Porous hollow MgO microspheres were synthesized and characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption isotherms. The removal properties of the MgO microspheres towards toxic fluoride were investigated, including adsorption kinetics, adsorption isotherms, and influences of pH and coexisting anions. The adsorption capacity was larger than 120 mg g⁻¹ at a pH of 7.0. The effects of anions on fluoride removal were also investigated. The results indicated that phosphate was the greatest competitor of fluoride for adsorptive sites. In addition, the removal mechanism was revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The reaction of MgO and water molecules resulted in the formation of Mg(OH)₂. The excellent adsorption properties towards fluoride resulted from the surface reaction between the generated Mg(OH)₂ and fluoride in solution.

For improving water scarcity and groundwater pollution from agriculture, two-year experiments (2011–2013) with three water levels (0.3, 0.5 and 0.8 evaporation (E) in 20-cm-diameter pans) and four nitrogen (N) levels (120, 140 and 190 kg·ha⁻¹ in 2012 and 120, 190 and 290 kg·ha⁻¹ in 2013) were conducted to study effects of water and N availability on water movement and N transport for a wheat crop under drip irrigation in the North China Plain. The results indicated that under drip irrigation, deep percolation at 1-m depth was stable at 0.5–0.8 E with the same N rate for winter wheat. At 0.5–0.8 E, deep percolation was also relatively stable with increasing N rate from 120 to 140 kg·ha⁻¹ or from 190 to 290 kg·ha⁻¹. The irrigation schedule and N rates only affected N leaching below the root zone of winter wheat (60-cm depth), while the N residual in the soil layer presented more risk to the environment than N leaching. In general, the 290-kg-ha⁻¹ N level was not recommended using drip fertigation for winter wheat in the North China Plain. The empirical equation given by the Ministry of Geology and Mineral Resources was also not recommended for estimating the drainage under drip irrigation.

It is important to reveal the physiological mechanism of water saving and yield increasing of mulched drip irrigation. Three treatments were applied at a spring maize field in Northeast China: mulched drip irrigation (MD), non-mulched drip irrigation (ND), and rain-fed practice (CK). Grain yield (GY), photosynthetic capacity (A_max), the maximum carboxylation rate (V_cmax), leaf nitrogen content (N_mass), and leakiness of the bundle-sheath cells to CO₂ (L) were determined. MD treatment increased 5-year (2014-2018) average GY by 18.6% compared with the CK. The GY showed significant linear positive correlations with A_max and V_cmax. The mean A_max and V_cmax for two years (2017-2018) of MD were significantly increased by 21.1% (P < 0.05) and 10.7% (P < 0.05), respectively, compared with CK. The increase of A_max and V_cmax was partially contributed by the descending L. And L of MD was decreased by 6.5-12.4% (P < 0.05) during the jointing and tasseling–milk stages. The relationships between A_max and N_mass, and between V_cmax and N_mass, were affected by mulching treatments, which indicates that the higher leaf N use efficiency of the MD and ND treatments. This study provides a theoretical basis for implementation of film-mulching and drip-irrigation technology in Northeast China.