Response of soil enzyme activity in flowering stages of maize to long-term fertilization in red soil

Objectives Soil enzyme activity is closely related to soil nutrient turnover and crop growth, especially in long-term fertilization. It is important to study key soil enzyme activities which drive soil available nutrients and crop uptake.

Methods Based on a long-term fertilization experiment in a red soil since 1986, which included treatments of CK (no fertilization), NPK (NPK fertilizers), 2NPK (double rates of NPK fertilizers), NPKM (NPK fertilizers and manure), OM (manure). After 31 years of fertilization treatments, soil samples were collected at the flowering stage of maize (18th, June, 2017), and soil sucrose invertase (INV), dehydrogenase (DEH), cellulase (CEL), urease (UR), polyphenol oxide (PHOX), acid phosphatase (ACP) and β-glucosidase (BG) were analyzed. Key soil enzyme activity indices were explored by redundancy analysis (RDA).

Results The application of fertilizer improved soil enzyme activities. Compared to CK treatment, NPKM treatment was more beneficial to increase soil enzyme activity than OM, NPK and 2NPK treatments. Compared with OM, the activities of INV, DEH, UR, PHOX, ACP and BG of NPKM treatment were increased by 13.7%, 13.5%, 10.6%, 10.5%, 5.6% and 13.4%, respectively; they were all improved than 2NPK treatment by 32.4%, 112.2%, 22.8%, 33.3%, 27.6% and 50.4%, respectively. However, there was no significant difference between NPK and 2NPK, excepted for CEL and UR. Soil pH, organic carbon, available nutrient contents and plant nutrient uptake in NPKM treatment were significantly higher than those in other treatments. The result of RDA indicated that INV, CEL and UR were the key enzymatic indices affecting soil and plant nutrient contents (R² > 0.90, P < 0.001).

Conclusions In the red soil, soil enzyme activities in response to different fertilization treatments were different at the flowering stage of maize. Compared with the application of chemical fertilizers, or manure alone, combination of organic and inorganic fertilizers could increase soil enzyme activities. The response of CEL and UR were sensitive to rates of nitrogen, phosphorus and potassium fertilizers. Furthermore, INV, CEL and UR were key indices to indicate soil nutrient turnover and movement in red soil.