Nitrous oxide emission in response to N application in irrigated sugarcane

ABSTRACT The objective of this study was to compare the emissions of nitrous oxide (N2O) resulting from the application of nitrogen (N) and potassium (K) doses in fertigated sugarcane, in comparison to emissions from conventional fertilizer application. The study was conducted in the experimental area of Embrapa Mid-North, Teresina, Piauí state, Brazil, from August 2014 to January 2015. The experimental design was in randomized blocks, analyzed in a (2 x 2) +1 factorial scheme, with four replicates. The treatments consisted of the combination of two doses of N and K2O (60-120 and 120-180 kg ha-1, respectively) and two methods of application (in soil and fertigation), and a control. The use of fertigation reduced the emissions of N2O in sugarcane compared with the crop under conventional fertilization. Increase in N dose from 60 to 120 kg ha-1 applied through fertigation did not affect N2O emissions, while 60 and 120 kg ha-1 applied in the soil led to 40.6 and 50.2% increases in N2O emissions, respectively. The application of 60 and 120 kg ha-1 of N in the soil led to higher N2O emission factor, being 1.39 and 2.08% higher than in the crop fertigated with 60 and 120 kg ha-1 of N, respectively.

Dung and farm dairy effluent affect urine patch nitrous oxide emissions from a pasture

Urine patches in grazed pastures have been identified as important sources of nitrous oxide (N2O) emissions. An increase in N2O emissions is possible where urine patches coincide with dung patches and farm dairy effluent (FDE) applications. The aim of the present study was to quantify the effects of dung additions and fresh FDE applications on N2O emissions from urine patches. A field experiment was conducted on a pasture site at the AgResearch’s Ruakura dairy farm in Hamilton, New Zealand. A closed soil chamber technique was used to measure the N2O emissions from a free-draining volcanic soil that received urine (492 kg N/ha, simulated urine patches), with or without dung (1146 kg N/ha) and fresh FDE (100 kg N/ha) and to compare these with controls receiving no urine. The addition of dung delayed the peak N2O fluxes from the urine patches by ~30 days. This could be due to temporary nitrogen (N) immobilisation during decomposition of carbon from the dung. However, over the whole measurement period (271 days), dung addition increased the N2O emission factor (EF, % of applied N emitted as N2O) for the urine from 1.02% to 2.09%. The application of fresh FDE increased the EF to 1.40%. The effluent- or dung-induced increases in N2O emissions from the urine patches were possibly caused both by the direct input of N from effluent or dung and through the indirect priming effect of addition of dung or effluent on the availability of N from urine patches for N2O production. We conclude that when EFs are used in calculations of N2O emissions from urine, consideration should be given to the likelihood of coincidence with dung or FDE applications.

Estimating a nitrous oxide emission factor for animal urine from some New Zealand pastoral soils

The Intergovernmental Panel on Climate Change methodology estimates that over 50% of total nitrous oxide (N2O) emissions in New Zealand derive from animal excreta-N deposited during grazing. The emission factor for excreta-N as used by this methodology has an important impact on New Zealand's total N2O inventory. The objectives of this study were to refine the N2O emission factor for urine by simultaneously measuring N2O emissions from 5 pastoral soils of different drainage class, in 3 different regions in New Zealand following a single application of urine; plus test various aspects of the soil cover method for determining emission factors. Cow urine and synthetic urine was applied to pastoral soils in autumn 2000 and N2O emissions were measured using closed flux chambers at regular intervals for 4–18 months following application. The N2O emission factors for cow urine estimated for the first 4 months after urine application varied greatly depending on rainfall and soil drainage class, and ranged from 0.3 to 2.5% of the urine-N applied, suggesting that adopting a single emission factor for New Zealand may be inappropriate. The largest emission factor was found in a poorly drained soil, and the lowest emission factor was found in a well-drained stony soil. Ongoing measurements on one of the soils resulted in an increase in emission factors as the N2O emissions had not reached background levels 4 months after urine application. To characterise urine-induced N2O emissions, we recommend measurements continue until N2O emissions from urine-amended soil return to background levels. Furthermore, we recommend using real animal urine rather than synthetic urine in studies when determining the N2O emission factor for urine.