Larry D. King

Phenolic acid content of soils from wheat-no till, wheat-conventional till, and fallow-conventional till soybean cropping systems

Soil core (0–2.5 and/or 0–10 cm) samples were taken from wheat no till, wheat-conventional till, and fallow-conventional till soybean cropping systems from July to October of 1989 and extracted with water in an autoclave. The soil extracts were analyzed for seven common phenolic acids (p-coumaric, vanillic,p-hydroxybenzoic, syringic, caffeic, ferulic, and sinapic; in order of importance) by high-performance liquid chromatography. The highest concentration observed was 4 μg/g soil forp-coumaric acid. Folin & Ciocalteus phenol reagent was used to determine total phenolic acid content. Total phenolic acid content of 0- to 2.5-cm core samples was approximately 34% higher than that of the 0- to 10-cm core samples. Phenolic acid content of 0- to 2.5-cm core samples from wheat-no till systems was significantly higher than those from all other cropping systems. Individual phenolic acids and total phenolic acid content of soils were highly correlated. The last two observations were confirmed by principal component analysis. The concentrations were confirmed by principal component analysis, tions of individual phenolic acids extracted from soil samples were related to soil pH, water content of soil samples, total soil carbon, and total soil nitrogen. Indirect evidence suggested that phenolic acids recovered by the water-autoclave procedure used came primarily from bound forms in the soil samples.

Modification of allelopathic effects ofp-coumaric acid on morning-glory seedling biomass by glucose, methionine, and nitrate

Studies of allelopathy have emphasized primarily the identification and quantification of phytotoxins in soils, with only limited attention directed toward how organic (carbon) and inorganic constituents (nutrients) in the soil may modify the action of such phytotoxins. In the present study, increasing carbon (C) levels (up to 108μg C/g soil) supplied as glucose, phenylalanine, orp-hydroxybenzoic acid did not alter morning-glory biomass, but similar C levels supplied as leucine, methionine, orp-coumaric acid were inversely related to morning-glory biomass. Similar joint action and multiplicative analyses were used to describe morning-glory biomass response to various C sources and to generate dose isolines for combinations ofp-coumaric acid and methionine at two NO3-N levels and for combinations ofp-coumaric acid and glucose at one NO3-N level. Methionine, glucose, and NO3-N treatments influenced the inhibitory action ofp-coumaric acid on biomass production of morning-glory seedlings. For example, results from the multiplicative analysis indicated that a 10% inhibition of morning-glory biomass required 7.5μgp-coumaric acid/g soil, while the presence of 3.68μg methionine/g soil thep-coumaric acid concentration required for 10% inhibition was only 3.75μg/ g soil. Similar response trends were obtained forp-coumaric acid and glucose. The higher NO3-N (14 vs. 3.5μg/g) treatments lowered the methionine and increased thep-coumaric acid concentrations required for 10% inhibition of morning-glory biomass. These results suggested that allelopathic interactions in soil environments can be a function of interacting neutral substances (e.g., glucose), promoters (e.g., NO3-N), and/or inhibitors (e.g., methionine andp-coumaric acid) of plant growth.

Allelopathic activity in wheat-conventional and wheat-no-till soils: Development of soil extract bioassays

The primary objective of this research was to determine if soil extracts could be used directly in bioassays for the detection of allelopathic activity. Here we describe: (1) a way to estimate levels of allelopathic compounds in soil; (2) how pH, solute potential, and/or ion content of extracts may modify the action of allelopathic compounds on germination and radicle and hypocotyl length of crimson clover (Trifolium incarnatum L.) and ivyleaved morning glory (Ipomoea hederacea L. Jacquin.); and (3) how biological activity of soil extracts may be determined. A water-autoclave extraction procedure was chosen over the immediate-water and 5-hr EDTA extraction procedures, because the autoclave procedure was effective in extracting solution and reversibly bound ferulic acid as well as phenolic acids from wheat debris. The resulting soil extracts were used directly in germination bioassays. A mixture of phenolic acids similar to that obtained from wheat-no-till soils did not affect germination of clover or morning glory and radicle and hypocotyl length of morning glory. The mixture did, however, reduce radicle and hypocotyl length of clover. Individual phenolic acids also did not inhibit germination, but did reduce radicle and hypocotyl length of both species. 6-MBOA (6-methoxy-2,3-benzoxazolinone), a conversion product of 2-o-glucosyl-7-methoxy-1,4-benzoxazin-3-one, a hydroxamic acid in living wheat plants, inhibited germination and radicle and hypocotyl length of clover and morning glory. 6-MBOA, however, was not detected in wheat debris, stubble, or soil extracts. Total phenolic acids (FC) in extracts were determined with Folin and Ciocalteus phenol reagent. Levels of FC in wheat-conventionaltill soil extracts were not related to germination or radicle and hypocotyl length of either species. Levels of FC in wheat-no-till soil extracts were also not related to germination of clover or morning glory, but were inversely related to radicle and hypocotyl length of clover and morning glory. FC values, solute potential, and acidity of wheat-no-till soil extracts appeared to be independent (additive) in action on clover radicle and hypocotyl length. Radicle and hypocotyl length of clover was inversely related to increasing FC and solute potential and directly related to decreasing acidity. Biological activity of extracts was determined best from slopes of radicle and hypocotyl length obtained from bioassays of extract dilutions. Thus, data derived from the water-autoclave extraction procedure, FC analysis, and slope analysis for extract activity in conjunction with data on extract pH and solute potential can be used to estimate allelopathic activity of wheat-no-till soils

