J. K. Syers

The fate of phosphorus during pedogenesis

Abstract The fate of phosphorus (P) during pedogenesis is considered with particular emphasis on vertical distribution within the profile. Information is based on P fractionation studies involving a range of soil sequences in New Zealand. Forms of P in soil parent materials are discussed in relation to soil P transformations. Soil chronosequences, developed in contrasting environments, provide useful information on the pedogenetic pathways of soil P. Although less well understood, soil toposequences can be used to elucidate the effects of slope and drainage on soil-forming processes which involve P.

SURFACE CHARGE AND SOLUTE INTERACTIONS IN SOILS

Many soil physical and chemical properties are controlled by the nature and the amount of surface charge and the variation of surface charge with soil solution characteristics. These properties include dispersion and flocculation, electrophoretic mobility, solubility, and the adsorption and movement of solutes. The surface reactions of charged particles are essential to the biogeochemical cycling of nutrients and pollutants and the pathway of detoxification of the latter when present at hazardous concentrations. Surface charge can be manipulated to take advantage of solid phase interactions relating to the movement of nutrient and pollutant ions in soils, the degradation of pesticides, and the decontamination of soils. This chapter brings together fundamental aspects of surface charge and recent developments on the implications of surface charge in relation to other soil properties, particularly solute interactions in soils. We first outline the development of charge on both permanent- and variable-charge surfaces. Then we discuss the various methods used to measure surface charge and factors affecting this charge. An attempt has been made to compare current theories on the nature of the charged solid surface-solution interface. The manipulation of surface charge can be achieved through liming and the addition of fertilizers containing specifically adsorbed ions. The practical implications of surface charge to soil properties have been discussed in relation to the dispersion and the flocculation of soils and the adsorption and leaching of inorganic cations and anions. Future research should focus on the development of methods to measure surface charge under in situ conditions and to explore further the role of surface charge in remediating contaminated soils

Phosphorus in Runoff and Streams

Publisher Summary This chapter discusses physical and chemical factors affecting the dynamics of phosphorus in runoff and streams. These factors determine not only the movement of phosphorus into runoff and streams but also its distribution between the aqueous and particulate phases. The factors affecting the dynamics and loads of phosphorus in runoff and streams illustrate the problems in interpreting the data thus far obtained. The major difficulty in data interpretation and comparison is the lack of uniformity in the forms of phosphorus measured. Surface runoff is a spasmodic rather that a continuous phenomenon, its composition at any location being highly heterogeneous and likely to change over short distances because the energy of the aqueous component, and therefore its ability to carry particulate material, varies with slope. The chapter explains the way the distribution of the phosphorus load between the solid and aqueous phases of surface runoff is measured. It also discusses the impact of phosphorus carried in streams on standing water.

Loss of nitrogen and phosphorus in tile drainage as influenced by urea application and grazing animals

The effects of urea fertiliser and grazing dairy cattle on the amounts of N and P forms transported in tile drainage from permanent pasture were investigated. In 4 weeks after an application of urea (60 kg N/ha) in July 1975 the increased loss of nitrate (NO3) and total nitrogen (TN) in tile drainage accounted for 2.0 and 2.3% respectively, of the applied fertiliser N. Grazing resulted in a dramatic increase in the concentrations of dissolved inorganic P (DIP) and particulate P (1.5- and 40-fold increases respectively). Concentrations of both NO3 and TN increased 5-fold immediately after grazing, although this effect was less sustained than that caused by urea application. Grazing was of comparable importance to urea application of the loss of NO3 and TN in tile drainage. The greater increase in the loss of particulate P (46.9 g/ha/4 weeks), compared to that of DIP (23.1 g/ha/4 weeks), resulted from a 50% increase in the amount of sediment carried. A 17% reduction in the amount of water discharged after g...

The effects of anion sorption on sorption and leaching of cadmium

The effect of chloride, sulfate, nitrate, and phosphate anions on the sorption and leaching of cadmium was examined in 2 soils (Manawatu silt loam and Egmont clay loam) which differ in their variable charge components. There was a larger sorption of cadmium in the presence of phosphate than in the presence of sulfate, nitrate, and chloride, and the difference was more pronounced in the Egmont soil. In soils, specific sorption of phosphate increases the negative charge. The increase in negative charge per unit amount of phosphate sorbed decreased with increasing phosphate sorption. The sorption of cadmium increased in response to phosphate sorption. The phosphate-induced cadmium sorption resulted from the increase in negative charge due to phosphate sorption. Column studies indicated that cadmium was less susceptible to leaching in the presence of phosphate than in the presence of nitrate.

