Dairy Manure Application Research Articles

Matrix‐based Fertilizers Reduce Nutrient and Bacterial Leaching after Manure Application in a Greenhouse Column Study

We tested the efficacy of matrix-based fertilizers (MBFs) to reduce Escherichia coli and Enterococcus spp., NH(4), NO(3), dissolved reactive phosphorus (DRP), and total phosphorus (TP) in leachate and soil after dairy manure application in greenhouse column studies. The MBFs are composed of inorganic N and P in compounds that are relatively loosely bound (MBF8) to more tightly bound (MBF9) mixtures using combinations of starch, cellulose, lignin, Al(2)(SO(4))(3)18H(2)O, and/or Fe(2)(SO(4))(3)3H(2)O to create a matrix that slowly releases the nutrients. One day after the first dairy manure application, E. coli numbers were greater in leachate from control columns than in leachate from columns receiving MBFs. After three dairy manure applications, E. coli and Enterococcus spp. numbers in leachates were not consistently different between controls and columns receiving MBFs. When MBF8 was applied to the soil, the total amount of DRP, TP, NH(4), and NO(3) in leachate was lower than in the control columns. Bermudagrass receiving MBFs had greater shoot, root, and total biomass than grass growing in the control columns. Grass shoot, root, and total biomass did not differ among columns receiving MBFs. Nitrogen and phosphorus bound to the Al(2)(SO(4))(3)18H(2)O or Fe(2)(SO(4))(3)3H(2)O-lignin-cellulose matrix become gradually available to plants over the growing season. The MBF8 and MBF9 formulations do not depend on organic or inorganic coatings to reduce N and P leaching and have the potential with further testing and development to provide an effective method to reduce N and P leaching from soils treated with animal waste.

Split Application of Nitrogen vs. Dairy Manure on Temperate Perennial Grasses

Split Application of Nitrogen vs. Dairy Manure on Temperate Perennial Grasses

Soil and runoff response to dairy manure application on New Mexico rangeland

Manure disposal is a major challenge for the fast-growing dairy industry in New Mexico. There are currently over 355,000 milking cows in the state and limited cropland on which to use the manure generated by these cows. On the other hand, 80% of the state lands classified as rangelands are suffering from a lack of organic matter and nutrients. Application of dairy manure to rangelands could serve a dual purpose: (1) manure disposal from dairies and (2) soil amendment to improve soil characteristics and promote herbaceous production. Manure was applied at two rates according to phosphorus (P) content: (1) a recommended (light) rate (54 kg P ha −1) to enhance blue grama growth and (2) a gross over-application (heavy) rate (493 kg P ha −1) to determine the effects on runoff and soil properties. Light applications enhanced soil properties including decreased sediment runoff, increased soil organic matter, increased extractable P, and increased soil moisture, whereas heavy applications increased soil salinity, sodium adsorption ratio, and runoff water. Dairy manure can be safely applied at light rates to conserve and enhance rangeland soil properties and their herbaceous productivity. Manure disposal at heavy rates are unsafe. Further study is required to find out if other safe disposal exists between the light and heavy treatments.

Predicting soil organic carbon sequestration in the southeastern United States with EPIC and the soil conditioning index

The Soil Conditioning Index (SCI) is a relatively simple model that predicts the consequences of cropping systems and tillage practices on the status of soil organic matter in a field. The SCI is administered by the USDA Natural Resources Conservation Service to predict a positive or negative trend in soil organic matter based on knowledge of field operations, erosion loss, and organic matter inputs but has not been adequately tested against long-term management conditions that could affect soil organic carbon (SOC) dynamics. We calibrated the Environmental Policy Integrated Climate model (EPIC v. 3060) for three major land resource areas in the southeastern United States using 5 to 10 years of measured SOC data to develop a predictive relationship of SOC for 50-year simulations with SCI values. Management systems included conventional tillage and no tillage in (1) a two-year rotation of wheat (Triticum aestivum L.)/sorghum (Sorghum bicolor [L.] Moench)-corn (Zea mays L.) with low and high fertilizer application on a Blackland Prairie site in Texas, (2) a two-year rotation of corn-cotton (Gossypium hirsutum L.) with and without dairy manure application on a Coastal Plain site in Alabama, and (3) in monoculture cotton on a Mississippi Upland site. Across sites and fertilizer conditions, SOC sequestration during 50 years of using EPIC was greater under no tillage (9.5 Mg ha-1 [4.2 tn ac-1]) than under conventional tillage (6.3 Mg ha-1 [2.8 tn ac-1]) (p

