Norfolk Soil Research Articles

Aggregate Distribution and the Associated Carbon in Norfolk Soils under Long-term Conservation Tillage and Short-term Cover Cropping

ABSTRACT Conservation agriculture practices have been widely implemented to improve soils and their sustainability. Here, we investigated the impacts of long-term conservation tillage (CS) on soil aggregates and their associated carbon (C) in a typical sandy Ultisols. The short-term effect of cover cropping was also investigated. Soils (0–5 and 5–15 cm) were collected from fields under 40-years CS and conventional tillage (CV), in which cover crop and fallow treatments were embedded as a split-plot design for four years. Soils were tested for bulk density, pH, mean weight diameter, dry aggregate distribution, and C contents. The CS only resulted in higher total C (TC) concentrations (13.56 ± 1.14 g kg−1) than CV (10.06 ± 0.53 g kg−1) at 0–5 cm. Similar depth impacts were observed in various aggregate size fractions (2000–250 µm, macroaggregates; 250–53 µm, microaggregates; 0–53 µm, clay-silt fraction). Soils were dominated by macroaggregates (>50%) at both depths with associated C concentrations following the order of clay-silt fraction > microaggregates > macroaggregates. Nonetheless, after accounting for soil bulk density long-term CS did not result in higher TC stocks than CV at both depths. Cover crops demonstrated no effect on C stocks at both depths. Poor soil structure and low clay contents of the tested soils may partially explain these neutral impacts, while relatively lower residue returns of cover crops to cash crops may also confound the positive management outcomes. Novel management practices to increase soil organic C in the bulk soils by increasing organic inputs and the soils’ capacity to preserve the inputs are needed.

Loamy sand soil approaches organic carbon saturation after 37 years of conservation tillage

AbstractConservation tillage is reported to increase soil organic carbon (SOC) and total nitrogen (TN) contents, but long‐term (>30 yr) field results quantifying the responses in Coastal Plain Ultisols are sparse. The distribution, accumulation, and topsoil storage of SOC and TN after 37 yr of crop production using conventional (CvT) or conservation tillage (CnT) on a Norfolk loamy sand (fine‐loamy, kaolinitic, thermic, Typic Kandiudults) were quantified. Soil samples were collected annually from the 0−5‐, 5−10‐, and 10−15‐cm depth increments beneath corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and cotton (Gossypium hirsutum L.) crops. Overall, SOC and TN accumulation in the 0−5‐cm depth were highest for Norfolk soil under CnT. Focusing on total long‐term changes for the 0−15‐cm sampling depth beneath various corn crops shows that CnT and CvT sequestered 24.7 and 21.4 Mg C ha−1, respectively. Between 1978 and 2016, there was a highly significant (P < .0001) exponential increase in SOC within the top 5‐cm soil depth. However, the exponential curves began to plateau suggesting the Norfolk topsoil was approaching its organic carbon (OC) storage capacity. These field measurements strongly indicate that additional topsoil SOC increases with current tillage and crop management practices are limited.

Biochar affects growth and shoot nitrogen in four crops for two soils.

To address the need for information on biochar effects on crop growth and nitrogen (N), a greenhouse study was conducted with carrot, lettuce, soybean, and sweet corn using sandy loam (Coxville series) and loamy sand (Norfolk series) soils and a variety of biochars. Biochar was produced from pine chips (PC), poultry litter (PL), swine solids (SS), switchgrass (SG), and two blends of PC plus PL (50/50% [55] and 80/20% [82], wt/wt), with each feedstock pyrolyzed at 350, 500, or 700 °C. The results confirmed that biochar can increase crop growth; however, the responses varied with crop, soil, and feedstock and to a lesser extent with pyrolysis temperature. In general, lettuce had large increases in shoot and root dry weights vs. no-biochar controls with many biochars, primarily the SS and 55 blend and to a lesser extent with 82 followed by PL, and then PC and SG, especially when grown in the Coxville soil. Biochar had more limited effects on carrot, sweet corn, and soybean weights. Some biochars decreased crop growth (e.g., PL at 700 °C) for soybean shoot and pod dry weights with the Norfolk soil. Shoot N concentrations decreased with SS, 55, and 82 for carrot, lettuce, and sweet corn with the Norfolk soil but tended to increase for soybean. Shoot N uptake increased or decreased depending on biochar feedstock and temperature, crop, and soil. These results confirm that biochar can increase crop growth and affect shoot N, which is essential for crop growth.

