Nonexchangeable Soil Research Articles

Cation Exchange Resins for Predicting Available K on K-Deficient Soils: Extraction Capacity among Different Soil K Pools and First Insights on the Contribution of K Solubilized by Rhizosphere Microbes

The contribution of non-exchangeable soil K in the total K availability may be essential to K deficient soils; however, less attention has been paid so far for proposing soil tests that assess the bioavailable structural K that is solubilized by soil microbes during a growing season. The objectives of this study were to evaluate cation exchange resins for their performance in predicting K uptake by plants; to investigate the relationships between rhizosphere soil microbes, different soil K pools, and soil parameters; and to assess their exchange capacity with respect to K derived by feldspars. A pot experiment with winter wheat was conducted on K deficient soils, several soil tests were examined, and rhizosphere K solubilizing microbial population was assessed. Single and multiple regressions showed that cation resins performed better in predicting total plant K uptake than the other chemical extractants (r2 = 0.64, r2 = 0.85, respectively, p ≤ 0.001), whereas the PCA analysis and Pearson correlation tests revealed a positive correlation between K derived by feldspars, K uptake, and the K solubilizing rhizosphere microbial population. The above was further confirmed by the mapping of cation resins of extraction capacity, which showed a significant contribution of K derived by feldspars (15.6%).

Yield of and nutrient-water use by maize exposed to moisture stress and K fertilizers in an inceptisol of West Bengal, India

Potassium (K) is important for both qualitative and quantitative traits of maize. However, role of this macronutrient is often being ignored, and is often applied as an optional nutrient, with no proper fertilizer recommendation. Present experiment focused on the role of K fertilization in determining soil K fractions, maize yield, K and water use by maize under different irrigation regimes. Result revealed that K-fertilization significantly improved available soil K, fractions of K (especially non-exchangeable, mineral and total fractions), maize yield, K uptake and water use efficiency. Imposition of moisture stress up to 50% available soil moisture deficit (ASMD) significantly increased all the aforementioned parameters over the no stress situation, while irrigation available at 75% ASMD reduced them significantly. Soil K fractions, under different K fertilizations and irrigation schedules, decreased with the increase in soil depth upto 90 cm. Only exception was non-exchangeable soil K which remained stable across soil depths. The relationship among different K fractions and available soil K was estimated. Available K was observed to have strongest correlation with water soluble and exchangeable K in all possible irrigation regimes. Path analysis studies revealed that water soluble K exerted highest direct effect on changes in maize grain yield and K uptake followed by exchangeable, non-exchangeable and mineral K under irrigation availability at 25 and 50% ASMD. However, exchangeable K exerted highest direct effect on maize grain yield at 75% ASMD.

A beech bark disease induced change in tree species composition influences forest floor acid–base chemistry

Beech bark disease (BBD) has demonstrable ecosystem consequences for eastern US forests stemming from American beech (Fagus grandifolia Ehrh.) mortality, often leading to increased dominance by its competitor, sugar maple (Acer saccharum Marsh.). We hypothesized that this BBD-induced shift in tree species composition leads to changes in soil acid–base chemistry, mediated through differences in leaf litter chemistry of the two species. Using a sequence of plots representing the progression of the disease in the Catskill Mountains, NY, USA, we examined the influence of tree species composition shift on soil chemistry. The BBD impact on tree species composition was confounded by variability in substrate (or nonexchangeable soil) calcium (Ca). While substrate Ca explained much of the variation in acid–base chemistry, increasing BBD was associated with increasing forest floor exchangeable Ca, sum of base cations, base saturation, cation-exchange capacity, and decreasing hydrogen. An apparent threshold effect of substrate Ca on sugar maple litter Ca concentration suggests that underlying soil Ca availability may contribute to the spatial extent and timeframe of BBD-induced shifts in species composition. The species compositional shift is a mechanism contributing to a vegetation effect on soil acid–base status and may partially counteract soil acidification in this acid deposition impacted region.

Initial physic nut nutrition and potassium balance in the soil-plant system

The objectives of this study were to evaluate the mineral nutrition and the response of physic nut to potassium fertilization as well as to assess whether the species can absorb K from the non-exchangeable soil fraction. The study was conducted in a greenhouse, in randomized blocks, and with four repetitions. Physic nut plants were cultivated in plastic recipients filled with 50 dm³ of a Dark Red Latosol fertilized with rates of 0, 40, 80, 120 and 160 mg K dm-3 of soil. One hundred and fifty days after planting, the height, stem diameter and leaf area of the plants were measured, and the dry mass, concentration in leaf and total accumulation of macro and micronutrients were determined, as well as the soil contents of exchangeable and non-exchangeable K. The K balance in the soil-plant system was also calculated. The increase of potassium fertilization resulted in a greater uptake of K, Ca and Mn but did not alter the total dry mass production of physic nut. The species can release and absorb K from the non-exchangeable soil fraction.

