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\begin{document}

\title{Soil organic carbon and iron oxides affects soil aggregate stability
under straw returning and potassium fertilizer in a rice--rape cropping
system}



\author[1]{Bin Xue}%
\author[2]{Li Huang}%
\author[3]{Jianwei Lu}%
\author[2]{Xiaokun Li}%
\author[1]{Ruili Gao}%
\author[2]{Kamran Muhammad}%
\affil[1]{Ningxia University}%
\affil[2]{Huazhong Agricultural University}%
\affil[3]{Huazhong Agriculture University}%


\vspace{-1em}



  
  \date{June 13, 2024}


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\begin{abstract}
Soil organic carbon (SOC) and iron (Fe) oxides are known to affect the
formation and stability of soil aggregates. However, the effects of SOC
and Fe oxides on soil aggregates stability under straw returning and
potassium (K) fertilizer application in paddy--upland rotation systems
are less well-studied. This study primarily investigated soil aggregates
dynamics and their stability indices (mean weight diameter, MWD;
geometric mean diameter, GMD), and soil binders (SOC and iron oxides)
after rice and rape harvests under four treatments: F1,mineral nitrogen
(N) and phosphorus (P) fertilizer; F2, mineral NPK fertilizer; F3,
mineral NP fertilizer with straw returning; F4, mineral NPK fertilizer
with straw returning in rice--rape cropping system. Straw returning
treatments (F3 and F4) significantly (P \textless{}0.05) increased MWD
and GMD, but the effect of K is not obvious. The soil aggregates
stability was higher after the rape harvest than rice harvest, but SOC
content was the opposite. Straw input can increase the contents of SOC,
alkane-C and aromatic-C concentrations, especially in \textgreater{}0.25
mm aggregates. Long-term straw incorporation significantly increased the
amorphous (Feo) and complex iron oxides (Fep) concentrations. SOC and
Fep in bulk soil and \textgreater{}5 mm aggregates were significantly
related with MWD, and significant relationship was observed between MWD
and Feo in \textless{}5 mm fractions. Thus, the high levels of SOC,
alkane-C, Feo and Fep in soil after straw returning were responsible for
the aggregate stability, but the effect of potassium application is not
obvious in a rice--rape cropping system.%
\end{abstract}%



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\item
  Straw returning significantly improved soil aggregation and stability.
\item
  The effect of K fertilizer on the stability of aggregates and binder
  is not obvious.
\item
  Seasonal variability affected soil aggregate stability and SOC
  contents.
\item
  SOC and Fep in \textgreater{}5 mm fractions improved the stability of
  aggregates, while Feo in \textless{}5 mm fractions.
\end{itemize}

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