Dairy Slurry Research Articles

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.

Potential use of anaerobically digested manure slurry to suppress Phytophthora root rot of chilli pepper

Anaerobic digestion is a promising way to treat the large amounts of animal manures produced from animal husbandry in terms of efficient recovery of energy by the anaerobic digestion and of more sustained use of the slurries. Side effects such as suppression of soil borne diseases are not yet well investigated and understood. The objective of the study was to evaluate the potential use of anaerobically digested slurry (ADS) to suppress Phytophthora capsici, the causative agent of Phytophthora root rot of chilli pepper. Mycelial growth and zoospore germination of P. capsici were inhibited by ADS and application of ADS significantly reduced the disease incidence under bioassay conditions. The percentage of reduction in zoospore germination of P. capsici and disease incidence by anaerobically digested pig slurry (ADP) were significantly greater than anaerobically digested dairy slurry (ADD). Filter-sterilization reduced disease suppression only to a certain degree. Exogenous applied ammonium and humic substances (HS) isolated from ADS suppressed P. capsici and the percentages of inhibition of hyphal growth and zoospore germination by HS extracted from ADP were greater than those derived from ADD. It is hypothesized that that the better control of Phytophthora root rot by ADP was attributed to the higher concentration of ammonium and the particular structure of HS.

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.

Seasonal dynamics and turnover of microbial phosphorusin a permanent grassland

Microbial activity is known to be high under permanent grassland, but consequences for soil phosphorus (P) dynamics and availability are not well understood. Our main objective was to assess the microbial P turnover derived from the seasonal fluctuations in microbial P (measured as hexanol-labile P (Phex) at 13 sampling times during 9 months) in a permanent grassland in Switzerland as affected by different P fertilization treatments (P inputs of 0 (NK) or 17 kg P ha−1 year−1 in the form of superphosphate (NPK) or dairy slurry (DS)). Plant P uptake, available inorganic P measured as resin-extractable P (Pres), potential organic P mineralization indicated by acid phosphomonoesterase activity and climatic conditions were also recorded. Despite significant differences in plant P uptake and Pres (NPK > DS > NK), the turnover rate of Phex was similar in all treatments (approximately once per growing season). Thus, the seasonal P flux through Phex was similar to the stock of Phex, which was about 18, 25 and 37 kg P ha−1 in NK, NPK and DS, respectively, and larger than the corresponding seasonal plant P uptake of 6, 17 and 12 kg P ha−1. The estimate of Phex turnover based on seasonal dynamics did not confirm previous tracer-based findings of a much faster Phex turnover under low availability of inorganic P, and the magnitude of Phex turnover depended on the number of sampling points taken into account. Fluctuations in Pres and Phex were related to soil moisture and indicated competition between plants and microorganisms for available P.

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.

The potential of algae blooms to produce renewable gaseous fuel

Ulva lactuca (commonly known as sea letuce) is a green sea weed which dominates Green Tides or algae blooms. Green Tides are caused by excess nitrogen from agriculture and sewage outfalls resulting in eutrophication in shallow estuaries. Samples of U. lactuca were taken from the Argideen estuary in West Cork on two consecutive years. In year 1 a combination of three different processes/pretreatments were carried out on the Ulva. These include washing, wilting and drying. Biomethane potential (BMP) assays were carried out on the samples. Fresh Ulva has a biomethane yield of 183LCH4/kgVS. For dried, washed and macerated Ulva a BMP of 250LCH4/kgVS was achieved. The resource from the estuary in West Cork was shown to be sufficient to provide fuel to 264 cars on a year round basis. Mono-digestion of Ulva may be problematic; the C:N ratio is low and the sulphur content is high. In year 2 co-digestion trials with dairy slurry were carried out. These indicate a potential increase in biomethane output by 17% as compared to mono-digestion of Ulva and slurry.

