摘要:

Soil water storage over a 2.85-m soil depth was measured from 200 aluminum access pipes, separated by 0.3 m in both directions, in a 1.2 × 15.0-m plot in dry and wet periods during 1988 and 1989. The objective was to determine the minimum plot size and number of soil water content measurements if measured with a neutron probe for small field trials. The minimum plot size representing the 15-m plot was found to be dependent on water storage variance and on the distance over which soil water storage measurements were spatially correlated. We concluded that a plot length of 5 m was needed to represent the mean and variance of the 15-m plot. Bootstrapping and temporal stability analysis were used to estimate the minimum number of observation tubes required to estimate the mean and variance of 1.2 × 5.0-m plots. Bootstrapping showed that at least 10 soil water storage measurements were required in the 5-m plot. Soil water storage distribution within the plot was found to be highly stable in time, especially for individual soil layers. Using temporal stability analysis, the number of required access pipes needed to estimate a plot-average soil water storage was further reduced to three. However, the variance of soil water storage was not conserved while reducing the number of measurement locations. We propose that a field study with small field trials should start with the maximum feasible plot size and number of measurement locations. In this initial phase, statistical techniques as proposed in this study can then be applied to reduce the required number of observations, using predetermined error limits.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Pesticide leaching may be affected by rainfall parameters and the amount and type of vegetation on the soil surface. This study was conducted to determine the effect of rainfall intensity and crop residue on the movement of [ring-14C]atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and bromide (Br) through no-till (NT) cores. Undisturbed soil cores (10 cm diameter by 8 cm depth) were taken from the surface horizon of a NT corn (Zea maysL.) field. The cores were surface treated with 1.3 kg ai ha−1atrazine and 150 kg ha−1of Br and subjected to simulated rainfall at 3, 6, 9, or 12 mm h−1. The amount of crop residue on the surface of another set of soil cores was adjusted to 0, 2000, 4000, and 8000 kg ha−1, then treated with atrazine and subjected to 9 mm h−1of simulated rain. Overall, the transport of atrazine and Br were significantly (P< 0.01) affected by rainfall intensity. An average of 92% (Br) and 52% (atrazine) of the total amount applied was leached through the soil cores by 2 pore volumes (520 ml) of simulated rain applied at 12 mm h−1compared with 61% for Br and 33% for atrazine at the 3-mm h−1rate. Covering soil cores with 2000 or 8000 kg ha−1of crop residue reduced atrazine leaching by 26 to 37%, respectively, compared with soil cores without crop residue. Soil cores covered with recently harvested vegetation reduced atrazine leaching by 39% compared with cores covered with aged crop residue.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Samples of soils made homoionic with K, Na, or Ca were reacted with solutions containing Cs ions, and the quantities of Cs sorbed and the rates of exchange were measured. The samples were then reacted with solutions containing K, Na, or Ca, and the quantities of Cs desorbed and the rates of exchange were again measured. Samples made homoionic with Na had a greater ion exchange capacity than samples made homoionic with K, and, in both cases, the ion exchange capacity increased with the organic matter content of the soil. For samples pretreated with Ca, the ion exchange capacity is not related in a simple way to the organic matter content. The kinetics were assessed by plotting the rate of exchange vs. the time and vs. the quantity exchanged. A first-order equation was obeyed during most of the run in Cs desorption experiments and during a limited part of the run in Cs adsorption experiments. An increase in the rate of Cs exchange was observed at the beginning of the experiments especially for Cs adsorption. This increase is presumably due to an increase of the ionic strength of the liquid phase during the exchange process.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Eleven samples, collected from three Norwegian cultivated soils under different management practices, were analyzed by sequential extraction to isolate five operationally defined fractions of Cd and Zn. On average, 47, 4, 33, and 5% of the sum of the Cd fractions (ΣCd) were found as weakly adsorbed (F1), adsorbed (F2), strongly adsorbed (F3), and very strongly adsorbed (F4) forms of the element, respectively. Eleven percent was regarded as incorporated in resistant minerals (F5). The relatively high proportion of the F1 fraction indicates that much of the Cd under these conditions, may be easily available to plants. In contrast to Cd, the highest percentages of ΣZn (31 and 47%), on average, were associated with strongly (F3) and incorporated with resistant minerals (F5), respectively. The F2 and F4 fractions contributed little to the sum of the fractions for both elements, and the low percentage of the weakly adsorbed (F1) for Zn is indicative of low mobility and availability of the element in these soils. For Cd, F1-F3 were directly correlated with OC and TFe. OC also seemed to be important in retaining F4, whereas F5 correlated best with clay. Positive correlations were also found between F1 and F3 of Zn with OC. The direct relation between F3 and TMn may indicate a stronger association of Zn with the oxides of Mn than of Fe in these soils. F5 of Zn correlated best with OC, TFe, and silt.