Dairy Slurry Application Research Articles

Humic Acids Combined with Dairy Slurry as Fertilizer Can Increase Alfalfa Yield and Reduce Nitrogen Losses

Dairy slurry could be a significant source of nitrogen (N) for plants, but mismanagement can lead to atmospheric ammonia losses or nitrate leaching into groundwater. To make the use of dairy slurry efficient and reasonable, the loss of N pollution to the environment should be reduced. We used repacked lysimeters to comprehensively determine ammonia emission and N leaching losses in an alfalfa–soil system. The application of dairy slurry had no significant effect on alfalfa yield at the same rate of N application in comparison to chemical fertilizer, and adding humic acids significantly increased yield by about 12%. However, the application of dairy slurry increased the ammonia emission rate significantly, leading to an increase in the cumulative amount of ammonia emission, while the addition of humic acids reduced the ammonia emissions by 11%. Chemical fertilizer and dairy slurry application significantly increased nitrate leaching compared to the control treatment, while the addition of humic acids can significantly reduce ammonium N leaching. Dairy slurry was proven to be as effective as chemical N fertilizer in achieving the optimum biomass, and adding humic acids can significantly reduce N loss to the atmosphere and groundwater. This study showed the possibility of replacing chemical fertilizer with dairy slurry in alfalfa production and the advantages of humic acids’ addition to alfalfa to maintain production yield and improve environmental friendliness.

Nutritive value, silage fermentation characteristics, and aerobic stability of grass-legume round-baled silages at differing moisture concentrations with and without manure fertilization and microbial inoculation.

For baled silages, production of clostridial fermentation products can be exacerbated by exceeding normal moisture targets (45% to 55%), and/or by the application of dairy slurry before harvest. Our objectives were to test a microbial inoculant as a mitigant of clostridial products in high-moisture, grass-legume (52% ± 13.8% cool-season grasses, 44.0% ± 14.0% legumes [predominately alfalfa]) baled silages in swards that were fertilized with dairy slurry. A secondary objective was to examine the effects of bale moisture and inoculation on the aerobic stability of these fermented silages following exposure to air. After the first-cutting was removed, three manure treatments were applied as a whole-plot factor: 1) control (no manure); 2) slurry applied immediately to stubble (63,250 L/ha); or 3) slurry applied after a 1-wk delay (57,484 L/ha). An interactive arrangement of bale moisture (64.1% or 48.4%) and inoculation (yes or no) served as a subplot term in the experiment. The inoculant contained both homolactic (Lactococcus lactis 0224) and heterolactic (Lactobacillus buchneri LB1819) bacteria. The experimental design was analyzed as a randomized complete block with four replications, and the study included 48 experimental units (1.2 × 1.2-m round bales). Total fermentation acids were affected (P ≤ 0.021) by slurry application strategies, but this was likely related to inconsistent bale moisture across slurry-application treatments. Concentrations of butyric acid were low, and there were no detectable contrasts comparing manure treatments (mean = 0.05%; P ≥ 0.645). Bale moisture affected all measures of fermentation, with bales made at 64.1% moisture exhibiting a more acidic final pH (4.39 vs. 4.63; P < 0.001), less residual water-soluble carbohydrates (2.1% vs. 5.1%; P < 0.001), as well as greater lactic acid (4.64% vs. 2.46%; P < 0.001), acetic acid (2.26% vs. 1.32%; P < 0.001), and total fermentation acids (7.37% vs. 3.97%; P < 0.001). Inoculation also reduced pH (4.47 vs. 4.56; P = 0.029), and increased acetic acid (1.97% vs. 1.61%; P < 0.001) and 1,2-propanediol (1.09% vs. 0.72%; P < 0.001) compared to controls. During a 34-d aerobic exposure period, maximum surface bale temperatures were not affected (P ≥ 0.186) by any aspect of treatment, likely due to the prevailing cool ambient temperatures; however, yeast counts were numerically lower in response to greater (P < 0.001) production of acetic acid that was stimulated by both high bale moisture and inoculation.

