Effect of Long-Term Differential Application of Inorganic Fertilizers and Farmyard Manure on Carbon Sequestration and GHG Emissions.

The emissions of greenhouse gases (GHGs) from soils under intensive cropping are altered by various nutrient, water, farmyard manure (FYM) and tillage management practices To identify sustainable nutrient management practices aimed at carbon (C) sequestration and reducing GHG emissions, five treatments viz., 100%NPK (T₁); 150% NPK(T₂) ; 100%N (T₃); 100%NPK+FYM (T₄); Control (T₅), of a long-term fertilizer experiment under maize-wheat cropping system in Northern India were selected for the study. At the start of the experiment in 1971, status of SOC was 2.2 g kg^-1 and in 2013-14 SOC status were 4.1, 4.2, 3.7, 5.2 and 2.7 g kg^-1 in T₁, T₂, T₃, T₄ and T₅ treatments_, respectively. After 42 years, maize and wheat grain yields in different treatments were 4.6 and 5.1 Mg ha^-1 in T₁, 5.0 and 5.4 Mg ha^-1 in T₂, 3.3 and 4.2 Mg ha^-1 in T₃, 5.9 and 5.8 Mg ha^-1 in T₄, and 2.3 and 1.7 Mg ha^-1 in T₅, respectively. This suggested that continuous application of balanced fertilizers and integrated nutrient management has resulted in the build-up of SOC and commensurating increase in grain yields. Total CO₂-equivalent GHG emission from T₁, T₂, T₃, T₄ and T₅ treatments were 9.9, 10.4, 8.8, 11.9 and 6.1 Mg CO₂-eq ha^-1 in 2013-14, portraying that gains in SOC were also associated with higher GHG emissions. Yield-scaled global warming potential (Ys-GWP) were worked out to identify best nutrient management practice with higher grain yields and lower GHG emissions. Ys-GWP for control treatment (3.1 Mg CO₂-eq Mg^-1) was significantly higher than the inorganic fertilizer and FYM treatments (2. 0 to 2.4 Mg CO₂-eq Mg^-1). It can be concluded that to meet the challenges of global warming and food security, balanced fertilization and integrated nutrient management should be adopted for achieving sustainable intensification of maize-wheat cropping system.