Use of water and EDTA extractions to estimate available (free and reversibly bound) phenolic acids in Cecil soils

Sterile and microbe reinfested Cecil Ap and Bt soil materials amended with 0 to 5 µmol/g of ferulic acid,p-coumaric acid,p-hydroxybenzoic acid, or vanillic acid were extracted after varying time intervals with water, EDTA, or NaOH to characterize sorption of cinnamic and benzoic acid derivatives and to determine the effectiveness of water and EDTA extractions in estimating concentrations of free and reversibly bound phenolic acids in soils. Basic EDTA (0.5 M, pH 8) extractions and water extractions provided good estimates of both free and reversibly bound cinnamic acid derivatives, but not of benzoic acid derivatives. Neutral EDTA (0.25 M, pH 7) and water extractions, however, were effective for both cinnamic and benzoic acid derivatives Rapid initial sorption of both cinnamic and benzoic acid derivatives was followed by slow long-term sorption of the cinnamic acid derivatives. Slow long-term sorption was not observed for the benzoic acid derivatives. The amount of sorption of phenolic acids in soil materials was directly related to the concentration of phenolic acids added to soil materials. The addition of a second phenolic acid to the soil materials did not substantially affect the sorption of each individual phenolic acid. Sodium hydroxide extractions, which were made only after phenolic acids in phenolic acid-amended and non-amended soil material were depleted by microbes, confirmed that neutral EDTA and water extractions of soils can be used to make accurate estimates of baseline (residual) levels of free and reversibly bound phenolic acids available to soil microbes and, thus, potentially to seeds and roots.

Corn root dry matter and nitrogen distribution as determined by sampling multiple soil cores around individual plants

Abstract Although models of nitrogen (N) flow in agroecosystems describe total plant N uptake, only limited data on roots exists. Underground dry matter and N distribution patterns in corn (Zea mays L.) were determined by isolating root segments from soil cores collected around plants at anthesis from a Typic Kanhapludult. Samples were collected from two treatments: no‐till with 70 kg N/ha and conventional tillage and planting with crimson clover (Trifolium incarnatum L.) as a N source. Seven soil cores (4.2 cm diameter) per plant were taken to recover roots in the 0‐ to 15‐cm and 15‐ to 30‐cm depth intervals. Sampling positions were at the base of the plant and at distances (perpendicular to the row) of 6, 16, and 27 cm into the trafficked interrow, and 11, 22, and 32 cm into the untrafficked interrow. Underground shoot and root segments were isolated from soil cores by hydropneumatic elutriation. Root distribution patterns in the no‐till treatment were similar in trafficked and untrafficked interrows, b...

Green manure as a nitrogen source for wheat in the southeastern United States

Interest in developing more sustainable cropping systems has led to renewed interest in legumes as N sources for crops. We conducted a 2-year study to compare the effects of green manure, green manure plus fertilizer, and fertilizer on wheat yield and N leaching potential. In 1991–92, wheat following corn and receiving 0, 45, or 90 kg N/ha was compared with wheat planted after plowing the autumn regrowth of red clover/johnsongrass hay (supplemented with alfalfa) that supplied 107 kg total N/ha. In 1992–93, wheat following corn and receiving 90 kg N/ha was compared with wheat following hay regrowth that either received fertilizer N at 45 kg/ha or 90 kg N/ha or was supplemented with alfalfa (total of 123 kg N/ha). Yield with only green manure averaged 65% of yield with 90 kg N/ha. Yields with green manure plus 45 or 90 kg N/ha were not different from yield with 90 kg N only. The first year, soil to a depth of 30 cm declined from as high as 40 kg/ha in the fall to less than 10 kg/ha as wheat growth increased in the spring. In contrast, concentration averaged 20 kg/ha throughout the growing season. Trends in soil inorganic N were similar the second year. Profile nitrate distribution indicated a greater potential for N leaching with fertilizer than with green manure. Soil from the site was used in a laboratory incubation study to determine the rate of N mineralization from white clover at 10°C. An average of 80% of the clover N was recovered as soil inorganic N; however, in the field study, recovery (soil inorganic N in the 0 to 30-cm zone + Nin above-ground wheat biomass) was only 21%. Supplementing green manures with spring applications of fertilizer N could decrease the leaching loss without decreasing wheat yield.

