Serpentine Soil Distributions and Environmental Influences

Serpentine soils occur in all but one of the twelve orders (Alexander 2004b), which is the highest level in Soil Taxonomy (Soil Survey Staff 1999), the primary system of soil classification utilized in this book (appendix C). They occur in practically every environment from cold arctic to hot tropical and from arid to perhumid (always wet). Thus the variety of serpentine soils is very great even though they occupy only a small fraction of the earth. Serpentine soils have been found in all states and provinces that are adjacent to the Pacific Ocean from Baja California to Alaska. They are most concentrated in the California Region, where they have been mapped in 34 counties in California and in 5 counties in southwestern Oregon. Serpentine lateritic (or “nickel laterite”) soils, which have not been mapped separately from other soils, are economically significant in California and southwest Oregon, even though they are not widely distributed in western North America. A representative serpentine soil is shown in figure 6-1. Serpentine soils, or soils in magnesic (serpentine) families, are represented in 11 of the 12 soil orders. Spodosols and Histosols in magnesic families occur only where there is a thin cover of nonserpentine materials over the serpentine materials, and there are no serpentine Andisols. Andisols contain amorphous and poorly ordered aluminum-silicate minerals, which are responsible for andic soil properties of these soils. Serpentine soil parent materials do not contain enough aluminum for the development of andic soil properties that are definitive of Andisols. Alfisols are soils with argillic (or natric) horizons having more than 35% exchangeable bases (Ca2+, Mg2+, Na+, and K+) on the cation exchange complex. Al3+ and H+ are the common nonbasic (acidic) cations on the exchange complex. The Mg2+ that serpentine soil parent materials release upon weathering keeps the basic cation status of soils high, unless they are leached intensively. Some of the soil horizon sequences are A-Bt, A-Btn, and A-Bt-Btk in Alfisols. Soils of Dubakella Series and other moderately deep Mollic Haploxeralfs with a mesic soil temperature regime are the most extensively mapped serpentine Alfisols in California and southwestern Oregon. Figure 6-1 is representative of the Mollic Haploxeralfs.

Response of high density apple orchards on coarsetextured soil to form of potassium applied by fertigation

This study tested the effects of fertigated potassium sources on orchard cation status. A randomized, complete block experimental design was maintained from 2000 to 2003, in a high density ‘Jonagold’/M.9 apple (Malus × domestica Borkh.) orchard planted in 1993 on a loamy sand. Seven K-fertigation treatments included annual application of either no K (control), 15 g K/tree as either potassium chloride or potassium magnesium sulphate (KMag) or 30 g K/tree as potassium chloride, KMag, potassium sulphate or potassium thiosulphate, applied daily during 6 wk midsummer to six replicate, four-tree plots. Fertigated K-forms did not affect yield, but increased soil K after 3 yr to 30-cm depth beneath the drip emitters. This increased leaf and fruit K concentrations. Fruit K/Ca ratio was also increased by K-fertigation. A high incidence of bitter pit at harvest was unaffected by fertigating K, but rather was associated with low harvest fruit Ca concentration and large fruit size. KMag increased soil Mg availability, but leaf and fruit Mg concentrations were slightly affected, indicating the difficulties of improving apple Mg status when co-applying K. Leaf and fruit Ca concentrations were minimally affected by treatments. Soil Ca declined slightly after 3 yr of K fertigation. Key words: Bitter pit, calcium, chloride, magnesium, Malus × domestica, sulphate, thiosulphate

Limitations of EGME retention to estimate the surface area of soils

The suitability of two procedures for the measurement of total surface area, based on 'the retention of ethylene glycol monoethyl ether (EGME), was investigated for a wide range of clay fractions and Australian soils. Experimental conditions for optimum precision and convenience of measurement were established. The procedures which utilized a higher vapour pressure of EGME achieved a higher retention of EGME by soils, reached the final condition of measurement more rapidly, and were less dependent on exchangeable cation status of the samples in confirmation of published work with pure smectite. The critical weakness of published procedures for soils is the assumption that the surface area occupied by an EGME molecule on a smectite reference sample can be applied to all soil surfaces. EGME retained per unit area by a range of soil and pure smectites, calculated from total surface area derived from crystal dimensions, and by a range of non-swelling minerals, related to measured BET-N2 areas, varied about fourfold between different mineral groups, and nearly twofold for different smectites. This variation could seriously over- or under-estimate estimates of total surface area, depending on the reference mineral chosen in relation to the mineral species being characterized. Alternatively, for soils free of clay minerals with internal surfaces, an empirical approach based on measured BET-N2 areas of representative soils may be feasible. A consideration of EGME retained in relation to BET-N2 areas may usefully complement X-ray diffraction procedures for characterizing randomly interstratified material in soil clay fractions.