Pathogen Prevalence and Influence of Composted Dairy Manure Application on Antimicrobial Resistance Profiles of Commensal Soil Bacteria

Composting manure, if done properly, should kill pathogenic bacteria such as Salmonella and Escherichia coli O157:H7, providing for an environmentally safe product. Over a 3-year period, samples of composted dairy manure, representing 11 composting operations (two to six samples per producer; 100 total samples), were screened for Salmonella and E. coli O157:H7 and were all culture negative. Nonpathogenic bacteria were cultured from these compost samples that could theoretically facilitate the spread of antimicrobial resistance from the dairy to compost application sites. Therefore, we collected soil samples (three samples per plot; 10 plots/treatment; 90 total samples) from rangeland that received either composted dairy manure (CP), commercial fertilizer (F), or no treatment (control, CON). Two collections were made appoximately 2 and 7 months following treatment application. Soil samples were cultured for Pseudomonas and Enterobacter and confirmed isolates subjected to antimicrobial susceptibility testing. Three species of Enterobacter (cloacae, 27 isolates; aeroginosa, two isolates; sakazakii, one isolate) and two species of Pseudomonas (aeruginosa, 11 isolates; putida, seven isolates) were identified. Five Enterobacter isolates were resistant to ampicillin and one isolate was resistant to spectinomycin. All Pseudomonas isolates were resistant to ampicillin, ceftiofur, florfenicol, sulphachloropyridazine, sulphadimethoxine, and trimethoprim/sulfamethoxazole and most isolates were resistant to chlortetracycline and spectinomycin. Pseudomonas isolates were resistant to an average of 8.6, 7.9, and 8 antibiotics for CON, CP, and F treatments, respectively. No treatment differences were observed in antimicrobial resistance patterns in any of the soil isolates examined. Results reported herein support the use of composted dairy manure as an environmentally friendly soil amendment.

Case Study: On-Farm Evaluation of Liquid Dairy Manure Application Methods to Reduce Ammonia Losses

<h2>ABSTRACT</h2> The volatilization of NH₃ from land-applied manure is not only a loss of valuable N, but also an air quality concern because NH₃ plays a role in the formation of airborne particulate matter, which can be a health hazard. The relative differences in potential NH₃ losses from land application of liquid dairy manure were determined via 3 methods: surface application, Aerway incorporation (shallow incorporation with a rolling tine aerator), and subsurface injection. Liquid manure was applied at a rate of 190m³/ha on 4 farms with average N and P application rates ranging from 28 to 130kg N/ha and 6 to 36kg P/ha, respectively. Average NH₃ concentrations were measured with passive samplers for 3 d after manure application and ranged from 0.03 to 0.21mg NH₃-N/m³ There were main effects of sampler height, day, and application method. The greatest NH₃ concentrations occurred during the first 48h after manure application. Concentrations of NH₃ measured at 1m (averaged over 48 h) indicated that surface and Aerway applications had the greatest concentrations (0.16 and 0.17mg NH₃-N/m³, respectively) whereas subsurface injection of manure resulted in a 67% decrease in NH₃ concentration, which was similar to the control plots (0.06 and 0.04mg NH₃-N/m³, respectively). Subsurface injection was the best method of liquid manure application for minimizing NH₃ losses.

Geographic information systems (GIS) based model of dairy manure transportation and application with environmental quality consideration

Survey information was used to develop a minimum cost spatial dairy manure transportation model where environmental quality and crop nutrient requirements were treated as constraints. The GIS model incorporated land use types, exact locations of dairy farms and farmlands, road networks, and distances from each dairy farm to receiving farmlands to identify dairy manure transportation routes that minimized costs relative to environmental and other constraints. Our analyses indicated that the characteristics of dairy manure, its bulk and relatively low primary N, P(2)O(5) and K(2)O nutrient levels limit the distribution areas or distances between the farms and the land over which the manure can be economically spread. Physical properties of the land limit the quantities of nutrients that can be applied because of excess nutrient buildup in soil and potential to harm nearby waterbodies and downstream people and places. Longer distances between dairy and farmland favor the use of commercial fertilizers due to the high cost of manure transportation. At $0.08 per ton per km transportation cost, the optimal cut-off distances for dairy manure application is 30km for N and 15km each for P(2)O(5) and K(2)O consistent rules. An analysis of dairy manure application to different crop types suggest that, on average, 1ha of land requires 61 tons of dairy manure to meet the recommended N, P(2)O(5) and K(2)O needs.

