Coby J. Hoogendoorn

Nitrogen concentration in the urine of cattle, sheep and deer grazing a common ryegrass/cocksfoot/white clover pasture

Abstract Total nitrogen (N) concentration in the urine of 12- to 18-month old female sheep, cattle and deer grazing a common pasture was measured in the morning, noon and evening for three consecutive days on two separate occasions in spring, and on a single occasion sampling in autumn. Mean (and range) of urine N concentrations for single urinations were 7.9 (1.4–17.8), 4.4 (0.9–13.2) and 4.1 (0.5–16.6) g N kg−1 fresh urine for sheep, cattle and deer, respectively. Wide ranges in urine N concentration were found within days, between days and between animals within the same species. Differences in urine N concentration between the three different species in any one measurement occasion were significant but inconsistent between measurement occasions. The results presented in this study may have implications for the development of process-based models capable of accounting for the spatially heterogeneous return of excretal N in grazed systems.

The effect of increasing rates of nitrogen fertiliser and a nitrification inhibitor on nitrous oxide emissions from urine patches on sheep grazed hill country pasture

Urine deposited by grazing animals represents the largest source of N2O emissions in New Zealand. Sheep-grazed hill pastures are an important component of New Zealand pastoral land, but information on N2O emissions from these areas is limited. The purpose of this study was to investigate the effect of increasing rates of fertiliser nitrogen and of a nitrification inhibitor on N2O emissions from urine patches. The study was carried out in grazed paddock-scale trials at the Ballantrae and Invermay Research Stations, New Zealand. The fertiliser N treatments were 0, 100, 300 and 750 (500 for Invermay) kg N/ha.year. Nitrous oxide measurements were conducted in the spring of 2005 and 2006, following applications of synthetic sheep urine with or without dicyandiamide (DCD) in these four N treatments. In both years and at both sites, N2O emissions increased with N fertiliser application rate in both urine and non-urine affected areas. The addition of DCD to the synthetic urine reduced N2O emissions from the urine affected areas during the measurement period by 60–80% at Ballantrae and by 40% at Invermay. The N2O emission factors for the artificial sheep urine (expressed as N2O-N lost as % of N applied) ranged from 0.01 to 1.06%, with the higher values generally found in the high N fertiliser treatments. The N2O emission factors were generally less than or similar to those from sheep urine applied to flat land pasture.

Nitrogen leaching from sheep-, cattle- and deer-grazed pastures in the Lake Taupo catchment in New Zealand

A replicated grazing study measuring nitrogen (N) leaching from cattle-, sheep- and deer-grazed pastures was conducted to investigate the impact of different animal species on N leaching in the Lake Taupo catchment in New Zealand. Leaching losses of nitrate N from intensively grazed pastures on a highly porous pumice soil in the catchment averaged 37, 26 and 25 kg N/ha.year for cattle-, sheep- and deer-grazed areas, respectively, over the 3-year study and were not significantly different (P > 0.05). Leaching losses of ammonium N were much lower (3 kg N/ha.year for all three species of grazer; P > 0.05). Amounts of dissolved organic N leached were significantly higher than that of mineral N (nitrate N + ammonium N), and over the 3-year study averaged 44, 43 and 39 kg N/ha.year for cattle-, sheep- and deer-grazed areas, respectively (P > 0.05). On a stock unit equivalence basis (1 stock unit is equivalent to 550 kg DM consumed/year), cattle-grazed areas leached significantly more mineral N than sheep- or deer-grazed areas (5.5, 2.9 and 3.4 g mineral N leached/24 h grazing by 1 stock unit, for cattle, sheep and deer, respectively) (P < 0.001). Likewise, based on the amount of N apparently consumed (estimated by difference in mass of herbage N pre- and post-grazing), cattle-grazed pastures leached more mineral N than sheep- or deer-grazed pastures (123, 75 and 75 g mineral N/kg N apparently consumed for cattle, sheep and deer, respectively) (P < 0.01). This study gives valuable information on mineral N leaching in a high-rainfall environment on this free-draining pumice soil, and provides new data to assist in developing strategies to mitigate mineral N leaching losses from grazed pastures using different animal species.

Nitrous oxide emission factors for urine and dung from sheep fed either fresh forage rape ( Brassica napus L.) or fresh perennial ryegrass ( Lolium perenne L.)