Dairy Slurry Application to Stubble-Covered Soil: A Study on Sustainable Alternatives to Minimize Gaseous Emissions

The development of sustainable application practices, which do not demand incorporation into the soil, is necessary to encourage slurry use in conservation agriculture (CA). Incorporation is the most common practice to reduce nitrogen losses from the applied slurry. However, in CA, soil disturbance must be avoided. Two experiments were conducted to evaluate strategies to reduce gaseous emissions from dairy slurry applied to stubble-covered soil without incorporation. We evaluated (1) effects on ammonia (NH3) emissions of pretreatment by acidification (ADS), irrigation (IR) and placement under the stubble (US); and (2) effects of ADS, IR, US and delayed fertilization (RDS T16) on greenhouse gases (GHG). The results of the evaluated strategies were compared to raw slurry (RDS) and ammonium sulphate (MS). Additionally, in experiment 2, the results were compared to ammonium sulphate (MB) and slurry injection (IN), both in bare soil. ADS, US and IR decreased NH3 emissions by 66%, 60% and 32.5%, respectively, with total N emissions NH3 emissions accounting for more than 79% of N losses in slurry-based treatments. Late application reduced N2O emissions by 48%. GHG emissions from ADS, US and IR were similar to those from MS, MB and IN. ADS, US and IR are the most suitable strategies for slurry application in CA.

Can Dairy Slurry Application to Stubble, without Incorporation into the Soil, Be Sustainable?

In many countries, livestock slurry must be injected or incorporated into the soil to reduce nitrogen losses. However, when the injection is not feasible, farmers adopting conservation practices discard the use of slurry as fertilizer. New approaches related to slurry treatment or application management can stimulate the use of slurry in conservation agriculture (CA). This study aimed to evaluate the agronomic effects of some new management strategies to use dairy slurry for fertilization of ryegrass grown on stubble-covered soil, using as reference standard practices (slurry injection and mineral fertilizer application). The following treatments were considered: (i) bare soil: control (CB), mineral fertilizer (MB), injection (IN); (ii) stubble: control (CS), acidified dairy slurry (ADS), raw dairy slurry (RDS), irrigation following RDS (IR), mineral fertilizer (MS), RDS placed under the stubble (US), raw slurry applied 16 days after sowing (RDS T16). Effects on ryegrass yield, apparent nutrient recovery (ANR) and soil chemical properties were assessed. ADS reached 94% equivalence to MS and performed similarly to IN for productivity, ANR and soil parameters showing to be a sustainable alternative to replace mineral nitrogen and a potential solution to enable dairy slurry application in CA without injection or incorporation into the soil.

Intensive Rain Hampers the Effectiveness of Nitrification Inhibition in Controlling N2O Emissions from Dairy Slurry-Fertilized Soils

Nitrification inhibitors have been proposed as a tool to mitigate nitrous oxide (N2O) emissions from agriculture, which are caused mainly by fertilization. The nitrification inhibitor 3,4-Dimethylpyrazole phosphate (DMPP) was tested in a winter rapeseed field after dairy slurry application in Central Estonia. N2O emissions were monitored using the closed chamber method. Soil and leachate chemical parameters were also analyzed. N2O emissions increased from pre-slurry application values of 316 and 264 µg m−2 h−1 for the control and treatment plot, respectively, to maximum values of 3130.71 and 4834 µg m−2 h−1, with cumulative emissions during the study period of 12.30 kg ha−1 for the control plot and 17.70 kg ha−1 for the treatment plot. The intense precipitation period that began with the application of the slurry resulted in changes in soil moisture and water-filled pore space (WFPS), modifying the nitrification/denitrification balance. Positive significant correlations (p = 0.016 and p = 0.037, for the control and treatment plot, respectively) were found between N2O fluxes and WFPS. Future studies should consider the role of nitrifier and denitrifier communities in order to better assess in-field nitrification inhibitor effectiveness.

