No‐tillage systems utilizing winter cover crops can reduce erosion and leaching losses. Fall‐seeded legumes can also supply significant amounts of N to subsequent corn (Zea mays L.) crops. The suitability of 14 fall‐seeded legumes, three small grains and four legume/grass mixtures was evaluated for winter covers from 1982 through 1985 on Matapeake silt loam (fine‐loamy, mixed, mesic, Typic Hapludult) and Mattapex silt loam(fine‐silty, mixed mesic, Aqualfic Normuldult) Coastal Plain soils as well as Delanco silt loam and Chester silt loam (fine‐loamy, mixed, mesic, Aquic Hapludult) Piedmont soils. Hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.) and Austrian winter peas [Pisum sativum (L.) Poir.] were the most promising cover crops. Fall growth and early soil coverage was highest with crimson and lowest with vetch which had higher winter survival and spring growth. Peas and, to a lesser extent, crimson clover stands were damaged in some years by Sclerotinia trifoliorum Eriks. In some years top growth of vetch contained up to 350 kg N/ha. While N concentration varied among species, total N production was determined more by dry matter yield. Legume cover crops had a greater influence on corn grain yields on the heavier textured soils and longer growing season of the Coastal Plain. In 1985, N contribution to the subsequent corn crop was reduced when small grains were seeded with annual legumes. Results from these studies show that winter annual legumes can reduce N costs while providing better soil protection during winter months.

Alfalfa grown at high soil moisture stress in growth chamber and field studies yielded less dry matter than that grown at low soil moisture stress. A higher percentage of leaves, higher percentage of in vitro digestibility (IVDDM), and lower percentages of acid detergent fiber (ADF) and lignin (ADL) often occurred in forage grown at high soil moisture stress. Soil moisture did not affect the percentage of crude protein (CP) consistently. Under controlled‐environment conditions, alfalfa grown at high temperatures (27 C day/21 C night) yielded less dry matter and had lower digestibility and higher ADF and ADL than that grown at lower temperatures (16 C day/10 C night). This occurred even though percentage of leaves and CP increased at high temperatures. The lowest ADF concentration (indicative of highest quality) occurred at low temperatures and high soil moisture stress; also, IVDDM was among its highest and ADL among its lowest levels under these conditions (also indicative of high quality). Low temperatures and low soil moisture stress were generally associated with a higher yield of a relatively higher quality forage than were high temperatures and high soil moisture stress. Crude protein failed to estimate alfalfa quality when forage was produced in diverse climates, confirming earlier reports.

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Dairy manure, as a passive by-product of livestock, is an important source of nutrients and organic matter to soils that support forage production. A split-plot experiment was conducted to determine the long-term (1994 -1999) effects of dairy manure and chemical fertilizer on soil quality properties and carbon (C) sequestration in an alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) forage systems. Five years after initiation of the experiment, soil core samples were collected randomly from between the alfalfa -orchardgrass rows under different treatments and analyzed or incubated to determine selected soil biological, chemical and physical properties. Results show that long-term application of dairy manure slurries significantly increased total organic, microbial biomass, potentially mineralizable, extractable and labile C pools, respectively, and improved soil aggregate stability by associated decrease in specific maintenance respiration rates, and subsequently enhanced soil quality. Relatively smaller amounts of total, microbial biomass, extractable and labile C pools with an increase in specific maintenance respiration rates, and increase in soil acidity accompanied by a decrease in aggregate stability suggest that long-term and continuous use of inorganic fertilizers for forage production did not improve soil quality or enhance C sequestration. The continuous cover of forage species, especially alfalfa, significantly improved soil quality over time as compared to orchardgrass species. The beneficial effects of organic amendments are important for proper disposal and utilization of dairy manures in forage production systems with an accompanied improvement in soil quality and C sequestration.

