Depth dynamics of soil N contents and natural abundances of ¹⁵N after 43 years of long-term fertilization and liming in sub-tropical Alfisol

ABSTRACT

The aim of this study was to understand impacts of long-term (43 years) fertilization on soil aggregation, N accumulation rates and δ¹⁵N in surface and deep layers in an Alfisol. Soil samples from seven treatments were analysed for N stocks, aggregate-associated N in 0–30 cm and the changes in δ¹⁵N in 0–90 cm depths. The treatments were: unfertilized control (control); recommended N dose (N); recommended N and phosphorus doses (NP); recommended N, P and potassium doses (NPK); 150% of recommended N, P and K doses (150% NPK); NPK + 10 Mg FYM ha⁻¹ (NPK + FYM) and NPK + 0.4 Mg lime ha⁻¹ (NPK + L). Results revealed that plots under NPK + FYM had ~39% higher total N concentrations than NPK + L in 0–30 cm soil layers. In NPK + L, macro-aggregates had 35 and 11% and microaggregates had 20 and 9% lower δ¹⁵N values than NPK + FYM in 0–15 and 15–30 cm soil layers, respectively. However, plots receiving NPK + FYM had ~39% greater deep soil (30–90 cm) N accumulation than NPK + L. These results would help understanding N supplying capacity by long-term fertilization and assist devising N management strategies in sub-tropical acidic Alfisols.

KEYWORDS:

• Wheat based cropping
• farmyard manure
• C/N ratio
• deep soil N accumulation
• δ¹⁵N,

Acknowledgment

The first author acknowledges the Fellowship given by the Indian Council of Agricultural Research and the Indian Agricultural Research Institute, New Delhi, to conduct this study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Indian Council of Agricultural Research;