Reserva mineral de potássio em Latossolo cultivado com Pinus taeda L.

No Brasil, aproximadamente 1,87 milhões de hectares são plantados com as espécies de Pinus, normalmente em solos pobres quimicamente. Os objetivos deste trabalho foram estudar a mineralogia das frações areia, silte e argila e estimar a reserva mineral de K por diferentes métodos de extrações químicas em solo naturalmente pobre nesse nutriente e cultivado com Pinus taeda L., no Segundo Planalto Paranaense. Foram selecionadas cinco árvores com maior diâmetro (árvores dominantes), em uma área de 500 m², para abertura de uma trincheira (1,6 m) na projeção da copa de cada árvore. Todos os perfis foram classificados como Latossolo Vermelho-Amarelo distrófico típico e apresentaram similaridade na morfologia e na sequência dos horizontes, cujas profundidades médias foram: O = 0,04 m, A1 = 0-0,09 m, A2 = 0,09-0,24 m, BA = 0,24-0,43 m, B1 = 0,43-0,66 m e B2 = 0,66-1,60+ m. As amostras coletadas em cada horizonte foram submetidas a análises físicas (granulometria) e químicas (pH, carbono orgânico, acidez potencial, Al3+ e bases trocáveis, P disponível, K total e não trocável), e as frações areia, silte e argila foram estudadas por difratometria de raios-X (DRX). As frações areia e silte dos solos apresentaram mineralogia bastante uniforme, com predomínio absoluto de quartzo e apenas ocorrência de discretas reflexões de mica por DRX. A fração argila também apresentou limitada ocorrência de minerais micáceos. Os tratamentos sequenciais para remoção de óxidos de Fe, gibbsita e caulinita foram eficientes para concentração de mica na fração argila, o que facilitou a identificação de biotita e muscovita por DRX. Os baixos teores de K não trocável obtidos com diferentes concentrações de HNO3 fervente (máximo de 91 mg kg-1) e de K total extraído com HF concentrado (máximo de 202,7 mg kg-1) foram consistentes com a pobreza das frações do solo em minerais primários, fontes desse nutriente. As correlações positivas e significativas entre os teores não trocáveis de K no solo e os teores e conteúdos do nutriente nas árvores indicaram a importância de formas de reservas do nutriente na nutrição da espécie em solos altamente intemperizados e pobres em K trocável.

Ability of alfalfa (Medicago sativa L.) to take up potassium from different micaceous minerals and consequent vermiculitization

Nonexchangeable soil K trapped between interlayers of clay minerals is an important source of K for plants grown on many soils. In this study, the ability of alfalfa, as the most important forage crop worldwide, to take up K from some micaceous minerals and to promote the transformation of micaceous minerals were investigated. Alfalfa was cultivated in pots that consisted of a mixture of Hamadan quartz sand and Amlash biotite, Hamadan muscovite and Hamadan phlogopite. Plants were irrigated with distilled water and complete or K-free nutrient solutions. After 90 days, K uptake by plants was measured by flame photometer. Also, the clay size particles in each pot were analyzed using x-ray diffraction. It was found that alfalfa was able to induce a significant release of interlayer K during cropping. The amount of K taken up by alfalfa was significantly higher for Hamadan phlogopite. X-ray diffractometry showed a strong vermiculitization of Hamadan phlogopite and Amlash biotite, but no X-ray detectable transformation of muscovite was recognized.

Potassium balance as influenced by farmyard manure application under continuous soybean–wheat cropping system in a Typic Haplaquept

