R.B. Thompson

Ammonia emission from grassland and livestock production systems in the UK.

Emissions of ammonia were measured from livestock excreta and fertilisers applied to grass swards, from grazed paddocks, from decomposing grass herbage and from an animal house containing dairy cows. Emissions from urine, dung, slurry and fertilisers were determined using a system of wind tunnels with each tunnel covering an area of 1 m(2). Emissions from grazed swards were determined using a micrometeorological mass balance method. From the results of these measurements, together with other published information, an inventory for ammonia emissions has been calculated for grassland and livestock production systems over the UK as a whole. It is estimated that emissions from grassland and cattle and sheep production amount to about 230 kt NH(3)-N annually, while emissions from pig and poultry production amount to about 40 kt and 80 kt NH(3)-N, respectively.

Ammonia volatilization from cattle slurry following surface application to grassland I. Influence of mechanical separation, changes in chemical composition during volatilization and the presence of the grass sward

Three experiments were conducted using a system of small wind tunnels to measure ammonia (NH3) volatilization from cattle slurry after surface application to land. In each experiment slurry was applied at a rate equivalent to 80 m3 ha-1, providing the equivalent of approximately 100 kg NH4+-N ha-1. The first experiment compared NH3 volatilization from the liquid fraction obtained by mechanical separation of slurry with that from unseparated slurry. The total NH3 loss over six days from unseparated and separated slurry were very similar, being 38 and 35% respectively of the NH4+-N applied. For the first five hours, the rate of NH3 loss was higher from the unseparated slurry, thereafter it was consistently lower. In the second experiment, slurry was ponded in a tray to examine whether impeded infiltration or changes in the NH4+ concentration or overall pH of the slurry influenced the rapid decline in rate soon after application that is characteristic of NH3 volatilization from animal slurries applied to land. It appeared, however, that other factors such as resistance to diffusion within the slurry and/or at the slurry surface were mostly responsible for the rapid decline in rate. In the third experiment, in which NH3 volatilization was measured from slurry applied to grassland or bare soil, the total loss from slurry applied to grassland was approximately 1.5 times that from slurry applied to bare soil.

Ammonia volatilization from cattle slurry following surface application to grassland. II. Influence of application rate, wind speed and applying slurry in narrow bands.

Three experiments were conducted to examine the influence of slurry application rate, wind speed and applying slurry in narrow bands on ammonia (NH3) volatilization from cattle slurry surface-applied to grassland. The experiments were conducted in the field using a system of small wind tunnels to measure NH3 loss. There was an inverse relationship between slurry application rate and the proportion of NH4+-N volatilized. From slurry applied at 20, 40, 60, 80, 100 and 120 m3 ha-1, the respective proportions of NH4+-N lost by NH3 volatization in 6 days were 60, 56, 49, 40, 44 and 44%. The negative relationship was most pronounced in the first 24 hours after application when 57–77% of the total loss for 6 days occurred. Wind speed had a positive effect on NH3 volatilization, although the effect was small in relation to the total loss; increasing the wind speed from 0.5 to 3.0 m s-1 increased the total 5 day loss by a factor of 0.29. The effect of wind speed was also most pronounced in the first 24 hours when much of the NH3 loss took place. The effect of reducing the surface area of the applied slurry was examined by comparing NH3 volatilization from slurry broadcast across plots with that applied in narrow bands. Although the rate of NH3 volatilization was considerably smaller from the banded application immediately after the slurry was applied, the difference between the treatments progressively narrowed until 2 days after application, after which a higher rate was maintained from the banded slurry. After 5 days the total loss from the banded application was 83% of that from broadcast slurry.

Denitrification in slurry-treated soil: Occurrence at low temperatures, relationship with soil nitrate and reduction by nitrification inhibitors

Abstract The influence of different amounts of carbon substrate on (i) denitrification at low soil temperatures and (ii) the relationship between denitrification and soil NO3− content was examined in a field experiment. Six treatments, cattle slurry, diluted cattle slurry plus NH4C1, and NH4C1 solution alone, with and without the nitrification inhibitor dicyandiamide (DCD) were applied to a grassland soil by injection in winter (January). The treatments provided the same initial quantity of NH4+-N (96 kg N ha−1) and volume of slurry or solution (80m3 ha−1); they differed in the amounts or organic material added and in the extent of conversion of NH4+ to NO3−. Total denitrification losses determined during 3 months from the slurry, diluted slurry plus NH4+, and NH4+ solution, without DCD, were 46, 8 and 5 kg N ha−1 respectively. From the three treatments with DCD they were 5 kg N ha−1. During this time, average daily soil temperatures remained below 6°C. As the amount of organic substrate from slurry was increased, denitrification became increasingly dependent on the soil NO3− content. Laboratory studies of denitrification potential (DNP), with nitrate non-limiting, confirmed that cattle slurry acted as a source of carbon for denitrification, and that the addition of glucose to soil at 4 and 8°C resulted in logarithmic increases in DNP.

