Effects of initial plant spacing and applied nutrients on stand development and productivity of Texas bluegrass in the Louisiana coastal plain

The native rhizomatous cool‐season perennial grass, Texas bluegrass (Poa arachnifera Torn), has recently been recognized again as a plant with considerable potential for range and pasture plantings. Throughout the first half of this century, sporadic efforts at evaluation and commercial use of Texas bluegrass were thwarted primarily by slow stand establishment and difficulties with seed processing. Subsequent advances in seed harvesting, processing, and planting equipment and selection of superior plant genotypes could reduce effects of these limitations. In much of the southern mid‐ and tall‐grass prairie regions and lower southeastern states where Texas bluegrass appears to have potential, there is no currently available sustainable cool‐season forage grass. Effects of initial plant spacing and lime, phosphorus (P), and nitrogen (N) application were evaluated in a field and a green house experiment on acid infertile Louisiana Coastal Plain soils. Stands from transplanting on 10‐ and 30‐cm spacings were comparable by the third growing season as the sparsely planted stand spread aggressively. The only consistent response to soil amendment was enhanced forage production from N fertilization in the spring. A plant photoperiodic response appears to limit potential to respond to N in autumn and winter. Forage production of dense stands and responses to spring application of N indicate that Texas bluegrass has considerable potential as a productive, sustainable cool‐season forage grass for at least some soils on the southeastern Coastal Plain as well as that recently reported for the southern mid‐ and tall‐grass prairie regions.     

三种耕作制度下密西西比州两种加入家禽垫料的土壤上磷动态研究

An experiment arranged in a randomized complete block design with three replications was conducted on a Lexington soil (fine-silty, mixed, active, thermic, Ultic Hapludalfs) and a Loring soil (fine-silty, mixed, active, thermic, Oxyaquic Fragiudalfs) in Mississippi from September 1997 to September 2000 on 18 runoff plots under natural rainfall condition to study the phosphorus (P) dynamics in poultry litter amended soils under three management systems combining tillage and planting date treatments to identify effective management practices in southern U. S. A. The management systems in the study were:1) tillage in the fall prior to litter application followed by a delayed planting of fall forages (CT-DP); 2) tillage followed by immediate planting of the fall forage with subsequent litter application (CT-IP); and 3) no-till with planting prior to litter application (NT-IP). The results indicated that there was significant increase in soil P after 3 years of poultry litter application for both Lexington and Loring soils (P <0.05). Based on P budget analysis, the majority of P from poultry litter application (> 90%), was accumulated in both soils. In Loring soil, soluble P mass in the runoff was significantly higher from NT-IP than from CT-DP and CT-IP over the entire study period (P <0.01). For both soils, there were no significant differences in sediment P mass between management systems. For Loring soil, CT-DP and CT-IP were effective management practices to mitigate negative effects due to poultry litter application.     

Using sod to manage nitrogen in orchard floors

Abstract

Irrigation of untilled orchard floors can lead to substantial leaching losses of nitrate‐nitrogen (NO₃‐N). Soil NO₃ that remains after cool weather in the fall is subject to leaching in the spring. Nitrate losses can be controlled through growing ground cover vegetation to cycle residual nitrogen (N) and/or limiting the amount of water applied. A study was initiated in lysimeters to compare sodded soil surfaces versus bare soil for controlling NO₃ leaching losses. Cool season vegetation (orchardgrass, western wheatgrass, white clover) and warm season grasses (bahiagrass and buffalograss) were compared for then‐effect on grapefruit seedling growth. A field verification in pecan orchards was conducted where clean‐till versus a grass soil cover was used to compare the relative movement of NO₃ through the profile. The presence of vigorously growing sods greatly reduced NO₃ losses the first year in the lysimeter study. The second year a shade screen was placed over the lysimeters, resulting in greatly reduced cool season sod growth and substantially reduced warm season sod growth. The best grapefruit growth occurred on bare soil; vigorous sod growth greatly reduced grapefruit tree growth. In the second year of the experiment, tree growth on bare soil began to absorb substantial amounts of N. The presence of even reduced receding sod growth still adversely affected grapefruit tree growth. In commercial pecan orchards, NO₃ distributions in a clean‐tilled orchard soil showed large quantities of NO₃ entering the water table (the highest quantity at the lowest depth of the soil profile) while in the presence of a sod much less NO₃ (highest profile NO₃ near the soil surface) was being lost to the water table. However, the NO₃ leaching patterns were of large leaching losses in clean tilled surfaces and small controlled leaching losses with sod surfaces.     

