Role of nitrogen fertilization in sustaining organic matter in cultivated soils.
Soil organic matter (SOM) is essential for sustaining food production and maintaining ecosystem services and is a vital resource base for storing C and N. The impact of long-term use of synthetic fertilizer N on SOM, however, has been questioned recently. Here we tested the hypothesis that long-term application of N results in a decrease in SOM. We used data from 135 studies of 114 long-term experiments located at 100 sites throughout the world over time scales of decades under a range of land-management and climate regimes to quantify changes in soil organic carbon (SOC) and soil organic nitrogen (SON). Published data of a total of 917 and 580 observations for SOC and SON, respectively, from control (unfertilized or zero N) and N-fertilized treatments (synthetic, organic, and combination) were analyzed using the SAS mixed model and by meta-analysis. Results demonstrate declines of 7 to 16% in SOC and 7 to 11% in SON with no N amendments. In soils receiving synthetic fertilizer N, the rate of SOM loss decreased. The time-fertilizer response ratio, which is based on changes in the paired comparisons, showed average increases of 8 and 12% for SOC and SON, respectively, following the application of synthetic fertilizer N. Addition of organic matter (i.e., manure) increased SOM, on average, by 37%. When cropping systems fluctuated between flooding and drying, SOM decreased more than in continuous dryland or flooded systems. Flooded rice ( L.) soils show net accumulations of SOC and SON. This work shows a general decline in SOM for all long-term sites, with and without synthetic fertilizer N. However, our analysis also demonstrates that in addition to its role in improving crop productivity, synthetic fertilizer N significantly reduces the rate at which SOM is declining in agricultural soils, worldwide.
International Rice Research Institute, New Delhi, India. j.k.ladha@cgiar.org
Jagdish K
JK
Ladha
C Kesava
CK
Reddy
Agnes T
AT
Padre
Chris
C
van Kessel
D000383:Agriculture / Q000379:methods; D002244:Carbon / Q000737:chemistry; D002980:Climate; D005308:Fertilizers / Q000032:analysis; D009584:Nitrogen / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*
D005308:Fertilizers; D009930:Organic Chemicals; D012987:Soil; D002244:Carbon; D009584:Nitrogen