Influence of integrated nitrogen and phosphorus management practices on soil microbial population dynamics

Introduction

Soil microorganisms play a crucial role in maintaining soil fertility by regulating organic matter decomposition, nutrient mineralization, and nutrient availability to plants. The size and activity of soil microbial populations are highly sensitive to changes in nutrient management practices and therefore serve as important indicators of soil biological health. Among soil microorganisms, fungi, bacteria, and actinomycetes contribute significantly to carbon and nutrient cycling processes. Excessive reliance on chemical fertilizers often leads to deterioration of soil biological properties, whereas integrated nutrient management involving organic residues, biofertilizers, and inorganic fertilizers improves microbial activity and diversity. Nitrogen and phosphorus are major nutrients influencing both plant growth and microbial metabolism. Organic amendments provide readily available carbon sources that stimulate microbial proliferation, while balanced phosphorus nutrition supports microbial energy transfer and cellular functions. Previous studies have reported increased microbial populations under integrated nutrient management systems compared to sole fertilizer application (Masto et al., 2006; Mandal et al., 2007) [4,3] . However, information on the combined influence of integrated nitrogen and phosphorus management practices on soil microbial populations at different crop growth stages is limited. Hence, the present investigation was undertaken to study the effect of nitrogen and phosphorus management practices on soil fungal, bacterial, and actinomycetes populations.

Materials and Methods

A field experiment was conducted during the agricultural years 2022-23 and 2023-24 at the experimental farm under irrigated conditions. The experiment was laid out in a factorial randomized block design with six nitrogen management options and three phosphorus management options, replicated three times. Soil samples were collected from the rhizosphere at 30 DAT, 60 DAT, and at harvest. Fungal, bacterial, and actinomycetes populations were enumerated using the serial dilution and plate count technique as described by Waksman and Fred (1922) [7] and Parkinson et al. (1971) [6] . The results were expressed as colony forming units (CFU) per gram of soil. Data were statistically analyzed using analysis of variance (ANOVA) as outlined by Gomez and Gomez (1984) [2] , and year-wise data were pooled for interpretation.

Results and Discussion

Fungal Population: Fungal population data (Table 1) indicated significant differences due to nitrogen and phosphorus management practices at all growth stages. Pooled data revealed that nitrogen management treatment T5 recorded the highest fungal population at 30 DAT (24.22), 60 DAT (33.71), and at harvest (26.49). The increase in fungal population under integrated nutrient management may be attributed to enhanced organic matter availability and improved soil micro-environment. Similar findings were reported by Mandal et al. (2007) [3] . Among phosphorus management options, application of 100% RDP as basal recorded significantly higher fungal populations at all stages. Interaction effects were nonsignificant, indicating independent effects of nitrogen and phosphorus treatments.

Table 1: Influence of Nitrogen and Phosphorus Management Practices on Fungi activity in soil

Bacterial Population

Bacterial population showed trends similar to fungal population (Table 2). Treatment T5 recorded significantly higher pooled bacterial population at 30 DAT (14.39), 60 DAT (19.58), and at harvest (15.72). Increased bacterial population under integrated treatments may be due to higher availability of labile carbon and nutrients. These results are in agreement with Dick et al. (1996) [1] and Masto et al.

(2006) [4] . Phosphorus management with 100% RDP (basal) significantly enhanced bacterial population compared to other treatments. Interaction effects were non-significant.

Actinomycetes Population

Actinomycetes population (Table 3) was significantly influenced by nutrient management practices. Treatment T5 recorded the highest pooled actinomycetes population at all stages, followed by T6. Actinomycetes populations increased from 30 DAT to 60 DAT and declined at harvest, reflecting their preference for stable organic substrates. These findings corroborate earlier reports by Nannipieri et al. (2003) [5] .

Conclusions:

The study demonstrated that integrated nitrogen and phosphorus management practices significantly enhanced soil fungal, bacterial, and actinomycetes populations at all crop growth stages. Treatments involving combined application of organic residues, bio-consortium, and recommended nitrogen dose proved superior to sole chemical fertilizer application. Phosphorus application at 100% recommended dose as basal consistently supported higher microbial populations. The non-significant interaction effects suggest independent contributions of nitrogen and phosphorus. Integrated nutrient management can be recommended as a sustainable strategy for improving soil microbial health and long-term soil fertility.

References

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