Production and water use in lettuces under variable water supply

The effects of a variable water supply on the water use, growth and yield of two crisphead and one romaine (i.e., Cos) lettuce cultivar were examined in a field experiment using a line source sprinkler system that produced a range of water regimes that occur in growers fields. Four locations at increasing distances from the main line were monitored through the season (i.e., from thinning to harvest, 28–63 days after planting (DAP)). These locations at the end of the season corresponded to: (1) rewatering to field capacity (FC); (2) watering with a volume 13% below that required in the field capacity treatment (0.87*FC); (3) 30% below FC (0.70*FC); and (4) 55% below FC (0.45*FC). A linear production function for dry matter accumulation and fresh weight vs. crop evapotranspiration (ETc) was determined for lettuce during this period, giving a water use efficiency for dry matter of 1.86 g m−2 mm−1 and for fresh weight of 48 g m−2 mm−1 . For lettuce irrigated to field capacity, ETc between thinning and harvest was 146 mm; maximum crop coefficients of 0.81–1.02 were obtained at maturity (55–63 DAP). For the three irrigation treatments receiving the largest water application, ETc was higher in the Cos culivar than in the two crisphead lettuce cultivars which had similar ETc. Plant fresh weight was more sensitive than dry weight to reduction in water supply. In the FC treatment, root length density and soil water extraction were greatest in the top 0–45 cm, and decreased rapidly below 45 cm depth. Soil water extraction by roots increased at lower depths when irrigation was reduced. Instantaneous rates of leaf photosynthesis and leaf water potential showed no response to the irrigation treatments in this study, despite differences in biomass production. Evaporation was determined to be the major component of ETc for 45 of the 63 days of the growing season. The large loss of water by evaporation during mid-season and the apparent insensitivity of lettuce to the volume of irrigation during this period may provide an opportunity for reducing irrigation applications.

CONSTRUCTION AND VALIDATION OF SMALL MOBILE WIND TUNNELS FOR STUDYING AMMONIA VOLATILIZATION

Ammonia volatilization is a major nitrogen (N) loss process for surface applied manures and urea fertilizers. Ammonia volatilization is a complex phenomenon requiring specialized research equipment to gather valid scientific data, which is essential for developing management practices to minimize N losses from farms and N inputs to neighboring ecosystems. The objectives of this work were: i) to describe a revised version of the small mobile wind-tunnels originally reported by Lockyer, and ii) to assess the ability of these wind tunnels to quantitatively recover ammonia lost from dilute solutions. The design, construction, cost (about

Gaseous nitrogen losses and ammonia volatilization measurement following land application of cattle slurry in the mid-Atlantic region of the USA

4000 each), physical calibration, and operation of the wind tunnels are described. The tunnels consist of two connected parts: i) a transparent plastic canopy which covers a 1-m 2 treatment area, and ii) a sheet-metal cylinder, which houses an adjustable speed motor with attached fan blade and an air sampler to monitor ammonia volatilization. Two ammonia loss-and-recovery experiments were conducted at constant wind speeds of 0.5 and 1.0 m s -1 to assess tunnel performance. Mean ammonia recoveries were 104µ6% at 0.5 m s -1 and 104µ18% at 1.0 m s -1 . These results demonstrate that the wind tunnels can be valid tools for collecting volatilized ammonia and for making relative comparisons among N management treatments. Obtaining valid comparison of different management treatments is essential for the development of improved N management practices that minimize ammonia losses from manures or fertilizers.

