Evaluation and prediction of nitrogen use efficiency and outputs in faeces and urine in beef cattle

Beef cattle production is valuable to food security, contributing meat of high nutritional value. However, beef cattle are rather inefficient in utilising dietary nitrogen (N), thus excreting substantial amounts of N in their urine and faeces and imposing an environmental burden. The aim of this study was to evaluate the main dietary factors affecting N use efficiency (NUE) in beef cattle and develop prediction models for N excretion in manure, faeces and urine. This knowledge is essential for the development and evaluation of cost-effective N mitigation strategies. A database of 289 treatment means was constructed from 69 published studies and 1194 animals. Data included diet contents of N, dry matter (DM), organic matter (OM), neutral-detergent fibre (NDF), acid-detergent fibre (ADF), ether extract, starch, ash, gross energy (GE), metabolisable energy (ME), and outputs of N in manure, in urine or in faeces. Regression equations to predict N outputs in manure (MNO), urine (UNO) and faeces (FNO), as well as various NUE indicators, were developed using residual maximum likelihood analysis. Evaluation of new and existing models was performed using the mean prediction error (MPE) to describe prediction accuracy. Manure, urine and faeces N outputs were predicted with improved accuracy (MPE from 0.557 to 0.162; from 0.764 to 0.208; and from 0.458 to 0.177, respectively) when DM or OM digestibilities, and/or diet contents of N, NDF, ADF, Starch, OM, GE, ME, and/or forage proportion in the diet were added as predictors in different equations already containing either DM intake, N intake or body weight as primary predictor. New and existing models displayed an under-prediction of N outputs at the highest range of actual N outputs (when MNO > 207 g/d, UNO > 109 g/d). However, some of the new equations had improved overall accuracy (best MPE for MNO, UNO and FNO being 0.162, 0.208 and 0.177, respectively) and, when DM digestibility, and contents of N, NDF, Starch and ME were added as predictors in different equations, the extent of this under-prediction was also reduced (occurring when MNO > 208 g/d, UNO > 132 g/d). The regression models for NUE, demonstrated that diets which are more digestible and contain less N and fibre and more ME, may reduce N excretions, but mitigation strategies will also need to account for the potential effect on animal productivity and health

Testing the use of static chamber boxes to monitor greenhouse gas emissions from wood chip storage heaps

This study explores the use of static chamber boxes to detect whether there are fugitive emissions of greenhouse gases (GHGs) from a willow chip storage heap. The results from the boxes were compared with those from 3-m stainless steel probes inserted into the core of the heap horizontally and vertically at intervals. The results from probes showed that there were increases of carbon dioxide (CO2) concentrations in the heap over the first 10 days after heap establishment, which were correlated with a temperature rise to 60 °C. As the CO2 declined, there was a small peak in methane (CH4) concentration in probes orientated vertically in the heap. Static chambers positioned at the apex of the heap detected some CO2 fluxes as seen in the probes; however, the quantities were small and random in nature. A small (maximum 5 ppm) flux in CH4 occurred at the same time as the probe concentrations peaked. Overall, the static chamber method was not effective in monitoring fluxes from the heap as there was evidence that gases could enter and leave around the edges of the chambers during the course of the experiment. In general, the use of standard (25 cm high) static chambers for monitoring fluxes from wood chip heaps is not recommended

Analysis of uncertainties in the estimates of nitrous oxide and methane emissions in the UK’s greenhouse gas inventory for agriculture

The UK’s greenhouse gas inventory for agriculture uses a model based on the IPCC Tier 1 and Tier 2 26 methods to estimate the emissions of methane and nitrous oxide from agriculture. The inventory 27 calculations are disaggregated at country level (England, Wales, Scotland and Northern Ireland). 28 Before now, no detailed assessment of the uncertainties in the estimates of emissions had been 29 done. We used Monte Carlo simulation to do such an analysis. We collated information on the 30 uncertainties of each of the model inputs. The uncertainties propagate through the model and result 31 in uncertainties in the estimated emissions. Using a sensitivity analysis, we found that in England and 32 Scotland the uncertainty in the emission factor for emissions from N inputs (EF1) affected 33 uncertainty the most, but that in Wales and Northern Ireland, the emission factor for N leaching and 34 runoff (EF5) had greater influence. We showed that if the uncertainty in any one of these emission 35 factors is reduced by 50%, the uncertainty in emissions of nitrous oxide reduces by 10%. The 36 uncertainty in the estimate for the emissions of methane emission factors for enteric fermentation 37 in cows and sheep most affected the uncertainty in methane emissions. When inventories are 38 disaggregated (as that for the UK is) correlation between separate instances of each emission factor 39 will affect the uncertainty in emissions. As more countries move towards inventory models with 40 disaggregation, it is important that the IPCC give firm guidance on this topic

Greenhouse gas and ammonia emissions from slurry storage: impacts of temperature and potential mitigation through covering (pig slurry) or acidification (cattle slurry)

