Diet Effects on Dairy Manure Nitrogen Excretion and Cycling

The amount and forms of (nitrogen) N excreted by ruminant livestock and post excretion manure N cycling are highly influenced by what is fed. For example, the relative amount of urinary N, faecal endogenous N of microbial and gut origin, and faecal undigested feed N is affected by how much dietary fibre and secondary compounds (e.g., tannins, polyphneolics) are consumed. Each manure N component has a different propensity for loss; for example via ammonia (NH3) volatilisation (Misselbrook et al., 2004), leaching, and cycles differently in the soil-plant continuum (Powell, 2003). We evaluated dairy diet effects on amount and forms of manure N excreted and post excretion cycling of manure N from different diets after application to soil

Assessment of nitrogen uptake and biological nitrogen fixation responses of soybean to nitrogen fertiliser with SPACSYS

Chemical fertiliser nitrogen addition will inhibit biological nitrogen fixation (BNF) for soybean (Glycine max [L.] Merr) growth. The optimal balance of these two nitrogen input sources has been a key issue for sustainable development in Northeast China. We used the data collected from a four-year experiment with varied irrigation and fertiliser treatments from 2007 to 2010 to evaluate the SPACSYS model. The validated model was run to investigate the responses to different management practices in seed yield, BNF, nitrogen content in seed and soil nitrogen budgets. Scenario testing showed average yield increase of 2.4% - 5.2% with additional 50-100 kg N/ha application. Irrigation at the reproductive stage improved seed yield in drier years with an increase of 12-33% compared with the rain-fed treatment. BNF was suppressed by fertiliser nitrogen application and drought stress with a decrease of 6-33% and 8-34%, respectively. The average nitrogen budget without fertilization indicated a deficit of 39 kg N/ha. To attain higher seed yield, applying fertiliser at 25-30 and 15-20 kg N/ha before sowing is advised in drier and wetter years, respectively. To achieve a higher seed nitrogen content, an application rate of 55-60 and 45-50 kg N/ha is recommended for drier and wetter years, respectively

Projected climate effects on soil workability and trafficability determine the feasibility of converting permanent grassland to arable land

CONTEXT Adapting to changes in climate and in consumer demand for commodities will force us to diversify land uses from the current status. Livestock grazing systems are dominant agricultural practices in the western regions of the British Isles. It has been suggested that grasslands in the region could be converted to other land uses, e.g. growing of cereal crops. We hypothesized that soil workability and trafficability would be important factors determining the feasibility and environmental impact of such conversion. OBJECTIVE Objectives were 1) to investigate the impacts of weather conditions under the current (baseline) climate on agronomic management and crop yield of winter wheat using the SPACSYS model; and 2) to assess potential impacts of the land use conversion (grassland converted into arable land) on the environment under soil conditions representative of the region under baseline and future climatic conditions. METHODS Using simulation modelling we investigated the impacts of baseline and future climates under the Representative Concentration Pathways (RCP2.6, 4.5 and RCP8.5) on soil workability and trafficability at sowing and harvest respectively of winter wheat and its consequences for crop productivity and key indices of environmental sustainability for three major soil types of the region. RESULTS AND CONCLUSIONS Under baseline and future projections, the probability of successfully sowing winter wheat on these soils was between 38 and 76%. Simulations showed that grassland conversion to arable in the region would not be sustainable in terms of carbon sequestration with a decline in soil carbon stock of 165 – 280 kg C ha–1 yr–1 on average over the simulation period. Rates of decline were greater when soil workability was taken into consideration. Although CO2eq emissions from silage–based grassland soil were higher than those from the converted arable land, these were offset by the greater net productivity of grassland making it a larger net sink for carbon. When soil workability at sowing was considered, the NUEcrop (crop N content/N fertilizer applied) for winter wheat was lower than that for perennial ryegrass on all soil types under the baseline climate and RCP2.6, but comparable or greater under RCP4.5 and RCP8.5. In terms of C sequestration, grassland conversion for production of winter wheat is unsustainable under these soil–climatic conditions. SIGNIFICANCE Our results demonstrated that soil workability is a major factor influencing the potential impact of land-use conversion in clay soils and a wetter climate

Opportunities for reducing environmental emissions from forage-based dairy farms

Modern dairy production is inevitably associated with impacts to the environment and the challenge for the industry today is to increase production to meet growing global demand while minimising emissions to the environment. Negative environmental impacts include gaseous emissions to the atmosphere, of ammonia from livestock manure and fertiliser use, of methane from enteric fermentation and manure management, and of nitrous oxide from nitrogen applications to soils and from manure management. Emissions to water include nitrate, ammonium, phosphorus, sediment, pathogens and organic matter, deriving from nutrient applications to forage crops and/or the management of grazing livestock. This paper reviews the sources and impacts of such emissions in the context of a forage-based dairy farm and considers a number of potential mitigation strategies, giving some examples using the farm-scale model SIMSDAIRY. Most of the mitigation measures discussed are associated with systemic improvements in the efficiency of production in dairy systems. Important examples of mitigations include: improvements to dairy herd fertility, that can reduce methane and ammonia emissions by up to 24 and 17%, respectively; diet modification such as the use of high sugar grasses for grazing, which are associated with reductions in cattle N excretion of up to 20% (and therefore lower N losses to the environment) and potentially lower methane emissions, or reducing the crude protein content of the dairy cow diet through use of maize silage to reduce N excretion and methane emissions; the use of nitrification inhibitors with fertiliser and slurry applications to reduce nitrous oxide emissions and nitrate leaching by up to 50%. Much can also be achieved through attention to the quantity, timing and method of application of nutrients to forage crops and utilising advances made through genetic improvements

How well does Miscanthus ensile for use in an anaerobic digestion plant?

This study examined the ability for early-harvested Miscanthus (Miscanthus x giganteus and Miscanthus sacchariflorus) to be stored in silage for later use in anaerobic digestion. Two silage additives favouring a homo and hetero-fermentation pathway were examined. The results show that silage additives are necessary to effectively ensile Miscanthus, otherwise untreated Miscanthus grasses incurred dry matter losses of 4% during three months' storage. The silage additives improved the lactic and acetic acid production in the Miscanthus silages however did not have any effect on the biogas yield. On a ‘per tonne volatile solids’-basis, Miscanthus produces half the biogas yield of maize. The outlook for the use of Miscanthus AD therefore depends on the yield when harvested in autumn. A minimum yield of 19–26.5 t DM/ha is needed for Miscanthus to match the biogas production from a similar area of maize yielding 10–14 t DM/ha

Influence of bedding material on ammonia emission from cattle barns

Dairy cattle barns are a major source of NH3 emissions to the atmosphere. Previous studies have shown that the bedding material used in the barn can influence the magnitude of NH3 emissions, but little is known about which bedding characteristics are important in this respect. The aims of this study were to assess, at a laboratory scale, the relative importance of the chemical [pH, cation exchange capacity (CEC), C:N] and physical (urine absorbance capacity, bulk density) characteristics of 5 bedding materials (chopped wheat straw, sand, pine shavings, chopped newspaper, chopped corn stalks, and recycled manure solids) on NH3 emissions from dairy cattle urine. Recycled manure solids were the most absorbent of the bedding types (4.2 g of urine/g of bedding), and sand was the least (0.3 g of urine/g of bedding). When beddings were soaked in urine to their absorbance capacities, NH3 emissions over 48 h (expressed as a proportion of the urine N absorbed) were not significantly different among bedding types, despite differences in initial bedding pH, CEC, and C:N. When equal volumes of urine were applied to equal depths of dry bedding, NH3 emissions over 48 h were significantly less from sand and pine shavings (23 and 42% of applied urine N, respectively) than from chopped newspaper, chopped corn stalks, and recycled manure solids (62, 68, and 65% of applied urine N, respectively), whereas emissions from chopped wheat straw (55% applied urine N) only differed significantly from that from sand. Differences in the chemical characteristics of the beddings did not explain differences in emission; NH3 emissions increased linearly with CEC contrary to expectations, and there was no significant relationship with initial bedding pH. The physical characteristics of bedding materials were of more importance, as NH3 emissions increased linearly with absorbance capacity and decreased as the bulk density of the packed beddings increased

Low frequency aeration of pig slurry affects slurry characteristics and emissions of greenhouse gases and ammonia

Low frequency aeration of slurries may reduce ammonia (NH3) and methane (CH4) emissions without increasing nitrous oxide (N2O) emissions. The aim of this study was to quantify this potential reduction and to establish the underlying mechanisms. A batch experiment was designed with 6 tanks with 1 m3 of pig slurry each. After an initial phase of 7 days when none of the tanks were aerated, a second phase of 4 weeks subjected three of the tanks to aeration (2 min every 6 h, airflow 10 m3 h−1), whereas the other three tanks remained as a control. A final phase of 9 days was established with no aeration in any tank. Emissions of NH3, CH4, carbon dioxide (CO2) and N2O were measured. In the initial phase no differences in emissions were detected, but during the second phase aeration increased NH3 emissions by 20% with respect to the controls (8.48 vs. 7.07 g m−3 [slurry] d−1, P < 0.05). A higher pH was found in the aerated tanks at the end of this phase (7.7 vs. 7.0 in the aerated and control tanks, respectively, P < 0.05). CH4 emissions were 40% lower in the aerated tanks (2.04 vs. 3.39 g m−3 [slurry] d−1, P < 0.05). These differences in NH3 and CH4 emissions remained after the aeration phase had finished. No effect was detected for CO2, and no relevant N2O emissions were detected during the experiment. Our results demonstrate that low frequency aeration of stored pig slurry increases slurry pH and increases NH3 emissions.&nbsp