1 Introduction
Sugarcane has become the most important cash crop in southern China.
During the lifetime of sugarcane crop, it suffers from various pests in
different development stages, and requires a large amount of pesticides
and fertilizers to sustain its growth and health (Franco et al., 2011;
Cherry et al., 2017). However, the heavy use of pesticides and
fertilizers in sugarcane cultivation causes serious impacts on the
agricultural environment, including agricultural non-point source
pollution, increasing cost efficiency, energy conservation and emission,
and effects on beneficial invertebrates, as well as threats to food
safety and quality (Bokhtiar & Sakurai 2005; Klaine et al., 2010;
Velasco et al., 2012). In 2015, China’s Ministry of Agriculture
introduced two actions that seek to achieve zero growth in the use of
chemical fertilizers and pesticides by 2020 (Jin & Zhou, 2018).
Pesticide-fertilizer combinations or mixture products have been thriving
and are increasingly applied in the farmland, as they serve a dual
purpose with both nutritional and insecticidal characteristics, which
could help achieve sugarcane pesticide-fertilizer integration and save
labor and costs (Achorn & Wright, 1982; Xie et al., 2017 & 2018).
Tiange, for instance, is a popular multifunctional pesticide-fertilizer
product used in sugarcane cultivation in southern China, could
effectively suppress pests including sugarcane borer, thrip, aphid, and
cockchafer (Xie et al., 2017). Xie et al. (2019) found that the
combination of 50% organic fertilizer replacement and 50% pesticide
reduction can produce the optimal results for both mitigating nutrient
loss and balancing tea yield and quality. Yein et al. (2013) reported
that pesticides and fertilizers in combination were much more effective
at controlling the root-knot nematode infesting mung than using only
pesticide or fertilizer alone. However, the domestic industry of
pesticide and fertilizer integration is in its initial stage, the
combination products currently lack industry standards and evaluation
systems, and the potential impact on rhizosphere microbiome is still
underestimated.
Rhizosphere microflora has been shown to be a key component of
agricultural ecosystems that not only plays a significant role in basic
soil processes but is also actively involved in enhancing soil fertility
and crop productivity (Haney et al., 2015; Huang et al., 2020; Korenblum
et al., 2020). However, research on the effects of pesticide and
fertilizer combinations (SPF) on the rhizosphere microbial diversity and
function of sugarcane is still rare. Currently, the overuse of synthetic
fertilizers and pesticides has been reported to cause adverse effects on
the soil microflora, and can substantially influence plant health and
productivity (Hartmann et al., 2015; Zhu et al., 2016). In particular,
fertilizers and pesticides tend to have long persistence in the soil,
which is bound to affect the soil microflora and consequently disturbing
soil health (Prashar & Shah, 2016). Previous studies have found that
chemical and bio-organic fertilizers have distinctive effects on the
structure and function of the soil microbiome (Cai et al., 2017; Xiong
et al., 2017). Compared with organic fertilizers, chemical fertilizers
have many disadvantages, despite the ability to stimulate the growth of
the fast-growing microbes by introducing more readily-available
nutrients (Esperschütz et al., 2007). For instance, a high concentration
of nitrogen fertilizer strongly modifies the composition of the soil
microbiome, which could negatively impact soil carbon cycling and
promote the abundance of fungal genera (Paungfoo-Lonhienne et al.,
2015). On the contrary, bio-fertilizers can improve soil health by
direct suppression of pathogens or via modification of the indigenous
microbial community (Xiong et al., 2017). In addition, organic
fertilizers introduce more organic carbon into the soil and hold a
closer neutral pH value, which is considered a dominant factor in
determining the composition of soil microbiomes (Pang et al., 2017).
Investigating shifts driven by SPF in the composition of the soil
microbiome would be helpful for maintaining and/or enhancing soil
fertility and productivity, as well as for protecting soil ecosystems
against disturbances (Tian et al., 2015). In this study, we hypothesized
that pesticide inputs supplemented with organic fertilizer could
maintain the composition of the soil microbiome more sustainably than
the conventional method based on applying the pesticide and fertilizer
separately. Here we conducted a field experiment to reveal any shifts in
the rhizosphere microbiome with different pesticide and/or fertilizer
treatments, as well as to compare treatment effects on the structure and
function of the soil microbiome. The objectives of this study were to:
(1) explore the effects of a SPF (pesticide and fertilizer combinations)
on the structure and diversity of sugarcane’s rhizosphere microbiome;
and (2) reveal the potential interactions between the dual reductions in
pesticide and fertilizer use and sugarcane quality.