Water use and production of a greenhouse pepper crop under optimum and limited water supply

To provide locally-determined field data for extension and environmental management purposes, gaseous N losses were measured following cattle slurry application to an arable silty-loam soil in the mid-Atlantic region of the USA. The field had been cropped to no-till maize. NH3 volatilization was measured with the micro-meteorological, integrated horizontal flux (IHF) method, and denitrification with a core incubation method using acetylene inhibition. An early-winter surface application (5 December 1996; 88 m3 ha−1 supplying 91 kg NH4+-N ha−1) was either unincorporated or immediately incorporated. NH3 volatilization was measured from the unincorporated application, and denitrification from both slurry treatments and appropriate control soils. Total NH3 loss from the unincorporated slurry application was 19% of applied NH4+-N; temperatures were cool (4–6 °C), and 25 mm of rain fell within 24 h of application. For 3 months, enhanced denitrification occurred from the two slurry treatments, with generally higher rates from the incorporated slurry. Total net denitrification loss from the surface-applied and incorporated slurry treatments was, respectively, 11 and 17% of applied NH4+-N. Denitrification loss over the winter/early-spring period was appreciable but not substantial, even where NH3 volatilization was restricted by immediate incorporation. From the spring application (30 April 1997, 39 m3 ha−1 supplying 51 kg NH4+-N ha−1), total NH3 loss was 71% of applied NH4+-N. These NH3 volatilization loss data and the similarity of climate suggest that NH3 loss factors from recent NW European work are likely to be generally applicable in the mid-Atlantic region. NH3 volatilization from the spring application was also measured using the Z-instrument (ZINST) approach, and with a system of small wind tunnels. A comparative assessment of the three methods is reported.

Feasibility of vermicomposting residues from olive oil production obtained using two stage centrifugation

Summary Sweet pepper, grown from Autumn to Spring, is a major crop in greenhouse vegetable production systems of the Mediterranean coast in south-eastern Spain. Irrigation water is limited in this region, yet little information is available to assist in irrigation management at the farm and regional levels. The aim of this work was to determine crop evapo-transpiration, water-use efficiency and the effect of continuous water deficits on crop growth and production of pepper grown in plastic greenhouses in two growing seasons. Three irrigation treatments were applied: T1, watered with 100% of the estimated crop water requirement; and T2 and T3 watered with 50% and 20% of the estimated crop water requirements, respectively. Seasonal crop evapo-transpiration (ETc) in treatment T1 was 346–362 mm. The effect of water deficit on crop growth became apparent approximately 80 d after transplanting. The contributions of soil water uptake to total ETc for treatments T2 and T3 were 20–22% and 43–47%, respectively. The response of ETc to water stress was apparent at a threshold value of 55% of available water content (AWC), suggesting an allowable depletion of soil moisture equivalent to 27 mm. For treatments T2 and T3, reductions in total fruit production (relative to treatment T1) were 33% and 62%, respectively; and reductions in marketable fruit production were 47% and 67%, respectively. Water deficit had little effect on total fruit number, but substantially increased the proportion of unmarketable fruits due to their small fruit size, and to high incidences of sunburn and blossom-end rot. Linear relationships were found between both shoot biomass and marketable fresh fruit production with ETc. Mean water use efficiency values for shoot dry matter (WUEb) were 4.5 – 4.7 g m–2 mm–1; for total fresh fruit production (WUEt) between 24 – 33 g m–2 mm–1; and for marketable fresh fruit production (WUEm) between 16.9 – 25.9 g m–2 mm–1. Water stress did not induce early fruit production, or influence the relative distribution of assimilates within the plant.

Feasibility of vermicomposting dairy biosolids using a modified system to avoid earthworm mortality

Abstract A laboratory study was undertaken to examine the feasibility of using vermicomposting to stabilize the waste product ‐ dry olive cake, for use as a soil amendment. Dry olive cake (C) is obtained from a new two stage centrifugation process used to extract olive oil from olives. Cattle manure (M) was examined as a comparison and as a co‐composting agent. Anaerobic sewage sludge (ANS) and aerobic sewage sludge (AES) were also assessed as co‐composting agents. Different ratios of cake to co‐composting agent were examined. The C:N ratios of the initial materials used were: C: 49, M: 14, ANS: 4 and AES: 8. Earthworm (Eisenia andrei), growth, clitellum development and cocoon production were monitored over 35 days. Dry olive cake alone was an inadequate substrate for vermicomposting on account of slow earthworm growth and infertility. The addition of manure or either sludge to the dry olive cake at certain ratios enhanced worm growth and reproduction so they were generally similar to that in the manure o...