摘要:

We present general optimal results in two dimensions and check their validity by comparison with exact results for a diffusivity obeying a power law. Because of the existence of a first integral of the diffusion equation, these exact results are obtained without iterations. The optimal results form the basis of a new method to estimate the soil-water diffusivity, by measuring the wetting front position when water is injected in the soil at different fluxes. The method is illustrated by analyzing earlier experiments.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Undisturbed soil samples (10 each), of 17 300-cubic centimeter volume, from 38 chemically and physically different soils were leached with 10 liters of solution of known nutrient concentration. The quality of the water draining from the soils was measured to determine how much of the added nutrient was retained by this volume of soil. Physical and chemical tests were used to estimate the total cations that could be stored by this volume of soil by textural and CEC classes. Equations are presented for ion and total cation storage withR2values in excess of 0.7 and showing a moderately low percentage of standard error ofŷ(predicted ion and total cation storage). Five soils were used to test the predictability of the equations. Ion storage for soils high in salt or organic content was difficult to predict, but storage was predictable for most ions.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Studies conducted on three podzol soils with original pH values of 5.0 to 5.4 showed that the sharpest decrease in boron concentration (from 117 to 388 down to 58 to 83 ppm) in barley (Hordeum vulgareL.) and pea (Pisum sativumL.) plant tissues occurred with addition of 2.5 g lime/kg soil. Such rates of lime resulted in soil pH values of 6.8 to 7.3. Additions of 5 g lime/kg soil resulted in soil pH values of 7.3 to 7.7 and further tissue B level decreases of lesser magnitude than the 2.5 g lime rate. A fourfold increase to 20 g lime did not result in further decreases in tissue B. At equivalent amounts of calcium, tissue B concentrations were much higher using CaSO4rather than CaCO3. Plant tissue B was related to soil pH rather than to the amount of Ca. Chloride used as a source of Ca resulted in poor to no growth of crops. The greatest decreases in hot-water-soluble (hws) B occurred with 10 g lime/kg soil. Beyond this rate, no further decreases in hws B occurred. Liming induced B deficiency in peas. Tissue B levels of 8 ppm in peas were associated with B deficiency, and levels of greater than 61 ppm were associated with B toxicity symptoms on the foliage.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Employing gas chromatographic acetylene reduction assay, we investigated nitrogen fixation as influenced by alternate flooded and nonflooded conditions in two paddy soils amended with cellulose. The soil nitrogenase activity was higher under submerged conditions than under nonflooded conditions. The alternate flooded and nonflooded regimes resulted in alterations of the nitrogenase activity. Thus, nitrogenase activity increased several times following a shift from nonflooded to flooded conditions. In contrast, the nitrogenase activity decreased when the flooded soil was returned to the nonflooded condition by draining. Moreover, soil submergence favored nitrogen fixation irrespective of the length of the pretreatment under nonflooded conditions.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

During the first 5 years of cultivation, a peat soil undergoes selective changes in the chemical composition of soluble phenolics. Of the 18 phenolics analyzed, compounds such as substituted hydroxycinnamic acids and 4-hydroxybenzoic acids appear to diminish more rapidly than 3,4-dihydroxybenzoic acid and 4-hydroxy-3-methoxybenzoic acids. It is suggested that phenolic compounds may be useful markers with which to follow the decomposition process in cultivated peat soils.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We monitored the composition of the soil air in native grassland and cultivated fields over several years on upper, middle, and lower slope sites on an Orthic Dark Brown Chernozemic soil. Soil carbon dioxide concentrations approximated 0.1 percent, volume per volume, in late April, started to increase in early May, reached maximum values of 1 to 2 percent, volume per volume, in June and July, and by late September had decreased to the same levels as in late April. The CO2concentrations varied considerably from year to year and were affected more by slope position than by vegetative cover. Comparison between CO2and O2gradients indicated that anaerobic respiration rarely occurred.The annual course of CO2evolution appeared related to climatic conditions during the growing season. Regression equations between CO2evolution, and water content or temperature of the 0− to 10-cm soil layer were rarely significant, but monthly mean CO2evolution correlated well with the mean temperature and total precipitation of that month. Carbon dioxide evolution increased markedly down the slope, reflecting increased productivity and possibly erosion, and was about twice as large under native grassland as on the cultivated fields that were fallowed every second year. Differences in CO2evolution were small between cropped and fallowed sites on similar slope positions. Average CO2evolution of the cultivated fields was estimated at 1900 kg C per hectare per year during the crop year and at 1800 kg C/ha/yr in the fallow year; the mean dry matter input was in the order of 1700 kg C/ha/yr.Accumulation of NO3-N in fallow fields was highest in the years with the lowest CO2evolution. The low accumulation of NO3-N appeared mainly due to immobilization of mineral nitrogen during periods of high soil respiration rates.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We tested 20 herbicides and 36 herbicide combinations for mutagenic activity, using the AmesSalmonella/mammalian microsomes assay. The results show that the herbicides and herbicide combinations tested are nonmutagenic with the Ames assay.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We measured the effects of winter wheat residue, residue placement, nitrogen fertilizer placement, and nitrogen rates on winter wheat growth in greenhouse pot and split root studies under conditions simulating cool-wet spring conditions in the Pacific Northwest. Phytotoxicity to winter wheat plants from decomposing winter wheat residue could not be demonstrated in these studies. When winter wheat straw was mixed with the soil, wheat plant yield decreased significantly, but the decrease was largely overcome by higher rates of N application; hence, in this case, N immobilization during straw decomposition, and not phytotoxicity, appeared to be a primary factor causing yield decreases.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

When soluble iron (Fe2+) was applied in two soils having similar natural pH values, Fe2+was immediately fixed or oxidized to Fe3+in the Wahiawa soil, which has a high level of native manganese, but not in the Paaloa soil, which is low in native Mn. It is shown that Fe2+is being oxidized at the expense of reduction of higher valence oxides of Mn. This has serious implications in the Fe nutrition of plants grown on high-Mn soils.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We examined the influence of calcium carbonate, organic matter, and the inorganic fraction of a calcareous soil on the chemical extractability of239Pu(IV) by using an equilibrium batch technique. The results showed that humic acids, CaCO3, the inorganic phase of the soil, and interaction of these materials could be important factors on the extractability of plutonium.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID