Effect of mineral superabsorbent on some characteristics of soil and growth parameters of onion (Allium cepa) under limited irrigation

Nowadays, using superabsorbent polymers such as pumice is one of practical approaches to increasing water storage in soil and increasing irrigation efficiency. To  investigate the effects of pumice on chemical and physical characteristics of soil, growth parameters and irrigation schedule of onion, an experiment in CRD design as factorial with three factors including: 1) soil type (with two raters: a) sandy loam  and b) clay loam, 2) irrigation schedule (with two rates: a) 7 and b) 4 days) and 3) pumice (with four  rates: 0, 2.5, 5 and 7.5 percentage by weight) and three replications was conducted. Results showed that increasing pumice rate could increase bulb dry matter, bulb diameter and bulb height. Pumice also could increase seales number in bulb, p and K concentration in plant and also available P and K concentration and CEC in soil. Pumice application in both soils, increased soil salinity, but in none of soils, soil EC was not more than 5 dS/m. Pumice application in both soils could decrease soil pH and compaction significantly. There was no significant difference between 5% and 7.5% of pumice rates, in bulb dry matter in sandy loam, height and diameter of bulb in clay loam, P and K concentration of onion and soil, CEC, compaction, salinity in sandy loam and drainage salinity. Between irrigation rates was no significant difference in none of properties, in treatments that received pumice. It can be concluded that using 5% pumice in soil, we can increase irrigation schedule of onion from 4 to 7 days.