Integrated modelling to assess N pollution swapping in slurry amended soils

In the present work, it was hypothesized that through modelling it is possible to overcome the constraints that arise in the quantification of N pollution swapping associated to slurry application practices when using individual experimental data. For this, environmental N losses were assessed under two methods of dairy slurry application to a double cropping system (rainfed oats (Avena strigosa)/irrigated maize (Zea mays)) in two different soils. An integrated experimentation and modelling approach was applied using the RZWQM2 model. The model was first tested using four years of experimental data concerning N fluxes to/from different environmental compartments (soil mineralization, N gas emissions, and N leaching). The model estimated emissions with overall efficiencies of ~70% and r2 ~ 0.75. Total N losses were higher for surface band application (95.4 and 40.2 kg ha−1 for the sandy and sandy loam soils, respectively). However, when slurry was injected, nitrate leaching considerably increased (by 107 and 64% for the sandy and sandy loam soils, respectively), even though gas emissions were minimized. This N swapping among path losses requires targeting of the N mitigation measures to the environmental compartment showing the highest vulnerability. Generally, the estimated emission factors (EFs) were lower than or equal to (slurry injection in the sandy loam soil) the IPCC default. The values showed high variability, reinforcing the need to use agricultural system specific EFs. The methodologies used in this study, focused on scenario analysis, can support policy as they can be used to set up integral strategies to decrease N emissions from livestock farming systems, taking into account possible synergies and antagonisms produced by the measures among NH3 and N2O emissions and NO3− leaching.

Risk Assessment of E. coli Survival Up to the Grazing Exclusion Period After Dairy Slurry, Cattle Dung, and Biosolids Application to Grassland

Grassland application of dairy slurry, cattle dung and biosolids offers an opportunity to recycle valuable nutrients (N, P and K), which may all introduce pathogens to the soil environment. Herein, a temporal risk assessment of the survival of Escherichia coli (E. coli) up to 40 days in line with the legislated grazing exclusion time points after application was examined across six scenarios: (1) soil and biosolids mixture, (2) biosolids amended soil, (3) dairy slurry application, (4) cattle dung on pasture, (5) comparison of scenario 2, 3 and 4, and (6) maximum legal vs. excess rate of application for scenario 2 and 3. The risk model input parameters were taken or derived from regressions within the literature and an uncertainty analysis (n=1000 trials for each scenario) was conducted. Scenario 1 results showed that E. coli survival was higher in the soil/biosolids mixture for higher biosolids portion, resulting in the highest 20 day value of residual E. coli concentration (i.e. C20, log10CFU g−1dw) of 1.0 in 100% biosolids or inoculated soil and the lowest C20 of 0.098 in 75/25 soil/biosolids ratio, respectively, in comparison to an average initial value of ~6.4 log10CFU g−1dw. The E. coli survival across scenario 2, 3 and 4 showed that the C20 value of biosolids (0.57 log10CFU g−1dw) and dairy slurry (0.74 log10CFU ml−1) was 2.9-3.7 times smaller than that of cattle dung (2.12 log10CFU g−1dw). The C20 values of biosolids and dairy slurry associated with legal and excess application rates ranged from 1.14 to 1.71 log10CFU ha−1, which is a significant reduction from the initial concentration range (12.99 to 14.83 log10CFU ha−1). The E. coli survival in un-amended soil was linear with a very low decay rate resulting in a higher C20 value than that of biosolids or dairy slurry. The risk assessment and uncertainly analysis showed that the residual concentrations in biosolids/dairy slurry applied soil after 20 days would be 45−57% lower than that of the background soil E. coli concentration. This means the current practice of grazing exclusion times is safe to reduce the risk of E. coli transmission into the soil environment.

Voluntary intake and digestibility by sheep of alfalfa ensiled at different moisture concentrations following fertilization with dairy slurry.

