Nitrogen supply and rainfall affect ammonia emissions from dairy cattle excreta and urea applied on warm‐climate pastures

Abstract

Cattle excreta and nitrogen (N) fertilizer deposited on tropical grasslands are important sources of ammonia (NH 3) emission. We conducted three field trials (wet, intermediate, and dry conditions) to quantify NH 3 emissions from urea fertilizer and simulated excretions of heifer urine and dung on warm-climate grasslands in Brazil. Heifer excreta were derived from pastures of palisadegrass [Urochloa brizantha (Hochst. ex A. Rich.) R. D. Webster 'Marandu'] under three forms of N supply (without or with N fertilization [0 or 150 kg N ha −1 yr −1 ] or mixed with forage peanut [Arachis pintoi 'Amarillo']). Cumulative NH 3-N emissions across rainfall conditions were 7.6-16.6% (mean, 11.7%) for urine, 1.4-2.9% (mean, 2.0%) for dung, and 11.2-20.5% (mean, 14.8%) for urea. Ammonia loss from urine was significantly greater than from dung under all rainfall conditions. Emission from urine and dung differed from those when urea was applied on palisadegrass. There were greater NH 3 emissions from urine in the wetter times of the year. Heifer excreta from N-fertilized pasture had greater NH 3 emission than excreta from the grass-legume mixture and unfertilized palisadegrass. Urea applied on palisadegrass presented greater NH 3 emissions in wet rainfall conditions compared with dry conditions but did not differ from intermediate conditions. Our study showed that N-fertilized systems increase N losses as NH 3 emission from excreta, and emissions from urea fertilizer must be included in this system. Heifer excreta and urea fertilizer deposited on warm-climate grasslands increased the NH 3 emissions mainly under wet conditions.

Ammonia Volatilization, Forage Accumulation, and Nutritive Value of Marandu Palisade Grass Pastures in Different N Sources and Doses

“…According to Vlek and Stumpe [29], NH 3 loss was a first order reaction, which was directly related to N concentration in the soil solution. This reaction also explains the lower losses by volatilization observed in experiment 2, because the amount of NH 4 + in the soil available for hydrolysis was less when the fertilization was done [11].…”

“…After the application of fertilizers in 21 days, evaluations of N losses by volatilization of NH 3 were carried out on the samples 1, 3, 5, 9, 14, and 21 days after application (DAA) of treatment, with the plots that did not receive fertilization as reference. Volatilized N quantification was performed according to the methodology described by Araújo et al [23] and Longhini et al [11]. NH 3 was captured by a semi-open chamber that consists of a transparent polyethylene terephthalate bottle (PET, soda bottle 2 L) with no bottom.…”

“…In experiment 1 and first fertilization in experiment 2, there was no occurrence of rain on the day of fertilization, which occasionally led to a peak volatilization on the 4th DAA, one day after the first rainfall, which were 4.7 and 7 mm respectively (Figure 2a,b). This was because under dry soil conditions, volatilization increases when a small amount of water of around 3 mm, was added to the soil [11,36]. According to Kissel et al [37], low rainfall may stimulate urea volatilization, because it was not sufficient to incorporate the fertilizer.…”

“…Nitrogen fertilization is known to increase forage dry matter yield and nutritional value, improving the chemical composition of the plant by increasing the crude protein content and decreasing the neutral detergent fiber (NDF) content [6][7][8]. However, NH 3 losses after fertilization decreasing N use efficiency in plants present a threat to the environment; it can acidify the soil from ammonia oxidation [9][10][11]. In addition, NH 3 acts as a secondary source of N 2 O, an important greenhouse gas [12][13][14].…”

“…The use of NH 3 EF from other countries, mainly in temperate climates, leads to uncertainties in Brazilian national inventories, requiring more studies to develop countryspecific EF [2,11,17]. Furthermore, the potential for NH 3 losses from different nitrogen fertilizers in tropical pastures has not yet been clearly determined.…”