摘要:

Lack of uniformity in soil physical and chemical characteristics is one of the main causes of variation in crop productivity. We investigated the effect of nonuniformity (spatial variability) of residual K on corn response in field conditions. Corn growth was strongly related to both the level and spatial variability of soil K. Increased variation of residual K from CV = 37.0% to CV = 48.5% resulted in yield losses and an increase in the critical level of exchangeable K from 0.16 to 0.24 cmol(+) ± Kg−1. Decrease in yield due to spatial variability of soil K was quantitatively expressed by the variability response index (VRI), i.e., the product of the variance of soil K and the second derivative of yield with respect to exchangeable K obtained under a relatively uniform distribution of soil K. The variability response index shows promise as a way to estimate crop loss due to excessive variability. There was a gradual decrease in the correlation coefficient between corn yield and ear leaf K with increasing spatial variability of residual K.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Twenty pedons of volcanic ash soils from southern Alaska used in this study have a cryic temperature regime and udic to perudic moisture regimes. They have distinctive morphological properties common to Andisols in many other parts of the world: (1) multisequum with abrupt or clear boundaries, (2) very friable granular structure in A horizons and friable subangular blocky structure in B horizons, and (3) loamy texture with a smeary consistency. They also have distinctive morphological properties common to Spodosols: (1) an organic horizon in all the pedons, (2) an albic or E horizon in most pedons, (3) underlying the E horizon, one or more horizons with hue redder than 10 YR in most pedons, and (4) a placic horizon below the spodiclike horizons in some pedons.The physical and chemical properties of the 13 pedons are presented and discussed. The properties of 7 pedons presented in previous studies are reviewed. All 20 pedons were found to meet the criteria of andic properties, and 19 of them also meet the chemical criteria of a spodic horizon. The pedons were classified according to bothSoil Taxonomyand the Andisol proposal. Andisols were proposed to be keyed out after Histosols, but before Spodosols (Leamy 1988). Those Andisols having chemical properties of spodic horizon are differentiated from Spodosols by not having an albic-spodic sequum within the required thickness of horizons with andic properties. A comparison of the two classifications and the implication for soil survey and interpretation are also discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We studied 11 representative pedons from four physiographic groups. When Feoxide was removed before particle-size analyses, the percentage of clay was higher than when Fe-oxide was present. It was also commonly higher than clay estimated by the factor 2.5 x 15 bar moisture content. Therefore, 2.8 would be a more suitable factor than 2.5.The criterion, sum of exchangeable cations x 100/clay % ≤ 12 meq does not alone separate the oxic or kandic horizons from other diagnostic horizons of the soils studied. All pedons studied met this criterion. The criterion CEC x 100/clay % ± 16 meq was somewhat more useful. One soil narrowly failed to meet this limit, until 2.8 was used instead of 2.5, as suggested above. A critical value of about 0.09 for the ratios: %Fe2O3-d/clay % and %Fe2O3-d minus %Fe2O3-o3/clay % may help to separate oxic and nonoxic horizons.5

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Inorganic contaminants are present in storm-water runoff from urban residential areas. The disposition of the major cations and anions in the alluvium deposits of a recharge basin, percolating water, and the mound of soil water below the basin were investigated relative to a nearby control site. This investigation was a component of the USEPA's Nationwide Urban Runoff Program in Fresno, California.The study basin has received urban storm-water runoff from a residential area for 16 yr. The recharge effects to a depth of 21 m have been an increase in exchangeable Ca2+and K+, a decrease in exchangeable Mg2+, and a minor increase in the exchangeable Na+with depth. The specific electrical conductance of the percolating water increased from an input value of 0.056 dS m−1to 0.097 dS m−1at a depth of 20.7 m where the recharge mound had formed.The concentrations of the major dissolved cations and anions in the urban residential storm-water runoff are low. The results indicate that these ions are not detrimental to the physicochemical properties of the surface soils or deep alluvium strata or to the groundwater quality resulting from recharging urban residential storm-water runoff.These results are important to the continued conservation of urban storm water and the preservation of the chemical and physical properties of the retention/recharge basin surface soils and deep alluvium stratum essential for continuing efficient basin recharge.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Relatively few data exist on the exchange reactions of Li in soils; rather, the bulk of the literature has dealt with simple ion exchange reactions on ideal exchangers, usually synthetic resins or pure clay minerals. Occasional observations of anomalous exchange of Li have been reported, without any clear explanation. This study was initiated to more carefully examine Li exchange in complex soil-solution and clay mineral systems. At the low concentrations employed, Li was sorbed preferentially by the southeastern U.S. soils evaluated over excesses of Na, K, Mg, and Ca in the adsorption solution phase. Trace amounts of Li were also sorbed to bentonite, kaolinite, and vermiculite clay samples in the presence of 0.01MMg(NO3)2(5.82, 3.67, and 8.37 μg g−1, respectively). The bentonite retained no Li against displacement byMNH4Cl, but both the kaolinite and vermiculite fixed a substantial portion of the total sorbed Li (57 and 60%, respectively). Similarly, at low Li additions to an Iredell surface soil sample (0 to 2.4 mmol kg−1), a significant portion of the sorbed Li was fixed against displacement byMNH4Cl,MCsCl, 0.5MMgCl2, and 0.05MHCl/0.012MH2SO4(e.g., 77.0, 79.2, 82.0, and 75.9%, respectively, at a 1.1 mmol kg−1loading). The rate of Li sorption to the Iredell surface soil was slowed in the presence of a 0.005MMgCl2background relative to an absence of background electrolyte. The extent of sorption was also reduced to 80% of that observed without supporting electrolyte, in agreement with the mass of Li observed to be fixed against displacement in the desorption study. The source and nature of sorption sites within soils and clay minerals that have this high selectivity for Li remain unclear, although vacant octahedral positions at the mineral edge may be responsible.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The effect of wetting front depth on the infiltration rate (IR) of Calcic Haploxeralf and Typic Chromoxerert soils was studied under field conditions using a rainfall simulator. In both soils the IR decreased more sharply when the wetting front was deeper, but this difference became smaller as the rainstorm continued. The infiltration rate of the soils at the end of the rainstorm (8 x 10−2m) was 8.5 x 10−3, 6.3 x 10−3, and 5.0 x 10−3m h−1for the Calcic Haploxeralf soil prewetted with water at amounts equivalent to 0, 3 x 10−2, and 2 x 10−1m, respectively, and 1.5 x 10−3, and 1.0 x 10−3m h−1for the Typic Chromoxereret soil prewetted with water at amounts equivalent to 0, and 2 x 10−1m, respectively. When the dry soil surface was covered with mulch, however, the steady-state value of the IR was 3.5 x 10−2m h−1for both soils. The high permeability of the soils during the rainstorm in the presence of mulch and the low steady-state IR values for the various prewetting treatments both suggest that the moisture regime in the profile had a negligible effect on the IR in the presence of soil crust.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Wetting-front instability, or gravity-driven fingering, can occur during vertical infiltration. Previous studies found that fingers persist over long periods of constant infiltration and in subsequent infiltration cycles. We present a physically based theory to explain finger persistence. The theory is tested using a new technique in which moisture contents are visualized by the transmission of light through unsaturated sand, recorded with a video camera, and then analyzed by video digitizing computer hardware. Theory and experiments show that hysteresis in the moisture characteristic relationship explains the persistence of fingers in time.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID