Biochar and crushed straw additions affect cadmium absorption in cassava-peanut intercropping system
Introduction
At present, the pollution of soil cadmium (Cd) has been worsening in China (Huang et al., 2018, Pan et al., 2017). Cd in soil is easily absorbed by plants, and high content of Cd not only causes slow growth of plants, dwarf plants, and low yields, but also directly or indirectly endanger human health (Boim et al., 2016; Hu et al., 2016; Liu et al., 2017a). Hyperaccumulators are used to extract heavy metals in soil and realize remediation; however, due to harsh agricultural production conditions and technical demands along with small biomass, it is hardly cultivated in the field in large scale. Moreover, high content of heavy metals in soil may poison the plants and result in unsatisfactory phytoremediation (Douchiche et al., 2012, He et al., 2013). Therefore, the application of energy plants with large biomass, which can be used for agricultural production, has become an important method in phytoremediation (Chen et al., 2017a; Pidlisnyuk et al., 2014).
Cassava (Manihot esculenta Crantz) is one of the three major tuberous crops in the world, which plays an important role in the feed and starch industry and the field of bioenergy (Okudoh et al., 2014). Cassava is a large biomass with a certain resistance to pollution and a capacity for easy accumulation of heavy metals, which has a great potential for phytoremediation and energy utilization (Jorgetto et al., 2014, Zeng et al., 2017). Peanut (Arachis hypogaea) is one of the most important cash and oil crops in the world, which has a strong absorptive capacity for Cd (Christou et al., 2017). Besides, intercropping is an effective agricultural practice for plant production, resource utilization, and phytoremediation by improving solar energy, enhancing soil microbial activity, and increases soil available nutrient content (Li et al., 2007; Li et al., 2011). It was found that cassava intercropped with peanut effectively uses land, light, and heat resources, reduces pests and diseases, and fertilizes the soil, to increase the yield and income at the same time (Lin et al., 2016).
Biochar is a carbon-rich solid made by pyrolysis of biomass under anoxic or anaerobic conditions, with high porosity and large specific surface area, negatively charged, and has a strong ion exchange capacity, which shows great potential applications in soil carbon sequestration, emission reduction, soil fertility improvement, and remediation of polluted soil (Jeffery et al., 2015; Mahar et al., 2015; Xu et al., 2016b). Moreover, it became a research hotspot all over thre world. In China, there are many crop straws burned every summer harvest or in later autumn and winter (Shi et al., 2014), causing serious atmospheric environmental pollution and posing a threat to human health. Therefore, recycling of waste straw is an ecological and economic approach that increased the utilization of straw (Chihchun and Ning, 2015, Wang et al., 2015). At present, straw returning is an advanced technology for soil cultivation and usage, which can significantly increase soil organic matter content, promote crop growth, and increase the microbial populations in the topsoil, thus improving the micro ecology of soil and crop yield (Qi et al., 2016, Rahman et al., 2016, Sun et al., 2017).
In recent years, there have been studies on cassava and peanut intercropping that mainly focus on cultivation techniques and economic benefits (Nyi et al., 2014; Pypers et al., 2015). There were few studies on Cd uptake by intercropping system, especially on the effect of biochar or straw application in this intercropping system. Therefore, a field plot experiment in Tielong Forest Farm was conducted to determine the effect of Cd absorption in monocropping and intercropping systems of cassava and peanut, to provide a research foundation for the subsequent cement pool plot experiment. The study mainly focused on the effect of Cd absorption on cassava and peanut intercropping system under biochar and crushed straw additions and aimed to provide a reference for realizing both remediation as well as production in Cd-contaminated soil and promoting sustainable development of agriculture and environment.
Section snippets
Test sites and test materials
The field plot test was carried out in the farmland of Tielong Forest in the Wengyuan county of Shaoguan City (24°50′N, 113°68′E). The research site was affected by frequent industrial and mining activities which discharge many heavy metals continuously, contaminating the surrounding farmland soil, surface water, and groundwater, endangering the growth of crops, and threatening the safety of drinking water and health of local residents. The pH of soil was 7.30, the organic matter content was
Yield and biomass of cassava and peanut in monocropping and intercropping systems
Intercropping reduced the yield and biomass of peanut but had no significant effect on cassava (Table 1). Compared with monocropping, the per hectare yield and biomass of aboveground and underground parts of peanut in intercropping system decreased significantly by 49.03%, 22.48%, and 20.01%, respectively (p < 0.05). The biomass of underground part of cassava in intercropping system decreased by 7.49% but the decrease was not significant (p > 0.05). Intercropping inhibited the growth of cassava
Conclusions
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The LER of cassava-peanut intercropping system was 1.43, which exceeded 1, showing an intercropping yield advantage. Under the unit area of hectare, compared with monocropping of cassava and peanut, the BCA of Cd in the intercropping system increased significantly by 24.98% and 25.59%, respectively. The MRER of Cd was 1.25, which exceeded 1, indicating that the intercropping pattern had an advantage in Cd removal. Therefore, cassava-peanut intercropping can reduce the Cd contents in all tissues
Acknowledgments
This work was financially supported by the National Key Research and Development Program of China (2017YFD0800900), the Science and Technology Planning Project of Guangdong Province, China (2015A020208012), Science and Technology Planning Project of Shaoguan City in Guangdong Province, China (2017sgtyfz301), and the Student Innovation Training Program 0f South China University (201710564109).
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