Decomposition of soil organic matter is modulated by soil amendments

Increasing soil microbial respiration is thought to increase the soil organic matter (SOM) decomposition and hence the soil fertility. It was hypothesized that whether N or C rich drivers enhance the SOM decomposition if amended with farmyard manure (FYM). Thus, an experiment was designed using four key drivers i.e. 1) Control (No-amendment), 2) Min-N (urea @ 30 kg N ha(-1) as N rich amendment), 3) HA (Humic acid @ of 2.5 kg ha(-1) as C rich amendment) and 4) EM (effective microbes @ 200 L Mg-1 FYM as microbial solution). These four key drivers were mixed with different levels of FYM i.e. (0, 5, 10, 15 and 20 Mg ha(-1)) and were added to 100 g soil in vials. These vials were incubated for 90 days at 25 degrees C and destructive periodic sampling were made after 1, 3, 15, 30, 45 and 90 days. The mineral N availability was 3 times higher with 20 Mg FYM ha(-1) than No-FYM treatment. The degrading order of soil organic carbon (EM > HA > Min-N > control) resulted in soil respiration of the same order. However, the degrading order of TN (EM > Min-N > HA > control) caused positive changes for mineral N availability with EM (31.3 parts per thousand day(-1)) and negative changes with Min-N (257 parts per thousand day(-1)). The mineral N availability last for 45 days with EM and 30 days for HA. According to principle component analysis, EM increased MBC, mineral N, soil respiration and has positive effects for PC-1 (63%) whereas Min-N increased the SOC and TN and has negative effects both for PC1 (63%) and PC-2 (22%). In conclusion, the SOM decomposition increased by Min-N (23%), EM (42%), HA (32%) with increasing FYM level from 0 Mg ha(-1) to 5, 10, and 15 Mg ha(-1), respectively. Thus, for C rich driver more FYM should be used than N rich driver for higher SOM decomposition.