Effects of inorganic and organic amendment on soil chemical properties, enzyme activities, microbial community and soil quality in yellow clayey soil

<div><p>Understanding the effects of external organic and inorganic components on soil fertility and quality is essential for improving low-yielding soils. We conducted a field study over two consecutive rice growing seasons to investigate the effect of applying chemical fertilizer (NPK), NPK plus green manure (NPKG), NPK plus pig manure (NPKM), and NPK plus straw (NPKS) on the soil nutrient status, enzyme activities involved in C, N, P, and S cycling, microbial community and rice yields of yellow clayey soil. Results showed that the fertilized treatments significantly improved rice yields over the first three experimental seasons. Compared with the NPK treatment, organic amendments produced more favorable effects on soil productivity. Notably, the NPKM treatment exhibited the highest levels of nutrient availability, microbial biomass carbon (MBC), activities of most enzymes and the microbial community. This resulted in the highest soil quality index (SQI) and rice yield, indicating better soil fertility and quality. Significant differences in enzyme activities and the microbial community were observed among the treatments, and redundancy analysis showed that MBC and available N were the key determinants affecting the soil enzyme activities and microbial community. The SQI score of the non-fertilized control (0.72) was comparable to that of the NPK (0.77), NPKG (0.81) and NPKS (0.79) treatments but significantly lower compared with NPKM (0.85). The significant correlation between rice yield and SQI suggests that SQI can be a useful to quantify soil quality changes caused by different agricultural management practices. The results indicate that application of NPK plus pig manure is the preferred option to enhance SOC accumulation, improve soil fertility and quality, and increase rice yield in yellow clayey soil.</p></div

Variations in rice yield under different fertilizations in 2012 and 2013.

<p>Variations in rice yield under different fertilizations in 2012 and 2013.</p

Variations in soil chemical properties under different fertilizations in 2012 and 2013.

<p>Variations in soil chemical properties under different fertilizations in 2012 and 2013.</p

Principal Component Analysis (PCA) of microbial community composition (relative content of individual PLFA molecules) in soils under different fertilizations in the late rice season of 2012 (a) and the early rice season of 2013 (c), and Redundancy Analysis (RDA) of the correlations between soil parameters (chemical properties and microbial biomass C/N) and microbial community composition in the late rice season of 2012 (b) and the early rice season of 2013 (d).

<p>The red arrows indicate the soil parameters that had a strong and significant impact on the microbial community composition (<i>P</i><0.05), and the corresponding explained proportion of variability is shown in the lower left corner. Abbreviations: <i>Avail</i>. available, <i>MBC</i> microbial biomass carbon, <i>MBN</i> microbial biomass nitrogen, <i>SOM</i> soil organic matter.</p

Variations in Microbial Biomass Carbon (MBC) and Nitrogen (MBN) under different fertilizations in 2012 and 2013.

<p>Vertical bars represent the SE (<i>n</i> = 3) and different letters above bars indicate significant differences between fertilizations at <i>P</i><0.05.</p

Monthly precipitation and mean air temperature over a two-year period (2012–2013).

<p>Monthly precipitation and mean air temperature over a two-year period (2012–2013).</p

Enzymes with corresponding commission number (EC), corresponding substrate, and the abbreviation used in this study.

<p>Enzymes with corresponding commission number (EC), corresponding substrate, and the abbreviation used in this study.</p

Variations in Soil Quality Index (SQI) under different fertilizations in the late rice season of 2012 (a) and the early rice season of 2013 (b).

<p>Variations in Soil Quality Index (SQI) under different fertilizations in the late rice season of 2012 (a) and the early rice season of 2013 (b).</p

Variations of the total PLFA, relative abundance of bacteria, ratio of gram-positive to gram-negative bacteria, and relative abundances of fungi and actinomycetes under different fertilizations in the late rice season of 2012 and the early rice season of 2013.

<p>Vertical bars represent the SE (<i>n</i> = 3) and different letters above bars indicate significant differences between fertilizations at <i>P</i><0.05.</p

Relationships between Soil Quality Index (SQI) values and rice yields in 2012 and 2013.

<p>Relationships between Soil Quality Index (SQI) values and rice yields in 2012 and 2013.</p