Electrochemical determination of free chlorine on pseudo-graphite electrode.

Pseudo-graphite from the University of Idaho Thermolyzed Asphalt Reaction also known as GUITAR is a new form of carbon. It shares morphological features with graphites, including basal and edge planes. Unlike graphites and other sp2-hybridized carbons, GUITAR has fast heterogeneous electron transfer across its basal planes and resistance to corrosion similar to boron-doped diamond electrodes. In this contribution GUITAR electrodes were examined as sensors for aqueous free chlorine (HOCl and OCl-) at pH 7.0 with cyclic voltammetric (CV) and chronoamperometric (CA) methods. Using CV at 50 mV s-1 GUITAR has a limit of detection of 1.0 µmol L-1, linear range of 0-5,000 µmol L-1, sensitivity of 215.8 µA L mmol-1 cm-2 and a signal stability of 4 days in constant exposure to 1 mmol L-1 free chlorine in pH 7.0, 0.1 mol L-1 phosphate buffer system. After 7 days of exposure GUITAR electrodes lost 37% of the former sensitivity, which was recovered by an in-situ regeneration procedure. The common aqueous ions, Ca2+, Na+, NO3-, SO42-, Cl-, CO32- and dissolved oxygen did not affect the response of the GUITAR-based sensor. The combination of limit of detection, linear range, sensitivity, sensor lifetime and its relative lack of interferences indicate that GUITAR is one of the best performers in free chlorine sensors.

[Soil moisture variation under different water and fertilization managements in apple orchard of Weibei dryland, China]. / 渭北旱塬苹果园不同水肥管理模式下的土壤水分差异.

To evaluate the variations of soil moisture under different water and fertilizer treatments in apple orchard in the Weibei dryland, a field experiment was carried out in 2013-2016 at Tianjiawa Village, Baishui County, Shaanxi Province. There were three treatments, i.e., farmers traditional model (only addition of NPK chemical fertilizer, FM), extension model (swine manure and NPK chemical fertilizer combined with black plastic film in tree row space, EM), and optimized model (swine manure and NPK chemical fertilizer combined with black plastic film in tree row space and planting rape in the inter-row of apple trees, OM). The results showed that OM treatment significantly increased soil water storage capacity in 0-200 cm soil layer. Water content of 0-100 cm soil layer was increased by 5.6% and 15.3% in the dry season compared with FM and EM treatment, respectively. Moreover, the soil water relative deficit index of OM was lower than that of EM in 200-300 cm soil layer. The rainfall infiltration in the dry year could reach 300 cm depth under OM. Meanwhile, OM stabilized soil water content and efficiently alleviated the desiccation in deep soil layer. Compared with FM and EM, the 4-year average yield of OM was increased by 36.6% and 22.5%, respectively. In summary, OM could increase water use efficiency through increasing the contents of available soil water and improving the soil water condition in shallow and deep layers, which help alleviate the soil deficit in deep layer and increase yield.