Storage of livestock slurries is a significant source of methane (CH4) and ammonia (NH3) emissions to the atmosphere, for which accurate quantification and potential mitigation methods are required. Methane and NH3 emissions were measured from pilot-scale cattle slurry (CS) and pig slurry (PS) stores under cool, temperate, and warm conditions (approximately 8, 11, and 17°C, respectively) and including two potential mitigation practices: (i) a clay granule floating cover (PS) and (ii) slurry acidification (CS). Cumulative emissions of both gases were influenced by mean temperature over the storage period. Methane emissions from the control treatments over the 2-mo storage periods for the cool, temperate, and warm periods were 0.3, 0.1, and 34.3 g CH4 kg−1 slurry volatile solids for CS and 4.4, 20.1, and 27.7 g CH4 kg−1 slurry volatile solids for PS. Respective NH3 emissions for each period were 4, 7, and 12% of initial slurry N content for CS and 12, 18, and 28% of initial slurry N content for PS. Covering PS with clay granules reduced NH3 emissions by 77% across the three storage periods but had no impact on CH4 emissions. Acidification of CS reduced CH4 and NH3 emissions by 61 and 75%, respectively, across the three storage periods. Nitrous oxide emissions were also monitored but were insignificant. The development of approaches that take into account the influence of storage timing (temperature) and duration on emission estimates for national emission inventory purposes is recommended

Advanced Processing of Food Waste Based Digestate for Mitigating Nitrogen Losses in a Winter Wheat Crop

The anaerobic digestion of food waste converts waste products into ‘green’ energy. Additionally, the secondary product from this process is a nutrient-rich digestate, which could provide a viable alternative to synthetically-produced fertilisers. However, like fertilisers, digestate applied to agricultural land can be susceptible to both ammonia (NH3) and nitrous oxide (N2O) losses, having negative environmental impacts, and reducing the amount of N available for crop uptake. Our main aim was to assess potential methods for mitigating N losses from digestate applied to a winter wheat crop and subsequent impact on yield. Plot trials were conducted at two UK sites, England (North Wyke-NW) and Wales (Henfaes-HF), to assess NH3 and N2O losses, yield and N offtake following a single band-spread digestate application. Treatments examined were digestate (D), acidified-digestate (AD), digestate with the nitrification inhibitor DMPP (D+NI), AD with DMPP (AD+NI), and a zero-N control (C). Determination of N losses was conducted using wind tunnels for NH3, and static manual and automatic chambers for N2O. The N offtake in both grain and straw was also measured. Ammonium nitrate (NH4NO3) fertiliser N response plots (from 75 to 300 kg N ha−1) were included to compare yields with the organic N source. Cumulative NH3-N losses were 27.6 % from D and D+NI plots and 1.5 % for AD and AD+NI of the total N applied, a significant reduction of 95 % with acidification. Cumulative N2O losses varied between 0.13 and 0.35 % of the total N applied and were reduced by 50 % with the use of DMPP. Grain yields for the digestate treatments were 7.52 – 9.21 and 7.23 – 9.23 t DM ha−1 at HF and NW, respectively. Yields were greater from the plots receiving acidified‐digestate relative to the non-acidified treatments but the differences were not significant. The yields (as a function of the N applied with each treatment) obtained for the digestate treatments ranged between 84.2 % (D+NI) and 103.6 % (D) of the yields produced by the same N rate from an inorganic source at HF. Advanced processing of digestate reduced N losses providing an environmentally sound option for N-management

Editorial: RAMIRAN 2017: Sustainable Utilisation of Manures and Residue Resources in Agriculture

peer-reviewedThe recycling of organic residues deriving from on-farm (e.g., livestock manure) or off-farm (e.g., sewage sludge, industrial by-products) is a central part of the circular economy toward developing more sustainable food production systems (e.g., EC, 2014). However, the safe, effective, and efficient use of organic “waste” streams as resources for nutrient provision and soil improvement in agricultural systems require several challenges to be addressed, summarized by Bernal (2017) as (i) to improve nutrient availability and soil cycling; (ii) to develop technologies for nutrient re-use; (iii) to reduce contaminants and improve food safety; (iv) to mitigate environmental emissions; and (v) to enhance soil health and function. Addressing these challenges needs multidisciplinary research within a whole systems context

Effects of urease and nitrification inhibitors on soil N, nitrifier abundance and activity in a sandy loam soil

Inhibitors of urease and ammonia monooxygenase can limit the rate of conversion of urea to ammonia and ammonia to nitrate, respectively, potentially improving N fertilizer use efficiency and reducing gaseous losses. Winter wheat grown on a sandy soil in the UK was treated with urea fertilizer with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), the nitrification inhibitor dicyandiamide (DCD) or a combination of both. The effects on soil microbial community diversity, the abundance of genes involved in nitrification and crop yields and net N recovery were compared. The only significant effect on N-cycle genes was a transient reduction in bacterial ammonia monooxygenase abundance following DCD application. However, overall crop yields and net N recovery were significantly lower in the urea treatments compared with an equivalent application of ammonium nitrate fertilizer, and significantly less for urea with DCD than the other urea treatments