Synthesis of Site-Specific Dye-Labeled Polymer via Atom Transfer Radical Polymerization (ATRP) for Quantitative Characterization of the Well-Defined Interchain Distance.

Novel difunctional initiators that incorporate Förster/fluorescence resonance energy transfer (FRET) pairs are generated to carry out atom transfer radical polymerization of styrene, methyl methacrylate, and n-butyl methacrylate monomers by an efficient manner. Based on the chemical structures of the initiators, the locations of the fluorophore moiety are dictated to be in the center of the chain with accurately quantified chain functionality (>90% labeling ratio). The site-specific integration of FRET dyes into separate polymer chain centers allows for characterization of the well-defined interchain distance quantitatively based on the response between these fluorescent probes. The reliability of this technique is verified in bulk state, which is in well agreement with the theoretical ones. This well-defined FRET system is expected to be a promising candidate to provide a distinct physical image at a microscopic level regarding scaling chain dimension, chain interpenetration, and polymer compatibility.

Controlling the localization of nanoparticles in assemblies of amphiphilic diblock copolymers.

We performed a dissipative particle dynamics (DPD) approach to study the self-assembly of AB diblock copolymer tethered nanoparticles (P) in dilute solutions. Different morphological aggregates, including spherical micelles, vesicles, disk-like micelles and rod-like micelles, were found by varying the interaction between block copolymers and nanoparticles. Most importantly, the nanoparticles can selectively localize in the different domains within the aggregates. When the repulsive interaction between block copolymers and nanoparticles aPA = aPB = 25, the nanoparticles are evenly distributed within the spherical micelles. While aPA or aPB increases, the nanoparticles gradually aggregate and separate from copolymers and then localize in the central portion of vesicular wall or disk-like and rod-like micelles. The degree of stretching of the tethered copolymer chains gradually grows with the increase of aPA or aPB, while the degree of stretching of solvophobic block B decreases when the morphologies change from spherical to disk-like micelles and further to rod-like micelles. This work illustrates that tuning the miscibility of copolymers and nanoparticles could be used to project the selective localization of nanoparticles within the aggregates self-assembled by diblock copolymer tethered nanoparticles in dilute solutions.

Nitrogen loss via runoff and leaching from paddy fields with the proportion of controlled-release urea and conventional urea rates under alternate wetting and drying irrigation.

Alternate wetting and drying irrigation (AWD) can reduce non-point source pollution from paddy fields by mitigating field water depth. However, the influence of compounding modes of polymer-coated urea (PCU) and conventional urea (CU) on nitrogen (N) loss via runoff and leaching from paddy fields under AWD conditions remains unclear. To address this question, in this study, a 2-year field experiment was set up with three N management treatments: (a) 100% CU (N1), (b) 60% PCU + 40% CU (N2), and (c) 100% PCU (N3), at an equivalent N rate of 240 kg ha-1 that was applied to traditional continuously flooded (CI) and AWD systems. The results of this experiment showed a high-risk period of N loss from the paddy fields within 7 d after basal fertilization and 5 days after tillering fertilization. AWD reduced irrigation frequencies by 3.5 times and total input of irrigation water by 38.1%, increasing water utilization from precipitation by 44.4% than CI and reducing the volume of runoff by 46.1% and leaching water by 22.1%. This reduced the total N (TN) loss through runoff and leaching under AWD. In the N2 and N3 treatment groups, N concentration in floodwater decreased from 33.8 to 24.9%, TN loss via runoff decreased by 35.3 to 25.0%, and leaching decreased by 41.7 to 30.3% from the paddy field compared to N1. With the same N mode, AWD showed a higher N uptake (from jointing to maturity stage) and rice yield compared to CI. Besides, N2 and N3 had higher N uptake compared to N1 under the two irrigation regimes. Moreover, the AWDN3 and AWDN2 treatments resulted in the lowest and second-lowest loss of TN via runoff (2.21 to 2.66 kg ha-1) and leaching (8.14 and 10.21 kg ha-1), respectively, from the paddy fields and had the relatively high N uptake in rice in the maturity stage. Remarkably, compared with N3, N2 had a comparable grain yield under CI; however, it showed a higher yield under AWD, suggesting that there is a positive interaction in the rice yield between the AWD and compounding N (PCU + CU) fertilization practice. Thus, AWD coupled with N2 could be recommended as a useful approach to reduce N loss via runoff and leaching from paddy fields, which could increase the grain yield of middle-season rice.

Nitrogen and phosphorus losses from paddy fields and the yield of rice with different water and nitrogen management practices.

The assessment and control of losses of nitrogen (N) and phosphorus (P) from paddy fields is critical to improve the quality of water and atmosphere on earth. A field experiment was conducted to investigate the effect of three N managements (local common N fertilization practice, urea mixed with controlled-release N fertilizer, and optimized and reduced N fertilizer, designated CN, U + CRF and ON, respectively) on N and P losses through runoff and leaching from a paddy field, and yield of rice under shallow-irrigation and deep-sluice (SIDS) and continuous flooding irrigation (FI) in the Jianhan Plain of China in 2016. The results showed that, compared with FI, SIDS significantly reduced the frequency of irrigation and amount of irrigation water, resulting in an increase of 16.2% in rainfall use efficiency, and therefore, a reduction in the amount of surface runoff and water that had leached. This was responsible for the decreased total N (TN) and total P (TP) losses through runoff leaching under SIDS. The U + CRF and ON treatments resulted in a significant reduction in losses of TN through runoff and leaching and the loss of TP through leaching compared to CN. SIDS resulted in comparable or greater soil TN and TP contents in the 0-40 cm soil depths after rice harvest; N and P accumulation at the jointing, filling and maturity stages; and yield of grain compared to FI. Moreover, the U + CRF and ON improved or maintained accumulation of N and P and yield of rice compared to CN. Compared with FI coupled with CN, SIDS coupled with the U + CRF or ON treatments significantly reduced losses of N and P from paddy fields and enhanced or maintained the accumulation of N and P and yield of rice grains. In conclusion, SIDS coupled with the new N management could be an effective approach to reduce losses of N and P from paddy fields and would be a positive improvement for high yield of middle-season rice grains in the Jianhan Plain of central China and other regions with similar environments.

Effect of nitrogen supply method on root growth and grain yield of maize under alternate partial root-zone irrigation.

A field experiment was carried out to investigate effect of nitrogen (N) supply method on root growth and its correlation with the above-ground parts in maize (Zea mays L.) under alternate partial root-zone irrigation (APRI) at Wuwei, northwest China in 2012 and 2014. The treatments included alternate N supply, conventional N supply and fixed N supply under APRI (designated AN, CN and FN, respectively), with an additional CN fertilizer treatment coupled with conventional irrigation (CK). Ridges were built in a west-east direction. Root weight density (RWD) in the 0-100 cm soil layer and shoot biomass at the V6, V12, VT, R2 and R6 stages, and grain yield and yield components at the R6 were determined. Results showed that RWD around the plant (i.e. under the plant, south and north of the plant) in the 0-40 cm soil layer varied among different treatments at the VT, R2 and R6 stages. The RWD north and south the plant were comparable during maize growth stages for AN, CN and CK, while FN significantly decreased the RWD of its no N supply side at the three stages and markedly decreased the RWD of its N supply side at the VT. AN and CN significantly increased the RWD, shoot biomass at the three stages, and grain yield compared with FN and CK. Grain yield was positively correlated with RWD in the 0-40 cm soil layer at the three stages. These results suggested that AN and CN produced a relatively uniform distribution of roots and a greater root biomass, which contributed to the enhanced shoot biomass and grain yield of maize under APRI.