Componente 3: Ejecución y fortalecimiento de las capacidades provinciales El componente incluye las actividades de coordinación de la ejecución, con enfoque en la

When calculating N2O emission we consider only 50 % of the N in applied manure and other organic fertilizers

Summary

 The contribution of manure to N2O emissions is minor in most parts of the world; exceptions are parts of EU and US.

 Manure use tends to be concentrated around livestock farms.

 Not all the nitrogen applied in manure is available for crops: we only consider the available fraction in calculating N2O emissions. Although the rest of the nitrogen also generates N2O, it does not contribute to crop growth; therefore we attribute those emissions to manure production in the livestock sector.

 An average of about 42% of manure-N is available in the first year of application, but crops inherit N also from previous manure applications: the total available nitrogen from manure is at least 50% of the applied manure-N on average.

 The assumption of 50% N availability is also consistent with data on manured area and the fraction of N for crops coming from manure.

Details

Our data on synthetic nitrogen applied to crops are not based on recommendations, but on actual sales data. Therefore emissions from manure-nitrogen are additional; they do not substitute those from synthetic nitrogen.

In most of the world, the contribution of manure to the total nitrogen supply of crops is very limited: it becomes important only in areas with large indoor production of livestock, such as some parts of EU and US. Very few countries provide estimates of manure-N per crop; these estimates have large statistical error, and, perhaps because of this, there seems no consistent pattern of which crops get the highest proportion of their N requirements from manure. Nevertheless, it is clear that crops which need little nitrogen, such as soybeans, get less manure than high-intensity crops like maize. Therefore, in allocating total national manure application to different crops and grassland, we preferred to assume that nitrogen from manure is proportional to synthetic nitrogen use per crop, rather than the alternative assumption that manure is distributed uniformly on all cropland.

Statistics are available for total manure-nitrogen application per country. We derived this data in the Edgar Database; it only counts the manure that is applied by farmers to fields (thus excluding manure deposited directly during grazing), and it also takes into account loss of nitrogen during storage.

Fraction of manure-nitrogen attributed to crops

A partnership led by AEA Technologies made a report for DG-ENV,‘Study on variation of manure N efficiency throughout Europe’ (AEA, 2011).

In particular it shows a table (table 16, repeated as table 3 in the summary) which shows different Member States’ estimates of the fraction of N in different types of fertilizer that is released in the year it is applied. We calculated an average value of 42%, weighted by the application (in terms of N) of each type of manure in each EU country; data we derived from EUROSTAT.

However, crops also receive nitrogen from manure that was applied in previous years, and this should be taken into account (AEA, 2011), because it also contributes to the total nitrogen supply and reduces the average requirement for synthetic nitrogen. AEA

depending principally on the rainfall, temperature and nature of the manure. The report concludes “Most authors reported only small percentages of N availability for successive years most of them being c. 2-3% of extra N available per year reaching average values from 60 to 80% for the total N recovery in a 6 to10 year period.”

This would indicate the correct fraction of manure-N to consider in cultivation emissions is 60-80%. But this may be slightly exaggerated, because most of the authors they review also reported higher-than-average N availabilities in the first year. However, it is reasonable to conclude that the % N released in subsequent years is at least (2% for 6 years = 12%). Adding this to the average release of 42% of the nitrogen in the first year indicates a total N release from manure of at least 54%. We take the round figure of 50% because the Member States’ estimates of % nitrogen availability in the AEA report are almost all rounded to the nearest multiple of 10%.

Therefore, in using the GNOC tool to calculate the average contribution of N from manure to the N2O emissions from crops, we consider half the N content of the manure. In the GNOC methodology this approximately halves the contribution of manure to N2O emissions in cultivation.

In processing GNOC data, we need to make an additional assumption about how the manure is distributed to different crops, for all countries. The only international data on N applications we have per-crop per-country is for synthetic N, so we need to find a relation between manure application and synthetic nitrogen application.

For a given country, we assume that the ratio of (manure N)/(synthetic N) is the same for all crops. This assumption gives estimates of manure use per crop which are closer to those reported in national surveys than our previous assumption that assumed the same kg manure per hectare for all crops in a region. (This assumption was adopted in JEC- WTWv4 and the draft input data for update of RED annex V, presented to stakeholders in April 2013: however we realized that it systematically over-estimated manure on low- intensity crops). Nevertheless USDA, 2009, as well as European manure use surveys, (DEFRA, 2016 and AGRESTE, 2014), show variations in the fraction of manure used for different crops, which vary by country and which we cannot fully capture with a general rule that can be applied to all countries.

Our data on synthetic nitrogen use is ultimately derived from sales data, so it is independent of the amount of manure used on a crop. That means assuming a higher fraction of N from manure for a crop would not decrease the amount of synthetic fertilizer in the calculations.

3.9 Correction of IPCC method for estimating N2O emissions