Sugarcane/soybean intercropping with reduced nitrogen input improves crop productivity and reduces carbon footprint in China.

Global climate change and decreases in available land are significant challenges that humans are currently facing. Alternative management approaches for sugarcane fields have great potential to help mitigate these problems in China. We hypothesized that soybean intercropping with reduced nitrogen input could increase crop productivity and reduce the carbon footprint (CF) of sugarcane fields in China. Therefore, a long-term field experiment from 2009 to 2017 in the Pearl River Delta of China was chosen to test this hypothesis. The results showed that the energy yields of sugarcane/soybean intercropping systems were 17.8%-39.4% higher than those of sugarcane monocropping systems. The energy yields of the same cropping systems using conventional and reduced N inputs (525 kg ha-1 and 300 kg ha-1) did not show a significant difference. Additionally, the CF values of the unit yield (CFY) for sugarcane/soybean intercropping were 3.2%-30.4% lower than those of the monocropping systems, showing the higher CF efficiency of the intercropping pattern, although the difference was not significant. The CF of the unit area (CFA) and the CFY of all the cropping patterns at the conventional N level were 19.5%-62.0% higher than that at the reduced N level, demonstrating that reducing the nitrogen input could significantly lower the CF of the sugarcane fields. In addition, the high N level cased negative effects in terms of increasing the crop productivity and reducing the CF of the soybean/sugarcane intercropping pattern. In conclusion, sugarcane/soybean intercropping with reduced N input improved crop productivity while lowering the CF of sugarcane fields in China. The sugarcane/soybean (1:2) intercropping with 300 kg N ha-1 system showed the best benefits in the Pearl River Delta of China. These advanced agricultural practices contributed to improved farmland use efficiency and clean production in an agricultural system.

Numerical simulation of stress wave interaction in short-delay blasting with a single free surface.

It is generally believed that stress wave superposition does occur and plays an important role in cutting blasting with a single free surface, in which explosive columns of several blast holes with short spacing are simultaneously initiated. However, considering the large scatter of pyrotechnic delay detonators that are used in most underground metal mines in China, the existence of stress wave superposition and the influence of this effect on rock fragmentation are questionable. In the present study, the stress wave interaction in short-delay blasting with a single free surface was studied through the use of the LS-DYNA code. Stress waves induced by two blast holes blasting with different delays were compared with the single blast hole case, and the effects of delay time, detonating location and spacing on stress wave superposition were investigated. The numerical results showed that for blast holes with a 1 m spacing, stress wave interaction only occurs when the delay time is 0 ms and does not occur for blasting with delays of more than 1 ms. An increase in the duration of a stress wave via optimizing the detonation location does not improve the stress wave interaction. For a 1 ms delay, stress wave superposition only occurs when the spacing is more than 4 m, which is a rare case in practice. The results indicated that the occurrence of stress wave superposition for blasting with a single free surface is strictly limited to conditions that would be difficult to achieve under the existing delay accuracy of detonators. Therefore, it is unrealistic to improve fragmentation via the stress wave interaction in field blasting. Furthermore, the numerical results of the stress wave interaction also show that there would be a great potential to reduce the hazardous vibrations induced by short-delay blasting by using electronic detonators with better control of delays in an order of several milliseconds.