Dairy slurry is used commonly as an animal-sourced fertilizer in agronomic production. However, residual effects of slurry application on intake and digestibility of alfalfa (Medicago sativa L.) silage from subsequent harvests are not well known. The objective of this study was to determine if moisture concentration of alfalfa silage and timing of dairy slurry application relative to subsequent harvest affected intake and digestibility by sheep. Katahdin crossbred ewes (n = 18; 48 ± 5.3 kg) in mid-gestation were stratified by BW and allocated randomly in each of two periods to one of six treatments arranged in a two × three factorial arrangement. Treatments consisted of recommended (RM; 46.8%) or low (LM; 39.7%) moisture at baling after either no slurry application (NS), slurry application to stubble immediately after removal of the previous cutting (S0), or slurry application 14 d after removal of the previous cutting (S14). Silages were chopped through a commercial straw chopper, packed into plastic trash cans, and then offered to ewes within 4 d of chopping. Period 1 of the intake and digestion study consisted of a 14-d adaptation followed by a 7-d fecal collection period. Period 2 followed period 1 after a 4-d rest and consisted of an 11-d adaptation followed by 7 d of fecal collection. Ewes were housed individually in 1.4 × 4.3-m pens equipped with rubber mat flooring. Feces were swept from the floor twice daily, weighed, and dried at 50 °C. Ewes had ad libitum access to water and were offered chopped silage for a minimum of 10% refusal (DM). Blood samples were collected immediately prior to feeding, and 4 and 8 h after feeding on the day prior to the end of each period. Organic matter intake (g/kg BW) and OM digestibility tended (P < 0.10) to be, and digestible OM intake (g/kg BW) was reduced by slurry application. Lymphocytes (% of total white blood cells) were greater (P < 0.05) from LM vs. RM and from NS vs. S0 and S14. Red blood cell concentrations were greater (P < 0.05) from S14 vs. S0 and from S0 and S14 vs. NS. Serum urea N concentrations did not differ (P > 0.17) across treatments. Therefore, moisture concentration of alfalfa silage within the range used in this study may not affect voluntary intake or digestibility, but slurry application may have an effect on digestible OM intake. Also, moisture concentration of alfalfa silage and time of dairy slurry application may affect specific blood hemograms.

Nitrous Oxide and Ammonia Emissions from Injected and Broadcast-Applied Dairy Slurry.

Trade-offs associated with surface application or injection of manure pose important environmental and agronomic concerns. Manure injection can conserve nitrogen (N) by decreasing ammonia (NH) volatilization. However, the injection band also creates conditions that potentially favor nitrous oxide (NO) production: an abundant organic substrate-promoting microbial activity, anaerobic conditions favoring denitrification, and large local concentrations of N. We assessed differences in NH volatilization and NO emissions with broadcast application versus shallow disk injection of dairy slurry during the 2011 to 2013 growing seasons on a well-drained silt loam that received average manure-N application rates of 180 kg N ha via injection or 200 kg N ha via broadcast. Ammonia emissions were measured using a photoacoustic gas analyzer and chambers, and NO emissions were measured using syringes to draw timed samples from vented chambers with analysis by gas chromatograph. Results point to a 92 to 98% (3.02-11.05 kg NH-N ha) reduction in NH volatilization (for the initial sampling) with injection compared with broadcasting manure but also reveal 84 to 152% (725.9-3187.8 g NO-N ha) greater cumulative NO emissions. Although losses of N via NO emission were at least three orders of magnitude less than NH volatilization, their potential role as a greenhouse gas is of concern. Despite the potential greenhouse gas trade-offs associated with shallow disk injection of manure, decreasing NH volatilization provides a substantial benefit, especially to farmers who are trying to conserve N and improve the N/P ratio of soil-applied manure.

Zeolite Combined with Alum and Polyaluminum Chloride Mixed with Agricultural Slurries Reduces Carbon Losses in Runoff from Grassed Soil Boxes.