Effects of dairy manure application rate and timing, and injector spacing and type on corn silage production☆

Abstract A 3-year field experiment was conducted with liquid dairy manure to determine the effects of application rate (80 and 160 m 3 ha −1 ), application timing (fall and spring), injector spacing (0·48 and 0·96 m) and injector type (chisel and sweep) on corn ( Zea mays L.) silage yield and nitrogen (N) recovery. Harvested N was increased over control plots by chisel injection, narrow injector spacing, spring manure applications, and the high rate of manure application. Silage yield was adversely affected by drought which occurred in the last 2 years of the experiment. Several main factors increased the quantity of N that was not recovered in harvested N or inorganic N in the 0–30 cm layer of soil: chisel > sweep (17%); high > low application rate (109%). Fall application at the low rate generally resulted in lower yield than did 168 kg N ha −1 applied as commercial fertilizer in the spring. There was no significant difference in silage N content between treatments receiving either manure or commercial N fertilizer. Manurial N concentration combined with application rate was determined to have more influence on silage yield than application timing or injector spacing or type.

A greenhouse study on the response of corn (Zea mays L.) to manure from beef cattle fed antibiotics

Abstract Manure from beef cattle receiving the antibiotics lasalocid or monensin or no antibiotic, was used at rates equivalent to 0, 11, 22 and 44t ha −1 (dry weight) in a greenhouse study with corn ( Zea mays L.). Monensin manure was lower in organic N and P but higher in K than were the other manures. In two successive crops, yields with the antibiotic manures were equal to or greater than yields with the control manure at rates of 22t ha −1 or less. Both antibiotic manures suppressed yield at the 44t ha −1 rate in the first crop but not in the second.

Slurry dairy manure as corn nutrient source

Abstract Application of slurry dairy manure were made on five different farms in the Piedmonts region of North Carolina for three consecutive springs and two falls. The manure supplied sufficient nutrients to produce corn (Zea mays L.) silage yields comparable with commercial fertilizer applications at soil test recommendations. The calculated availability of manurial N varied between farms. Yield was usually not significantly different for fall and spring applications of manure, but sometimes the spring manure application resulted in greater yield. The use of a nitrification inhibitor in fall-applied dairy slurry did not give significant yield differences when compared with similar fall treatments that did not receive this material. For maximum manure utilization efficiency application rates should be below 224kg N ha −1 (80 m 3 manure ha −1 ). The slurry manure nutrient concentrations were found to vary considerably between farms and from season to season at a given farm, indicating the desirability of seasonal manurial analysis. Some test sites, due to previou manure and/or fertilizer applications, were found to be unresponsive to either manure or fertilizer applications. Nitrogen availability (NA) was found to vary with site; however, spring manure applications appear to give higher NA values.

Variation in 15N enrichment of crimson clover labeled under field conditions

Plant material labeled with 15N is often used to determine recovery of N from green manure crops by subsequent crops. In this study, 15N enriched crimson clover (Trifolium incarnatum L.) was grown at a field site where it was to be utilized in a subsequent experiment. A foliar spray of (NH4)2SO4 (99 atom % excess 15N) was applied to a 1.2 m × 8.8 m plot of crimson clover at a rate of 10 kg N ha−1 in early March 1990, immediately prior to the period of rapid vegetative growth. Clover shoots harvested in April contained 1.72 atom % excess 15N. Total N concentration of enriched clover was similar to that in adjacent untreated clover. Clover shoots contained 20% of the applied 15N, and an additional 27% was recovered from the surface soil horizon (0 to 15 cm). A gradient was observed across the plot, with clover enrichment increasing from 1.3 to 2.2 atom % excess 15N. Recovery of applied 15N in soil was highest in the subplots with lowest clover enrichment. Variability in 15N enrichment was also observed among plant parts: leaves from the basal half of shoots had 2.2 atom % excess 15N; while leaves from the terminal half of shoots, terminal stems, and basal stems had between 1.1 and 1.4 atom % excess 15N.