Recycling Newsprint on Agricultural Land with the Aid of Poultry Litter

The large volume of cellulose products, primarily newsprint and yard waste, that are disposed of in landfills and the resistance of these products to decomposition led to an evaluation of the disposal of ground newsprint on agricultural land. A field study was conducted with cotton to evaluate the effects of trenching and mixing the excavated soil with ground newsprint and/or poultry litter. Decomposition rate of newsprint and potential for environmental contamination were investigated in a Cahaba-Wickham-Bassfield sandy loam (Typic Hapludult) soil. The experimental variables included different ratios of soil, ground newsprint, and/or poultry litter applied on the soil surface and in trenches 0.61 m or 1.22 m deep. When ground newsprint and excavated soil were mixed without adjusting the C:N ratio of the backfill, the newsprint was still present seven months after application. However, adjusting the C.N ratio of the excavated soil and ground newsprint with poultry litter provided the nitrogen necessary to completely decompose the ground newsprint within seven months. Soil surface application of ground newsprint required adjusting the C:N ratio to control the occurrence of plant pathogenic organisms. Extractable soil nutrients were increased when poultry litter was added, including P and K which are of concern with respect to surface and groundwater contamination. Extractable Zn, Cu, and Mn levels were increased by the addition of poultry litter, but their levels were in the ranges that most row crops will tolerate. The metals Cr and Pb, found in some printer's ink, may be of concern if repeated application of newsprint is made to the same site. Soil organic matter content was increased from 11.9 g kg-1 to 23.8 g kg-1 in the 50:40:10 backfill mixture of soil, newsprint, and poultry litter seven months after application.     

Phosphorus and trace metal dynamics in soils amended with poultry litter and granulates

Environmental sustainability of animal agriculture is strongly dependent upon development of approaches to minimize the potential environmental impacts of applying animal manures. The excess manure and its nutrients (primarily phosphorus) in intensive animal production regions may need to be exported to other areas to comply with increased regulations on manure management. In our previous study we generated a variety of granulated products from poultry litter to achieve export of excess litter from the southwestern Ozarks, AR, USA. Our objective in the present study was to determine the effect of the application of poultry litter and granulated litter products on phosphorus (P), arsenic (As), copper (Cu) and zinc (Zn) dynamics in two Arkansas soils (Dewitt silt loam and Hector sandy loam). Poultry litter and granulated products were mixed with the surface horizon (0–15 cm) of soils at two application rates: P‐based (100 kg total P per hectare) and N‐based (160 kg plant‐available N per hectare). Soil–litter mixtures were incubated at 25 °C for 21 days. Sub‐samples were removed at 1, 7 and 21 days to determine the solubility and availability of P, As, Cu and Zn in soils. Results suggest that when litter was applied at 100 kg total P per hectare, contents of P, As, Cu and Zn were significantly greater in the soils amended with litter and granulated products than in the control (soil alone). However, the contents of P, As, Cu and Zn did not significantly differ in the soils amended with either normal litter or granulated litter products at total P or plant‐available N‐based application rates. This suggests that poultry litter granulation is a sound management practice that can be used to reduce concerns with fresh litter transport and potentially improve P and trace element balances in intensive poultry production regions, especially when applied on a plant‐available N basis.     

Phytoremediation and Modeling of Contaminated Soil using Eastern Gamagrass and Annual Ryegrass

The effectiveness of a warm season grass (eastern gamagrass), a cool season grass (annual ryegrass) and a rotation of warm and cool season grasses in the remediation of soil freshly contaminated with trinitrotoluene (TNT) and polybrominated biphenyls (PBBs) was evaluated. A total of 96 columns were filled with a Weswood silt loam soil that was mixed with TNT and PBB compounds to a target concentration of 10 mg of each contaminant. Chemical losses during this two-year field lysimeter experiment were similar for all experimental treatments and at all depths. Although higher microbial biomass was found in the rhizosphere soil, enumeration of soil microorganisms revealed a robust population in both the bulk and rhizosphere soils and the microbial growth was not dependent on root exudates only. Microbial degradation rates in the freshly contaminated soil were more affected by soil properties and the chemical characteristics of the contaminant than the presence of roots. The field data collected from the lysimeter experiment was used to calibrate a recently developed phytoremediation model. The phytoremediation computer model successfully simulated TNT soil concentrations in the column lysimeters. The model may be a valuable tool for the selection and optimization of phytoremediation methods at contaminated field sites.     