Nitrogen management strategies in organic winter oilseed rape (Brassica napus L.) production

The efficiency of four different organic fertilisers applied to winter oilseed rape, before (early) or at the beginning of regrowth in spring (normal application time), was studied in two row spacing systems of 12 and 48 cm with inter row hoeing to provide strategies to optimise spring nitrogen (N) fertilisation to organic winter oilseed rape. Six annual field experiments were performed during 2005–2008 in south central Sweden. The following amendments, i.e., Vinass from yeast production, Biofer meat and bone meal, dairy slurry and chicken manure, were applied at a rate corresponding to 100 kg N ha−1. Crop N uptake, seed yield and oil content indicated greater and earlier N availability of Vinass after application compared with the other amendments. Yield increased by 1,300 kg ha−1 at early spring application (27 March) of Vinass and by 700 kg ha−1 when applied at normal application time (18–26 April). The yield increase was 400 kg ha−1 regardless of application time of Biofer, chicken manure and dairy slurry. The substantially greater yield increase in the Vinass application in relation to the other fertilisers demonstrated the yield potential when N is available earlier. The smaller effect on the yield by the other organic amendments indicated that the N release was not synchronised with the crop demand, and available too late during crop development to affect yield or less N was available due to N losses. Consequently, only Vinass can be recommended for spring application. The two row spacing systems tested can both be recommended, since yield levels were similar.

Influence of animal slurries composition and relative particle size fractions on the C and N mineralization following soil incorporation

Animal slurries are often applied to agricultural soils as a source of nutrients and organic matter to maintain or improve soil fertility. The degradation in soil of the slurries-derived carbon (C) and nitrogen (N) has been studied in previous works but there is still little information about the influence of their particle size fractions on such dynamics. Two aerobic incubations (126 days), using a sandy loamy soil amended with pig and dairy slurry and their relative four particle size fractions obtained by sieving (>2000 μm, 2000–500 μm, 500–100 μm, <100 μm), were simultaneously performed, to investigate the effects of the slurries composition and respective particle size fractions on the soil C and N mineralization/immobilization processes. Our results showed that the higher amounts of recalcitrant C were present in the grossest fractions of both slurries, while the finest fractions presented the highest amounts of ready degradable C, suggesting that the carbon speciation is related with the particle size of the fractions. In both slurries, the finest fractions (<100 μm) led to the highest N availability values in soil, being the slurries particle size inversely correlated with the N availability. N availability in soil is also related with the C and N speciation in each slurry type. Results show that, for a same application rate, dairy slurry should be more efficient to increase soil OM content than pig slurry. However, pig slurry led to a higher availability of mineral N in soil (920 mg g−1 of the total N applied against 420 mg g−1 in dairy slurry).

Gaseous Nitrogen and Bacterial Responses to Raw and Digested Dairy Manure Applications in Incubated Soil

A study was conducted under laboratory conditions to compare rates of nitrous oxide (N(2)O) and ammonia (NH(3)) emissions when soil was amended with anaerobically digested dairy manure slurry containing <30% food byproducts, raw dairy manure slurry, or urea. Slurries were applied via surface and subsurface methods. A second objective was to correlate genes regulating nitrification and denitrification with rates of N(2)O production, slurry treatment, and application method. Ammonia volatilization from incubated soil ranged from 140 g kg(-1) of total N applied in digested slurry to 230 g kg(-1) in urea. Subsurface application of raw dairy manure slurry decreased ammonia volatilization compared with surface application. Anaerobic digestion increased N(2)O production. Cumulative N(2)O loss averaged 27 g kg(-1) of total N applied for digested slurry, compared with 5 g kg(-1) for raw dairy slurry. Genes of interest included a 16S rRNA gene selective for β-subgroup proteobacterial ammonia-oxidizers, amoA, narG, and nosZ quantified with quantitative polymerase chain reaction (qPCR) and real-time polymerase chain reaction (RT-PCR). Application of anaerobically digested slurry increased nitrifier and denitrifier gene copies that correlated with N(2)O production. Expression of all genes measured via mRNA levels was affected by N applications to soil. This study provides new information linking genetic markers in denitrifier and nitrifier populations to N(2)O production.

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.

Relationships between Dairy Slurry Total Solids, Gas Emissions, and Surface Crusts

Livestock slurry storages are sources of methane (CH₄), nitrous oxide (NO₂), and ammonia (NH₃) emissions. Total solids (TS) content is an indicator of substrate availability for CH₄ and N₂O production and NH₃ emissions and is related to crust formation, which can affect these gas emissions. The effect of TS on these emissions from pilot-scale slurry storages was quantified from 20 May through 16 Nov. 2010 in Nova Scotia, Canada. Emissions from six dairy slurries with TS ranging from 0.3 to 9.5% were continuously measured using flow-through steady-state chambers. Methane emissions modeled using the USEPA methodology were compared with measured data focusing on emissions when empty storages were filled, and retention times were >30 d with undegraded volatile solids (VS) remaining in the system considered available for CH₄ production (VS carry-over). Surface crusts formed on all the slurries. Only the slurries with TS of 3.2 and 5.8% were covered completely for ∼3 mo. Nitrous oxide contributed <5% of total greenhouse gas emissions for all TS levels. Ammonia and CH₄ emissions increased linearly with TS despite variable crusting, suggesting substrate availability for gas production was more important than crust formation in regulating emissions over long-term storage. Modeled CH₄ emissions were substantially higher than measured data in the first month, and accounting for this could improve overall model performance. Carried-over VS were a CH₄ source in months 2 through 6. The results of this study suggest that substrate availability regulates emissions over long-term storage and that modifying the USEPA model to better describe carbon cycling is warranted.

Low-Disturbance Manure Incorporation Effects on Ammonia and Nitrate Loss

Low-disturbance manure application methods can provide the benefits of manure incorporation, including reducing ammonia (NH3) emissions, in production systems where tillage is not possible. However, incorporation can exacerbate nitrate (NO3⁻) leaching. We sought to assess the trade-offs in NH3 and NO3⁻ losses caused by alternative manure application methods. Dairy slurry (2006-2007) and liquid swine manure (2008-2009) were applied to no-till corn by (i) shallow (<10 cm) disk injection, (ii) surface banding with soil aeration, (iii) broadcasting, and (iv) broadcasting with tillage incorporation. Ammonia emissions were monitored for 72 h after application using ventilated chambers and passive diffusion samplers, and NO3⁻ leaching to 80 cm was monitored with buried column lysimeters. The greatest NH3 emissions occurred with broadcasting (35-63 kg NH3-N ha⁻), and the lowest emissions were from unamended soil (<1 kg NH-N ha⁻¹). Injection decreased NH-N emissions by 91 to 99% compared with broadcasting and resulted in lower emissions than tillage incorporation 1 h after broadcasting. Ammonia-nitrogen emissions from banding manure with aeration were inconsistent between years, averaging 0 to 71% that of broadcasting. Annual NO3⁻ leaching losses were small (<25 kg NO3-N ha⁻¹) and similar between treatments, except for the first winter when NO3⁻ leaching was fivefold greater with injection. Because NO3⁻ leaching with injection was substantially lower over subsequent seasons, we hypothesize that the elevated losses during the first winter were through preferential flow paths inadvertently created during lysimeter installation. Overall, shallow disk injection yielded the lowest NH3 emissions without consistently increasing NO3⁻ leaching, whereas manure banding with soil aeration conserved inconsistent amounts of N.

Comparison of Denaturing Gradient Gel Electrophoresis and Microarray Technology for Detection of Betaproteobacteria Ammonia-Oxidizing Communities

Methods linking environmental function and microbial community composition are limited by phylogenetic resolution and throughput time. Denaturing gradient gel electrophoresis (DGGE) allows for resolution of ammonia-oxidizing bacteria strains separated by as little as one base pair (bp) in 16S rRNA gene sequence but is low throughput. In contrast, microarrays are high throughput. We have designed a microarray platform to identify the majority of environmental strains of betaproteobacterial ammonia oxidizers using signature oligonucleotide sequences. Seventy-seven target sequences or single-nucleotide polymorphisms (SNP) were derived from 183 betaproteobacterial ammonia oxidizer 16S rRNA gene sequences representing the genera Nitrosospira and Nitrosomonas of the β sub-class of Proteobacteria and the cluster groups of strains within each genera identified using DNA homology values. These sequences were obtained from the National Center for Biotechnology Information database. Templates isolated from pure cultures of betaproteobacterial ammonia oxidizers and soil samples incubated with and without dairy slurry were amplified using primers CTO189f and CTO654r. Amplicons were analyzed via DGGE and microarray hybridization. Mixtures of pure culture strains of betaproteobacterial ammonia oxidizers were used to simulate environmental samples containing a known number of sequences and template concentrations. Our DNA oligonucleotide microarray demonstrated highly specific detection of individual betaproteobacterial ammonia oxidizer strains amplified from pure cultures, model communities, and soil samples and provided resolution of community composition comparable to that of DGGE. High-throughput analyses of betaproteobacterial ammonia oxidizer communities will further our knowledge of their ecology and link process level functions to management practices such as dairy slurry applications and specific strains of betaproteobacterial ammonia-oxidizing bacteria.

