摘要:

The equationI=atb+Kstis proposed as a model of infiltration. This is a combination of the Lewis-Kostiakov equation and Philip's two-term infiltration equation, but it has the advantage of eliminating the lapses of both those equations. The formulas by whichaandbcan be predicted in advance are also presented.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

The amount of nitrogen fertilizer needed by a sugarbeet crop can be estimated more accurately by considering the release of N from soil, especially from organic matter. The analytical data of Nhwsare closely related to N produced on incubation and give an index of N-supplying capability of soil of a specific sampling site. As nitrate N is not measured by the Nhwsprocedure, Nhwsvalues remain nearly constant over the cropping season. Nevertheless, a long-term influence of farm management measures is evident.Nhwsof subsoil is correlated to yield and optimum N requirement, respectively.A diagram that includes Nhwsin topsoil and subsoil can be an aid to better estimating the N-supplying capability of a soil. Comparative calculations of Nhwsdata of field trials showed that estimating the N requirement from Nhwscaused very few errors.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

We evaluated the phosphorus fertility of 19 typical, California, annual grassland, pasture soils by comparing nine soil P tests: total, Bray and Kurtz methods 1 and 2, two Olsen extractions (1:10 and 1:20 soil: extractant ratios), and the “North Carolina,” Truog, Morgan, and Bingham methods. Soil P test results were correlated with subclover-annual grass forage production and P content in the field and in the greenhouse. Correlation of soil P with actual yields and P uptake was generally better in the field than in the greenhouse. Phosphorus in the Bray and Kurtz 1 and the Olsen 1:10 and 1:20 extracts gave the best predictions of field forage production (respectively,r= 0.82, 0.73, and 0.67; P < 0.01). The relative values of the various tests in predicting field forage P content were quite similar with actual yields. The Bray and Kurtz 1 method was the most precise (r= 0.87), and the Olsen extracts were also highly correlated (P < 0.01).Bray and Kurtz 1 extractable soil P accounted for about 67 percent of the variation in subclover-annual grass forage yield and about 76 percent of the variation in forage P content. These were about 14 percent higher than with the Olsen extractants. When we consider relative precision and facility (a 60-second extraction time), the Bray and Kurtz 1 method appears to be of greater potential value for routine testing of annual pasture soils in north-coastal California.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

We studied the adsorption of twos-triazine and two substituted urea herbicides by three different soil humic acids, using elementary analyses and infrared spectroscopy.Obtained data show that adsorption occurs in all cases, involving such mechanisms as ionic bonds, only for thes-triazines; H-bonding; van der Waals forces; and possibly charge transfer in boths-triazine-HA and substituted urea-HA complexes.The extent of adsorption is higher fors-triazines than for substituted ureas, in the order: prometone > methoprotryne > monuron > fenuron.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

We studied the effects of both electrolyte concentration (C) and sodium adsorption ratio (SAR) on phosphorus retention by three arid-zone, surface soil samples differing in texture. The soil samples were previously equilibrated with NaCl-CaCl2mixed salt solutions to render samples of different SAR values.The results indicate that phosphorus retention by the three soils increases as C increases or as SAR decreases. These effects should be considered when appraising phosphorus fertilizer application to salt-affected soils.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Losses of applied ammonium sulfate, urea, or organic nitrogen (rice straw) to flooded soils were evaluated using labeled nitrogen-15. In a laboratory batch incubation experiment, loss of applied ammonium15N or urea15N was influenced by soil type. Soils with high cation exchange capacity and organic matter decreased losses of applied N. No appreciable losses were observed when these soils were treated with organic15N (rice straw). In a field experiment on a flooded Crowley silt loam soil, losses of applied ammonium15N and urea15N were high in the absence of rice plants, and losses of N were significantly reduced in the presence of rice plants.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