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Mehlich 1 (M1), Mehlich 3 (M3), and Ammonium Bicarbonate DTPA (AB-DTPA) have been used to determine the available micronutrients in soils. However, the forms of micronutrients extractable by these extractants are not known. The objectives of this study were: (i) to examine the correlation between the forms of Zn or Cu (readily soluble, organically bound, precipitated, and residual) in soils determined by a sequential extraction procedure and M1, M3, or AB-DTPA-extractable Zn or Cu and (ii) to directly determine the quantity of each form of Zn and Cu in soils that can be extracted by M1, M3, or AB-DTPA. The results show strong correlations between the organically bound or precipitated forms of Zn or Cu and the amounts extractable by any of the above three extractants. It appears that in sandy soils, Zn and Cu extractable by M1, M3, or AB-DTPA contain most of the readily soluble and the organically bound forms as well as a small fraction of the precipitated and residual forms. The rankings of these three extractants for extraction of organically bound Zn and Cu are M1 = M3 > AB-DTPA and M3 = AB-DTPA > M1, respectively. All of the above three extractants were equally effective in extracting the precipitated form of Zn or Cu. The efficacy of extraction of the residual form of Zn and Cu decreased in the order M3 > M1 = AB-DTPA.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Gaseous N emissions arising from biological denitrification in soils is of economic and environmental consequence. However, the biological and physical processes controlling emissions are complex, and, therefore, mathematical simulation is useful in understanding them. A mathematical model was constructed from a hypothesis based on preferential reduction of O2, followed by NO3−and then N2O during microbial oxidation of carbon substrates. The hypothesis allowed the model to reproduce the time course of N2O and N2production and consumption during anaerobic incubations of soil amended with 37.5 to 300 μg NO3−-N g−1soil. Biologically based models of denitrification, coupled to physically based models of the soil environment, may allow greater insight into the dynamics of denitrification and N2O emission in the field.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The dynamic processes controlling N2O evolution in the field are complex; therefore, estimates of long-term evolution from periodic measurements are likely to be unreliable. Greater reliability in such estimations may be possible by reproducing these processes mathematically within a dynamic simulation model. A mathematical hypothesis for denitrification and N2O production was used within a larger ecosystem simulation model to study N2O evolution under laboratory and field conditions. Hourly N2O fluxes estimated by the model were compared with fluxes recorded over an inundated soil core during a 10-day laboratory incubation after a 100-g N Mg−1amendment with15N-KNO3. Estimated values were within 20% of those recorded for fluxes, ranging from 0 to 4 mg N m−2h−1. Recovery of both mineral and labeled N from the amendment after 10 days was estimated within 2 g Mg−1of recorded values. Hourly N2O fluxes estimated by the model were also compared with fluxes recorded during spring thaws during 2 years at a field site in central Alberta. Fluxes ranging from 0.1 to 10.0 mg N m−2h−1were reproduced by the model after different fertilizer treatments. Increased rates of N2O evolution followed periods of saturation in the upper profile caused by snowmelt. These increased rates continued for about 1 week in both years before declining as soil drying progressed. In the model, evolution arose from the volatilization, during drainage, of aqueous N2O generated from biological NO3- reduction that occurred during periods of low aqueous O2concentrations caused by water accumulations in the thawing soil profile. The simulated evolution supports the hypothesis that denitrification accompanies soil thawing after snowmelt at this site.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The increases in urea consumption in crop production have encouraged research activities evaluating various materials as potential urease and nitrification inhibitors. This report presents results of three experiments testing lignosulfonate (LS), a waste product of the pulp and paper industry, as a urease and nitrification inhibitor. The first experiment was for urea hydrolysis in a clay soil with or without bulk-digested (BD) or sugar-free (SF) calcium lignosulphonate (CaLS). The second experiment studied the effect of BD on jack bean urease activity in solution. The third experiment evaluated the effect of BD or SF on changes in soil NO3−content. Calculation of half-life times of urea showed that application of either BD or SF reduced urea hydrolysis in the soil at high rates, with SF being more effective than BD. The decreases in urea hydrolysis were attributed to inhibition of urease activity by LS as indicated by the solution incubation experiment. After incubation for 24 h, 80% urea remained in solutions with simultaneous additions of jack bean urease and BD, compared with 20% in solutions without BD. For incubation of the soil without urea, NO3-N contents with LS additions were 0.5 to 10.1% of that without LS, and NO4-N contents were significantly higher than NO3-N contents. Low NO3-N content after incubation of the soil with LS was attributed to immobilization by microbes, inhibition of nitrification, and possibly induced denitrification of native NO3-by sugars added with LS.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID