Effects of Organic Fertilizers with Different Maturities on Soil Improvement and Soybean Yield

The maturity degree of organic fertilizer affects its application effect, but this application effect difference and the underlying reasons for it remain largely unclear. This study explored the effects of cattle manure compost with different maturities on soybean yield, soil physicochemical properties, and biological properties, and the underlying reasons for the differences in the application effects of organic fertilizers with different maturities. The results showed that the T21d treatment (GI = 62.5%, germination index) had the optimal effect on increasing soybean yield, and its effect on improving basic soil physicochemical properties, active organic matter components, enzyme activity, and microbial diversity was the most obvious. Compared with the control (CK), the soybean yield was increased by 15.1% under T21d treatment, and the soil organic matter (OM), alkali-hydrolyzed nitrogen (AN), available phosphorus (AP), and available potassium (AK) contents were increased by 29.9%, 25.0%, 22.2%, and 8.4%, respectively; the dissolved organic matter (DOM), extractable humus (HE), humic acid (HA), and fulvic acid (FA) contents in the soil were increased by 96.5%, 22.6%, 16.7%, and 30.6%, respectively; and the activities of soil phosphatase, neutral protease, urease, and cellulase were increased by 45.4%, 164.1%, 33.9%, and 128.9%, respectively. However, the fertilizer efficiency under the T28d, T45d, and T60d treatments with high-maturity organic fertilizers was lower than that under T21d. In general, the appropriate maturity of organic fertilizers has a positive effect on soil improvement and yield increase, but the excessive maturity of organic fertilizers reduces their application effects.