Data for: Nitrous oxide emissions from groundnut and millets farms in semi-arid peninsular India

Nitrous oxide (N2O) emissions response curves for crops grown outside
temperate regions have been rare and have thus far arrived at conflicting
conclusions. Most studies reporting N2O emissions from tropical cropping
systems have examined only one or two nitrogen fertilizer application
rate(s) which precludes the possibility of discovering nonlinear changes
in emission factors (EF, % of added N converted to N2O-N) with increasing
fertilizer-N rates. To examine the relationship between N rates and N2O
fluxes in a tropical region, we compared farming practices with three or
four N rates for their yield-scaled impacts from three crops in peninsular
India. We measured N2O fluxes during nine seasons between 2012 and 2015,
with N application rates ranging between 0 and 70, 0 and 90, and 0 and 480
kg-N ha-1 for foxtail-millet (Setaria italica L., locally called korra),
groundnut (Arachis hypogaea L., also called peanut) and finger-millet
(Eleusine coracana L., locally called ragi), respectively. In two cases,
the highest N application rate greatly exceeded crop-N needs. Potential
climate smart farming agricultural practices (with low/optimized N rates)
led to a 50-150% reduction in N2O emissions intensity (per unit yield)
along with a reduction of 0.2-0.75 tCO2e ha-1 season­­-1 as compared to
high N conventional applications. We found a non-linear increase in N2O
flux in response to increasing applied N for both N-fixing and non
N-fixing crops and the extent of super-linearity for non N-fixing crops
was much higher than what has been reported earlier. If a linear fit is
imposed on our datasets, the emission factors (EFs) for finger-millet and
groundnut were ~3.5% and ~1.8%, respectively. Our data shows that for
low-N tropical cropping systems, even when they have low soil carbon
content, increase in N use to levels just above crop needs to enhance
productivity might lead to relatively small increase in N2O emissions as
compared to the impact of equivalent changes in fertilizer-N use in
systems fertilized far beyond crop N needs.