In New Zealand, agriculture is predominantly based on pastoral grazing systems and animal excreta deposited on soil during grazing have been identified as a major source of nitrous oxide (N2O) emissions. Forage brassicas (Brassica spp.) have been increasingly used to improve lamb performance. Compared with conventional forage perennial ryegrass (Lolium perenne L.), a common forage in New Zealand, forage brassicas have faster growth rates, higher dry matter production and higher nutritive value. The aim of this study was to determine the partitioning of dietary nitrogen (N) between urine and dung in the excreta from sheep fed forage brassica rape (B. napus subsp. oleifera L.) or ryegrass, and then to measure N2O emissions when the excreta from the two different feed sources were applied to a pasture soil. A sheep metabolism study was conducted to determine urine and dung-N outputs from sheep fed forage rape or ryegrass, and N partitioning between urine and dung. Urine and dung were collected and then used in a field plot experiment for measuring N2O emissions. The experimental site contained a perennial ryegrass/white clover pasture on a poorly drained silt-loam soil. The treatments included urine from sheep fed forage rape or ryegrass, dung from sheep fed forage rape or ryegrass, and a control without dung or urine applied. N2O emission measurements were carried out using a static chamber technique. For each excreta type, the total N2O emissions and emission factor (EF3; N2O-N emitted during the 3- or 8-month measurement period as a per cent of animal urine or dung-N applied, respectively) were calculated. Our results indicate that, in terms of per unit of N intake, a similar amount of N was excreted in urine from sheep fed either forage rape or ryegrass, but less dung N was excreted from sheep fed forage rape than ryegrass. The EF3 for urine from sheep fed forage rape was lower compared with urine from sheep fed ryegrass. This may have been because of plant secondary metabolites, such as glucosinolates in forage rape and their degradation products, are transferred to urine and affect soil N transformation processes. However, the difference in the EF3 for dung from sheep fed ryegrass and forage rape was not significant.

Short-term measurement of N2O emissions from sheep-grazed pasture receiving increasing rates of fertiliser nitrogen in Otago, New Zealand

The purpose of this short-term study was to investigate the effect of increasing fertiliser nitrogen (N) application rates on nitrous oxide (N2O) emissions over the late winter/early spring period from sheep-grazed pasture in Otago rolling hill country. We measured N2O gas emissions from plots on a mottled Fragic Pallic hill soil receiving 0, 100 and 500 kg N/ha.year for 2 years. Plots were sampled weekly for 10 weeks over the 2006 winter/spring period using a static chamber method. Increased N fertiliser rate and the attendant increase in stocking rate significantly increased total N2O emissions (P < 0.05). Total N2O emissions for the measurement period were estimated to be 0.08, 0.13 and 1.36 kg N2O-N/ha (s.e.m, 0.1, 0.18 and 0.45) for the 0, 100 and 500 N treatments, respectively. Our results suggest that high application rates of fertiliser N (i.e. 500 kg N/ha.year) and attendant increased stocking rates may significantly increase emissions of N2O even in dry winter/spring conditions in Otago rolling hill country. These results will assist in the development of best management guidelines for reducing N2O emissions from fertiliser N in hill country.

Simple models of carbon and nitrogen cycling in New Zealand hill country pastures: exploring impacts of intensification on soil C and N pools

Concerns about climate change and water quality make it necessary to have a better understanding of the cycling of carbon (C) and nitrogen (N) within landscapes. In New Zealand, pastoral farming on hill country is a major land use, and there is little information available at a landscape level on the cycling of C and N within these systems, particularly the impacts of land use intensification. Published information on the individual components of C and N cycles in hill country pastoral systems was used to construct simple C and N models for two notional hill country paddocks with contrasting amounts of annual net herbage accumulation (NHA). These simple models of C and N cycling were used to explore the potential impacts of intensification on soil C and N pools. The C and N models constructed illustrate that both the C and N cycles in hill country pastoral farming are characterised by large fluxes in and out of the system and relatively small annual accumulations or depletions of their respective soil pools. The mechanisms by which these inward and outward fluxes are generated differ greatly between C and N. Most of the C cycling through the soil/plant/animal system in a year is sourced from the atmosphere through photosynthesis in that same year and the annual quantity of C ingested by grazing animals is only approximately 25% of that fixed annually. In contrast, the annual quantity of N ingested by grazing animals is 300–400% of that added to the system annually by fixation, and most of this ingested N (>80%) is returned to the soil in animal excreta. This contrasts with <25% of ingested C returned in animal excreta. Grazing animals, with their propensity to exhibit camping behaviour, are therefore much more influential in the spatial redistribution of N than C in hill country pastures. The simple C and N models presented in this paper indicate that while land use intensification results in increased inputs of both C and N to the soil, intensification is also likely to result in increased losses of C and N from the soil pool. Which of these processes dominates in a given situation determines whether intensification will result in an increase or decrease of soil C and N. Based on a simple C model, we postulate that if intensification increases NHA by one unit there is likely to be an increase in soil C unless at the same time increased grazing pressure results in at least a three-unit increase in dry matter eaten/harvested.

Nitrogen fertiliser application rates and nitrogen leaching in intensively managed sheep grazed hill country pastures in New Zealand

ABSTRACT Effects of rates of nitrogen (N) fertiliser application on mineral N leaching from grazed New Zealand hill country were investigated. Paddocks of 12–25° slope received annual N inputs of 0, 100, 200, 300, 400, 500 or 750 kg N ha−1 and were rotationally grazed by non-lactating ewes, stocking rate being increased to utilise extra pasture production generated from N application. Mineral N leaching was measured using in situ minilysimeters (150 mm diameter and 300 mm depth) with leachate collected at monthly intervals or after each accumulation of 100 mm rain. Average annual net herbage accumulation ranged from 11 to 16 t dry matter ha−1 for the N treatments. Total mineral N leaching increased linearly with fertiliser N application rate. Potential increases in N leaching for commonly used fertiliser N regimes were estimated to be 11% (for 20 kg N ha−1) to 29% (for 50 kg N ha−1 application rate).