Ibuprofen Sorption to Coastal Plain Soils

Ibuprofen is commonly detected in onsite wastewater systems. Such onsite systems are abundant in coastal plain areas, globally. Coastal plain soils have unique mineralogy. Rapid subsurface transport may occur in coastal plain soils due to their characteristic permeable soils and seasonally high water tables. Laboratory batch sorption studies were conducted on Norfolk, Goldsboro, and Lynchburg, three archetypical coastal plain soils, with varying physicochemical properties, to evaluate ibuprofen sorption. Sorption distribution coefficients (KD values) across all three soils ranged from 0.63 to 1.26 L kg−1. Sorption of ibuprofen to Norfolk and Goldsboro soils was able to be modeled using a Freundlich isotherm; however, the Lynchburg soil, was not, likely due to soil heterogeneity. In general, sorption of ibuprofen was influenced by soil organic carbon content.

Biochars impact on water infiltration and water quality through a compacted subsoil layer

Soils in the SE USA Coastal Plain region frequently have a compacted subsoil layer (E horizon), which is a barrier for water infiltration. Four different biochars were evaluated to increase water infiltration through a compacted horizon from a Norfolk soil (fine-loamy, kaolinitic, thermic, Typic Kandiudult). In addition, we also evaluated biochars effect on water quality. Biochars were produced by pyrolysis at 500°C from pine chips (Pinus taeda), poultry litter (Gallus domesticus) feedstocks, and as blends (50:50 and 80:20) of pine chip:poultry litter. Prior to pyrolysis, the feedstocks were pelletized and sieved to >2-mm pellets. Each biochar was mixed with the subsoil at 20g/kg (w/w) and the mixture was placed in columns. The columns were leached four times with Milli-Q water over 128d of incubation. Except for the biochar produced from poultry litter, all other applied biochars resulted in significant water infiltration increases (0.157–0.219mLmin−1; p<0.05) compared to the control (0.095mLmin−1). However, water infiltration in each treatment were influenced by additional water leaching. Leachates were enriched in PO4, SO4, Cl, Na, and K after addition of poultry litter biochar, however, their concentrations declined in pine chip blended biochar treatments and after multiple leaching. Adding biochars (except 100% poultry litter biochar) to a compacted subsoil layer can initially improve water infiltration, but, additional leaching revealed that the effect remained only for the 50:50 pine chip:poultry litter blended biochar while it declined in other biochar treatments.

Efficacies of designer biochars in improving biomass and nutrient uptake of winter wheat grown in a hard setting subsoil layer

In the Coastal Plains region of the United States, the hard setting subsoil layer of Norfolk soils results in low water holding capacity and nutrient retention, which often limits root development. In this region, the Norfolk soils are under intensive crop production that further depletes nutrients and reduces organic carbon (C). Incorporation of pyrolyzed organic residues or “biochars” can provide an alternative recalcitrant C source. However, biochar quality and effect can be inconsistent and different biochars react differently in soils. We hypothesized that addition of different designer biochars will have variable effects on biomass and nutrient uptake of winter wheat. The objective of this study was to investigate the effects of designer biochars on biomass productivity and nutrient uptake of winter wheat (Triticum aestivum L.) in a Norfolk’s hard setting subsoil layer. Biochars were added to Norfolk’s hard setting subsoil layer at the rate of 40Mgha−1. The different sources of biochars were: plant-based (pine chips, PC); animal-based (poultry litter, PL); 50:50 blend (50% PC:50% PL); 80:20 blend (80% PC:20% PL); and hardwood (HW). Aboveground and belowground biomass and nutrient uptake of winter wheat varied significantly (p⩽0.0001) with the different designer biochar applications. The greatest increase in the belowground biomass of winter wheat over the control was from 80:20 blend of PC:PL (81%) followed by HW (76%), PC (59%) and 50:50 blend of PC:PL (9%). However, application of PL resulted in significant reduction of belowground biomass by about 82% when compared to the control plants. The average uptake of P, K, Ca, Mg, Na, Al, Fe, Cu and Zn in both the aboveground and belowground biomass of winter wheat varied remarkably with biochar treatments. Overall, our results showed promising significance for the treatment of a Norfolk’s hard setting subsoil layer since designer biochars did improve both aboveground/belowground biomass and nutrient uptake of winter wheat.

