Nitrous oxide emissions and dynamics of soil nitrogen under ¹⁵N‐labeled cow urine and dung patches on a sandy grassland soil

Abstract

Grazing animals highly influence the nutrient cycle by a direct return of 80% of the consumed N in form of dung and urine. In the autumn‐winter period, N uptake by the sward is low and rates of seepage water in sandy soils are high, hence high mineral‐N contents in soil and in seepage water as well as large losses of N2O are expected after cattle grazing in autumn. The objective of this study was the quanitfication of N loss deriving from urine and dung leaching and by N2O emission. Therefore the deposition of urine and dung patches was simulated in maximum rates excreted by cows by application of 15N‐labeled cow urine and dung (equivalent to 1030 kg N ha–1 and 1052 kg N ha–1, respectively) on a sandy pasture soil in N Germany. Leachate was collected in weekly intervals from free‐draining lysimeters, and 15N‐NO$ _3^- $, 15N‐NH$ _4^+ $, and 15N‐DON (dissolved organic N) were monitored over 171 d. Furthermore, the 15N‐N2O emission rates and the dynamics of inorganic 15N in the upper soil layer were monitored in a field trial, adjacent to the lysimeters. After 10 d following the urine application, the urea was completely hydrolyzed, shown by a 100% recovery of urine‐N in the soil NH$ _4^+ $. The following decrease of 15N‐NH$ _4^+ $ in the soil was higher than the increase of 15N‐NO$ _3^- $, and some N loss was explained by leaching. Amounts of 51% and 2.5% of the applied 15N were found in leachate as inorganic N, 2.4% and 0.7% as DON derived from urine and dung, respectively. Release of N2O from urine and dung patches applied to the pasture was low, with losses of 0.05% and 0.33% of the applied 15N, respectively. Overall loss of dung‐derived N was very low, but as the bulk dung N remained in the soil, N loss after mineralization of the dung needs to be investigated.

Isotopic composition of soil, vegetation or cattle hair no suitable indicator of nitrogen balances in permanent pasture

“…The overall values calculated are in line with literature values on N inputs with excreta (e.g. Virkajärvi et al 2010;Wachendorf et al 2008). The balances for areas Table 2 Nitrogen soil surface balances for the whole plot (plot balance) or for areas affected by dung (dung pats), urine (urine patches), grazing without N input through the animals (grazed areas) or the total area not affected by dung pats (urine ?…”

“…This might have been related to small overall N losses and small differences between N balances. Although N losses per dung and especially urine patch can be substantial (Wachendorf et al 2005(Wachendorf et al , 2008Yamulki et al 2000), losses integrated over the plot area would still be expected to be small as 92 to 97% of the plot areas had negative N balances (grazed areas, Table 2). Here, the N cycle would be relatively tight with active pools in soil and vegetation of similar sizes and a limited potential for fractionations (Robinson 2001).…”

Additive effects of dung amendment and plant species identity on soil processes and soil inorganic nitrogen in grass monocultures

“…During grazing, vegetation-fixed carbon (C) and herbage nitrogen (N) is removed from a large area of pasture and much of it (75-90 % ingested N) is returned as high-concentration, excretal patches (Afzal and Adams 1992). Growing evidence suggests that the excreta from large herbivores may promote field-scale N losses via leaching or gaseous N emissions (Yamulki et al 1998;Hutchings et al 2007;Wachendorf et al 2008). To date, however, mechanistic understanding of grassland responses to animal excreta is limited, and accurate accounting of urine and dung in models of grassland function remains a challenge (Hutchings et al 2007).…”

The interactive effects of various nitrogen fertiliser formulations applied to urine patches on nitrous oxide emissions in grassland

“…However, there were no significant differences between urine and urine + various of microbial activity by urine as well as the denitrification of indigenous soil N pool (Lambie et al, 2012). In fact, Wachendorf et al (2008) found that 75% of urine-induced N 2 O emission originated from the indigenous soil mineral N pool in a German soil. In the case of fertiliser treatments, there was a clear N 2 O peak observed only in the CAN treatment (Figure 2c).…”