Impact of Tillage and Fertilizer Application Method on Gas Emissions in a Corn Cropping System

Tillage and fertilization practices used in row crop production are thought to alter greenhouse gas emissions from soil.This study was conducted to determine the impact of fertilizer sources,land management practices,and fertilizer placement methods on greenhouse gas(CO₂,CH₄,and N₂O)emissions.A new prototype implement developed for applying poultry litter in subsurface bands in the soil was used in this study.The field site was located at the Sand Mountain Research and Extension Center in the Appalachian Plateau region of northeast Alabama,USA,on a Hartsells fine sandy loam(fine-loamy,siliceous,subactive,thermic Typic Hapludults).Measurements of carbon dioxide(CO₂),methane(CH₄),and nitrous oxide(N₂O)emissions followed GRACEnet (greenhouse gas reduction through agricultural carbon enhancement network)protocols to assess the effects of different tillage(conventional vs.no-tillage)and fertilizer placement(subsurface banding vs.surface application)practices in a corn(Zea mays L.)cropping system.Fertilizer sources were urea-ammonium nitrate(UAN),ammonium nitrate(AN)and poultry litter(M)applied at a rate of 170 kg ha^-1 of available N.Banding of fertilizer resulted in the greatest concentration of gaseous loss(CO₂ and N₂O)compared to surface applications of fertilizer.Fertilizer banding increased CO₂ and N₂O loss on various sampling days throughout the season with poultry litter banding emitting more gas than UAN banding.Conventional tillage practices also resulted in a higher concentration of CO₂ and N₂O loss when evaluating tillage by sampling day.Throughout the course of this study,CH4 flux was not affected by tillage,fertilizer source,or fertilizer placement method.These results suggest that poultry litter use and banding practices have the potential to increase greenhouse gas emissions.     

Apparent Use Efficiency of Nitrogen and Phosphorus from Litter Applied to Bermudagrass

More than 80% of broiler (chicken, Gallus gallus domesticus) litter produced annually is applied as a plant nutrient source, particularly for nitrogen (N) and phosphorus (P), to pastures. However, N losses during the process of litter N mineralization limit availability of N to crops. This study determined broiler litter N and P availability and apparent use efficiency (ANUE, APUE) to bermudagrass [Cynodon dactylon] during the first year after litter application. Treatments consisted of three litter rates (3.3, 6.6, and 13.2 Mg ha^?1), a commercial N fertilizer rate that provided 358 kg N ha^?1 as ammonium nitrate (NH₄NO₃), and an untreated control. Results showed bermudagrass dry-matter (DM) yield increased significantly with increase in litter rate. Commercial N fertilizer produced significantly greater DM yield than 3.3 and 6.6 Mg ha^?1 of litter but produced less DM yield than 13.2 Mg ha^?1 of litter. The overall average of ANUE from litter was 39% compared to the 59% from fertilizer. The mean litter N availabilities to bermudagrass during the first year after litter application were 48.5, 112.5, and 222 kg ha^?1, corresponding to the 3.3, 6.6, and 13.2 Mg ha^?1 litter rates, respectively. The overall mean of litter N mineralization, which was surface broadcast to bermudagrass plots during the first year, was 59.5% of the total litter N applied. The APUE, averaged across the rate and locations, was 13.6%, which was quite smaller than the ANUE of 39%. This finding of small APUE also validates the potential for P accumulation in soil after long-term animal manure application.     

Coupling of dry matter and nitrogen accumulation in millet and ryegrass

Abstract

The logistic model has proven very useful in relating dry matter production of warm‐season and cool‐season forage grasses to applied nitrogen (N). A recent extension of the model coupled dry matter and plant N accumulation through a common response coefficient c. The objective of this analysis was to apply the extended model to both warm season pearl millet [Pennisetum typhoides (Burm.) Staph and C. E. Hubb.] and cool season ryegrass [Lolium multiflorum Lam.], and to establish a common response coefficient, c, between accumulation of dry matter and plant N for the two grasses in rotation. Analysis of variance established the validity of this hypothesis. The model accurately described response of dry matter, plant N removal, and plant N concentration to applied N, with an overall correlation coefficient of 0.9954. Furthermore, the model closely described the relationship between yield and plant N removal. The logistic equation is well behaved and simple to use on a pocket calculator. It can be used to estimate yield and plant N removal in evaluation of agricultural practices and the influences on environmental quality.     