Multi-objective optimisation of a model of the decomposition of animal slurry in soil: Tradeoffs between simulated C and N dynamics

To formulate best management practices for animal slurry, it is important to understand and predict its decomposition in the soil. Slurry decomposition dynamics can be studied by measuring CO2 fluxes and soil mineral nitrogen concentration during laboratory incubations and subsequently calibrating a simulation model. Carbon and nitrogen dynamics are linked and both should be properly simulated. In this work we wanted to identify the tradeoffs between errors in the simulation of C respiration and of soil inorganic N concentration.We optimised six parameters of CN-SIM (a mechanistic dynamic simulation model), using data of respired C and soil inorganic N measured during a 180-day laboratory incubation of five dairy slurries on three soils. Optimisation was carried out with a multi-objective genetic algorithm (NSGA-II), by minimising the Relative Root Mean Squared Error (RRMSE) between observations and simulations.The simulation of C respiration was frequently conflicting with the simulation of inorganic N, i.e. low RRMSE–CO2 corresponded with high RRMSE–N and vice versa. When minimising RRMSE–CO2 a set of parameters was obtained that enhanced microbial N immobilisation and reduced the turnover of the organic pools, to match the observed decrease of inorganic N in the 28 days after slurry addition to soil. Remineralisation occurring in the following 150 days caused a marked overestimation of inorganic N. When minimising RRMSE–N, the optimisation provided parameters that strongly reduced remineralisation of immobilised N by markedly diminishing C respiration, with a consequent underestimation of CO2 emission. A modified version of the model, containing a simple implementation of denitrification and of clay fixation/release of ammonium, performed better than the original model for most treatments.We conclude that the mineralisation/immobilisation turnover in the model is not fully adequate to represent C and N dynamics. We also discuss the implementation of changes (time-varying microbial efficiency and C to N ratio; simulation of ammonium clay fixation and emissions of N2/N2O) to improve model performance.

Links among Nitrification, Nitrifier Communities, and Edaphic Properties in Contrasting Soils Receiving Dairy Slurry

Soil biotic and abiotic factors strongly influence nitrogen (N) availability and increases in nitrification rates associated with the application of manure. In this study, we examine the effects of edaphic properties and a dairy (Bos taurus) slurry amendment on N availability, nitrification rates and nitrifier communities. Soils of variable texture and clay mineralogy were collected from six USDA-ARS research sites and incubated for 28 d with and without dairy slurry applied at a rate of ~300 kg N ha(-1). Periodically, subsamples were removed for analyses of 2 M KCl extractable N and nitrification potential, as well as gene copy numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Spearman coefficients for nitrification potentials and AOB copy number were positively correlated with total soil C, total soil N, cation exchange capacity, and clay mineralogy in treatments with and without slurry application. Our data show that the quantity and type of clay minerals present in a soil affect nitrifier populations, nitrification rates, and the release of inorganic N. Nitrogen mineralization, nitrification potentials, and edaphic properties were positively correlated with AOB gene copy numbers. On average, AOA gene copy numbers were an order of magnitude lower than those of AOB across the six soils and did not increase with slurry application. Our research suggests that the two nitrifier communities overlap but have different optimum environmental conditions for growth and activity that are partly determined by the interaction of manure-derived ammonium with soil properties.

Comparison of Raw Dairy Manure Slurry and Anaerobically Digested Slurry as N Sources for Grass Forage Production

We conducted a 3-year field study to determine how raw dairy slurry and anaerobically digested slurry (dairy slurry and food waste) applied via broadcast and subsurface deposition to reed canarygrass (Phalaris arundinacea) affected forage biomass, N uptake, apparent nitrogen recovery (ANR), and soil nitrate concentrations relative to urea. Annual N applications ranged from 600 kg N ha−1in 2009 to 300 g N ha−1in 2011. Forage yield and N uptake were similar across slurry treatments. Soil nitrate concentrations were greatest at the beginning of the fall leaching season, and did not differ among slurry treatments or application methods. Urea-fertilized plots had the highest soil nitrate concentrations but did not consistently have greatest forage biomass. ANR for the slurry treatments ranged from 35 to 70% when calculations were based on ammonium-N concentration, compared with 31 to 65% for urea. Slurry ANR calculated on a total N basis was lower (15 to 40%) due to lower availability of the organic N in the slurries. No consistent differences in soil microbial biomass or other biological indicators were observed. Anaerobically digested slurry supported equal forage production and similar N use efficiency when compared to raw dairy slurry.

