Comparative effect of incorporated and surface spread crop residues, poultry manure and their biochars on soil health indicators along a soil profile

Biochar is being touted as a wonderful amendment for improving soil health. However, its effectiveness for alkaline soils that are poor in organic matter has rarely been evaluated, particularly in long term field experiments. We laid down a field experiment based on wheat-maize crop rotation where we either incorporate or spread on surface the residues of the previous crop (wheat or maize), poultry manure or biochar(s) derived from these organic amendments. They are applied at the rate of 2 tons ha^-1 before sowing each crop. It was hypothesized that the organic amendments applied in their feedstock or biochar form will considerably differ in space and time vis-à-vis soil health indicators. Moreover, tillage (incorporation i.e., conventional tillage vs surface spreading i.e., no tillage) would significantly alter the effect of these organic amendments. Over two years and four cropping seasons, the CO₂-C emissions from the field were significantly higher (12-17%) when residues or biochar were incorporated. However, the feedstocks (residues/manure) induced significantly higher CO₂-C emissions than their respective biochars across the tillage treatments (13-23%). Furthermore, the ammonia emissions were significantly reduced when biochars were added (5-11%) where surface spreading, or incorporation didn’t induce any difference. First soil sampling was done till 75 cm in depth increments of 15 cm, after two years of the experiment (Nb: the experiment is running). Microbial biomass (MBC) was significantly higher in upper layers (0-15 cm, 15-30 cm) in the plots incorporated with residues while all other amendments or tillage treatments showed similar MBC. No change in MBC was observed below 30 cm in any treatment. The soil organic carbon content (& stocks) were slightly but significantly higher (by 5-14%) in upper layers where biochars were incorporated, whereas incorporating residues increased soil organic carbon compared to biochar surface spreading. The extracellular enzymatic activity particularly of β-glucosidase, was significantly altered to 60 cm in some treatments with residue addition (incorporation or spreading) inducing higher activity. The leucine aminopeptidase activity remained unchanged throughout the soil profile in most of the treatments. However, chitinase activity was significantly higher in some biochar amended soils. These preliminary results indicate that residues/manure as well as their biochar significantly improve soil health indicators and that their method of application (incorporation vs spreading) significantly alter their effects. However, it must be noted that both types of amendments have improved different soil health indicators at this stage of the experiment.