Carbon mineralization in two ultisols amended with different sources and particle sizes of pyrolyzed biochar

Biochar produced during pyrolysis has the potential to enhance soil fertility and reduce greenhouse gas emissions. The influence of biochar properties (e.g., particle size) on both short- and long-term carbon (C) mineralization of biochar remains unclear. There is minimal information on the potential effects of biochar particle sizes on their breakdowns by soil microorganism, so it is unknown if the particle size of biochar influences C mineralization rate and/or stability in soils. In order to evaluate the effect of different sources (BS) and particle sizes (BF) of biochar on C loss and/or stability in soils, an incubation study on C mineralization of different biochar sources and particle sizes was established using two soils (ST): Norfolk soil (fine loamy, kaolinitic, thermic, typic Kandiudults) and Coxville soil (fine loamy kaolinitic, thermic, Paleaquults). In separate incubation vessels, these soils were amended with one of two manure-based biochars (poultry litters, PL; swine solids, SS) or one of two lignocellulosic-based biochars (switchgrass, SG; pine chips, PC) which were processed into two particle sizes (dust, <0.42mm; pellet, >2mm). The amount of CO2 evolved varied significantly between soils (p⩽0.0001); particle sizes (p⩽0.0001) and the interactions of biochar source (p⩽0.001) and forms of biochars (p⩽0.0001) with soil types. Averaged across soils and sources of biochar, CO2-C evolved from dust-sized biochar (281mgkg−1) was significantly higher than pellet-sized biochar (226mgkg−1). Coxville soils with SS biochar produced the greatest average CO2-C of 428mgkg−1 and Norfolk soils with PC had the lowest CO2-C production (93mgkg−1). Measured rates of carbon mineralization also varied with soils and sources of biochar (Norfolk: PL>SS>SG⩾PC; Coxville: PC>SG>SS>PL). The average net CO2-C evolved from the Coxville soils (385mgkg−1) was about threefold more than the CO2-C evolved from the Norfolk soils (123mgkg−1). Our results suggest different particle sizes and sources of biochar as well as soil type influence biochar stability.

Designing relevant biochars as soil amendments using lignocellulosic-based and manure-based feedstocks

Biochars are a by-product of the biofuel processing of lignocellulosic and manure feedstocks. Because biochars contain an assemblage of organic and inorganic compounds, they can be used as an amendment for C sequestration and soil quality improvement. However, not all biochars are viable soil amendments; this is because their physical and chemical properties vary due to feedstock elemental composition, biofuel processing, and particle size differences. Biochar could deliver a more effective service as a soil amendment if its chemistry was designed ex ante with characteristics that target specific soil quality issues. In this study, we demonstrate how biochars can be designed with relevant properties as successful soil amendments through feedstock selection, pyrolysis conditions, and particle size choices. Biochars were produced by pyrolysis of parent lignocellulosic feedstock sources—peanut hull (PH; Archis hypogaea), pecan shell (PS; Carya illinoensis), switchgrass (SG; Panicum virgatum), pine chips (PC; Pinus taeda), hardwood wastes (wood), and poultry litter manure (PL; Gallus domesticus), as well as blends of these feedstocks at temperatures ranging from 250 to 700 °C. Additionally, blended feedstocks were made into pellets (>2 mm) prior to pyrolysis at 350 °C. Dust-sized (<0.42 mm) biochar was obtained through grinding of pelletized biochars. After chemical characterization, the biochars were evaluated as fertility amendments in a Norfolk soil (fine-loamy, kaolinitic, thermic, Typic Kandiudult) during two different pot incubation experiments. PL biochars were alkaline and enriched in N and P, whereas biochar from lignocellulosic feedstocks exhibited mixed pH and nutrient contents. Blending PL with PC resulted in lower biochar pH values and nutrient contents. In pot experiment 1, most biochars significantly (P < 0.05) raised soil pH, soil organic carbon, cation exchange capacity, and Mehlich 1 extractable P and K. PL biochar added at 20 g kg−1 resulted in excessive soil P concentrations (393 to 714 mg kg−1) and leachate enriched with dissolved phosphorus (DP, 22 to 70 mg L−1). In pot experiment 2, blended and pelletized PL with PC feedstock reduced soil pH and extractable soil P and K concentrations compared to pot experiment 1. Water leachate DP concentrations were significantly (P < 0.05) reduced by pelletized biochar blends. Short-term laboratory pot experiments revealed that biochars can have different impacts at modifying soil quality characteristics. Keying on these results allowed for creating designer biochars to address specific soil quality limitations. In the process of manufacturing designer biochars, first, it is important to know what soil quality characteristics are in need of change. Second, choices between feedstocks, blends of these feedstocks, and their accompanying particle sizes can be made prior to pyrolysis to create biochars tailored for addressing specific soil quality improvements. Utilization of these principles should allow for effective service of the designed biochar as a soil amendment while minimizing unwanted ex facto soil quality changes and environmental effects.

