Info

A. Direct soil emissions

Synthetic fertilizer use 0.00281

Animal waste 0.000143

Biological N2 fixation 0.008201

Crop residue 0.03509

Cultivated histosols 0.000259

Sub-Total 0.031

B. Animal production

Animal waste management systems 0.0000027

C. Indirect emissions

Atmospheric deposition 0.00028

Nitrogen leaching and run off 0.00133

Human sewage -

Sub-Total 0.0016

Total emissions 0.048

for indirect emissions) and external review of all parameters, emission factors and methodologies by specialists.

Indeed, IPCC method has been used to prepare regional estimates on N2O emission. Yang et al. (2003) have estimated N2O emissions from rice fields and uplands in Taiwan during 1990-2000. Few estimates have been done for Indian agriculture as well. Using FAO database and IPCC 1996 guidelines, Krishna Prasad et al. (2003) have estimated N2O emissions from Indian agriculture during 19612000 (Table 8.2). According to another estimate, N2O emission from Indian agriculture, for the base year 1994-1995 was calculated to be 0.08 Tg (39TgCO2 equivalent) (Bhatia et al. 2004). Several other regional estimates for N2O emissions from agriculture or particular crops calculated by IPCC methodology are now available (Sokona 1995; Van Moortel et al. 2000; Boeckx et al. 2001; Li et al. 2001). Comparison of IPCC methodology derived N2O emissions with other UK-derived inventories suggested that the IPCC methodology had overestimated N2O emissions (Brown et al. 2001).

8.4 Contribution of Agriculture to Atmospheric N2O Loading

Nitrous oxide budget is generally estimated by using available data on N inputs, area under cultivation and N2O emission factors for various agricultural activities in varied cropping systems under different soil and climate. Initially, several researchers have estimated fertilizer derived annual N2O emissions by using annual fertilizer consumption viz. 6-20TgN2O-Nyr-1 (Hahn and Junge 1977); 0.5 (0.2— 2.1) Tgyr-1 (Eichner 1990); 0.6-2.3 Tgyr-1 (Bolle et al. 1986); 0.2-0.6 Tgyr-1 (McElroy and Woofsy 1985) etc. A continent-wise break up of direct and indirect emissions of N2O from agricultural fields is also available (IPCC 1996b) (Table 8.3). Various other estimates differ widely on the percentage contribution of agriculture in anthropogenic N2O emissions viz. 96% (Duxbury et al. 1993); 81% (Iserman 1994); 76% (Cole et al. 1996) and 65% (Mosier et al. 1998a). It was once suggested that

Table 8.3 Estimates of direct and indirect emissions of N2O from applications of fertilizer N (synthetic or animal waste) to agricultural soils and from soils growing N-fixing crops (Mt N2O-Nyr'1) (IPCC 1996b)_

Region

Estimated N2O from Mineral N Animal waste

N-fixation

Total

Range

Africa

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