Application of manure to no-till soils: phosphorus losses by sub-surface and surface pathways

The acceleration of surface water eutrophication attributed to agricultural runoff has focused attention on manure management in no-till. We evaluated losses of phosphorus (P) in sub-surface and surface flow as a function of dairy manure application to no-till soils in north-central Pennsylvania. Monitoring of a perennial spring over 36 months revealed that dissolved reactive P (DRP) concentrations increased 3- to 28-fold above background levels whenever manure was broadcast to nearby field soils. A study conducted with 30-cm deep intact soil cores indicated that incorporation of manure by tillage lowered P loss in leachate relative to broadcast application, presumably due to the destruction of preferential flow pathways. More P was leached from a sandy loam than a clay loam soil, although differences between soils were not as great as differences between application methods. In contrast, rainfall simulations on 2-m2 field runoff plots showed that total P (TP) losses in surface runoff differed significantly by soil but not by application method. Forms of P in surface runoff did change with application method, with DRP accounting for 87 and 24% of TP from broadcast and tilled treatments, respectively. Losses of TP in leachate from manured columns over 7 weeks (0.22–0.38 kg P ha−1) were considerably lower than losses in surface runoff from manured plots subjected to a single simulated rainfall event (0.31–2.07 kg TP ha−1). Results confirm the near-term benefits of incorporating manure by tillage to protect groundwater quality, but suggest that for surface water quality, avoiding soils prone to runoff is more important.

Effects of Dairy Manure Compost and Supplemental Inorganic Fertilizer on Coastal Bermudagrass

Management strategies for using raw and composted dairy manures on perennial forages are not well defined. This study compared the effects of raw or composted dairy manure alone, or in combination with supplemental inorganic fertilizers (IFs), on ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] yield. Composted manure was split applied with 14.5 Mg ha−1 in 2002 and 2003 for a total of 29 Mg ha−1 (C1), or single applications of raw dairy manure (M) at 54 Mg ha−1, or composted manure at 29 (C2) or 58 (C3) Mg ha−1 were applied in 2002. These treatments were compared with an IF check (112 kg N ha−1 cutting−1 plus 49 kg P ha−1 yr−1 plus 93 kg K ha−1 cutting−1) and an untreated check (UC). Selected compost and manure plots also received supplemental inorganic N at rates of 0, 56, 84, and 112 kg ha−1 cutting−1, or 112 kg N ha−1 cutting−1 plus inorganic P (49 kg P ha−1 yr−1) or K (93 kg K ha−1 cutting−1). Maximum yields were obtained with 56 kg N ha−1 cutting−1 in 2002, and with 84 kg N ha−1 cutting−1 in 2003 and 2004. In 2004, supplemental inorganic P increased forage yields with the lower rate of compost (C2), and supplemental inorganic K increased forage yields of C2 and M treatments compared with the compost or M treatments alone

Assessing manure management strategies through small-plot research and wholefarm modeling

Plot-scale experimentation can provide valuable insight into the effects of manure management practices on phosphorus (P) runoff, but whole-farm evaluation is needed for complete assessment of potential trade offs. Artificially-applied rainfall experimentation on small field plots and event-based and long-term simulation modeling were used to compare P loss in runoff related to two dairy manure application methods (surface application with and without incorporation by tillage) on contrasting Pennsylvania soils previously under no-till management. Results of single-event rainfall experiments indicated that average dissolved reactive P losses in runoff from manured plots decreased by up to 90% with manure incorporation while total P losses did not change significantly. Longer-term whole farm simulation modeling indicated that average dissolved reactive P losses would decrease by 8% with manure incorporation while total P losses would increase by 77% due to greater erosion from fields previously under no-till. Differences in the two methods of inference point to the need for caution in extrapolating research findings. Single-event rainfall experiments conducted shortly after manure application simulate incidental transfers of dissolved P in manure to runoff, resulting in greater losses of dissolved reactive P. However, the transfer of dissolved P in applied manure diminishes with time. Over the annual time frame simulated by whole farm modeling, erosion processes become more important to runoff P losses. Results of this study highlight the need to consider the potential for increased erosion and total P losses caused by soil disturbance during incorporation. This study emphasizes the ability of modeling to estimate management practice effectiveness at the larger scales when experimental data is not available.

Assessing manure management strategies through small-plot research and wholefarm modeling

Plot-scale experimentation can provide valuable insight into the effects of manure management practices on phosphorus (P) runoff, but whole-farm evaluation is needed for complete assessment of potential trade offs. Artificially-applied rainfall experimentation on small field plots and event-based and long-term simulation modeling were used to compare P loss in runoff related to two dairy manure application methods (surface application with and without incorporation by tillage) on contrasting Pennsylvania soils previously under no-till management. Results of single-event rainfall experiments indicated that average dissolved reactive P losses in runoff from manured plots decreased by up to 90% with manure incorporation while total P losses did not change significantly. Longer-term whole farm simulation modeling indicated that average dissolved reactive P losses would decrease by 8% with manure incorporation while total P losses would increase by 77% due to greater erosion from fields previously under no-till. Differences in the two methods of inference point to the need for caution in extrapolating research findings. Single-event rainfall experiments conducted shortly after manure application simulate incidental transfers of dissolved P in manure to runoff, resulting in greater losses of dissolved reactive P. However, the transfer of dissolved P in applied manure diminishes with time. Over the annual time frame simulated by whole farm modeling, erosion processes become more important to runoff P losses. Results of this study highlight the need to consider the potential for increased erosion and total P losses caused by soil disturbance during incorporation. This study emphasizes the ability of modeling to estimate management practice effectiveness at the larger scales when experimental data is not available.

Bacterial Transport from Agricultural Lands Fertilized with Animal Manure

A plot scale study was conducted to determine bacterial transport in runoff from cropland treated with poultry litter and dairy manure applied at phosphorus (P) agronomic rates. Treatments included surface application of dairy manure, surface application of poultry litter, incorporation of dairy manure and control. A rainfall simulator was used to induce runoff 1 and 2 days after manure application. Runoff was analyzed to determine the concentration of indicator bacteria-fecal coliform, Escherichia coli, and Enterococcus. Observed edge-of-field bacterial concentrations were 102 to 105 times higher than Virginia’s in-stream bacteria criteria for primary contact recreation waters. No significant treatment effects were observed on edge-of-field bacteria concentration or yield. Results suggest that the manure application based on agronomic P rates may yield significant bacterial loading to downstream waterbodies if rainfall occurs soon after manure application. This research underscores the need for BMPs that reduce runoff volumes and filter pollutants associated with animal manures.

Soil and Tissue Phosphorus, Potassium, Calcium, and Sulfur as Affected by Dairy Manure Application in a No‐Till Corn, Wheat, and Soybean Rotation

The hypothesis of this study was that surface applied liquid manure may provide sufficient nutrients to silage corn (Zea mays L.), wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.] under a no‐till system in the cool wet climate of Atlantic Canada. A 2‐yr field study was conducted investigating the effect of crop rotation and fertility on P, K, Ca, and S availability to corn silage, spring milling wheat, and soybean in Nova Scotia, Canada. The rotations consisted of all six possible combinations of corn, wheat, and soybean, and the fertility treatments consisted of three rates of liquid dairy manure (LDM1–3) at 32.1, 48.1, and 64.3 Mg ha−1, a mineral fertilizer treatment, and a control (no fertility applied). In general, nutrient availability as measured by Mehlich 3 (M3) was not well correlated with tissue concentration. Tissue S in corn was lower when it was grown after soybean than when grown after wheat, and was highest in the LDM1 and in the control treatments. Rotation × fertility effects observed in the wheat nutrient removals were accountable to similar differences in yield. Wheat uptake of P was significantly affected by fertility, with the highest removal of P occurring in the NPK treatment, which also provided the highest yield. Results indicate that Ca uptake by wheat may be hindered by competition with K, and that K applied in manure at higher rates could build up over time. Potassium recovery in wheat was higher from the inorganic NPK treatment (37%) than from manure (from 16 to 4%). There were few differences in M3 available nutrients in 2001. However in 2002, LDM application resulted in higher M3 concentrations of K and Ca; there was a drop in P availability with the LDM3 (at 64.3 Mg ha−1) application; and S availability was highest at LDM1 and LDM3 (32.1 and 64.3 Mg ha−1, respectively). Further long‐term studies may be needed to determine if surface applied LDM with no incorporation can sustain silage corn, soybean, and wheat nutrient requirements for P, Ca, K, and S, and maintain efficient nutrient use overtime under no‐till conditions.

