Nitrous oxide emission and mitigation from maize-wheat rotation in the upper Indo-Gangetic Plains

Due to its lower water requirement, methane emission and soil degradation, a maize-wheat rotation (MWR) may be a more attractive alternative to rice-wheat rotation (RWR), in the upper Indo-Gangetic plains (IGP) of India. However, N2O emission from MWR needs to be quantified to propose management practices for N2O mitigation. A field experiment was conducted at the Indian Council of Agricultural Research-Indian Agricultural Research Institute (ICAR-IARI), New Delhi, to assess the impacts of various N sources on N2O emission and its mitigation from the MWR. Six treatments -N0 (control), urea, urea + farmyard manure (FYM), FYM, urea + nitrification inhibitor (NI) and neem oil coated urea (NOCU) were investigated during 2012-2014. Results show ranges of N2O-N emissions from MWR of 0.59-0.69, 1.82-1.86, 1.81-1.85, 1.71-1.77, 1.38-1.52, 1.57-1.61 during 2012-2013, and of 0.62-0.68, 1.86-1.90, 1.78-1.84, 1.72-1.76, 1.40-1.46, 1.52-1.60 during 2013-2014, for N0, urea, urea + FYM, FYM, urea + NI and NOCU treatments, respectively. The 2-year pooled N2O-N emission of MWR decreased by 23% in urea + NI and by 16% in NOCU with higher grain yield as compared to conventional urea application. Application of FYM with urea and FYM alone also reduced N2O-N emission; however, the grain yields of these treatments were decreased. Thus, the study suggests that the application of NOCU and NI with urea can mitigate N2O-N emissions from the maize and wheat crops. Hence, the use of NOCU and application of NI with urea could be a better option to mitigate N2O-N emissions from MWR of the upper IGP of India.