Nutrient availability and corn growth in a poultry litter biochar‐amended loam soil in a greenhouse experiment

Nutrient‐rich biochar produced from animal wastes, such as poultry litter, may increase plant growth and nutrient uptake although the role of direct and indirect mechanisms, such as stimulation of the activity of mycorrhizal fungi and plant infection, remains unclear. The effects of poultry litter biochar in combination with fertilizer on mycorrhizal infection, soil nutrient availability and corn (Zea mays L.) growth were investigated by growing corn in a loam soil in a greenhouse with biochar (0, 5 and 10 Mg/ha) and nitrogen (N) and phosphorus (P) fertilizer (0, half and full rates). Biochar did not affect microbial biomass C or N, mycorrhizal infection, or alkaline phosphomonoesterase activities, but acid phosphomonoesterase activities, water‐soluble P, Mehlich‐3 Mg, plant height, aboveground and root biomass, and root diameter were greater with 10 Mg/ha than with no biochar. Root length, volume, root tips and surface area were greatest in the fully fertilized soil receiving 10 Mg/ha biochar compared to all other treatments. The 10 Mg/ha biochar application may have improved plant access to soil nutrients by promoting plant growth and root structural features, rather than by enhancing mycorrhizal infection rates.     

Tillage and amendment effects on soil carbon and nitrogen mineralization and phosphorus release

The influence of tillage and nutrient amendment management on nutrient cycling processes in soil have substantial implications for environmentally sound practices regarding their use. The effects of 2 years of tillage and soil amendment regimes on the concentrations of soil organic matter variables (carbon (C), nitrogen (N) and phosphorus (P)) and C and N mineralization and P release were determined for a Dothan fine-sandy loam soil in southeastern Alabama. Tillage systems investigated were strip (or conservation) and conventional tillage with various soil nutrient amendments that included no amendment, mineral fertilizer, and poultry waste (broiler litter). Surface soil (0–10 cm depth increment) organic matter variables were determined for all tillage/amendment combinations. Carbon and N mineralization and P release were determined on surface soils for each field treatment combination in a long-term laboratory incubation. Soil organic P concentration was 60% greater in soils that had been conventionally tilled, as compared with strip-tilled, both prior to and following laboratory incubation. Carbon and N mineralization results reflected the effects of prior tillage amendment regime, where soils maintained under strip-till/broiler litter mineralized the greatest amount of C and N. Determination of relative N mineralization indicated that strip tillage had promoted a more readily mineralizable pool of N (6.1%) than with conventional till (4.2%); broiler litter amendments had a larger labile N fraction (6.7%) than was found in soils receiving either mineral fertilizer (4.1%) or no amendment (4.7%). Tillage also affected P release measured during the incubation study, where approximately 20% more inorganic P was released from strip-tilled soils than from those maintained under conventional tillage. Greater P release was observed for amended soils as compared with soils where no amendment was applied. Results from this study indicate that relatively short-term tillage and amendment management can significantly impact C, N, and P transformations and transfers within soil organic matter of a southeastern US soil.     

Influence of organic by-products and nitrogen source on chemical and microbiological status of an agricultural soil