ORIGIN OF THE LABILE PHOSPHATE POOL IN SOILS

When the amount of inorganic phosphate (P) sorbed by contrasting subsoils was expressed as a fraction of the overall Langmuir sorption maximum for that soil, the sorption data plotted on essentially the same isotherm. This reflected the similarity in the Langmuir sorption constants relating to sorption energy for each soil. The values of the sorption energy constants suggested that sorbed P existed in two very distinct forms, namely chemisorbed P and more-physically sorbed P which involved a potential-determining (p.d.) sorption mechanism. An isotherm for each sorption type was developed which permitted the calculation of the amounts of P sorbed in each form by each soil. The amounts of inorganic P extracted by the Olsen biocarbonate reagent, or those which were isotopically exchangeable during 30 min, were found to be considerably greater than the amounts of more-physically sorbed P resulting from several different P additions to each soil. In the case of a calcareous soil, however, the amount of P extracted by the Olsen reagent was essentially the same as that present in the more-physically sorbed form. In contrast, the amount of P removed in two consecutive extractions with distilled water from each of the soils, containing different amounts of both forms of sorbed P, demonstrated that only the more-physically sorbed P was removed. This is consistent with the p.d. character and exclusive reversibility of more-physical sorption. The P sorption model developed using unfertilized soils was also shown to be applicable to a range of topsoils with contrasting properties and fertilizer and liming histories. For each soil the estimate of the amount of more-physically sorbed P, obtained from the sorption isotherm for the soil, was essentially the same as the amount of P removed from the soil by two water extractions. The data obtained are used to propose a nonempirical definition of labile P in soils.

Development and evaluation of a kinetic model to describe phosphate sorption by hydrous ferric oxide gel

Abstract Isotherms for the sorption of inorganic phosphate (P) by hydrous ferric oxide gel (Fe gel) were described by a three-equation Langmuir sorption model. Each equation described sorption within a distinct concentration range or region (I, II, and III) of the overall isotherm. Regions I and II involved chemisorption, whereas region III involved a more physical sorption type. With increasing sorption time between 0.7 and 28.7 days, the extent of sorption in region I increased by more than 30%. In contrast, the extent of sorption in regions II and III remained essentially constant. An equation was developed, based on the change in the sorption maximum of region I ( b I ) with increasing sorption time, which described the change in solution P concentration with time. The increase in b I with time, evaluated by the closeness of fit of this relationship to experimental data, was found to depend on two factors: first, the extent to which P was chemisorbed, and this was affected by pH and ionic strength; second, the batch of Fe gel used. For two different levels of P addition, the proportion of sorbed P which remained extractable in 0.1 M NaOH, decreased with increasing sorption time. After 30 days only 88% of the sorbed P remained NaOH-extractable. The data obtained indicated that the increasing chemisorption of P with increasing sorption time involves the diffusion of sorbed P into the bulk of the Fe gel particles. This concept is discussed in relation to mechanisms proposed by previous workers to explain the time-dependence of P sorption.

Plant availability of phosphorus in superphosphate and a phosphate rock as influenced by earthworms

Abstract The effect of earthworms on the plant availability of phosphorus (P) in superphosphate and Chatham Rise phosphorite (CRP) was evaluated in a glasshouse experiment using perennial ryegrass over seven harvests. A mixed earthworm population of Lumbricus rubellus (Hoff.) and Allolobophora caliginosa (Savigny) was used. Increases in the yield of ryegrass in the presence of earthworms varied from 2 to 32%, whereas increases in P uptake by ryegrass ranged from 0 to 40% over seven harvests. With superphosphate, the initial increases in both ryegrass yield and P uptake by ryegrass in the presence of earthworms ranged from 20 to 40% at first harvest to less than 10% by the seventh. In marked contrast, earthworms increased the agronomic performance of pelletized CRP by 15 to 30% throughout the trial period. An increase in plant-available soil N concentrations due to earthworm activity probably explains the initial difference in the performance of superphosphate. The increased agronomic effectiveness of CRP appears to result from the incorporation and intimate mixing of the PR with the soil by earthworms. The implications of the results obtained in the present study to the interpretation of glasshouse and field trials evaluating P fertilizers are also discussed.

The determination of total phosphorus in soils and parent materials

Abstract The amounts of total P extracted by Na2CO3 fusion and by HF and HClO4 digestion procedures from selected New Zealand soils and parent materials were compared. It is suggested that Na2CO3 fusion is the most reliable procedure. Digestion with HClO4 gave low results with strongly weathered materials and with samples which contained apatite inclusions within constituent primary minerals; whereas digestion with HF gave slightly low results only with samples which contained included apatite. Incomplete extraction of P by HClO4 and HF digestion procedures from samples which contained apatite inclusions was ascribed to the partial resistance to attack of the host minerals. Because of occlusion within highly crystalline iron and aluminium oxides, secondary inorganic P in strongly weathered soils was less readily extracted by HClO4 digestion than by Na2CO3 fusion or HF digestion.

Effect of pH and calcium content of soil on earthworm cast production in the laboratory

Abstract The relative importance of pH and Ca content of soil in determining cast production by Allolobophora caliginosa (Savigny) was evaluated by a mini-frame technique using soil to which increasing amounts of four inorganic Ca salts were added. Whereas soil pH increased with the addition of increasing amounts of CaCO 3 and Ca(OH) 2 , it remained constant with increasing amounts of CaSO 4 and Ca(NO 3 ) 2 . Over the range of values studied, cast production increased with increasing pH and Ca level but did not increase with increasing Ca when soil pH was constant. Decreases in cast production were obtained above pH 7.3 with CaCO 3 and above 6.7 with Ca(OH) 2 . Separate studies suggested that a high osmotic pressure of the soil solution resulting from the addition of high levels of soluble Ca(NO 3 ) 2 was responsible for the dramatic decrease in cast production obtained with this salt. The present study has provided useful methods for related studies of the effect of a range of fertilizer materials on earthworm activity.