The crop production in Ethiopia is markedly constrained by soil nutrient depletion and limited fertilizer input. Nitrogen is among the most yield-limiting factors of cereal crops, especially in sub-Saharan Africa (SSA...The crop production in Ethiopia is markedly constrained by soil nutrient depletion and limited fertilizer input. Nitrogen is among the most yield-limiting factors of cereal crops, especially in sub-Saharan Africa (SSA). A meta-analysis of 82 studies was carried out to evaluate the response of major cereal crops, viz. wheat, maize, barley, teff, and sorghum, to nitrogen fertilization in Ethiopia. The results showed that N-application significantly increased yields of all the five crops examined herein. The average yields of the treatment effects over controls for the five crops were 3775.8 kg∙ha<sup>−1</sup> and 2593.3 kg∙ha<sup>−1</sup>, respectively. The overall yield response to nitrogen treatments for all the crops was 64.8% (wheat, 96.5%;maize, 40.65%;barley 84.36%;teff, 50.48%;and sorghum;23%). Overall, nitrogen agronomic efficiency (AE<sub>N</sub>) and partial factor productivity (PFP<sub>N</sub>) were 18.2 and 71.81 kg∙kg<sup>−1</sup>, respectively. A downtrend of nitrogen use efficiency with an increase in N rate was realized. The yield response was higher for the nitrogen treatment effects of >100 kg∙N∙ha<sup>−1</sup> (123.9%), clay soils (75.46%), low initial soil organic carbon (SOC) and available phosphorous (AP) (92.4% and 101.6%), respectively, Therefore, we recommend the application of nitrogen fertilizer (>100 kg∙N∙ha<sup>−1</sup>), especially on infertile soils for improved grain yield and NUE in aforementioned cereal crops in Ethiopia and similar regions in sub-Saharan Africa (SSA).展开更多
本文设计了一台喷气增焓(EnhancedVaporInjection,EVI)低温空气源热泵系统,研究补气对系统性能和参数的影响,测试EVI系统在低温下稳定运行的可行性。结果表明,EVI改善了空气源热泵低温运行排气温度过高的问题,实现了-20℃环境温度下的...本文设计了一台喷气增焓(EnhancedVaporInjection,EVI)低温空气源热泵系统,研究补气对系统性能和参数的影响,测试EVI系统在低温下稳定运行的可行性。结果表明,EVI改善了空气源热泵低温运行排气温度过高的问题,实现了-20℃环境温度下的稳定运行;补气提高了系统性能,多个测试工况下,41℃出水温度时制热量最高提升了43.0%,性能系数(Coefficient of Performance,COP)最高提升了28.3%;相对补气量的增加对系统的性能改善呈现先增加后变缓至下降的趋势,存在一个最优的相对补气量使得系统能效最高;打开补气阀后吸气压力和排气压力均有所提高;-12℃环境温度时吸气压力较关闭补气阀时提高了14.1%,排气压力较关闭补气阀时提高了2%。展开更多
文摘The crop production in Ethiopia is markedly constrained by soil nutrient depletion and limited fertilizer input. Nitrogen is among the most yield-limiting factors of cereal crops, especially in sub-Saharan Africa (SSA). A meta-analysis of 82 studies was carried out to evaluate the response of major cereal crops, viz. wheat, maize, barley, teff, and sorghum, to nitrogen fertilization in Ethiopia. The results showed that N-application significantly increased yields of all the five crops examined herein. The average yields of the treatment effects over controls for the five crops were 3775.8 kg∙ha<sup>−1</sup> and 2593.3 kg∙ha<sup>−1</sup>, respectively. The overall yield response to nitrogen treatments for all the crops was 64.8% (wheat, 96.5%;maize, 40.65%;barley 84.36%;teff, 50.48%;and sorghum;23%). Overall, nitrogen agronomic efficiency (AE<sub>N</sub>) and partial factor productivity (PFP<sub>N</sub>) were 18.2 and 71.81 kg∙kg<sup>−1</sup>, respectively. A downtrend of nitrogen use efficiency with an increase in N rate was realized. The yield response was higher for the nitrogen treatment effects of >100 kg∙N∙ha<sup>−1</sup> (123.9%), clay soils (75.46%), low initial soil organic carbon (SOC) and available phosphorous (AP) (92.4% and 101.6%), respectively, Therefore, we recommend the application of nitrogen fertilizer (>100 kg∙N∙ha<sup>−1</sup>), especially on infertile soils for improved grain yield and NUE in aforementioned cereal crops in Ethiopia and similar regions in sub-Saharan Africa (SSA).
文摘本文设计了一台喷气增焓(EnhancedVaporInjection,EVI)低温空气源热泵系统,研究补气对系统性能和参数的影响,测试EVI系统在低温下稳定运行的可行性。结果表明,EVI改善了空气源热泵低温运行排气温度过高的问题,实现了-20℃环境温度下的稳定运行;补气提高了系统性能,多个测试工况下,41℃出水温度时制热量最高提升了43.0%,性能系数(Coefficient of Performance,COP)最高提升了28.3%;相对补气量的增加对系统的性能改善呈现先增加后变缓至下降的趋势,存在一个最优的相对补气量使得系统能效最高;打开补气阀后吸气压力和排气压力均有所提高;-12℃环境温度时吸气压力较关闭补气阀时提高了14.1%,排气压力较关闭补气阀时提高了2%。
