Changes in soil aggregate‐associated enzyme activities and nutrients under long‐term chemical fertilizer applications in a phosphorus‐limited paddy soil

Abstract

Paddy soils in subtropical China are usually deficient in phosphorus (P) and require regular application of chemical fertilizers. This study evaluated the effects of chemical fertilizers on the distribution of soil organic carbon (SOC), total nitrogen (N) and available P, and on the activity of the associated enzymes in bulk soil and aggregates. Surface soils (0-20 cm) were collected from a 24-yr-old field experiment with five treatments: unfertilized control (CK), N only (N), N and potassium (NK), N and P (NP), and N, P and K (NPK). Undisturbed bulk soils were separated into >2, 1-2, 0.25-1, 0.053-0.25 and <0.053 mm aggregate classes using wet sieving. Results showed that both NPand NPK-treated soils significantly increased mean weight diameter of aggregates, SOC, available P in bulk soil and aggregates, as compared to CK. Most SOC and total N adhered to macro-aggregates (>0.25 mm), which accounted for 64-81% of SOC and 54-82% of total N in bulk soil. The activities of invertase and acid phosphatase in the 1-2 mm fraction were the highest under NPK treatment. The highest activity of urease was observed in the <0.053 mm fraction under NP treatment. Soil organic carbon and available P were major contributors to variation of enzyme activities at the aggregate scale. In conclusion, application of NP or NPK fertilizers promoted the formation of soil aggregates, nutrient contents and activities of associated enzymes in P-limited paddy soils, and thus enhanced soil quality.

An assessment of various pools of organic phosphorus distributed in soil aggregates as affected by long‐term P fertilization regimes

“…There might be several reasons for this: (i) Input of long-term continuous mineral P fertilizer combined organic manure to the study soil, which better sustained the supply capacity of labile Po and likely influenced P distribution in soil aggregates (Ahmed et al, 2016;Khan et al, 2021); (ii) low lower P use efficiency by the NPM treatment in bulk soil (Table S1) (Guo et al, 2008); and (iii) SOC was able to activate soil P, and the higher SOC was showed in the NPM treatment (Table 1) because soil Po availability principally was controlled by microbial community, which was strongly regulated by SOC (Chen et al, 2021). In this study, we also found that the application of NP fertilizer significantly increased labile Po in the soil aggregates compared with CK (Figure 2a) and improved the soil structure because of an increase of Olsen-P and SOC contents in the soil aggregates (Table 1), thereby promoting the growth of microorganisms and enzyme synthesis (Li et al, 2017), which can in turn influence Po soil stabilization (Dodd & Sharpley, 2015). The following reasons can explain this intriguing response: Firstly, the significant variability of labile Po fractions in the NP treatment could result from differences in soil properties in soil aggregates compared with CK (Table 1).…”

Soil Microbial Communities and Enzyme Activities after Long-Term Application of Inorganic and Organic Fertilizers at Different Depths of the Soil Profile

“…Soil enzymes are dominantly hydrolases, which help to acquire carbon, nitrogen, and phosphorus for support of primary metabolism; or oxidoreductases, which contribute to decomposition of organic compounds [27]. Measured activities of such enzymes reflect the intensity and direction of various biochemical processes in soil environment and can be used for evaluation of microbial demands for nutrients and for expressing the response of ecosystem, which reflects changes in the environment as such [28,29].…”

The use of biologically based phosphorus fractions to evaluate soil P availability in reduced P‐input paddy soils

“…For example, Li et al . () reported that soil Pi pools increased significantly after the addition of P sources to soil. Similarly, Boschetti et al .…”