Carbon (C) losses from agricultural soils to surface waters can migrate through water treatment plants and result in the formation of disinfection by-products, which are potentially harmful to human health. This study aimed to quantify total organic carbon (TOC) and total inorganic C losses in runoff after application of dairy slurry, pig slurry, or milk house wash water (MWW) to land and to mitigate these losses through coamendment of the slurries with zeolite (2.36-3.35 mm clinoptilolite) and liquid polyaluminum chloride (PAC) (10% AlO) for dairy and pig slurries or liquid aluminum sulfate (alum) (8% AlO) for MWW. Four treatments under repeated 30-min simulated rainfall events (9.6 mm h) were examined in a laboratory study using grassed soil runoff boxes (0.225 m wide, 1 m long; 10% slope): control soil, unamended slurries, PAC-amended dairy and pig slurries (13.3 and 11.7 kg t, respectively), alum-amended MWW (3.2 kg t), combined zeolite and PAC-amended dairy (160 and 13.3 kg t zeolite and PAC, respectively) and pig slurries (158 and 11.7 kg t zeolite and PAC, respectively), and combined zeolite and alum-amended MWW (72 and 3.2 kg t zeolite and alum, respectively). The unamended and amended slurries were applied at net rates of 31, 34, and 50 t ha for pig and dairy slurries and MWW, respectively. Significant reductions of TOC in runoff compared with unamended slurries were measured for PAC-amended dairy and pig slurries (52 and 56%, respectively) but not for alum-amended MWW. Dual zeolite and alum-amended MWW significantly reduced TOC in runoff compared with alum amendment only. We conclude that use of PAC-amended dairy and pig slurries and dual zeolite and alum-amended MWW, although effective, may not be economically viable to reduce TOC losses from organic slurries given the relatively low amounts of TOC measured in runoff from unamended slurries compared with the amounts applied.

Soil mineral nitrogen dynamics following repeated application of dairy slurry

Repeated applications of animal slurry to soil can lead to residual nitrogen (N) effects from mineralization of organic N carried over from the previous year and from remineralization of previously immobilized N. We studied the effect of repeated slurry applications on soil mineral N (SMNt: nitrate‐N plus soluble, exchangeable and non‐exchangeable ammonium‐N) dynamics in a simplified, aerobic laboratory incubation. The experiment evaluated the effects of up to four applications (84‐day intervals) of two different liquid cow slurries, ammonium sulphate and water (unfertilized control, CON) to sandy loam and clay loam soils. The slurries came from heifers (HEI) and lactating dairy cows (COW). Both soil types showed net N mineralization in HEI during each 84‐day interval after application (3–6% of slurry‐N), whereas decomposition of COW induced net N immobilization at 16% of slurry‐N. The effect observed for COW might have come from its larger C to organic‐N ratio. After each application to the clay loam soil, 36–64% of the ammonium applied was not recoverable at day 0 because of ammonium fixation by clay minerals, and an average of 20% of fertilizer‐N was measured as non‐exchangeable ammonium at day 84. Recovery of N applied with both HEI and COW at day 84 increased significantly with subsequent applications to clay loam soil, but not to sandy loam soil. Residual effects in clay loam soil ranged from 2 to 11% of applied N, which probably resulted from slow mineralization of recalcitrant organic fractions in the slurry and partial stabilization of microbial by‐products within the soil.HighlightsA novel incubation approach was used to study residual N effects of ammonium sulphate and slurries. Fertilizers were applied one, two, three or four times to a sandy loam (SL) and a clay loam (CL) soil. Residual N effects were small; less slurry NH4‐N was available in CL than SL because of clay fixation. Mineralization of residual slurry‐N and stabilization of microbial by‐products were slow.

Seasonal persistence of faecal indicator organisms in soil following dairy slurry application to land by surface broadcasting and shallow injection

