BARLEY ROOT GROWTH PARAMETERS IN RESPONSE TO SOWING DATE AND DEFICIT IRRIGATIONAmir Tabarzad and Ali Asghar Ghaemi
Barley is one of the main agricultural crop with capability of growing under semi-arid region, where drought and sowing date are the major concerns. The objective of the present study was to investigate the effects of three levels of irrigation consisted of full irrigation (FI: 100% water requirement of plant), 75 and 50 percent of full irrigation (0.75 FI and 0.5 FI) and dry land (rain-fed; DL) and four sowing dates included of planting on October 23th (T1), November 6th (T2), November 22th (T3) and on December 6th (T4) on root growth parameters of a local cultivar of barley (Bahman) during the 2012 and 2013 growing seasons. The root length density (RLD) in upper soil layer was significantly more than that obtained in deeper soil layers at all irrigation and sowing date treatments. On an average, the mean relative RLD values were about 61.3%, 23.5% and 15.2% in 0-30, 30-60 and 60-90 cm soil depth respectively in 2012 and were about 59.3%, 24.8% and 15.9% in 0-30, 30-60 and 60-90 cm respectively in 2013. In general, increasing soil depth for every 30 cm from 30 to 90 cm showed that root density of about 40% and 64% reduced in 2012 and 2013. Results revealed that, the grain yield decreased due to water stress and delay in sowing date. The specific root surface area (SSA) significantly increased with increase in soil depth from 0-30 cm to 60-90 cm in all treatments. The maximum values of SSA were 133.38 and 174.59 m2 kg-1 in 60-90 cm of soil depth at 0.75 FI and DL treatments for the first and second years, respectively. Our finding showed that the water stress affected the root development of barley and decreased the root length density in early and late sowing dates. Within each date of sowing, water stress induced thinner roots in deeper soil layers compared with upper soil layer that are the most active in water uptake and may contribute to the water stress tolerance. It is concluded that among the sowing dates, delaying in sowing date led to decrease in root length density and vertical root development for all irrigation treatments. Furthermore, delay in sowing date only induced thinner and most active root for water uptake in deeper soil layers and did not affect the production of thin root in upper 30 cm soil profile.
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