Effect of soil water potential on radish ( Raphanus sativus L.) growth and water use under drip irrigation

Abstract

Radish ( Raphanus sativus L.) is a moisture loving vegetable and is widely planted in China. Soil water is one of most important factors affecting the yield and quality of radishes. Field experiments for the effect of soil water potential on radish growth and water use were carried out in 2001 and 2002. The experiment included five treatments, which controlled soil water potential (SWP) at 20 cm depth immediately under emitter higher than −15, −25, −35, −45 and −55 kPa. The results show that different SWP treatments affected temporal and spatial distribution of soil water. As the target SWP value decreased, the average SWPs between 0 and 90 cm depth decreased, and the dry domain in the root zone became larger. The variability of SWPs values at 0–90 cm depths before and after irrigation increased as the target values decreased. Irrigations scheduled between −15 and −55 kPa had no significant effects on radish growth and yield, but affected radish root distribution and market quality. The lower the target SWP value was, the more radish roots developed. The lowest radish cracking rate and the most radishes of Grade 1 occurred at a SWP of −35 kPa in 2002. Different SWP treatments affected radish evapotranspiration (ET) and WUE. The total radish ET decreased as SWPs decreased in both years. The highest radish WUE values were achieved with SWPs of −55 and −35 kPa in 2001 and 2002, respectively, and the lowest WUE values were recorded at a SWP of −15 kPa in both years. The SWP of −35 kPa at 20 cm depth immediately under drip emitter can be used as an indicator for radish drip irrigation scheduling in the North China Plain.