The effect of 30 years of continuous cropping, fertilization and manuring on the potassium (K) balances, the soil K pools and the non-exchangeable K release in a Typic Haplaquept soil from Almora, India under a rainfed soybean–wheat cropping system were investigated. The apparent K balance was measured as the difference between the total K added and that removed by the crops. The results showed that the total removal of K by the crops exceeded the amount of total K applied to the soil in all the treatments showing a net negative K balance. This ranged from 3.7 in the plots under NK to 81.7 kg ha − 1 year − 1 in the N + FYM treated plots. Continuous annual application of recommended doses of NPK + 10 t FYM (NPK + FYM) to soybean resulted in an accumulation (+ 56 kg K ha − 1 ) of exchangeable K (1 N NH 4OAc extractable K) in the 0–45 cm soil depth over the study period, despite the highest average annual uptake of K by the system (150.8 kg ha − 1 year −1). However, there was a net depletion of exchangeable K (− 80 kg K ha − 1 ) in that soil depth under the NPK treated plots. The results also revealed that the content of non-exchangeable K decreased substantially from 3482 kg ha − 1 to 2677 and 2896 kg ha − 1 in the 0–45 cm soil layer after 30 years of cropping in the plots under NPK + FYM and NPK treatments, respectively. There was a significant decline in total soil K with the removal of non-exchangeable soil K in the surface (0–15 cm) soil layer ( R 2 = 0.526, P < 0.001, n = 36). Thus, long-term application of non-revised recommended fertilizer rates may threaten sustainability of the rainfed continuous soybean–wheat system.

Potassium Efficiency of 10 Potato Cultivars as Related to Their Capability to Use Nonexchangeable Soil Potassium by Chemical Mobilization

Ten potato cultivars were grown in low potassium soil with and without potassium (K) in a pot experiment to test their K efficiency. Two harvests (29 and 83 days after planting) were taken to obtain final dry matter (shoot+tubers) accumulation (DMA) rates of shoot and root growth and K uptake rate per unit root (K influx). Under K deficiency, DMA of different cultivars varied by a factor of more than 2. Based on absolute DMA without K, the cultivars, Linda, Oktan, Ponto, and Maas were more K efficient than Quarta and Belana. Results show that with the same root length, more K efficient cv. Oktan had higher relative shoot growth rate and produced more DMA than less K efficient cv. Quarta in the absence of K by taking up more K per plant from soil and maintaining higher shoot K concentration. The more K efficient cv. Oktan could take up more K per plant due to its higher K influx, and its higher influx was because of its capacity to use higher nonexchangeable soil K. The DMA, K uptake, and K influx in 10 cultivars were more correlated to the quantity of nonexchangeable K depleted (r=0.850, 0.981, and 0.608) than to that of exchangeable K (r=0.284, 0.363, and 0.315, respectively). Stepwise regression analysis indicated that capacity to use nonexchangeable K is the main factor controlling K efficiency of different cultivars followed by root length to DMA ratio and K influx.

Suprimento de potássio de solos do Rio Grande do Sul para arroz irrigado por alagamento

Cultivos em vasos têm sido utilizados para avaliar a capacidade dos solos em suprir potássio para as plantas. Com este objetivo, foi realizado um estudo com amostras de dois Planossolos, um Chernossolo e um Gleissolo do estado do Rio Grande do Sul, nos quais a cultura do arroz irrigado por alagamento não tem respondido à adubação potássica. Os solos foram cultivados durante 50 dias, em casa de vegetação, com arroz (Oriza sativa.l cv. BR-IRGA 409). Foram quantificados o potássio acumulado na parte aérea das plantas e os teores de K trocável e K não-trocável, extraídos dos solos por NH4OAc 1 mol L-1 pH 7 e por HNO3 1 mol L-1 fervente, respectivamente, antes e depois do cultivo. O K acumulado pelas plantas de arroz diferiu entre os solos, decrescendo na seqüência: Gleissolo &gt; Chernossolo &gt; Planossolo 1 &gt; Planossolo 2. O K trocável não foi a única forma do elemento no solo que supriu o nutriente às plantas de arroz, ocorrendo contribuição de formas de K não-trocável.

Potassium uptake efficiency of young plants of three potato cultivars as related to root and shoot parameters

Three potato cultivars, Kufri Badshah, Kufri Chandramukhi, and Kufri Jyoti were grown in low potassium (K) soil with and without K in a pot experiment to test their K uptake efficiency. Two harvests were taken to obtain final dry matter accumulation (DMA) rates of shoot and root growth and K uptake per unit root (K-influx). Relative DMA without K (expressed as percent of DMA with K) was 66, 75, and 90% for Kufri Badshah, Kufri Jyoti, and Kufri Chandramukhi, respectively, showing that Kufri Chandramukhi had a higher K uptake efficiency than other cultivars. High K uptake efficiency of Kufri Chandramukhi was due to its high K-influx while low K uptake efficiency of Kufri Badshah and Kufri Jyoti was due to low K-influx which nullified the effect of their high root-shoot (DMA) ratio. The potassium efficient cultivar, Kufri Chandramukhi, utilized more K from non-exchangeable soil source (46%) than Kufri Jyoti (25%) or Kufri Badshah (17%).

