[Response of root dynamics to nitrogen addition and the influencing factors in a Tibetan alpine steppe, China]. / é’è—é«˜åŽŸé«˜å¯’è‰åŽŸæ ¹ç³»åŠ¨æ€å¯¹æ°®æ·»åŠ çš„å“åº”åŠå ¶è°ƒæŽ§å› ç´ .

A field manipulative experiment was carried out during 2015 and 2016 to examine the changes and influencing factors of root production, turnover rate, and standing crop under different nitrogen (N) addition levels, i.e., 0, 1, 2, 4, 8 and 16 g N·m-2·a-1, in a Tibetan alpine steppe. The results showed that root production and standing crop decreased linearly or exponentially with increasing N addition rates. Compared with control, 16 g N·m-2·a-1 significantly reduced the two-year average root production and standing crop by 43.0% and 45.7%, respectively. Root turnover rate increased first and then decreased along the N addition gradient, with the maximum appearing under 2 and 4 g N·m-2·a-1 treatments for 2015 and 2016, respectively. Results from linear mixed-effects models showed that root starch content was the main factor modulating the N-induced changes in root production and turnover rate, explaining 21.7% and 25.4% of their variations. Root protein content mainly contributed to the variations in standing crop, with an explanation of 20.8% of its variance. Overall, N addition had negative effect on root production and standing crop, and low N promoted while high N inhibited root turnover rate. Root metabolic parameters were the main factors modulating the N-induced changes in root dynamics.

[Effects of nitrapyrin-nitrogen (N) fertilizer application rates on N utilization and N2O emission in summer maize field.] / ä¸åŒæ°®è‚¥å–·æ¶‚å¡å•¶å¯¹å¤çŽ‰ç±³ç”°æ°®ç´ åˆ©ç”¨åŠåœŸå£¤N2O排放的影响.

To reduce the N2O emission from soil and enhance N utilization by crop, a field experiment was carried out to study the effects of nitrapyrin-N fertilizer application rates (0, 180, 270, 360 kg N·hm-2) on soil N2O emission and N apparent loss, grain yield and N utilization of summer maize. Results showed that the soil N2O emission under different N fertilizer treatments mainly occurred in periods from sowing to seedling, and from jointing to tasseling. Soil N2O emission peaks were observed after basal and top dressing events. Maize yield increased with N fertilizer rates but there was no significant difference between 270 and 360 kg N·hm-2, and the net income of these two treatments was 5209 and 5426 yuan·hm-2, respectively. Compared with no N fertilizer treatment, the N uptake in the N fertilizer treatments was increased by 109.6%-134.1%. The treatment of 270 kg N·hm-2 had the highest agronomic N efficiency and N use efficiency, but the N apparent loss was low. The treatment with nitrapyrin-N fertilization rate of 270 kg N·hm-2 appeared to be the optimal rate to obtain high maize yield and N use efficiency, and low soil N2O emission and N apparent loss.

[Effects of dicyandiamide combined with nitrogen fertilizer on N2O emission and economic benefit in winter wheat and summer maize rotation system].

Aiming at the problems of excessive and unreasonable fertilizer application, lower nitrogen use efficiency, increasing N2O emission from soil and fertilizer in current intensified agricultural productions, a field experiment was conducted to study the effects of dicyandiamide (DCD) combined with nitrogen fertilizer application at different levels, i.e., 150, 225, 300 kg . hm-2, on N20 emission and relevant economic benefit in a typical winter wheat-summer maize rotation system in North China Plain. The results showed that DCD application decreased N2O emission fluxes and cumulative emissions by 25.6%-32.1% and 23.1%-31.1% in the year-round. There was a significant positive exponential correlation between N2O flux and soil surface temperature or soil moisture content. The effect of soil moisture on N2O emission was stronger in wheat season than in maize season, while the effect of temperature on N2O emission was on the contrary. The yields of winter wheat and summer maize with DCD addition were increased by 16.7%-24.6% and 29.8%-34.5%, respectively, and the average economic income of two seasons was increased by 7973.2 yuan . hm-2. Therefore, appropriate rate of N fertilizer combined with DCD could not only increase crop yield and economic income, but also reduce N2O emission. Considering environmental and economic benefit under this experimental condition, DCD combined with nitrogen of moderate level (total N amount 225 kg . hm-2) was a good nitrogen management mode in North China.