M. J. Krogmeier

Effects of phenolic acids on seed germination and seedling growth in soil

SummaryIt is commonly assumed that the adverse effect of plant residues on crop yields is largely or partly due to phytotoxic compounds leached from these residues or produced by their decomposition. There has been substantial support for the hypothesis that the phytotoxic compounds responsible for reduced crop yields are phenolic acids such as p-coumaric acid, p-hydroxybenzoic acid, and ferulic acid. To test the validity of this hypothesis, we studied the effects of nine phenolic acids (caffeic acid, chlorogenic acid, p-coumaric acid, ellagic acid, ferulic acid, gallic acid, p-hydroxybenzoic acid, syringic acid, and vanillic acid) on (1) seed germination of corn (Zea mays L.), barley (Hordeum vulgare L.), oats (Avena sativa L.), rye (Secale cereale L.), sorghum [Sorghum bicolor (L.) Moench], wheat (Triticum aestivum L.), and alfalfa (Medicago sativa L.) on germination paper and soil, (2) seedling growth of alfalfa, oats, sorghum, and wheat on germination paper and soil, and (3) early plant growth of corn, barley, oats, rye, sorghum, and wheat in soil. The results showed that although the phenolic acids tested affected germination and seedling growth on germination paper, they had no effect on seed germination, seedling growth, or early plant growth in soil even when the amounts applied were much greater than the amounts detected in soil. We conclude that the adverse effect of plant residues on crop yields is not due to phenolic acids derived from these residues.

Effect of nickel deficiency in soybeans on the phytotoxicity of foliar-applied urea

The leaf-tip necrosis commonly observed after foliar fertilization of soybean [Glycine max (L.) Merr.] plants with urea is usually attributed to ammonia formed through hydrolysis of urea by plant urease. We recently found, however, that although addition of a urease inhibitor (phenylphosphorodiamidate) to foliar-applied urea increased the urea content and decreased the ammonia content and urease activity of soybean leaves, it increased the leaf-tip necrosis observed after foliar fertilization. We concluded that this necrosis was due to accumulation of toxic amounts of urea rather than formation of toxic amounts of ammonia. To confirm this conclusion, we measured the urea content, urease activity, and leaf-tep necrosis of leaves of soybean plants treated with urea after growth of the plants in nutrient solutions containing different amounts of nickel (Ni), which is an essential component of urease. We found that the urease activity of these leaves decreased, and that their urea content and leaf-tip necrosis increased, with decrease in the Ni content of the nutrient solution. Besides supporting the conclusion that the leaf-tip necrosis observed after foliar fertilization of soybean with urea is due to accumulation of toxic amounts of urea in the soybean leaves, these observations indicate that Ni-deficient plants may have a lower urease activity than plants that are not deficient in Ni and may therefore be more susceptible to leaf burn when foliar-fertilized with urea.

Evaluation of ammonium thiosulfate as a soil urease inhibitor

Interest in use of ammonium thiosulfate (ATS) in conjunction with urea as a fertilizer has been stimulated by recent reports that this compound retards hydrolysis of urea by soil urease and thereby reduces volatilization of urea N as ammonia from soils fertilized with urea. We evaluated ATS as a soil urease inhibitor by studying its effects on urea hydrolysis, seed germination, and early seedling growth in soil. We found that ATS significantly retarded urea hydrolysis only when applied at rates as high as 2,500 or 5,000µg g−1 soil, whereasN-(n-butyl) thiophosphoric triamide (NBPT) (a patented inhibitor of urea hydrolysis in soil) caused substantial retardation of urea hydrolysis when applied at rates as low as 1µg g−1 soil. We also found that ATS had an adverse effect on germination of corn or wheat seeds in soil when applied at the rate of 2,500 or 5,000µg g−1 soil and caused a dramatic reduction of early seedling growth of corn or wheat when applied at the rate of 1,000, 2,500, or 5,000µg g−1 soil. These findings indicate that ATS has little, if any, potential value for retarding hydrolysis of urea fertilizer in soil.

Effects of urease inhibitors on germination of seeds in soil

Abstract The effects of 23 urease inhibitors on germination of seeds in soil were investigated. The urease inhibitors tested were 2/5‐dimethyl‐l,4‐benzoquinone, 1/4‐benzoquinone, hydroquinone, 2,5‐dichloro‐l,4‐benzoquinone, phenylmercuric acetate, catechol, phenylphosphorodiamidate, phosphoric triamide, N‐(4‐nitrophenyl)‐phosphoric triamide, N‐(diaminophosphinyl)benzeneacetamide, 4‐chloro‐N‐(diaminophosphinyl)benzamide, N‐3‐(trifluoromethyl‐phenyl)phosphoric triamide, 4‐fluoro‐N‐(diaminophosphinyl)‐benzamide/ 4‐cyano‐N‐(diaminophosphinyl)benzamide, N‐(diamino‐phosphinyl)‐3‐pyridinecarboxamide, N‐(diaminophosphinyl)‐benzamide, N‐phenylphosphoric triamide, phosphorodiamidic acid, N‐(n‐butyl)thiophosphoric triamide, thiophosphoric triamide, 4‐chlorophenylphosphorodiamidate, 2,4‐diphenoxy‐2,4,6,6‐tetraaminocyclotriphosphazene, and 2‐phenoxy‐2,4,4,6,6‐pentaaminocyclotriphosphazene. Germination tests were performed with seeds of alfalfa (Medicago sativa L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare...