Fertilizer equivalent value and upper limit value of dairy slurry applied in renovating sward in Hokkaido

Fertilizer equivalent value and upper limit value of dairy slurry applied in renovating sward in Hokkaido

Dissolved phosphorus composition of grassland leachates following application of dairy‐slurry size fractions

AbstractAppropriate management of P from slurry can increase crop production and decrease nutrient loss to water bodies. The present study examined how the application of different size fractions of dairy slurry influenced the quantity and composition of P leached from grassland in a temperate climate. Soil blocks were amended (day 0 = start of the experiment) with either whole slurry (WS), the &gt; 425 μm fraction (coarse slurry fraction, CSF), the &lt; 45 μm slurry fraction (fine liquid slurry fraction, FLF), or not amended, i.e., the control soil (CON). Deionized water was added to the soil blocks to simulate six sequential rainfall events, equivalent to 250 mm (day 0.2, 1.2, 4.2, 11.2) or 500 mm of rainfall (day 18.2 and 25.2), with leachates collected the following day. The results showed that total dissolved P (TDP), dissolved reactive P (DRP), dissolved unreactive P (DUP), orthophosphate, phosphomonoester, and pyrophosphate concentrations generally decreased with the increasing number of simulated rain events. Total dissolved P was leached in the following order WS &gt; FLF ≈ CSF &gt; CON. Dissolved organic C was correlated with TDP, DRP, and DUP in leachates of all treatments. The highest concentrations of dissolved phosphomonoesters and pyrophosphate (147 μg P L–1 and 57 μg P L–1, respectively) were detected using solution 31P‐NMR spectroscopy in the WS leachates. Overall, there were significant differences observed between slurry treatments (e.g., relative contributions of inorganic P vs. organic P of dissolved P in leachates). Differences were independent from the rate at which slurry P was applied, because the highest dissolved P losses per unit of slurry P applied were measured in the FLF, i.e., the treatment that received the smallest amount of P. We conclude that the specific particle‐size composition of applied slurry influences dissolved P losses from grassland systems. This information should be taken in account in farm‐management approaches which aim to minimizing dissolved slurry P losses from grassland systems.

Codigested dairy slurry as a phosphorus and nitrogen source for Zea mays L. and Amaranthus cruentus L.

AbstractResidues from biogas production contain essential plant nutrients such as nitrogen (N), phosphorus (P), and potassium (K) but also organic matter, and should be recycled in crop production. For efficient re‐use as fertilizers, the availability of nutrients for crops and the effect of the residues on soil fertility need to be evaluated. Focusing on the element P, we compared effects of codigested slurry with dairy slurry, highly soluble mineral NPK fertilizer, and a control without any P supply (NK). Codigested slurry used in this experiment was based on anaerobic digestion of dairy slurry, maize silage, and wheat grain. The fertilizing effects were tested in an 8‐week pot experiment on a sandy and a loamy soil using two crop species (Zea mays L., Amaranthus cruentus L.). The plant P uptake was up to 64% greater in the slurry treatments than in the treatment without P. The effect of codigested slurry on P uptake was comparable to that of dairy slurry and mineral P. Plant N uptake from codigested slurry was lower than that from mineral N (NK, NPK), but tended to be higher than from dairy slurry. The water‐soluble and double lactate–soluble P content of the soil was lower in the slurry treatments than in the mineral‐P treatments and accompanied by higher contents of microbial‐bound P. Differences between both organic fertilizers were detected for dehydrogenase activity which was up to 32% lower in soils fertilized with codigested slurry than it was in soils fertilized with dairy slurry. Our results indicate that codigestion of slurries in biogas plants does not substantially alter their fertilizer value as P and N sources for crops.