增施氮肥可以加速棉花秸秆的分解，进而通过增加土壤氮素的供应能力和棉株氮素的吸收能力来提高棉花的产量。长期秸秆还田和高施氮量条件下，改变种植密度和施氮量是否可以提高棉花产量的研究目前尚不清楚。本研究于2016年至2017年在山东聊城进行，试验设置三个种植密度和五个施氮量，种植密度分别为5.25（D_5.25）、6.75（D_6.75）和8.25（D_8.25）株m^-2，施氮量分别为0（N₀）、105（N₁₀₅）、210（N₂₁₀）、315（N₃₁₅）和420（N₄₂₀）kg ha^-1，量化了种植密度和施氮量对棉花产量、氮肥利用、叶片衰老、土壤无机氮和表观氮平衡的影响。与常规组合（D_5.25N₃₁₅）相比，种植密度增加28.6％、施氮量减少33.3％（D_6.75N₂₁₀）可以保持较高的棉花产量，而种植密度增加28.6％、施氮量减少66.7％（D_6.75N₁₀₅）仅可在第一年实现高产；生物量则随着种植密度和施氮量的增加而增加，两年均在D_8.75N₄₂₀获得最高值。与D_5.25N₃₁₅相比，D_6.75N₁₀₅时NAE和NRE分别增加30.2％和54.1％，而D_6.75N₁₀₅时NAE和NRE则分别增加104.8％和88.1％；施氮量105 kg ha^-1时土壤无机氮急剧下降，但在D_6.75N₂₁₀未发现差异；施氮量105 kg ha^-1时，土壤氮素缺乏发生，但在D_6.75N₂₁₀时，土壤氮素缺乏未发生；施氮量为210-420 kg ha^-1时叶片净光合速率和氮浓度均高于其他处理。综上，秸秆还田条件下，D_6.75N₂₁₀是黄河流域棉区和其他具有类似生态的地区的优先组合。

To optimize the spatial distribution of cotton bolls and to increase the yield, the relationship between yield components and boll spatial distribution was investigated among different Bt (Bacillus thuringensis) cotton varieties.  A five-year field experiment was conducted to reveal the reasons for the differences in lint yield and fiber quality across three Bt cotton varieties with different yield formations from 2013 to 2017.  The lint yield of Jiman 169 (the average yield from 2013–2017 was 42.2 g/plant) was the highest, i.e., 16.3 and 36.9% higher than Lumianyan 21 (L21) and Daizimian 99B (99B), respectively.  And the differences in boll weight among the three cultivars were similar to the lint yield, while the others yield components were not.  So the increase in lint yield was mainly attributed to the enlargement in boll weight.  However, the change in fiber quality was inconsistent with the lint yield, and the quality of L21 was significantly better than that of Jimian 169 (J169) and 99B, which was caused by the diversity of boll spatial distribution.  Compared with 99B, the loose-type J169 had the highest number of large bolls in inner positions; the tight-type L21 had a few large bolls and the highest number of lower and middle bolls.  And approximately 80.72% of the lint yield was concentrated on the inner nodes in Jiman 169, compared with 77.44% of L21 and 66.73% of 99B during the five-year experiment.  Although lint yield was significantly affected by the interannual changes, the lint yield of J169 was the highest and the most stable, as well as its yield components.  These observations demonstrated the increase in lint yield was due to the increase in boll weight, and the large bolls and high fiber quality were attributed to the optimal distribution of bolls within the canopies.

The rapidly growing demand for food, feed and fuel requires further improvements of land and water management, crop productivity and resource-use efficiencies. Combined field experimentation and crop growth modelling during the past five decades made a great leap forward in the understanding of factors that determine actual and potential yields of monocrops. The research field of production ecology developed concepts to integrate biological and biophysical processes with the aim to explore crop growth potential in contrasting environments. To understand the potential of more complex systems (multi-cropping and intercropping) we need an agro-ecosystem approach that integrates knowledge derived from various disciplines: agronomy, crop physiology, crop ecology, and environmental sciences (soil, water and climate). Adaptation of cropping systems to climate change and a better tolerance to biotic and abiotic stresses by genetic improvement and by managing diverse cropping systems in a sustainable way will be of key importance in food security. To accelerate sustainable intensification of agricultural production, it is required to develop intercropping systems that are highly productive and stable under conditions with abiotic constraints (water, nutrients and weather). Strategies to achieve sustainable intensification include developing tools to evaluate crop growth potential under more extreme climatic conditions and introducing new crops and cropping systems that are more productive and robust under conditions with abiotic stress. This paper presents some examples of sustainable intensification management of intercropping systems that proved to be tolerant to extreme climate conditions.