Dairy Manure Type, Application Rate, and Frequency Impact Plants and Soils

The impacts of dairy rations on manure chemistry, manure N mineralization in soils, and crop N uptake have been evaluated after single manure applications. No information is available on these impacts when manure is applied to soils at different rates and frequencies. Manure from lactating dairy cows (Bos taurus) fed three diets differing in crude protein (CP) content were applied to a Plano (fine‐silty, mixed, superactive, mesic Typic Argiudolls) and a Rosholt (coarse‐loamy, mixed, superactive, frigid Haplic Glossudalfs) soil at two application rates (225 or 450 kg total N ha−1) and three application frequencies (once, twice, or thrice). Oat (Avena sativa L.), sorghum [Sorghum bicolor (L.) Moench] and sorghum ratoon were grown in succession during a 170‐d period. Plant responses to manure from different CP diets were much less than responses due to soil type and manure application rate and frequency. Manure N uptake efficiency by plants was greatest for manure derived from a low‐CP diet than manure derived from either the medium‐ or high‐CP diets. Manure application rate and frequency increased NO3 levels in oat and sorghum shoots, which if used as forage could have detrimental impacts on dairy cow health. No significant differences were measured in second‐crop (sorghum) yield or N uptake due to a previous manure application at either N application rate. Third‐crop (sorghum ratoon) yield and N uptake were significantly increased, however, due to previous manure applications, but only in pots that received two manure applications at the high rate. Longer term, repeated applications of dairy manure derived from different diets at lower rates could provide more pronounced impacts on plants and soils than those observed during this relatively short‐term greenhouse study.

Discharge of Escherichia Coli from Agricultural Surface and Subsurface Drainage Water: Tillage Effects

Drainage water from agricultural fields with applied manure can degrade the bacterial quality of surface and groundwater. The impact of conventional tillage (CT) and zero tillage (ZT) practices on Escherichia coli (E.coli) discharge through artificially drained soils is not well understood. Consequently, two field trials were conducted during 2002–2004. The first trial involved fall applications of beef manure while the second involved spring applications of dairy manure. Both surface and subsurface drainage water were monitored in the first trial while only subsurface drainage water was monitored in the second. Under fall applied beef manure (trial 1), no differences (p > 0.05) were observed in E.coli concentrations (cfu/100 ml) in combined drainage water under both tillage systems. However, during 2003–2004, subsurface drainage water under ZT had higher E.coli concentrations and loads than drainage water under CT. When the combined (surface + subsurface) annual E.coli loads were considered, CT loads were greater than ZT during 2002–2003 with an opposite situation during 2003–2004. Overall, annual E.coli loads were similar under ZT (4.7 × 1010 cfu/ha) and CT (4.8 × 1010 cfu/ha). Spring dairy manure application (trial 2) produced significant (p > 0.03) tillage effect on E.coli loads in subsurface drainage water only during the second year. During the study period, ZT plots (1.55 × 1010 cfu/ha) discharged 5× more E.coli than CT (0.23 × 1010 cfu/ha). A longer duration of ZT practices resulted in higher subsurface flow volumes and subsequently greater loads of E.coli discharge in both trials.

Effects of Dairy Manure and Weed Management on Weed Communities in Corn on Wisconsin Cash-grain Farms

A reason given by cash-grain farmers for not using manure from neighboring livestock operations is that manure may cause greater field weediness. To address this concern, trials were established in corn on 11 cash-grain farms, in which manure from six nearby dairy farms was spread for the first time in at least 10 yr. A split-plot design was used in which manured and nonmanured treatments were established as whole-plots, and split-plot treatments were either with or without the farmer's regular weed control. In the multisite analysis, weed seedling density at the time of corn emergence was not greater in the manured vs. nonmanured treatments. At 7 to 8 wk following planting, weed density was not greater in the manured plots. Just before corn canopy closure, weed biomass also did not differ between manured and nonmanured treatments. Although neither weed species richness nor species diversity differed significantly between manured and nonmanured treatments, these measures did have significant environment-by-manure interactions, indicating that weed species distributions responded differently to manure across the different trial environments. However, farmers' weed control practices were highly successful in both the manured and nonmanured plots. Large portions (280 m2) of all whole plots were visually inspected for introduced weed species after all weed control practices had been completed. The manured treatments did not differ significantly in the set of species observed, suggesting that manure did not introduce new weed species. Thus, this exploratory study showed that, contrary to some farmers' concerns, an application of dairy manure neither increased field weediness nor required alterations in the farmers' weed control programs.Nomenclature: Corn, Zea mays L.