Potassium supplying power of a Typic Ustochrept profile using quantity/intensity technique in a long-term fertilized plot

The effect of 27 years of continuous cropping, fertilization and manuring on potassium (K) supplying capacity of a Typic Ustochrept soil profile from Delhi, India under a maize–wheat–cowpea (fodder) cropping system was investigated by employing the quantity/intensity (Q/I) approach. The predominant mineral suite of the &lt;2 μm clay fraction was illite. The values of equilibrium activity ratio of K in solution in equilibrium with the soil (ARKE), labile pools of K (KL), immediately available K (ΔK0), K available with difficulty (KX) and water soluble+exchangeable K (1 M NH4OAc K) in different soil layers (0 to 105 cm) under different treatments were in the following order: 100% nitrogen, phosphorus and potassium (NPK)+farmyard manure (FYM) &gt; 100% NPK &gt; control (no fertilizer) &gt; 100% N &gt;100% NP. The ARKE value, a measure of availability or intensity of labile K in soil decreased with profile depth due to greater K fixation by specific sites in the lower layers. The quantity of specifically sorbed K (KX) and the potential buffering capacity of soil (PBCK) showed a increasing trend with soil depth. In soil without K fertilizer treatments (control, 100% N and 100% NP) about 100% of the total K uptake by crops was from non-exchangeable soil K reserve as compared to 49·5 and 32·2% when annually 84 kg K/ha and 84 kg K/ha+FYM at the rate of 15 t/ha were applied. The results showed the greatest depletion of non-exchangeable K reserves in the plots which did not receive K fertilization. To ensure sustained crop production under intensive cropping, application of recommended dose of NPK plus FYM is required.

Potassium Fertilization Effects on Alfalfa in a Mediterranean Climate

Potassium fertilization rates for alfalfa (Medicago sativa L.) have been increasing with intensive cropping systems or decreasing with policies that generally lead to reduced fertilizer inputs. In this case, nutrient buildup or maintenance of high soil test levels may not be desirable and drawdown of K reserves may be beneficial in the short term. The objective of this research was to evaluate the effects of potassium fertilization of alfalfa in areas of high soil exchangeable K levels and long growing seasons. A field experiment was established under irrigation from 1993 to 1997 in the Mediterranean environment of the Ebro Valley (Spain) on a silty clay loam soil. The treatments were five annual rates of K (0, 41.5, 83, 166, and 332 kg K ha−1) and two rates of K (166 and 332 kg K ha−1) applied prior to seeding on two alfalfa cultivars. The average annual dry matter (DM) yield was 21.5 Mg ha−1 and showed a small linear response to K fertilization (Pr &gt; F = 0.0589). Total K removal in the herbage increased linearly with each rate of K and reached 1728 kg K ha−1 with the application of 332 kg K ha−1 yr−1, compared with 1546 kg K ha−1 without K fertilization. At the end of the experiment, soil ammonium acetate extractable K (Ke) increased little with K rates, and the differences were observed only in the first 30 cm of depth. Despite the uptake of 1546 kg K ha−1, soil Ke values did not change appreciably, suggesting that much of the K uptake was derived from the fertilizer and from nonexchangeable soil K fractions. Although K fertilization slightly increased alfalfa DM yields in this high testing Mediterranean soil, the economic benefit of this limited response does not justify the expense.

Base cation biogeochemistry and weathering under oak and pine: a controlled long-term experiment

Large earthen-walled lysimeters at the San Dimas Experimental Forest in southern California present a unique opportunity to assess vegetation effects on biogeochemical processes and cation release by weathering in controlled soil-vegetation systems where archived samples of soil parent material are available for comparison. The lysimeters were filled in 1937 with homogenized fine sandy loam derived on site from the weathering of diorite, and planted in 1946 with scrub oak (Quercus dumosa) and Coulter pine (Pinus coulteri). Changes in base cation contents were measured in above-ground biomass, and total and exchangeable soil pools to a depth of 1 meter. All cations in the non-exchangeable soil pool decreased relative to the initial fill material, indicating release by weathering. Sodium and K were depleted from both exchangeable and non-exchangeable pools of the soils. Plant uptake of Na was minimal, whereas K storage in vegetation exceeded the loss from the exchangeable soil pool. In both soil-vegetation systems, but especially for oak, there was an increase in exchangeable Ca and Mg. For all base cations, storage in above-ground biomass was greater for oak, whereas losses by weathering from the non-exchangeable soil pool were greater under pine. Strong evidence supports biocycling as a controlling mechanism resulting in greater Ca and Mg release by weathering under pine. In addition, decreases in non-exchangeable Ca and Mg were strongly correlated to decrease in Si under oak, whereas no correlation was observed under pine. We conclude that weathering reactions or stoichiometry differed between vegetation types.

