Chemical equilibria and quantity—Intensity relationship of zinc in some acid soils of India

Laboratory studies were conducted to investigate the nature of chemical equilibria of zinc in some acid soils of Himachal Pradesh (India). The results indicated that one of the chemical reactions controlling zinc ion activity in the ambient soil solution may be represented by the equation:

$\text{Si(OH)}{}_4\text{+ 2H}{}_2\text{O ? Zn(OH)}{}_2\text{(}\text{crys.}\text{) + SiO}{}_2\text{(}\text{amorph.}\text{) + 2H}{}_3\text{O}{}^{\mathrm{+}}$

Sequential extraction of ⁶⁵Zn-equilibrated soils provided a measure of the intensity of its different forms and their relative contribution to the pool of potentially available zinc in such soils. Adsorption-desorption parameters have been derived from a quattitative treatment of these phenomena as defined by the Langmuir equation. A supply parameter, $\text{√}\text{cq}\text{√K}{}_1\text{K}{}_2$, integrating the combined effects of quantity, intensity and buffering capacity has been derived from the adsorption studies. A linear relationship between the supply parameter and cumulative desorption of applied zind in these soils has been noted. The desorption of zinc from these soils is an exponential process. The solubility relationship of zinc is expressed in terms of the theory of simultaneous equilibria of competitive chemical reactions which obviates the necessity of assuming a single physico-chemical model in predicting and relating the activity of zinc in the ambient soil solution and its surface reactivity on solid phases in the immediate vicinity of plant roots to its ultimate transport and uptake by plants.     

Use of p-benzoquinone and hydroquinone for retardation of urea hydrolysis in soils

Studies to evaluate p-benzoquinone (PBQ) and hydroquinone (HQ) for retardation of urea hydrolysis in soils showed that the effects of these compounds increase markedly with the amount of PBQ or HQ added and decrease markedly with time and with increase in temperature from 10 to 40°C. They also indicated that PBQ and HQ inhibit soil urease activity by identical mechanisms. The effects of various soil properties on the effectiveness of PBQ and HQ for retardation of urea hydrolysis in soils were investigated by studies with 25 surface soils selected to obtain a wide range in pH, texture and organic-matter content. Simple correlation analyses showed that the inhibitory effects of PBQ or HQ on urea hydrolysis in these soils were correlated very highly significantly with organic C content ($\text{r}\text{= ? 0.76}{}^{71}$), total N content ($\text{r}\text{= ? 0.74}{}^{71}$), urease activity ($\text{r = ? 0.70}{}^{71}$) andcation-exchange capacity ($\text{r}\text{= ? 0.62}{}^{71}$). The effects of these compounds also were highly significantly correlated with sand content ($\text{r}\text{= 0.57}{}^7$) and were significantly correlated with silt content ($\text{r}\text{= ? 0.421}$), clay content ($\text{r}\text{= ? 0.491}$) and surface area ($\text{r}\text{= ? 0.491}$), but were not significantly correlated with pH or CaCO₃ equivalent. Multiple-regression analyses indicated that the effectiveness of PBQ and HQ for retardation of urea hydrolysis in soils tends to increase with decrease in soil organicmatter content.     

Effect of fulvic acid on the crystallization of aluminum hydroxides

Effects of addition of increasing amounts of fulvic acid (FA) on the crystallization of aluminum hydroxides from AlCl₃, solution, neutralized to different degrees, were investigated. All systems were allowed to age at 30°C for 70 days.In the absence of FA, gibbsite was formed at pH 6, a mixture of nordstrandite and bayerite at pH 8, and bayerite crystallized at pH 10. At pH 6 and 8, the addition of increasing amounts of FA (up to 10 mg/l or $\text{FA/Al molar ratio}\text{? 10}{}^{\mathrm{?2}}$) first delayed and then inhibited the crystallization of these aluminum-hydroxide polymorphs but tended to favor the crystallization of pseudoboehmite, an aluminum oxyhydroxide. At pH 10, the addition of FA totally inhibited crystallization and precipitation.Our data suggest that FA so strongly complexes Al that it prevents its full hydroxylation to Al(OH)₃. Another explanation is that the action of FA on the crystallization of aluminum hydroxides resembles that of salts in that FA appears to favor the formation of Al-O-Al (oxo) over that of

(ol) linkages. Either reaction mechanism throws new light on the genesis of some bauxites, which consist of submicroscopic boehmite-like particles which are very similar to pseudoboehmite.     