Dairy farming generates large volumes of liquid manure (slurry), which is ultimately recycled to agricultural land as a valuable source of plant nutrients. Different methods of slurry application to land exist; some spread the slurry to the sward surface whereas others deliver the slurry under the sward and into the soil, thus helping to reduce greenhouse gas (GHG) emissions from agriculture. The aim of this study was to investigate the impact of two slurry application methods (surface broadcast versus shallow injection) on the survival of faecal indicator organisms (FIOs) delivered via dairy slurry to replicated grassland plots across contrasting seasons. A significant increase in FIO persistence (measured by the half-life of E. coli and intestinal enterococci) was observed when slurry was applied to grassland via shallow injection, and FIO decay rates were significantly higher for FIOs applied to grassland in spring relative to summer and autumn. Significant differences in the behaviour of E. coli and intestinal enterococci over time were also observed, with E. coli half-lives influenced more strongly by season of application relative to the intestinal enterococci population. While shallow injection of slurry can reduce agricultural GHG emissions to air it can also prolong the persistence of FIOs in soil, potentially increasing the risk of their subsequent transfer to water. Awareness of (and evidence for) the potential for ‘pollution-swapping’ is critical in order to guard against unintended environmental impacts of agricultural management decisions.

Dairy slurry application to grasslands and groundwater quality in a volcanic soil

Research in volcanic-ash soils has shown that they largely capture the dairy slurry following application to land; however, their hydrological properties would favor nutrient leaching. Our objective was to evaluate the contribution of biogeochemical and hydrological controls on the pollution of groundwater by cattle slurry applied to a permanent grassland growing on a volcanic soil. We sampled groundwater chemistry since 10 months before the fertilization (three samplings), and 16 months after, with samplings 1-2 months after the fertigation. Following fertilization, ammonium, exchangeable potassium, and magnesium soil concentrations increased in the fertilized plots compared to the control plots. In contrast, no effect of slurry on groundwater quality was detected, with the exception of dissolved organic nitrogen, a main component of dairy slurry that increased in the groundwater below the fertilized plots. Despite the fact that biogeochemical controls predominate, hydrological aspects would be important when rainfall is high, evapotranspiration is low, groundwater table level is high, and water movement in the saturated zone increases. We concluded that the application of slurry to pastures under rates comparable to a high fertilization in the short term, does not generally impact the groundwater quality in volcanic ash-derived soils.

Measuring and Modeling Soil Carbon Respiration following Repeated Dairy Slurry Application

Farm animal manure slurries are repeatedly applied to soils. The portion of slurry organic matter not decomposed within its application year is left to mineralize over subsequent years, which results in a residual effect of high C mineralization in historically-amended vs. nonamended soils. This process was modeled in laboratory incubation by applying water, ammonium sulfate, heifer (HEI), or dairy cow (COW) slurry between 1 and 4 times (at Day 0, 84, 168, and 252) to soils of contrasting textures [sandy-loam (SL) and clay-loam (CL)]. Respired CO2 was measured 6 to 10 times after each application along the trial period. Results showed daily respiration rates decreased as application frequency increased and that rates were significantly higher in slurry-amended, compared to control treatments. Furthermore, the contribution of slurry-derived CO2 respiration increased as application frequency rose (from 37 to 68% between the first and fourth applications of HEI and from 58 to 80%, respectively, of COW). The labile fraction of potentially mineralizable slurry C, estimated with a first-order kinetic decomposition model, was also increased with application frequency. The two slurries differed in potentially mineralizable C during the 84 d after the application events. However, there were no differences between the two slurries in the potential mineralizable C (1.43% of applied C) that contributed to respiration after 84 d of application. This small residual effect has never been quantified before in an incubation experiment. This small residue C is very important to farm practices in which slurries are continuously applied for decades.

Ammonia emission from a permanent grassland on volcanic soil after the treatment with dairy slurry and urea

