Various physical, chemical and biological soil
properties in surface (0-5 cm) and subsurface (5-15 cm) soil were determined
in a 4-year field experiment conducted at Punjab Agricultural University
Ludhiana, India with sixteen treatments consisted of different combinations of
fertilizer N (0, 20 and 25 kg N ha-1), P (0, 60 and 75 kg P2O5 ha-1), FYM (0 and 10 t·ha-1) and wheat (Triticum
aestivum L.) residue (WR) (0 and 6 t·ha-1) applied to
summer-grown soybean (Glycine max L.)
and fertilizer N (0, 120 and 150 kg N ha-1), P (0, 60 and 75 kg P2O5 ha-1), and soybean residue (SR) (0 and 3 t·ha-1) applied
to winter-grown wheat crop continuously in
both conventional tillage (CT) and conservation agriculture (CA), arranged in a
split-split plot design with tillage system in main blocks, under
irrigated subtropical conditions. Application of fertilizer N, P, FYM and crop
residue (CR) significantly increased water stable aggregates and had profound
effects in increasing the mean weight diameter as well as the formation of
macro-aggregates, which were the highest in both surface (85%) and
subsurface (81%) soil layers with application of 20 kg N + 60 kg P2O5 + 10 t FYM + 6 t WR ha-1 applied to soybean and 120 kg N + 60 kg P2O5 + 3 t SR ha-1 applied to wheat crop in CA, respectively, and were 83% and 77% in CT treatments
after 2 years. Hence, better aggregation was found with 100% NP + FYM + CR,
where macro-aggregates were greater than 50% of total soil mass. The same
treatment also enhanced total organic C (TOC) from 3.8 g·kg-1 in
no-NP-FYM-CR control to 5.8 g·kg-1 in surface layer and from 2.7 to
3.6 g·kg-1 in subsurface layer after 2 years leading to the 41% and
39% higher TOC stocks over CT-Control in 0-15 cm soil layers of CT
and CA, respectively. The changes in TOC stocks after 4 years were 52% and 59%.