Growth and nitrogen productivity of drip-irrigated winter wheat under different nitrogen fertigation strategies in the North China Plain

Excessive application of nitrogen (N) fertilizer is the main cause of N loss and poor use efficiency in winter wheat (Triticum aestivum L.) production in the North China Plain (NCP).Drip fertigation is considered to be an effective method for improving N use efficiency and reducing losses,while the performance of drip fertigation in winter wheat is limited by poor N scheduling.A two-year field experiment was conducted to evaluate the growth,development and yield of drip-fertigated winter wheat under different split urea (46%N,240 kg ha^(-1)) applications.The six treatments consisted of five fertigation N application scheduling programs and one slow-release fertilizer (SRF) application.The five N scheduling treatments were N0–100 (0%at sowing and 100%at jointing/booting),N25–75 (25%at sowing and 75%at jointing and booting),N50–50(50%at sowing and 50%at jointing/booting),N75–25 (75%at sowing and 25 at jointing/booting),and N100–0 (100%at sowing and 0%at jointing/booting).The SRF (43%N,240 kg ha^(-1)) was only used as fertilizer at sowing.Split N application significantly (P<0.05) affected wheat grain yield,yield components,aboveground biomass (ABM),water use efficiency(WUE) and nitrogen partial factor productivity (NPFP).The N50–50 and SRF treatments respectively had the highest yield(8.84 and 8.85 t ha^(-1)),ABM (20.67 and 20.83 t ha^(-1)),WUE (2.28 and 2.17 kg m^(-3)) and NPFP (36.82 and 36.88 kg kg^(-1)).This work provided substantial evidence that urea-N applied in equal splits between basal and topdressing doses compete economically with the highly expensive SRF for fertilization of winter wheat crops.Although the single-dose SRF could reduce labor costs involved with the traditional method of manual spreading,the drip fertigation system used in this study with the N50–50 treatment provides an option for farmers to maintain wheat production in the NCP.

Low-Lying Isomers of(TiO_(2))_(n)(n=2-8)Clusters

Although there are diverse bond features of Ti and O atoms,so far only several isomers have been reported for each(TiO_(2))n cluster.Instead of the widely used global optimization,in this work,we search for the low-lying isomers of(TiO_(2))_(n)(n=2-8)clusters with up to 10000 random sampling initial structures.These structures were optimized by the PM6 method,followed by density functional theory calculations.With this strategy,we have located many more low-lying isomers than thosereported previously.The number of isomers increases dramatically with the size of the cluster,and about 50 isomers were found for(TiO_(2))_(7) and(TiO_(2))_(8) with the energy within 30 kcal/mol.Furthermore,new lowest isomers have been located for(TiO_(2))_(5) and(TiO_(2))_(8),and isomers with three terminal oxygen atoms,five coordinated oxygen atoms as well as six coordinated titanium atoms have been located.Our work highlights the diverse structural features and a large number of isomers of small TiO_(2) clusters.