Ammonia (NH3) is an air pollutant largely emitted from agricultural activities including the application of livestock manures and fertilizers to grassland. This gas has been linked with important negative impacts on natural ecosystems. In southern Chile, the use of inorganic and organic fertilizers (e.g. slurries) has increased in cattle production systems over recent years, heightening the risk of N losses to the wider environment. The objectives of this study were to evaluate on permanent grasslands on a volcanic ash soil in southern Chile: 1) the N loss due to NH3 volatilization following surface application of dairy slurry and urea fertilizer; and 2) the effect of a urease inhibitor on NH3 emissions from urea fertilizer application. Small plot field experiments were conducted over spring, fall, winter and summer seasons, using a system of wind tunnels to measure ammonia emissions. Ammonia losses ranged from 1.8 (winter) to 26.0% (fall) and 3.1 (winter) to 20.5% (summer) of total N applied for urea and slurry, respectively. Based on the readily available N applied (ammoniacal N for dairy slurry and urea N for urea fertilizer), losses from dairy slurry were much greater, at 16.1 and 82.0%, for winter and summer, respectively. The use of a urease inhibitor proved to be an effective option to minimize the N loss due NH3 volatilization from urea fertilizer, with an average reduction of 71% across all seasons. The results of this and other recent studies regarding N losses suggest that ammonia volatilization is the main pathway of N loss from grassland systems in southern Chile on volcanic ash soils when urea and slurry are used as an N source. The use of good management practices, such as the inclusion of a urease inhibitor with urea fertilizer could have a beneficial impact on reducing N losses due NH3 volatilization and the environmental and economic impact of these emissions.

Effect of dairy slurry application rate and forage type on production, soil nutrient status and nitrogen‐use efficiency

AbstractSeven forage types (diploid and tetraploid perennial ryegrass, Italian ryegrass and hybrid ryegrass, a low‐input mixture of perennial ryegrass, cocksfoot, timothy and meadow fescue, a mixture of perennial ryegrass and white clover, and monoculture of red clover) were sown in late July 2004. Each received one of four rates of dairy cattle slurry in three annual applications by trailing shoe, which supplied average nitrogen (N) inputs of 0·0, 114·9, 204·8 and 301·2 kg N ha−1 annum−1. Treatments were cut either three or four times annually over four years. Average dry‐matter yield (DM) response to slurry N was 15·6 kg DM kg−1 N. Lowest recovery of slurry N was in the second application each year (after first cut). The data suggest that slurry applied to Italian ryegrass, and also to swards containing legumes on soils with high phosphorus content, will produce a lower DM response to slurry N and result in a lower slurry N recovery than on swards of perennial ryegrass or cocksfoot‐dominant low‐input mixtures. Apparent recovery of slurry N was low at the second cut, especially when first‐cut yields had been high. To maximize slurry N recovery, application to regrowths with potentially slow rates of growth or high legume content should be avoided.

Effects of pig and dairy slurry application on N and P leaching from crop rotations with spring cereals and forage leys

Two crop rotations dominated by spring cereals and grass/clover leys on a clay soil were studied over 2 years with respect to nitrogen (N) and phosphorus (P) leaching associated with pig or dairy slurry application in April, June and October. Leaching losses of total N (TN), total P (TP), nitrate-N and dissolved reactive P (DRP) were determined in separately tile-drained field plots (four replicates). Mean annual DRP leaching after October application of dairy slurry (17 kg P ha−1) to growing grass/clover was 0.37 kg ha−1. It was significantly higher than after October application of pig slurry (13 kg ha−1) following spring cereals (0.16 kg ha−1) and than in the unfertilised control (0.07 kg P ha−1). The proportion of DRP in TP in drainage water from the grass/clover crop rotation (35 %) was higher than from the spring cereal rotation (25 %) and the control (14 %). The grass/clover rotation proved to be very robust with respect to N leaching, with mean TN leaching of 10.5 kg ha−1 year−1 compared with 19.2 kg ha−1 year−1 from the cereal crop rotation. Pig slurry application after cereals in October resulted in TN leaching of 25.7 kg ha−1 compared with 7.0 kg ha−1 year−1 after application to grass/clover in October and 19.1 kg ha−1 year−1 after application to spring cereals in April. In conclusion, these results show that crop rotations dominated by forage leys need special attention with respect to DRP leaching and that slurry application should be avoided during wet conditions or combined with methods to increase adsorption of P to soil particles.

