Effect of spread and shallow irrigation wetted area and application of organic mulch on citrus decline amelioration

Abstract

Citrus decline threatens the orchards in the southern part of Iran. Roots begin to die-out before citrus decline deterioration. In this study, the effect of expanding the irrigation wetted area and decreasing the irrigation depth, and application of compost as organic mulch on root development and amelioration of citrus decline in Valencia orange trees (Citrus scinensis L. Osbeck) was investigated. Experimental factors contained the different percentage of irrigation wetted area and decreasing irrigation effective root depth by drip irrigation system at three levels - control (30-40% with 60 cm effective root depth), 50-60% with 45 cm effective root depth and 70-80% with 30 cm effective root depth under tree canopy area and the factor of annual application of compost as organic mulch at two levels - control (without) and application of 80 kg compost under tree canopy area with 10 cm thickness as ground cover, after rotating the top soil at 10 cm depth for all treatments. The results showed that, annual application of compost as organic mulch under tree canopy area and expanding the irrigation wetted area with decreasing irrigation effective root depth, significantly improved fibrous root length and density at a lower soil depth and decreased the indices of citrus decline such as root rot percentage, leaf and fruit drop and shoot die back. Also these treatments increased the water productivity and fruit quality of in declining Valencia orange trees.