摘要：
Improving soil quality is critical for increasing rice yield, and biochar could be a beneficial soil amendment for high yield. This study was conducted to determine the effects of continuous (repeated seasonal) applications of biochar on nitrogen (N) uptake and utilization in rice. A fixed field experiment was done in Yongan Town, Hunan Province, China, in six continuous seasons (the early and late rice-growing seasons from 2015 to 2017). Results showed that biochar application did not significantly affect soil N uptake in the first four seasons. The effect of biochar application on fertilizer N uptake was not significant in three of the first four seasons. In the fifth and sixth seasons, biochar application resulted in 14-26% increases in soil N uptake but 19-26% decreases in fertilizer N uptake. Soil N availability did not explain the increased soil N uptake with biochar application. The decreased fertilizer N uptake with biochar application was attributed to both decreased fertilizer N availability and increased N loss through ammonia volatilization. As a consequence of a compensation between the increased soil N uptake and the decreased fertilizer N uptake, the effect of biochar application on total N uptake was not significant in the fifth and sixth seasons. However, biochar application led to 7-11% increases in internal N use efficiency in the fifth and sixth seasons and 6% increase in grain yield in the sixth season. Our study suggests that the effects of repeated seasonal applications of biochar on N uptake and utilization in rice depend on the duration of biochar application. Longer continuous applications of biochar can increase internal N use efficiency and grain yield in rice with insignificant change in total N uptake.
通讯机构：
[Jagadish, S. V. Krishna] I;[Jagadish, S. V. Krishna] K;IRRI, DAPO Box 7777, Manila, Philippines.;Kansan State Univ, Dept Agron, Manhattan, KS 66506 USA.
摘要：
High day and night temperatures affect the rate and duration of grain filling and starch packaging differently in a developing rice grain.Rice grain yield and quality are predicted to be highly vulnerable to global warming. Five genotypes including heat-tolerant and susceptible checks, a heat-tolerant near-isogenic line and two hybrids were exposed to control (31 degrees C/23 degrees C, day/night), high night-time temperature (HNT; 31 degrees C/30 degrees C), high day-time temperature (HDT; 38 degrees C/23 degrees C) and high day- and night-time temperature (HNDT; 38 degrees C/30 degrees C) treatments for 20 consecutive days during the grain-filling stage. Grain-filling dynamics, starch metabolism enzymes, temporal starch accumulation patterns and the process of chalk formation were quantified. Compensation between the rate and duration of grain filling minimized the impact of HNT, but irreversible impacts on seed-set, grain filling and ultimately grain weight were recorded with HDT and HNDT. Scanning electron microscopy demonstrated irregular and smaller starch granule formation affecting amyloplast build-up with HDT and HNDT, while a quicker but normal amylopast build-up was recorded with HNT. Our findings revealed temporal variation in the starch metabolism enzymes in all three stress treatments. Changes in the enzymatic activity did not derail starch accumulation under HNT when assimilates were sufficiently available, while both sucrose supply and the conversion of sucrose into starch were affected by HDT and HNDT. The findings indicate differential mechanisms leading to high day and high night temperature stress-induced loss in yield and quality. Additional genetic improvement is needed to sustain rice productivity and quality under future climates.
作者机构：
[Shan, Shuanglu; Zou, Yingbin; Jiang, Peng; Gao, Wei; Huang, Min] Hunan Agr Univ, Southern Reg Collaborat Innovat Ctr Grain & Oil C, Changsha 410128, Hunan, Peoples R China.;[Uphoff, Norman; Huang, Min] Cornell Univ, IP CALS, Ithaca, NY 14853 USA.;[Yuan, Longping; Ma, Guohui] China Natl Hybrid Rice Res & Dev Ctr, State Key Lab Hybrid Rice, Changsha 410125, Hunan, Peoples R China.
通讯机构：
[Huang, Min] H;[Huang, Min] C;Hunan Agr Univ, Southern Reg Collaborat Innovat Ctr Grain & Oil C, Changsha 410128, Hunan, Peoples R China.;Cornell Univ, IP CALS, Ithaca, NY 14853 USA.
关键词：
Grain yield;Hybrid rice;Nitrogen inputs;Sustainable crop production
摘要：
Increasing rice yield with fewer external inputs is critical to ensuring food security, reducing environmental costs, and improving returns. Use of hybrid rice has expanded greatly in China due to its higher yield potential. Meanwhile, large and increasing amounts of nitrogen (N) fertilizers have been used for expanding rice production in China. It is not clear to what extent the success of hybrid rice in China is associated with N fertilizer inputs. We observed that the higher grain yield with N fertilizer in hybrid rice was driven more by a higher yield without N fertilizer than by increases in grain yield with N fertilizer under moderate to high soil fertility conditions. Our results suggest that greater application of N fertilizers is not needed to benefit from hybrid rice production under moderate to high soil fertility conditions, and that improving and maintaining soil fertility should be a focus for sustaining hybrid rice production. Moreover, our study also indicates that zero-N testing may be a potentially useful tool to develop hybrid rice with high yield and without requirement of greater external N inputs under moderate to high soil fertility conditions.
