Comparison of watermark soil moisture content with selyaninov hydrothermal coefficient

Abstract

Agricultural producers determine irrigation scheduling practices for crops water requirement better when the soil water content of their fields is known. Selyaninov Hydrothermal Coefficient (HTC) is used for identifying drought during the active vegetation period in Lithuania, based on the water balance equation. Farmers make measurements of soil moisture simply with humidity sensors, for example Watermark type. The Watermark soil moisture block is sold as a qualitative indicator of soil moisture for applications such as irrigation scheduling. The Watermark sensors utilized a local soil water retention relationship in order to convert soil water potential into volumetric water content. Soil humidity values established using Watermark type humidity sensors and value interpretations are based on manufacture indications. However, they have not been adapted to Lithuanian conditions. Errors in soil moisture measurements (or other methods of soil moisture determination) require that irrigation commences at a higher threshold of the measured soil moisture content, so that with a given statistical probability (coincidence level), the true value of soil moisture content is not lower than the threshold. Soil moisture was measured with Watermark soil moisture sensors placed at 20 and 50 cm depths. After analyzing the values taken throughout the whole period and summarizing the results it has been identified that plant growth condition period evaluation according to HTC and factual soil humidity reserves differs by 20%. HTC meaning dependencies during vegetation period using Watermark measured humidity, strong or averagely strong interrelation is determinate, in most cases – statistically significant.