We assessed the influence of the addition of four municipal or agricultural by-products (cotton gin waste, ground newsprint, woodchips, or yard trimmings), combined with two sources of nitrogen (N), [ammonium nitrate (NH₄NO₃) or poultry litter] as carbon (C) sources on active bacterial, active fungal and total microbial biomass, cellulose decomposition, potential net mineralization of soil C and N and soil nutrient status in agricultural soils. Cotton gin waste as a C source promoted the highest potential net N mineralization and N turnover. Municipal or agricultural by-products as C sources had no affect on active bacterial, active fungal or total microbial biomass, C turnover, or the ratio of net C:N mineralized. Organic by-products and N additions to soil did not consistently affect C turnover rates, active bacterial, active fungal or total microbial biomass. After 3, 6 or 9 weeks of laboratory incubation, soil amended with organic by-products plus poultry litter resulted in higher cellulose degradation rates than soil amended with organic by-products plus NH₄NO₃. Cellulose degradation was highest when soil was amended with newsprint plus poultry litter. When soil was amended with organic by-products plus NH₄NO₃, cellulose degradation did not differ from soil amended with only poultry litter or unamended soil. Soil amended with organic by-products had higher concentrations of soil C than soil amended with only poultry litter or unamended soil. Soil amended with organic by-products plus N as poultry litter generally, but not always, had higher extractable P, K, Ca, and Mg concentrations than soil amended with poultry litter or unamende soil. Agricultural soil amended with organic by-products and N had higher extractable N, P, K, Ca and Mg than unamended soil. Since cotton gin waste plus poultry litter resulted in higher cellulose degradation and net N mineralization, its use may result in faster increase in soil nutrient status than the other organic by-products and N sources that were tested. Received: 15 May 1996     

Recycling of Chicken and Duck Litter Ash as a Nutrient Source for Japanese Mustard Spinach

ABSTRACT

Recycling combusted poultry litter ash as a soil amendment would potentially ameliorate problems normally associated with poultry waste management. We evaluated the effect of chicken litter ash (CLA) and duck litter ash (DLA) as nutrient sources for Japanese mustard spinach (Brassica rapa L. var. perviridis) grown on a sand dune soil. Chicken and duck litter were ashed at five temperatures: 200, 400, 600, 800, and 900°C and the resulting ash samples were applied at the rate of 100 kg phosphorus (P) ha^?1. Laboratory analysis showed the highest P extraction with citric acid from CLA and DLA obtained at 600°C. Chicken litter ash was richer in P and potassium (K) than DLA but the later contained more calcium (Ca) and magnesium (Mg). The amount of ammonium acetate soluble calcium (Ca), magnesium (Mg), and K recovered increased with increasing temperature except for Ca and Mg at the highest temperatures, 800 and 900°C. Plants grown in pots with the CLA and DLA obtained at 400°C had the highest P concentration, yielding significantly more biomass with dense green leaf color but on average, the DLA amended soil had greater biomass. However, the P level was higher in CLA treated plants than DLA due to the higher available P level (citric acid soluble). Increases in electrical conductivity and pH of the soil were noted after harvest due to litter ash application. Our experiment demonstrated that poultry litter is potential source of P and other nutrients for horticutural crops.     

Effects of the Establishment of a Forested Riparian Buffer and Grazing on Soil Characteristics

Poultry-litter applications to pastures can result in relatively high soil phosphorus (P) levels, which in turn can contaminate runoff and degrade surface water quality. New management protocols for temperate grasslands are needed to reduce the risk of P transport to surface water. The effects of three land-use treatments on soil characteristics related to P runoff were investigated using small watersheds with 8% slope near Booneville, Arkansas, U.S. The land use treatments were (1) haying of bermudagrass overseeded with winter annual forage (ryegrass or rye), (2) rotationally grazed, and (3) rotationally grazed with 12-m-wide tree buffer on the downhill portion of the plot. Plots and trees were established in 2003. Annual spring application of poultry litter (5.6 Mg ha^?1) to the hayed or grazed portions of the plots was started in 2004. Grazing treatments were imposed shortly thereafter. By the summer of 2008 (4 years of treatments), soil concentrations of Bray 1–extractable P and soluble reactive P had increased significantly from approximately 40 and 4 mg P kg^?1 soil, respectively, to more than 200 and 30 mg P kg^?1 soil, respectively, in the areas of the plots receiving poultry litter. Soil bulk density in the portions of the plots being grazed had increased significantly also. The soil collected from the forested riparian buffer in 2008 had similar soil bulk densities and Bray 1–extractable P concentrations as the plots did in 2003 before treatments were imposed.     