In a greenhouse study, we determined the optimum level or range of soil matric potential (SMP) for rapid, early-season soybean growth and development. Sharkey clay (Vertic Haplaquept, very fine, montmorillonitic, thermic) and Dubbs silt loam (typic Hapludalf, fine-silty, mixed, thermic) surface soils were equilibrated before planting to SMPs of near –0.3, —0.4, —0.5, —0.6, and —0.7 bar, as measured with tensiometers inserted into individual plastic pots. The plant water status resulting from the SMPs was evaluated by measurement of xylem pressure potential (PP). At 35 days after planting, plants were harvested, and dry weights of leaves, stems, and roots were determined. Leaf area index (LAI) and shoot-root ratios were calculated, and nodes/plant and plant height were also measured.Shoot weights and LAIs of plants growing in soils with —0.3, —0.4, and —0.5 bar SMP did not differ, but both declined significantly at —0.6 and —0.7 bar SMP. Root density values in the —0.3− to —0.6-bar SMP range were not significantly different, but were significantly higher than the value measured at the —0.7-bar SMP. The amount of shoot mass supported by a unit of root mass progressively declined as SMP decreased. The Sharkey clay supported more shoot dry matter and leaf area production than did the Dubbs silt loam at all SMPs of the study. This was attributed to a more favorable water status of the plants growing in the Sharkey clay, as determined from the PP measurements. The results of this study indicated that for the most rapid vegetative growth and development of soybeans, SMP should be kept above —0.6 bar.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Soil samples for microelement extraction are often taken with little regard to field moisture content and stored under a variety of conditions. In order to study the effects of these practices on extractable microelements, we incubated three soils for 2 weeks at various temperatures and moisture contents. The temperatures were 10, 25, and 40°C, and the moisture levels were 5, 1/3, and 0 bars tension. The soils were extracted for diethylenetriamine pentaacetic acid manganese, iron, copper, and zinc after air-drying, as well as in the moist state.Extractable Mn, Fe, and Cu increased with increased temperatures when the soils were incubated at the 0-bar moisture level. Temperature had no effect on these elements at the dryer moisture levels. Increased temperatures decreased Zn extractability in many cases for samples air-dried prior to extraction. Large increases in extractable Mn and smaller increases in Fe and Cu resulted when soils were incubated at 0-bar moisture. Changes in the extractable Mn, Fe, and Cu between the two drier moisture levels were mostly nonsignificant. Extractable Zn decreased with increasing moisture levels. Air-drying the soils prior to extraction caused increased extractable Mn and Fe, when compared with moist extraction at the lower two incubation moisture levels, but at the 0-bar level this pattern was reversed. Extractable Cu and Zn increased upon air-drying the samples prior to extraction, as compared with moist extraction, in nearly every case.Varying temperature and moisture caused significant changes in the extractability of all the microelements studied. The effect of air-drying increasing extractability at low incubation moisture and decreasing extractability at high moisture is particularly important. The conditions of soil moisture prior to air-drying may influence the effects of air-drying on extractable soil microelements.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Sand shinnery oak grows only on sandy soils in its range. This study examined the effects of soil water, oxygen, and temperature upon radicle elongation. Radicles grew equally well at soil temperatures of 20 to 22°C and 28 to 30°C, but low soil water content (—3 bar) prevented root growth. Soil oxygen treatments of 5, 10, and 15 percent allowed similar root extension at all concentrations. Oxygen diffusion rates (ODR) in the field on three soils—two with oak and one with grassland—were much lower in the soil with 30 percent oak canopy cover than in the 14 and 0 percent oak-covered soils. Soil water availability and not high soil oxygen levels on coarse-textured soils are believed to be of most importance in allowing this oak to dominate on sandy soils.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

We reviewed and compared several greenhouse studies on the effects of low soil oxygen (O2) levels upon plant response. The studies are discussed with particular reference to stomatal closure. Both indirect and direct observations of stomatal closure at low soil O2diffusion rates (ODR) were compiled. Plant response was similar over a wide range of species, including tomato (Lycopersicon esculentum), sunflower (Helianthus, sp.), jojoba (Simmondsia chinensis), cotton (Gossypium hirsutumandG. barbadense), and wheat (Triticum aestivum). The studies reviewed indicate that elimination of soil O2from the profile can cause stomatal closure even at optimum matric potentials. When ODR dropped below 20 x 10−8g.cm−2sec−1, leaf diffuse resistance rose as an exponential function in all the species observed. In some of the studies, photosynthesis and water use were observed to drop when ODR fell below 20 x 10−8g.cm−2sec.−1Whereas stomatal response to low soil O2levels was highly consistent, the effect of low soil O2on plant water potential was not. This suggests that theories pointing to increased root resistance resulting from low soil O2as the cause of stomatal closure do not fully explain some of the observed data. This in turn suggests that stomatal response under the described conditions may not be entirely a passive mechanical response.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID