Root characteristics of Alhagi sparsifolia seedlings in response to water supplement in an arid region,northwestern China

The effect of variation in water supply on woody seedling growth in arid environments remain poorly known.The subshrub Alhagi sparsifolia Shap.（Leguminosae）,distributed in the southern fringe of the Taklimakan Desert,Xinjiang,northwestern China,has evolved deep roots and is exclusively dependent on groundwater,and performs a crucial role for the local ecological safety.In the Cele oasis,we studied the responses of A.sparsifolia seedling roots to water supplement at 10 and 14 weeks under three irrigation treatments （none water supply of 0 m3/m2 （NW）,middle water supply of 0.1 m3/m2 （MW）,and high water supply of 0.2 m3/m2 （HW））.The results showed that the variations of soil water content （SWC） significantly influenced the root growth of A.sparsifolia seedlings.The leaf area,basal diameter and crown diameter were significantly higher in the HW treatment than in the other treatments.The biomass,root surface area （RSA）,root depth and relative growth rate （RGR） of A.sparsifolia roots were all significantly higher in the NW treatment than in the HW and MW treatments at 10 weeks.However,these root parameters were significantly lower in the NW treatment than in the other treatments at 14 weeks.When SWC continued to decline as the experiment went on （until less than 8％ gravimetric SWC）,the seedlings still showed drought tolerance through morphological and physiological responses,but root growth suffered serious water stress compared to better water supply treatments.According to our study,keeping a minimum gravimetric SWC of 8％ might be important for the growth and establishment of A.sparsifolia during the early growth stage.These results will not only enrich our knowledge of the responses of woody seedlings to various water availabilities,but also provide a new insight to successfully establish and manage A.sparsifolia in arid environments,further supporting the sustainable development of oases.

Evapotranspiration and water-use efficiency of irrigated colored cotton cultivar in semiarid regions

Irrigation studies provide a framework for evaluating agricultural production and the water resource management in locations where water is scarce. Field experiments were conducted at Barbalha- CE (northwestern Brazil) during 2004 and 2005 cropping seasons to investigate the effects of different irrigation water depths on the water-use efficiency and yield of the BRS 200-brown cotton cultivar (Gossypium hirsutum L.). Three irrigation treatments were applied: T1 = 80%;T2 = 100% and T3 = 120% of the potential evapotranspiration (ETp). The Bowen ratio-energy balance was used to obtain crop evapotrnaspiration (ETc) while daily reference evapo-transpiration (ETo) was obtained by the Penman-Monteith approach. Irrigation water was applied by a sprinkler system during both cropping seasons. The daily evapotranspiration ranged from 2.59 mm·day-1 at the emergence to 5.89 mm·day-1 at first square growth stage with an accumulated value of 528.7 mm as a mean of the two cropping seasons. The average crop coefficient across both years (2004-2005) was 0.90, with minimum and maximum values of 0.46 and 1.17 at emergency and first flower growth stages, respectively. The results also showed that the increase in irrigation from 80% to 120% of ETp resulted in a significant increase in the seed-cotton yield (from 2476.0 to 3289.5 kg·ha-1), while lint percentage and water-use efficiency (WUE) were slightly reduced from 35.7% to 35.6% and from 0.60 to 0.53 kg·m-3, respectively. These results suggests that the cotton crop (cultivar BRS-200 brown) reaches higher water-use efficiency when irrigated with 80% of the crop evapotrnaspiration obtained as a function of the reference evapotranspiration and the crop coefficient proposed by FAO. However, the maximum seed-cotton yield is obtained when irrigated with 120% of that crop evapotranspiration.