Phosphorus leaching through intact soil cores as influenced by type and duration of manure application

Leaching of phosphorus (P) in manure-amended soils has received increased attention as a significant source of non-point source P pollution. Intact soil cores were collected from fields on a farm in Southern New York to test the effects of long-term dairy or poultry manure application on P leaching. Nine fields were selected (four poultry, four dairy, and one unamended) to represent a broad range of P saturation levels (5.3 to 62.4%) in the topsoil (0–7.5 cm). Water was applied weekly at a rate matching a 1-year return period storm for the study area (230 mm h−1). Dissolved reactive P (DRP) losses in leachate from all soil cores ranged from 0.007 to 0.055 kg P ha−1, except in two fields with long-term histories of dairy and poultry manure application, where losses averaged 0.21 and 0.45 kg P ha−1, respectively. Hydrographs of the field with the dairy manure history suggested preferential flow as an explanation of leachate P enrichment. In the poultry manure amended field, high levels of soil P saturation throughout the profile suggested subsoil P desorption as a factor controlling leachate P. Surface application of dairy manure to the soil cores (167 kg total P ha−1) increased the mean leachate DRP concentration from 1.5 to 10.5 fold. After five leaching events spanning 22 days, DRP concentrations remained 2.0 to 13.4 fold above pre-manure application levels. This study points to saturation of P in subsoils by long-term manure application as a key concern to P loss in leachate and highlights the role of annual manure additions on subsurface P loss potential.

Genetic Variability in Tetany Potential of Orchradgrass as Influenced by Application of Dairy Manure and Chemical Fertilizer

Genetic Variability in Tetany Potential of Orchradgrass as Influenced by Application of Dairy Manure and Chemical Fertilizer

Changes in physical properties of a loess soil in China following two long-term fertilization regimes

A 13-year long-term experiment on the Loess Plateau of China was used to evaluate the effect of two different fertilizer regimes on the soil's physical/hydraulic properties. The fertilizer regimes included (i) control without any fertilizer (C), (ii) applications of chemical fertilizer (NPK), and (iii) applications of chemical fertilizer plus dairy manure (MNPK). Undisturbed soil cores were collected from the field to determine soil water retention curves and hydraulic conductivity (saturated and unsaturated). In addition, gravimetric water content, soil bulk density, porosity and saturated hydraulic conductivity were measured several times during the crop growing season to check seasonal variations. Annual application of manure increased soil water retention at the two soil depths tested (0–5 and 10–15 cm) relative to the control treatment ( P ≤ 0.1), by 13 to 32% at tension ranges from 0 to 300 kPa for the 0–5 cm layer, and by 5 to 19% from 0 to 2 kPa for the 10–15 cm layer. The field soil water content was also significantly increased at 0–10 cm depth ( P ≤ 0.05). Saturated hydraulic conductivity did not show any significant differences among treatments on the sampling dates due to large variations in the data. In contrast, the MNPK and NPK treatments decreased unsaturated hydraulic conductivity compared with C at 0–5 cm depth. No significant differences between treatments in this variable were observed at 10–15 cm depth. Generally, NPK showed similar effects to C. Soil physical properties (bulk density and porosity) showed significant seasonal variations.

Estimates of Residual Dairy Manure Nitrogen Availability Using Various Techniques

It is common practice to repeatedly apply dairy manure to the same fields. To accurately assess the total plant availability of manure nutrients, it is necessary to account for the nutrients remaining in soil from previous manure applications. A field experiment studying manure nitrogen (N) uptake by corn (Zea mays L.) was conducted from 1998 to 2003 on a Plano silt loam (fine-silty, mixed, mesic, Typic Argiudolls). Plots received two rates of semisolid manure either every year, every 2 yr, or every 3 yr to estimate first-, second-, and third-year dairy manure N residuals. Residual manure N availability was estimated from single and multiple manure applications using (i) the fertilizer N equivalence method, (ii) the apparent recovery (difference) method, (iii) relative effectiveness method, and (iv) recovery of (15)N-labeled manure. Second-year availabilities after a single manure application using the fertilizer equivalence, difference, and relative effectiveness methods were estimated to be 12, 8, and 4% of total manure N applications, respectively. Estimates of third-year availability by these methods were 3, 1, and 5%, respectively. Measurement of (15)N recovered from labeled manure was 6 and 2% in the second and third year, respectively. Fertilizer equivalence, difference, and relative effectiveness methods showed great year to year variability, reducing the confidence in the residual manure N availability estimates by these methods, but using (15)N-labeled manures reduced variability substantially. Based on this and other studies, we suggest that second- and third-year residual N availability from a single application of semisolid dairy manure would be 9 to 12%, and 3 to 5% of the original manure N application, respectively.