Long‐term phosphorus solubility in soils receiving poultry litter treated with aluminum,calcium, and iron amendments

Abstract

Phosphorus (P) runoff from poultry litter applied to fields can adversely impact water quality. The majority of P in runoff from poultry litter is soluble, so decreasing the solubility of P could lessen the impact of poultry litter on water quality. The objective of this study was to determine long‐term P solubility in soils receiving poultry litter treated with aluminum (Al), calcium (Ca), and iron (Fe) amendments at various soil pHs. Soil pH was adjusted to 4.0, 5.0, 6.0, 7.0, and 8.0 using elemental sulfur (S) or CaCO₃ with some soil left at its native pH. The pH‐adjusted soil was then incubated with either no litter (control), litter alone (litter control), or litter amended with alum, A1₂(SO₄)₃.16H₂O, (100 or 200 g/kg), Ca(OH)₂ (25 or 50 g/kg), or FeSO₄ .7H₂O (100 or 200 g/kg). The soil was then allowed to equilibrate in the dark at room temperature for 0, 7, 49, 98, and 294 days. After equilibration, soils were extracted with deionized water and soluble reactive P levels were determined. Water‐soluble P levels decreased with time in all treatments, including the control and litter control treatments. Soil pH also affected soluble reactive P levels, with the lowest levels generally observed at pH 8.0. Addition of both unamended and chemically‐amended litter to soil significantly increased P concentrations at all combinations of pH and sampling time. Addition of chemically‐amended litter to soil significantly reduced soluble reactive P compared to unamended litter. With all treatments, an apparent equilibrium was reached at 98 d after treatment. Amendment of litter with either FeSO₄ .7H₂O or alum resulted in the lowest soluble reactive P levels after 294 days. Use of chemical amendments to limit P solubility has potential and should be pursued as a means of reducing eutrophication of sensitive surface waters where poultry litter is applied as a fertilizer.     

Response of texas bluegrass to season of nitrogen fertilization on the Louisiana coastal plain

Texas bluegrass (Poa arachnifera Torr.) has shown potential for use as a cool‐season perennial pasture grass in the southern Great Plains, where it occurs as a natural component of rangeland plant communities, and into the western Coastal Plain. Responsiveness of this grass to nitrogen (N) fertilization appeared to be limited to the spring growing period in initial evaluations in Louisiana. A field plot experiment was conducted to assess forage production and quality responses to season of N fertilization on the Syn‐1 population of Texas bluegrass. Winter forage production responses to 50 kg N ha^‐1 were obtained in the 1997–98 growing season but not in 1998–99 after stands had been depleted by summer drought. Greatest yield increases resulted from spring N application, however, fall plus winter fertilization provided the most uniform distribution of forage through the cool season. Forage fiber fractions, in vitro digestibility, and crude protein were not affected by N fertilization. Both amount and distribution of Texas bluegrass forage, but not forage quality, can be manipulated by time of N fertilization.     

Soil Properties and Macro Cations Status impacted by Long‐Term Applied Poultry Litter

Abstract

Most ethnic populations worldwide consume poultry products. Whereas poultry litter (PL) is a traditionally inexpensive and effective fertilizer to improve soil quality and agricultural productivity, overapplication to soils has raised concerns because excess nutrients in runoff could accelerate the eutrophication of fresh bodies of water. A long‐term field experiment of land application of PL to soils used for pasture growth has been maintained for nearly two decades in the Sand Mountain region of north Alabama, USA. In this work, several soil parameters impacted by the long‐term applied litter were characterized. The findings clearly support previous general observations that long‐term applied litter on pasture soils altered soil properties and macrocation levels. Unlike other studies, however, the effects of applied litter at multiple rates and years were examined, thus revealing the dynamic impacts on soil properties. Hay yields increased with the increase of years of PL application, regardless of the applied rate. This observation was consistent with previous observations that the labile phosphorus (P) portion in these soils increases with application years whereas total P increases with the cumulative applied PL amounts. Poultry litter application did not markedly affect soil electric conductivity, bulk density, or sodium (Na) or potassium (K) levels, especially at the soil surface (0–20 cm). Soil pH, carbon (C), C/nitrogen (N) ratio, calcium (Ca), and magnesium (Mg) were profoundly affected at all three soil depths (0–20, 20–40, and 40–60 cm). Most soil parameters analyzed in this study reached peak values with 10–15 years of applied litter. This observation suggests that there was a turning point of impact for applied litter around 10 years: prior to that the soil macrocations were altered positively as a result of accumulative functions. Continuous litter application may negatively alter a soil's capacity to retain macrocations, leading to less impact observed in this study. In other words, pasture soils with more than 10 years of applied litter would have higher potential for leaching and runoff. Our observation suggested that best management practices for land application of PL should take into consideration the different effects of PL application history.     