Biochars Impact on Soil-Moisture Storage in an Ultisol and Two Aridisols

Droughts associated with low or erratic rainfall distribution can cause detrimental crop moisture stress. This problem is exacerbated in the USA’s arid western and southeastern Coastal Plain due to poor rainfall distribution, poor soil water storage, or poorly-aggregated, subsurface hard layers that limit root penetration. We hypothesized that soil physical deficiencies may be improved by biochar applications. Research indicates a single biochar will not serve as a universal supplement to all soils; consequently, biochars may need to be designed with physico-chemical properties that can ameliorate specific soil physical deficiencies. We conducted a laboratory study that examined the effect of biochar on soil moisture retention and aggregate formation. Eight biochars were made from four feedstocks at two different pyrolysis temperature classes ( 500°C; 932°C) and were characterized for their physical and chemical properties. In addition, we included a biochar made using fast pyrolysis of hardwood wastes. All biochars were mixed at 2% w/w with either a Norfolk loamy sand (Fine-loamy, kaolinitic, thermic Typic Kandiudults), a Declo silt loam (Coarse-loamy, mixed, superactive, mesic xeric Haplocalcids), or a Warden silt loam (Coarse-silty, mixed, superactive, mesic xeric Haplocambids). Amended soils were laboratory incubated in pots for up to 127 days. About every 30 days, bulk density was measured and then each pot was leached with 1.2 to 1.3 pore volumes of deionized water. Gravimetric and volumetric soil moisture contents were determined after free drainage had ceased and again 2 and 6 days after leaching. The Norfolk-treated soils were later dry-sieved, and the sum by weight of their 0.5- to 1.0-mm aggregates was determined. In general, the biochar surface area and surface tension increased when produced under higher pyrolytic temperatures (>500°C). After leaching, Norfolk soils treated with switchgrass biochars had the most significant increase in soil moisture capacities. Similar increases were found in the Declo and Warden soils. Formation of 0.5- to 1.0-mm aggregates in the Norfolk loamy sand varied with biochar. Biochars enhanced the moisture storage capacity of the Ultisol and Aridisols thereby potentially reducing the on-set of crop moisture stress; however, the effect varied considerably with biochar feedstock and pyrolysis temperature.

Influence of Pyrolysis Temperature on Biochar Property and Function as a Heavy Metal Sorbent in Soil

While a large-scale soil amendment of biochars continues to receive interest for enhancing crop yields and to remediate contaminated sites, systematic study is lacking in how biochar properties translate into purported functions such as heavy metal sequestration. In this study, cottonseed hulls were pyrolyzed at five temperatures (200, 350, 500, 650, and 800 °C) and characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, and by ATR-FTIR. The characterization results were compared with the literature values for additional source materials: grass, wood, pine needle, and broiler litter-derived biochars with and without post-treatments. At respective pyrolysis temperatures, cottonseed hull chars had ash content in between grass and wood chars, and significantly lower BET surface area in comparison to other plant source materials considered. The N:C ratio reached a maximum between 300 and 400 °C for all biomass sources considered, while the following trend in N:C ratio was maintained at each pyrolysis temperature: wood≪cottonseed hull≈grass≈pine needle≪broiler litter. To examine how biochar properties translate into its function as a heavy metal (NiII, CuII, PbII, and CdII) sorbent, a soil amendment study was conducted for acidic sandy loam Norfolk soil previously shown to have low heavy metal retention capacity. The results suggest that the properties attributable to the surface functional groups of biochars (volatile matter and oxygen contents and pHpzc) control the heavy metal sequestration ability in Norfolk soil, and biochar selection for soil amendment must be made case-by-case based on the biochar characteristics, soil property, and the target function.