Selected forage and soil conservation grasses and legumes were evaluated in the greenhouse for their abilities to stimulate dissipation of PCB, TNT, and pyrene in a soil. The grasses tested were tall fescue (Festuca arundinacea Schreb), reed canarygrass( Phalaris arundinacea L.), switchgrass ( Panicum variegatum L.), and deertongue (Panicum clandestinum L.). The legumes were alfalfa (Medicago sauva L.), crownvetch (Coronilla varia L.), sericea lespedeza (Lespedeza cuneata Dum-Cours.), and flatpea (Wagner pea) ( Lathyrus sylvestris L). The plants were grown in 13.5x15.0 cm pots containing soils that were fortified with 100 mg/kg nominal concentrations of the respective compounds andaged in the laboratory. After six months, 51% or less of an initial 100 mg/kg dose of aroclor 1248 was recovered from soils planted with reed canarygrass, switchgrass, and flatpea. Between 64-70% of the initial dose was recovered from soils planted with tall fescue, deer tongue, and sericea lespedeza, and about 80 % 1646 KUDJO DZANTOR, CHEKOL, AND VOUGH or more was recovered from soils that were planted with alfalfa and crownvetch as well as soil that was left implanted. During the same period, <0.5% of the initial dose of TNT and <3% of pyrene were recovered from soils that were fortified with those compounds, including unplanted controls. Laboratory flask experiments that compared the dissipation of TNT and pyrene in natural soils and soils containing microbial inhibitor suggested that microbial transformation accounted for a major portion of the loss of TNT and pyrene in this soil. A comparison of the dissipation of TNT and pyrene in two different soils reinforces previously well-documented strong role of organic matter in the overall fate of TNT and pyrene in soil.

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This article presents the results of a study that was conducted to determine the effectiveness of using alfalfa (Medicago sativa L.) to enhance the phytoremediation of three different types of chemical contaminants. The chemicals studied were trinitrotoluene (TNT), the polycyclic aromatic hydrocarbon (PAH) pyrene, and the polychlorinated biphenyl (PCB) Aroclor 1248. Experiments were conducted using soils that contained high and low organic matter content. The results indicated that recoveries of pyrene and TNT from soil were highly dependent on the soil organic matter content, while the recovery of PCB was not. Significantly low levels of pyrene and TNT were recovered from all treatments in the soil with 6.3 percent organic matter content compared to recovery levels found in soil with 2.6 percent organic matter. The presence of alfalfa plants had a significant effect on the transformation of TNT and PCB in the low organic matter content soil only and had no effect on the fate of pyrene. In the low organic matter soil, only 15 percent and 17 percent of the initial TNT and PCB levels, respectively, were transformed in the unplanted control soils compared to 66 percent and 77 percent in the alfalfa planted pots. In both soil types, pyrene dissipation could not be attributed to the presence of alfalfa plants. Overall, it was concluded that under high soil organic matter conditions, adsorption and covalent binding to the soil organic matter appeared to be the dominant force of pyrene and TNT removal. The effectiveness of using alfalfa to enhance PCB and TNT transformations was more significant in the lower organic matter soil; thus phytoremediation had a greater effect in soils with lower organic matter content. © 2001 John Wiley & Sons, Inc.

Legume cover crops are valuable N sources for no‐tillage corn (Zea mays L.). However, little research has been done in assessing the management options for legume cover crops. Field studies were conducted on a Coastal Plain Matapeake silt loam soil (fine‐silt, mixed, mesic Typic Hapludult) from 1983 through 1986 to determine the effects of various harvest management schedules on total N contribution of legume cover crops, subsequent corn grain and silage yields, and total forage (combined cover crop and corn herbage) production. A crimson clover (Trifolium incarnatum L.) cover crop was subjected to no harvest; spring silage harvest with clippings removed (spring silage); and simulated pasture harvests with clippings from multiple harvests removed (pasture removed) or returned (pasture returned). A no‐cover control treatment was also included. No‐tillage corn was grown in the cover crop residues and two fertilizer N (FN) rates (0 and 90 kg ha−1) were applied in a split‐block design to each harvest management treatment. Averaged over 3 yr, multiple harvests of the cover crop vs. a spring silage harvest resulted in lower cover crop herbage yields (3.0 vs. 4.7 Mg ha−1) and total N content (114 vs. 146 kg N ha−1) for the multiple harvests. Corn grain and silage yields and corn N uptake were consistently higher following crimson clover cover than for no cover, regardless of harvest management, and were generally higher when the cover was left in place than following removal of the cover. There were FN responses regardless of harvest management treatment. The reduction in corn silage yield when the cover crop was harvested and removed was less than the cover crop herbage dry matter yield, resulting in greater total forage production when the cover crop was harvested as forage. Results suggest that harvest management options of a crimson clover cover crop offer flexibility in either optimizing subsequent corn grain yields or total forage production for no‐tillage cropping systems and provide control over how cover crop N is utilized in the overall cropping system.