The distribution of nitrogen in some highly organic tropical volcanic soils

The qualitative and quantitative distribution of N-compounds in 10 tropical soils, and in a number of humic materials extracted from representative samples thereof, was determined after 6 N HCl hydrolysis.Eighty to 98% of the total N in the soils and humic materials was hydrolysable by 6n HCl. Slightly less than one half the hydrolysable N in the soils and humic fractions consisted of amino acids. Well-drained soils and fulvic acids extracted from them contained unusually high concentrations of the acidic amino acids, aspartic and glutamic acids. Between 80 and 95% of the amino acids in the soils was accounted for in the humic materials + NaOH-insoluble organic residues. NH⁺₄-N released by acid hydrolysis was generally higher for the soil samples than for the humic materials. Amino sugar-N constituted relatively small proportions of the total N in the soils and humic fractions.Our data suggest that large quantities of amorphous allophanic materials coupled with relatively high enzymic activity are responsible for the observed accumulation of acidic amino acids in the well-drained tropical volcanic soils.     

Volatilization of sulfur from unamended and sulfate-treated soils

Volatilization of sulfur from unamended and sulfate-treated soils was studied by sensitive gas chromatographic techniques using a flame photometric detector fitted with a sulfur filter. The soils employed were surface samples of 25 Iowa soils selected to obtain a wide range in properties. No release of volatile sulfur compounds was detected when 11 of these soils were incubated under aerobic or waterlogged conditions before or after treatment with sulfate (400 μg sulfate S/g soil). Fourteen soils released volatile sulfur compounds when incubated under waterlogged conditions before and after addition of sulfate, but only 4 of these soils released volatile sulfur compounds when incubated under aerobic conditions. Where volatilization of sulfur was observed, the volatile sulfur detected was identified as dimethyl sulfide or as dimethyl sulfide associated with smaller amounts of carbonyl sulfide, carbon disulfide, methyl mercaptan, and (or) dimethyl disulfide. No trace of hydrogen sulfide was detected. Where release of volatile sulfur was observed, the amount of sulfur volatilized at 30°C in 60 days under aerobic or waterlogged conditions was very small and did not account for more than 0–05% of the sulfur in the unamended or sulfate-treated soils studied. It is concluded that gaseous loss of sulfur from unamended or sulfate-treated soils is insignificant under conditions likely to be encountered in the field.     

Screening method for the detection of aflatoxin, ochratoxin, zearalenone, penicillic acid, and citrinin.

A modification of the official method for ochratoxins and a screening method for zearalenone, aflatoxin, and ochratoxin is described and expanded to include citrinin and penicillic acid. The method uses 0.5N phosphoric acidchloroform (1+10) in the initial extraction; the extract is divided and eluted from 2 columns to provide a quantitative thin layer chromatographic (TLC) method for aflatoxin and ochratoxin in corn and dried beans. Aflatoxin and zearalenone are eluted from one column and ochratoxin, penicillic acid, and citrinin from the other. Ochratoxin A recoveries are low (50%) in peanuts. Zearalenone, penicillic acid, and citrinin were qualitatively recovered from corn and beans; zearalenone and penicillic acid were recovered from peanuts but citrinin was not. Several TLC solvents were used to separate interferences.     

Studies on soil fumigation—III: Effects on enzyme activities,bacterial numbers and extractable ninhydrin reactive compounds

Fumigation of a field soil with chloropicrin and methyl bromide, either singly or in combination, differentially decreased soil enzyme activities and viable bacterial numbers and increased the amounts of ninhydrin reactive compounds extractable with acidified Tris buffer. Chloropicrin treatment was more effective than methyl bromide.The rates of hydrolysis of both an amide and a peptide derivative were decreased by chloropicrin treatment and remained relatively low despite changes in activities over 325 days. By contrast, caseinase activity initially was decreased by both chloropicrin and methyl bromide fumigation, but activities of the fumigated soils recovered to exceed those of untreated soils. Thereafter, caseinase activities of fumigated and untreated soils exhibited relatively large fluctuations, which were partly associated with seasonal drying of the soils in the field.Chloropicrin but not methyl bromide fumigation markedly depressed the viable bacterial populations, which subsequently increased to be above those of the untreated soils. There was no consistent relationship between the release of ninhydrin reactive compounds following fumigation and changes in bacterial numbers or changes in enzyme activity. Autolytic reactions are probably important in the early stages of amino-nitrogen release in fumigated soils. Net gains in caseinase activity may be partly due to the production de novo of extracellular proteases by microorganisms or to the release of intracellular proteases from killed cells.     

Studies on soil fumigation—I: Effects on ammonium,nitrate and phosphate in soil and on the growth,nutrition and yield of wheat

Fumigation of field soil with chloropicrin alone or followed by methyl bromide, each at 220Kg·ha^?1, released 20–30 parts/10⁶ NH⁺₄-N which persisted for 75 days; such fumigation also doubled the amount of bicarbonate-extractable phosphate 28 days after fumigation. Soil fumigation increased both the vegetative and grain yields as well as increasing the content of N in the grain and the content of K and Cl in the tops at ear emergence. Root growth and the phosphate uptake activity of the roots were increased by soil fumigation.     

The effect of delayed autumn harvest on the survival of varieties of perennial ryegrass

The reactions of five early and five late varieties of perennial ryegrass to stimulation of bulky autumn growth and deferment of harvesting were compared in terms of spring growth and subsequent recovery during three winters. Winterkill was marked in 1971–72, particularly when harvesting was deferred to late November, in early varieties S24 and Presto Pajbjerg and in the late variety S23. Least affected among early varieties were Premo and Barvestra (tetraploid) and among late varieties, Perma and Barpastra (tetraploid). All varieties showed rapid recovery. The results are discussed in terms of the significance of winterkill, and the effects of age of sward, variety susceptibility and deferment of autumn defoliation. It is concluded that the form of winterkill which occurs in the west of Scotland can have serious consequences to farm productivity in severe winters. Autumn growth left standing into November can also lead to winterkill. Under good management, varietal differences are unimportant. In a severe winter, no varieties of perennial ryegrass are reliable.