Influence of soil properties on heavy metal sequestration by biochar amendment: 1. Copper sorption isotherms and the release of cations

The amendment of carbonaceous materials such as biochars and activated carbons is a promising in situ remediation strategy for both organic and inorganic contaminants in soils and sediments. Mechanistic understandings in sorption of heavy metals on amended soil are necessary for appropriate selection and application of carbonaceous materials for heavy metal sequestration in specific soil types. In this study, copper sorption isotherms were obtained for soils having distinct characteristics: clay-rich, alkaline San Joaquin soil with significant heavy metal sorption capacity, and eroded, acidic Norfolk sandy loam soil having low capacity to retain copper. The amendment of acidic pecan shell-derived activated carbon and basic broiler litter biochar lead to a greater enhancement of copper sorption in Norfolk soil than in San Joaquin soil. In Norfolk soil, the amendment of acidic activated carbon enhanced copper sorption primarily via cation exchange mechanism, i.e., release of proton, calcium, and aluminum, while acid dissolution of aluminum cannot be ruled out. For San Joaquin soil, enhanced copper retention by biochar amendment likely resulted from the following additional mechanisms: electrostatic interactions between copper and negatively charged soil and biochar surfaces, sorption on mineral (ash) components, complexation of copper by surface functional groups and delocalized π electrons of carbonaceous materials, and precipitation. Influence of biochar on the release of additional elements (e.g., Al, Ca) must be carefully considered when used as a soil amendment to sequester heavy metals.

Impact of Biochar Amendment on Fertility of a Southeastern Coastal Plain Soil

Agricultural soils in the southeastern U.S. Coastal Plain region have meager soil fertility characteristics because of their sandy textures, acidic pH values, kaolinitic clays, low cation exchange capacities, and diminutive soil organic carbon contents. We hypothesized that biochar additions will help ameliorate some of these fertility problems. The study objectives were to determine the impact of pecan shell-based biochar additions on soil fertility characteristics and water leachate chemistry for a Norfolk loamy sand (fine-loamy, kaolinitic, thermic typic Kandiudults). Soil columns containing 0, 0.5, 1.0, and 2.0% (wt/wt) biochar were incubated at 10% (wt/wt) moisture for 67 days. On days 25 and 67, the columns were leached with 1.2 to 1.4 pore volumes of deionized H2O, and the leachate chemical composition determined. On days 0 and 67, soil samples were collected and analyzed for fertility. The biochar had a pH of 7.6, contained 834.2 and 3.41 g kg−1 of C and N, respectively, and was dominated by aromatic C (58%). After 67 days and two leaching events, biochar additions to the Norfolk soil increased soil pH, soil organic carbon, Ca, K, Mn, and P and decreased exchangeable acidity, S, and Zn. Biochar additions did not significantly increase soil cation exchange capacity. Leachates contained increasing electrical conductivity and K and Na concentrations, but decreasing levels of Ca, P, Mn, and Zn. These effects reflect the addition of elements and the higher sorption capacity of biochar for selective nutrients (especially Ca, P, Zn, and Mn). Biochar additions to the Norfolk soil caused significant fertility improvements.