Soil compaction and poultry litter effects on factors affecting nitrogen availability in a claypan soil

Soil compaction may affect N mineralization and the subsequent fate of N in agroecosystems. Laboratory incubation and field experiments were conducted to determine the effects of surface soil compaction on soil N mineralization in a claypan soil amended with poultry litter (i.e., Turkey excrement mixed with pine shavings as bedding). In a laboratory study, soil from the surface horizon of a Mexico silt loam soil was compacted to four bulk density levels (1.2, 1.4, 1.6 and 1.8 Mg m⁻³) with and without poultry litter and incubated at 25 °C for 42 days. A field trial planted to corn (Zea mays L.) was also conducted in 2002 on a Mexico silt loam claypan soil in North Central Missouri. Soil was amended with litter (0 and 19 Mg ha⁻¹) and left uncompacted or uniformly compacted. Soil compaction decreased soil inorganic N by a maximum of 1.8 times in the laboratory study; this effect was also observed at all depths of the field trial. Compacted soil with a litter amendment accumulated NH₄⁺-N up to 7.2 times higher than the noncompacted, litter-amended soil until Day 28 of the laboratory incubation and in the beginning of the growing season of the field study. Ammonium accumulation may have been due to decreased soil aeration under compacted conditions. Application of litter increased soil N mineralization throughout the growing season. In the laboratory study, soil inorganic N in unamended soil was negatively correlated with soil bulk density and the proportion of soil micropores, but was positively related with soil total porosity and the proportion of soil macropores. These results indicate that soil compaction, litter application and climate are interrelated in their influences on soil N mineralization in agroecosystems.     

Influence of Organic Amendments on the Accumulation of 137Cs and 90Sr from Contaminated Soil by Three Grass Species

Bahia grass (Paspalum notatum), johnson grass (Sorghum halpense) and switchgrass (Panicum virginatum) werecompared for their ability to accumulate ¹³⁷Csand ⁹⁰Sr from three different contaminated soilsin the presence and absence of either sphagnum peator poultry litter amendments. Above-ground plantbiomass did not differ between plants that were notexposed to these radionuclides and those that wereexposed to soil containing ¹³⁷Cs or ⁹⁰Sr.After three harvests, bahia, johnson and switchgrassplants accumulated from 17.2 to 67.3% of the¹³⁷Cs and from 25.1 to 61.7% of the ⁹⁰Sradded to the soil. Poultry litter and peat mossamendments increased aboveground plant biomass,activity of ¹³⁷Cs or ⁹⁰Sr in plant tissue, %accumulation of ¹³⁷Cs or ⁹⁰Sr from soil andthe plant bioconcentration ratio at each harvestcompared to the control (no amendment) treatment. Thegreatest increases in plant biomass, and radionuclideaccumulation were observed with poultry litter foreach of the three grass species. Johnson grass hadgreater aboveground plant biomass, activity of¹³⁷Cs and ⁹⁰Sr in plant tissue, %accumulation of ¹³⁷Cs or ⁹⁰Sr from soil andbioconcentration ratio in each soil amendment, at eachharvest compared to bahia and switchgrass. Thegreatest accumulation of ¹³⁷Cs and ⁹⁰Sr wasmeasured in johnson grass grown in soil that wasamended with poultry litter. These results suggestthat plant species selection and agronomic practicesmay need to be considered to maximize phytoremediationof radionuclide contaminated soils.     

Distribution and Dynamics of Phosphorus in an Agricultural Watershed with a Long-Term History of Poultry Waste Application

The objective of this research is to investigate the effects of long-term broiler litter application on soil phosphorus (P) and water quality and examine the spatial variations of soil P at a private poultry farm in Mississippi. Results indicated that the littered soil had 86 times more Mehlich III–extractable P in the surface horizon compared to the nonlittered soil. When compared to the runoff from nonlittered soil, mean soluble phosphate (PO₄)-P concentrations in the littered soil's runoff were 85 times greater throughout the study. Mass loss of P from the littered field was significantly greater than from the nonlittered field, and it decreased with each sequential runoff event. There were no linear relationships between the spatial variations of litter application rates and the P spatial variability in the littered soil; however, the variations in soil P levels could be a result of the cumulative effects of more than 20 years of litter application.