Nutrient and microbial loss in relation to timing of rainfall following surface application of dairy farm manure slurries to pasture

This study investigated nutrient and faecal microbe (Escherichia coli) loss in surface runoff following application of dairy manure slurry to intact soil monoliths. Time between manure slurry application and first simulated rainfall event varied from 0 to 20 days. Manure slurries of varying dry matter (DM) content, ranging from 3 to 14%, were also investigated. Results indicated that phosphorus (P), nitrogen (N) and E. coli concentrations decreased with time since application because of chemical and physical breakdown of the manure. Greatest risk to water quality occurred when rainfall was received within 2 days of manure slurry application. When the period between manure slurry application and first rainfall event was ≥10 days, concentrations of N, P and faecal microbes was generally similar to those from dairy grazed pasture. Variation in slurry DM content appears to have little effect on measured runoff concentrations. Results suggest that manure slurries should be applied ≥2 days before rainfall events likely to cause surface runoff in order to limit nutrient and faecal microbe loss when applying manure slurries.

Ammonia volatilization following dairy slurry application to a permanent grassland on a volcanic soil

Agriculture is the largest source of ammonia (NH3) emission to the atmosphere. Within the agricultural sector, the application of slurry to grasslands as fertilizer is one of the main emission sources. This is a common practice in southern Chile, where most dairy production systems are grazing-based. In Chile, there are few published data of gaseous emissions following slurry application to grassland. The aim of this study was to evaluate NH3 volatilization following dairy slurry application to a permanent grassland on an Andosol soil. Ammonia volatilization was measured in four field experiments (winters of 2009 and 2011 and early and late springs of 2011) using a micrometeorological mass balance method with passive flux samplers following dairy slurry application at a target rate of 100 kg total N ha−1. The accumulated N loss was equivalent to 7, 8, 16 and 21% of the total N applied and 22, 34, 88 and 74% of total ammoniacal nitrogen (TAN) applied for winters 2009 and 2011, and early and late spring 2011, respectively. Ammonia emission rates were high immediately after application and declined rapidly with time, with more than 50% of the total emissions within the first 24 h. Losses were highly influenced by environmental conditions, increasing with temperature and lack of rainfall. Taking into consideration the low N losses via leaching and nitrous oxide emissions reported for the study area, results indicate that NH3 volatilization is the main pathway of N loss in fertilized grasslands of southern Chile. However, dairy slurry application could be an important source of nutrients, if applied at a suitable time, rate and using an appropriate technique, and if soil and climate conditions are taken into consideration. This could improve N use efficiency and reduce N losses to the wider environment.

Low nitrogen leaching losses following a high rate of dairy slurry and urea application to pasture on a volcanic soil in Southern Chile

Dairy slurry is an important plant nutrient source. However, mismanagement (e.g. high application rate) can lead to nutrient losses to the wider environment. There are few data on slurry management and its effect on nitrogen (N) losses specific to Southern Chile, although existing studies suggest that N leaching on volcanic Chilean soils might be expected to be low. The objective of this study was to evaluate the effect of heavy dairy slurry application on N leaching losses and compare it with an inorganic fertiliser on a volcanic soil of Southern Chile. A field experiment was carried out at the Agricultural Research Institute, Remehue Research Centre, on a volcanic soil of Southern Chile (40°35′S, 73°12′W) from March 2008 to March 2010. There were two N application treatments, with a target application rate of 400kgNha−1yr−1 as either dairy slurry (S) or urea (U) split into four even applications over the year. Additionally, a control (C) treatment with no N addition was included. N leaching was measured using ceramic suction cups (3 per plot), with samples taken every 100mm of drainage during the drainage season. Despite the high N rate and application time, N leaching losses were small with no significant differences between treatments in either year (P>0.05). Concentrations of NO3−–N for each sampling period never exceeded c. 5.5mgL−1 and annual mean values were below 0.5mgL−1 for all treatments. Cumulative N leaching losses were small at 1.4 and 1.2kgha−1yr−1 (C), 2.8 and 4.2kgha−1yr−1 (S) and 2.4 and 3.3kgha−1yr−1 (U) for 2008 and 2009, respectively. We suggest that this could be explained mainly by the unique N retention properties of volcanic soils in Southern Chile and/or gaseous N losses.