Effects of aliphatic acids on seed germination and seedling growth in soil

Abstract It is commonly assumed that the adverse effect of plant residues on crop yields is largely, or partly, due to phytotoxic compounds leached from these residues or produced by their decomposition, and it has been suggested that the phytotoxic compounds responsible for reduced crop yields are aliphatic acids such as acetic acid, butyric acid, and propionic acid. To test the validity of this hypothesis, we studied the effects of different amounts of acetic acid, butyric acid, and propionic acid on seed germination and seedling growth of corn (Zea mays L.), barley (Hordeum vulgare L.), and wheat (Triticum aestivum L.) in soils. The data obtained showed that the aliphatic acids tested had adverse effects on seed germination and seedling growth only when the amounts applied were much greater than the amounts reported to occur in soils treated with plant residues. We conclude that the adverse effect of plant residues on crop yields is not due to aliphatic acids derived from these residues.

Effects of nitrification inhibitors on germination of various seeds in soil

SummaryThe effects of 19 nitrificiation inhibitors on germination of seeds in soil were investigated. The nitrification inhibitors tested were sodium azide, potassium azide, potassium ethyl xanthate, nitrapyrin (N-Serve), etridiazole (Dwell), 3-mercapto-1,2,4-triazole (MT), 2-amino-4-chloro-6-methylpyrimidine (AM), 2,4-diamino-6-trichloromethyl-s-triazine, 2-mercaptobenzothiazole (MBT), 4-amino-1,2,4-triazole (ATC), sodium thiocarbonate (STC), guanylthiourea (ASU), thiourea (TU), dicyandiamide (DCD), sulfathiazole (STC), phenylacetylene, 2-ethynyl-pyridine, 3-methylpyrazole-l-carboxamide (MPC), and ammonium thiosulfate (ATS). Germination tests were performed with seeds of alfalfa (Medicago sativa L.), wheat (Triticum aestivum L.), rye (Secale cereale L.), barley (Hordeum vulgare L.), sorghum [Sorghum bicolor (L.) Moench], oats (Avena sativa L.), and corn (Zea mays). Only 2 of the 19 nitrification inhibitors studied (potassium azide and sodium azide) reduced germination of the seeds tested when applied at the rate of 12.5 μg g−1. The other inhibitors studied had no effect on the germination of wheat, alfalfa, barley, corn, oat, rye, or sorghum seeds when they were applied at the rate of 125 μg g−1 soil, and most of them had no effect on seed germination when applied at the rate of 625 μg g−1 soil.

Effects of thiosulfate and tetrathionate on urease activity and seedling growth

Abstract Interest in use of ammonium thiosulfate (ATS) in conjunction with urea as a fertilizer has been stimulated by reports that ATS retards hydrolysis of urea by soil urease. We recently found, however, that ATS significantly retarded urea hydrolysis in soil only when applied at very high rates (>2,500 (μg/g soil) that adversely affected seedling development. Because ATS is rapidly oxidized in soil, we compared the effects of thiosulfate and its oxidation products (tetrathionate, sulfite, and sulfate) on urea hydrolysis and seedling development in soil and hydrolysis of urea by jackbean urease. We found that the inhibitory effect of thiosulfate on urea hydrolysis in soil is due to tetrathionate formed by oxidation of thiosulfate and that both thiosulfate and tetrathionate have an adverse effect on seedling growth of wheat and corn in soil. Tetrathionate at concentrations of 2,500 and 5,000 μ.g/mL inhibited hydrolysis of urea by jackbean urease, whereas thiosulfate had no inhibitory effect at these con...

Effects of water‐soluble constituents of plant residues on water uptake by seeds

Abstract There has been strong support for the hypothesis that the adverse effects of plant residues on crop yields are due to phytotoxic compounds derived from these residues. This hypothesis is based largely on studies showing that, when compared with distilled water, aqueous extracts of plant residues have an adverse effect on seed germination and seedling growth. Because seed germination and seedling growth are reduced by a delay in germination resulting from slow uptake of water by seeds, we studied the possibility that the adverse effects of aqueous extracts of plant residues on seed germination and seedling growth might be at least partly due to water uptake by seeds being retarded by water‐soluble constituents of these residues. To test this possibility, we compared the rates of water uptake and germination of seeds of corn (Zea mays L.), soybean [Glycine max. (L.) Merrill], and wheat (Triticum aestivum L.) when these seeds were treated with distilled water and with aqueous extracts of corn, sorgh...