Depth dynamics of soil N contents and natural abundances of N-15 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 (43years) fertilization on soil aggregation, N accumulation rates and N-15 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 N-15 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 + 10Mg FYM ha(-1) (NPK + FYM) and NPK + 0.4Mg lime ha(-1) (NPK + L). Results revealed that plots under NPK + FYM had similar to 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 N-15 values than NPK + FYM in 0-15 and 15-30 cm soil layers, respectively. However, plots receiving NPK + FYM had similar to 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