Liang Yuan

Review grain yield and nitrogen use efficiency in rice production regions in China

Abstract As one of the staple food crops, rice ( Oryza sativa L.) is widely cultivated across China, which plays a critical role in guaranteeing national food security. Most previous studies on grain yield or/and nitrogen use efficiency (NUE) of rice in China often involved site-specific field experiments, or small regions with insufficient data, which limited the representation for the current rice production regions. In this study, a database covering a wide range of climate conditions, soil types and field managements across China, was developed to estimate rice grain yield and NUE in various rice production regions in China and to evaluate the relationships between N rates and grain yield, NUE. According to the database for rice, the values of grain yield, plant N accumulation, N harvest index (HI N ), indigenous N supply (INS), internal N efficiency (IE N ), reciprocal internal N efficiency (RIE N ), agronomic N use efficiency (AE N ), partial N factor productivity (PEP N ), physiological N efficiency (PE N ), and recover efficiency of applied N (RE N ) averaged 7.69 t ha −1 , 152 kg ha −1 , 0.64 kg kg −1 , 94.1 kg kg −1 , 53.9 kg kg −1 , 1.98 kg kg −1 , 12.6 kg kg −1 , 48.6 kg kg −1 , 33.8 kg kg −1 , and 39.3%, respectively. However, the corresponding values all varied tremendously with large variation. Rice planting regions and N rates had significant influence on grain yield, N uptake and NUE values. Considering all observations, N rates of 200 to 250 kg ha −1 commonly achieved higher rice grain yield compared to less than 200 kg N ha −1 and more than 250 kg N ha −1 at most rice planting regions. At N rates of 200 to 250 kg ha −1 , significant positive linear relationships were observed between rice grain yield and AE N , PE N , RE N , IE N , and PFP N , and 46.49, 24.64, 7.94, 17.84, and 88.24% of the variation in AE N , PE N , RE N , IE N , and PFP N could be explained by grain yield, respectively. In conclusion, in a reasonable range of N application, an increase in grain yield can be achieved accompanying by an acceptable NUE.

Characterization of pH-fractionated humic acids derived from Chinese weathered coal

To reduce the compositional and structural heterogeneity of humic acids (HAs) and achieve better use of HA resources, in this study, we report a new sequential dissolution method for HAs derived from Chinese weathered coal. This method was used to separate HAs into seven fractions by adjusting the pH (3-10) of the extraction solution. The results showed that the HA fractions derived from Chinese weathered coal were concentrated up to 90.31% in the lower pH solutions (3-7). The compositional and structural characteristics of the HA fractions were determined by elemental analysis; ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), and solid-state 13C-nuclear magnetic resonance (NMR) spectroscopies; and other techniques. The results showed significant differences among the HA fractions. The concentrations of the total acidic groups and the carboxyl groups decreased with the increasing pH of the extraction solution. However, the HA fractions derived from extraction solutions with pH 3-4 had relatively lower aromaticity but a higher protonated carbon content. The HA fractions derived from extraction solutions with pH 6-7 had the highest aromaticity and the greatest abundance of COO/N-C=O. This study demonstrated that adjusting the pH of the extraction solution is one way to fractionate HAs from Chinese weathered coal and to obtain HA fractions with compositions and structures that could serve as useful material for study and utilization.

Nutrient uptake requirements with increasing grain yield for rice in China

Abstract Improved estimates of nutrient requirements for rice ( Oryza sativa L.) in China are essential to optimize fertilization regulation for increasing grain yields and reducing the potential of environmental negative influences, especially under high-yielding intensive systems. A database involving rice grain yields, nutrient concentrations and accumulations collected from on-field station experiments in the literatures published from 2000 to 2013 in China was developed to understand the relationships between grain yields and plant nutrient uptakes, and to quantify nutrient requirements for different yield levels. Considering all data sets, rice grain yield ranged from 1.4 to 15.2 t ha −1 with the mean value of 7.84 t ha −1 , and ca. 10.4% of yield observations were higher than the yield barrier level of 10 t ha −1 . N requirement to produce one ton grain was 21.10 kg for the yield range −1 with a high variation of 45.8%. Except of the yield range −1 , the values of N requirement, firstly increased from 18.78 kg for yield range 4.0–5.5 t ha −1 to 20.62 kg for yield range 7.0–8.5 t ha −1 , then decreased slightly to 19.67 and 19.17 kg for the yield range 8.5–10 and >10 t ha −1 , respectively. Phosphorus (P) and potassium (K) requirements showed increasing trends, from 3.51 and 19.87 kg per t grain for −1 yield range to 4.10 and 21.70 kg for >10.0 t ha −1 range. In conclusion, nutrient requirement varied with increasement of grain yield, and N, P and K presented various response trends, increasing, declining or stagnating, which would be of great benefit for improving fertilizer strategies.