Water percolation in a tropical alfisol under conventional plowing and no-till systems of management

Field studies were conducted to investigate percolation and redistribution of water in a gravelly Alfisol under conventional and no-tillage systems. Five cm of water tagged with chloride was applied to the soil surface by sprinkling and flood irrigation. Soil samples for water and chloride determinations were obtained immediately after infiltration and at 5, 24 and 48 h after infiltration initiation.Depending on the mean initial soil moisture content ($\text{θ}{}_{\mathrm{<mtext>i</mtext>}}$) and method of water application, mean infiltration rate ranged from 4.6 to 42.9 cm h^?1 for plowed compared to a range of 15 to 120 cm h^?1 for the no-till treatment. In the conventionally plowed soil at $\text{θ}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0.077}\text{cm}{}^3\text{cm}{}^{\mathrm{?3}}$, water penetrated toa depth of 30 cm immediately after infiltration for both sprinkling and flood application. Within 5 h of infiltration initiation, the profile was wetted to 80 cm depth and most of the applied water was retained in the 0–80 cm layer. Samples obtained at subsequent times did not indicate appreciable additional percolation. At $\text{θ}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0.195}\text{cm}{}^3\text{cm}{}^{\mathrm{?3}}$, however, water penetrated to 80 cm depth immediately after infiltration and about 57% of the applied water was retained for sprinkling as well as flood application. At 24 h, retentions were reduced to 17 and 25% for sprinkling and flood application, respectively. Similar results were obtained in no-till fallow or no-till soil cultivated to maize. Percolation in soil under both systems was rapid during the first 5 h after infiltration initiation but decreased rapidly afterwards. After 24 h, however, soil under no-till had more mean water content over the 0–80 cm depth than conventionally plowed treatment.Chloride profile indicated that a large percentage of the added water percolated beyond 80 cm depth without displacing the initially present water. More chloride recovery than water in profiles at high θ_i also indicated some adsorption of chloride in these soils. Adsorption seemed more in the no-till system than in tilled soil.     

Effects of nitrite toxicity on soil bacteria under aerobic and anaerobic conditions

Isolates of a soil Pseudoimonas, as well as other soil bacteria, showed a different sensitivity towards NO^?₂ when grown under aerobic or anaerobic conditions. The tolerance to NO^?₂ was increased in the presence of O₂: for instance, a concentration of $\text{200parts}\text{10}{}^6$ of NO^?₂-N proved to be toxic to a Pseudomonas sp. under anaerobic conditions, whereas over $\text{400 parts}\text{10}{}^6$ were needed aerobically to suppress its growth completely. The addition of NO^?₃ as an electron acceptor for anaerobic respiration did not overcome the inhibitive effect of NO^?₃. The pH range, at which NO^?₂ was utilized anaerobically, was narrowed with increasing NO^?₂ concentration (pH 6.8–8.8 at $\text{70 parts}\text{10}{}^6$ of NO^?₂-N and 7.4–8.5 and $\text{140 parts}\text{10}{}^6$ of NO^?₂-N).Tolerance to nitrite varied considerably among the bacteria tested. Each species was able to overcome the inhibitory effect of NO^?₂ up to a certain concentration, while the length of the lag phase was related to NO^?₂ concentration.     

Ineffectiveness of ethylene as a regulator of soil microbial activity

When soils from arable, grassland and woodland environments were incubated aerobically in the presence of up to 50 parts $\text{C}{}_2\text{H}{}_4\text{10}{}^6$, no significant effect of the gas on respiration could be detected. It was concluded that the emanation of C₂H₄ from anaerobic microsites was not responsible for the general regulation of soil microbial activity.