Effects of polyacrylamide and organic matter on microbes associated to soil aggregation of Norfolk loamy sand

Polyacrylamide (PAM) has been reported to increase aggregation and improve soil physical properties in loamy sand soils, but nothing is known about the effects of PAM on microbes involved in aggregate formation. We studied the effects of PAM (0, 30 and 120 mg kg −1) and organic matter (wheat [ Triticum aestivum] and pecan [ Carya illinoinensis]) incubated in a Norfolk soil (a blend of 90% E horizon and 10% Ap horizon) for 96 days at 10% water content on microorganisms that have the ability to aggregate soil. We used an in vitro soil sedimentation assay to test the aggregative ability of the predominant, heterotrophic bacteria from the culturable portion of microaggregates (0.25–0.05 mm), fatty acid methyl ester (FAME) profiling to identify the isolates, and DNA sequencing to find their position in a phylogeny with known taxa. Among all the identified bacterial species, 19 were soil aggregators. There was a PAM effect across all residue types indicating that the highest proportion of soil aggregating isolates was at 120 mg kg −1 PAM. This suggests that soil conditions created by the addition of 120 mg kg −1 PAM favored the growth of bacteria functioning as soil aggregators. There was evidence of interaction between PAM and residue type. Differences were found in the PAM effect but only when no residue was added. The amount of soil aggregating basidiomycete fungi from the different aggregate size fractions was also determined using an enzyme-linked immunosorbent assay (ELISA). There was a higher amount of soil aggregating basidiomycete fungi in macroaggregates (2.00–1.00 and 1.00–0.50 mm classes) generated from PAM and/or wheat residue amended soil compared to the control soil, but no difference was found in treatments with pecan residue added. This suggests that PAM and PAM with wheat can be utilized as a source of nutrient for the basidiomycetes, but pecan appeared to inhibit their growth. This study is the first to provide evidence that adding PAM to soil favored the growth and survival of specific fungi and bacterial species functioning as soil aggregators in vitro.

WATER TREATMENT RESIDUALS AMENDED SOILS RELEASE Mn, Na, S, AND C

Drinking water treatment facilities remove impurities from raw water sources using various chemicals. The by-product produced from the purification process is called water treatment residuals (WTR). If WTR contain residual chemicals from the purification process, soluble elements may be released potentially causing chemical imbalances in soil and groundwater systems. The study objectives were to: (i) examine Mn, Na, S, and total organic carbon (TOC) released from soil and deionized water leachate from a Norfolk soil (fine-loamy, kaolinitic, thermic Typic Kandiudult) incubated for 60 days with 0 (untreated) and 60 g kg−1 of three different WTR; and (ii) assess effects of oxidation-reduction potential on Mn stability and solubility. The WTR were obtained from a North and South Carolina drinking water treatment facility that treated raw water using alum [Al2(SO4)3], caustic soda (NaOH), and potassium permanganate (KMnO4). During incubation, treatments were maintained between 5% and 10% moisture, and oxidation-reduction potential was measured using a Pt electrode. After 60 days, treatments were leached with 1.2-pore volumes of deionized water. Soils were then analyzed for Mn, Na, and S, and leachates were analyzed for TOC and similar elements using inductively coupled plasma spectroscopy. At this time, WTR-treated soils were slightly acidic, moderately reduced, and enriched in extractable Mn, Na, and S concentrations. Water leachates from WTR-treated soil were also enriched with Mn, Na, S, and TOC. Divalent Mn was the dominant oxidation state, making Mn more susceptible to leaching. One WTR enriched with Mn caused Norfolk soil Mn concentrations to exceed crop sensitive stress threshold levels. It is recommended that a prescreening procedure should be used to determine if WTR applied to soil will release elements that may cause plant growth problems.

Amendments to Increase Aggregation in United States Southeastern Coastal Plain Soils

Many U.S. southeastern Coastal Plain soils have a cemented subsurface hard layer that restricts root growth and decreases productivity. Soil properties are improved by tillage but might also be improved by amending the soil. Wheat (Triticum aestivum L.) residue and polyacrylamide (PAM) were used to amend a Norfolk soil mix of 90% E horizon (the hard layer) and 10% Ap horizon (to assure microbial presence). Our hypothesis was that incorporation of wheat residue and/or PAM would improve physical properties, making the soil more amenable to root growth. Treatments contained 450 g of soil mix, 6.44 g kg ground wheat stubble, and 0, 30, or 120 mg kg -1 of PAM (an anionic, linear formulation of size 12 MDa and 35% charge density). Duplicate sets of replicated treatments were incubated at 10% gravimetric water content for 30 and 60 days. Treatments were leached with 1.3 pore volumes of water. After leaching and equilibration to stable water contents, soil strengths were measured with a 3-mm-diameter flat-tipped bench-top penetrometer. At 30 days, the treatments were not significantly different; but at 60 days, treatments differed. Polyacrylamide decreased bulk density when added at the higher rate of 120 mg kg -1 to the soil. The higher PAM rate also decreased the amount of water that was added to maintain treatments at 10% water content. Wheat residue amendments decreased penetration resistances and increased aggregation. Wheat residue and PAM amendments improved soil physical properties, especially when treatments were allowed to incubate for 60 days.

Organic matter and polyacrylamide amendment of Norfolk loamy sand

Loamy sand soils of the southeastern USA Coastal Plains often have poor physical properties because they contain cemented subsurface hard layers that restrict root development and yield. Their physical properties can be improved by adding amendments. Polyacrylamide (PAM) amendments and/or organic matter (OM) in the form of ground wheat ( Triticum aestivum L.) stubble or pecan ( Carya illinoensis) branches were mixed into a blend of 90% E horizon and 10% Ap horizon (to assure microbial presence) obtained from a Norfolk soil (Acrisol or fine-loamy, siliceous, thermic Typic Kandiudult). We hypothesized that incorporation of these amendments would improve soil physical properties by reducing strength and improving aggregation. Amended treatments contained 450 g of soil, OM, and 30 or 120 mg kg −1 of PAM (12 mg mol −1, anionic, and 35% charge density); treatments were incubated for 96 days at 10% (w/w) water content. Twice during the incubation period, treatments were leached with 1.3 pore volumes of deionized water. After leaching and equilibrating to stable water contents, treatments were analyzed for bulk densities and probed with a 5-mm diameter flat-tipped bench-top penetrometer to measure penetration resistances. Though penetration resistances increased for the highest level of PAM amendment, they showed no significance when both PAM and OM were added to the soil. When compared to controls, treatments with PAM at 120 mg kg −1 had decreased bulk densities. Treatments with both rates of PAM had decreased requirements for water needed to maintain treatments at 10% water contents. Aggregation increased with increasing amounts of PAM but showed no consistent trend when both PAM and OM were added to the soil. Because PAM increased aggregation and water holding capacities in these coastal soils, it could reduce the need for deep tillage. However, more work needs to be done to determine an effective mix of PAM and OM.

Is phosphorus fertilization necessary for watermelon production on high phosphorus soils?

Nutrient loading has created water quality problems in the Chesapeake Bay watershed of the United States. This study was designed to examine if a high yield of quality watermelon [Citrullus lanatus (Thunb.) Matsum. &amp; Nakai] can be produced with reduced phosphorus (P) fertilizer inputs and the use of a preceding cover crop on high P soils of the Eastern Shore of Maryland. Watermelon was planted on a Norfolk soil (fine loamy, siliceous, thermic type kandiudults) in a split plot design, with four replications. The main plot treatments were cover crops (rye versus no cover) and the sub-plot treatments were five different P-fertilizer rates ranging from 0 to 60 kg P ha-1, at 15 kg ha-1 increments. Following harvest, all P fertility regimes left behind “excessive” P levels based on soil tests. The addition of P-fertilizer to these soils was unnecessary for the production of a high yield of marketable quality watermelons. In two of three sites, the use of cover crops preceding the watermelon crop increased yields and fruit size. Use of a rye cover crop and reduced P-fertilizer inputs could have a positive environmental impact by reducing the risk of P over-loading without negatively impacting watermelon yield and quality. Key words: Watermelon quality, phosphorus-reduction, rye cover crop, phosphorus loading

Tillage Effects on Canopy Position Specific Cotton Fiber Properties on Two Soils

The benefits of conservation tillage on soil water availability are well established, but this soil management practice generally does not affect cotton (Gossypium hirsutum L.) fiber properties of the whole crop. The objective was to determine whether soil management practices affect canopy position specific fiber properties on two soils. A 3‐yr field study was conducted with plots on two soil types [Bonneau loamy sand (loamy, siliceous, thermic Arenic Paleudult) and Norfolk loamy sand (fine‐loamy, siliceous, thermic Typic Kandiudult)]. Treatments in the study were cover crop [none and rye (Secale cereale L.)] and tillage system (disk tillage and conservation tillage). Fiber properties were determined from hand picked samples at three canopy positions (first sympodial position bolls at Mainstem Nodes 6 and 7, 9, and 10, and 12 and 13). Yield and fiber properties of the whole crop were determined after machine harvesting. In two of the 3 yr, conservation tillage had 34% higher yield than disk tillage. Conservation tillage had higher fiber length uniformity every year, but no consistent differences between tillage systems occurred for the other fiber properties. Cover crop did not influence within‐canopy fiber properties. When differences occurred between tillage systems for fiber length at specific canopy positions, fibers from conservation tillage were about 1 mm longer than fibers from disk tillage. Fiber length uniformity results were similar to those for fiber length. Disk tillage resulted in cotton with 0.22 lower micronaire units than conservation tillage at Mainstem Nodes 6 and 7 when rainfall was plentiful in 1997, but had micronaire that was 0.82 units higher than conservation tillage at that canopy position during the dryer year of 1998. Within canopy variability for micronaire was greater on the more drought susceptible Bonneau soil than on the Norfolk soil. Results indicate that tillage management can influence canopy position specific fiber property distribution.

Diversity of Root Bacteria from Peanut Cropping Systems

Abstract Rhizobacteria play an important role in sustainable agriculture via plant growth and biological control of pests in a number of ecosystems. Understanding the interactions of crop rotation and rhizobacteria on peanut production is a critical research need. Development of a database on the rhizobacteria obtained from continuous and rotational fields of peanut was initiated in 1997 and terminated in 2000. Peanut was planted in monoculture for 4 yr. In rotational plots, peanut, cotton, corn, and peanut were planted in sequence. Rhizobacteria were isolated from the roots of crop plants grown in a Norfolk soil near Florence, SC. These isolates were identified by composition of fatty acids from gas chromatography analysis (GC/FAME). Arthrobacter and Bacillus were the major genera from non-rhizosphere soils. At initiation of this study in July 1997, the plots selected for continuous peanut had more diversity in rhizobacteria than those plots selected for rotation. In July 2000, rhizobacteria diversity was greater from peanut roots in the rotation cropping system than continuous peanut. Even though rhizobacteria diversity was greater in the rotation system, higher peanut yields were recorded in the continuous peanut system in 2000. Burkholderia spp. were always isolated from the peanut and other crop rhizospheres at each sampling date.

Managing phosphorus for yield and quality of sweet corn grown on high phosphorus soils of Maryland's eastern shore

Reducing P fertilization to address water quality problems has raised concerns among producers regarding crop yield and quality. A 3 yr study was conducted at three sites to examine whether reduction in P fertilization rate and/or use of a preceding rye cover crop affect the yield and quality (sugar concentration and ear weight) of sweet corn (Zea mays L.) grown on soils with “excessive” plant-available P. The experimental design was a split plot with four replications conducted on Norfolk soils. The main plots were no cover crop and a rye cover crop. The subplots were five P fertilizer treatments ranging from 0 to 60 kg P ha-1 at 15 kg P increments. With or without a preceding rye cover crop or P fertilization, postharvest soil test P (Mehlich-1) levels remained “excessive” to a depth of 40 cm. Also, yield of sweet corn was not affected by P fertilization and/or use of a preceding rye cover crop. Without cover cropping, sugar content and ear weight response to P fertilization was positive on site 2 for sugar, and on sites 2 and 3 for ear weight. Utilization of cover cropping positively influenced sweet corn sugar and ear weight sampled at early milk stage without affecting the final yield. In processing sweet corn production, profitability is determined mainly by the yield of marketable ears. Therefore, the small, inconsistent increases in sugar content and ear weight in response to P fertilization, without an increase in yield is not of a major significance to the farmer. On high P soils, P fertilization is unnecessary for the production of quality, high-yield processing corn. The use of a rye cover crop is suggested as a method of reducing the risk of P loss into the surrounding watershed. Key words: Sweet corn yield, sweet corn quality, P fertilization, rye cover crop, phosphorus management, high P soils