % compared to recommended dose of lime and fertilizer application and B:C ratio increased from 1.53 to 1.91. Effect of rice husk ash in ameliorating soil acidity was found to be on par with application of lime based on pH in acid sulphate soils of Kuttanad zone.

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