A new approach to quantify the utilization of non-exchangeable soil potassium by plants

To predict the contribution of soil K fractions of different mobility to K supply of plants, the kinetics of K release from soil was related to the kinetics of K uptake of young sugar beet and wheat plants. For this purpose K release rates from soil were measured by continuously percolating samples of a luvisol with 0.01 M CaCl2 solution and effective diffusion coefficients, De, were determined. Two soil K fractions of different mobility were obtained. De values of the more mobile ‘exchangeable K’ and the less mobile ‘non-exchangeable’ K fraction were found to be 58.9 × 10−9 and 8.2 × 10−9 cm2 s−1, respectively. In a pot experiment, sugar beet and wheat plants were grown, for 15 days and both root growth and K uptake were measured. K uptake kinetics of both crops was determined in a separate experiment using flowing solution culture. To integrate these data quantitatively, the simulation model of Claassen et al. (1986) was applied. Results show that calculated total K uptake agreed closely with real K uptake of the plants. On this basis, 64 and 79% of the K taken up by wheat and sugar beet plants was derived from the rapidly released ‘exchangeable’ and 21–36% from the less mobile ‘non-exchangeable’ soil K fraction.

Utilization of non-exchangeable soil potassium in relation to soil type, plant species and stage of growth

The stage of growth at which three plant species, a grass, a legume and a cereal, absorbed initially non-exchangeable potassium (Kn) from two soils, a red podzolic and a krasnozem, was examined by sequential harvesting in a glasshouse experiment. Large amounts of Kn were removed from the red podzolic soil, which contained greater amounts of micaceous material, in the order setaria &gt; maize &gt; lucerne. Uptake of Kn appeared insignificant after exchangeable Kn as measured on the bulk soil, had been depleted by about 60%, and its contribution to total plant uptake thereafter was independent of species. For setaria and maize, plant K concentrations at this time were above the critical level, so that Kn represents a potassium resource that can be exploited during normal growth of an appropriate species. Uptake of Kn from the krasnozem was relatively small. The red podzolic soil yielded much more Kn than a similar soil in earlier experiments. This was attributed to differences in clay mineralogy, possibly associated with differences in the weathering stages reached by the two soils. Thus, it is not possible to infer the pattern of release of Kn simply from a knowledge of Great Soil Group and parent material.

POTASSIUM STATUS OF IRRIGATED BROWN CHERNOZEMIC SOILS OF SOUTHERN ALBERTA

A series of 10 field experiments conducted over a 4-yr period (1973–1976) on three of the most important Brown Chernozemic soils in the irrigated area of southern Alberta gave no significant yield responses to applied K (at rates of 0, 50, 100 and 150 kg ha −1 in 1973 and 0, 127, 254 and 508 kg ha−1 in the other years), using potato (Solanum tuberosum L.) as the test crop. The experiments included several cultivars, a variety of growing conditions, and diverse cropping histories. In addition, the K concentration of uppermost mature leaf blades obtained at the 10%-bloom stage were only slightly affected by K treatments, except in 1 yr (1975). The increased K uptake in 1975 was related to greater precipitation before irrigation was applied (66, 99 and 94 mm, respectively) during April, May and June in comparison with the long-term average of 32, 54 and 76 mm. The effects of early-season soil moisture stress were partially confirmed in a controlled environment (CE) experiment in which maintenance of soil water potentials between −30 and −20 kPa throughout the season caused greater uptake of added K in comparison with soil moisture stress in the 0–15 cm zone prior to the 10%-bloom stage. Yields of tubers were depressed with the stressed treatment, but there was no yield response to added K. Leaf analyses from the field experiments indicate that the critical K level of 43 g kg−1, which was established earlier for the Russet Burbank cultivar growing on Podzol soils is too high for irrigated Chernozemic soils, and that 30 g kg−1 would be a more valid tentative value. In a second CE experiment, designed to quantify the fate of applied K during intensive cropping, no yield responses to K applications were obtained with alfalfa on a coarse-textured Cavendish sandy loam during a 2-yr period. With no applied K, crop uptake reduced exchangeable K levels throughout the entire profile (66 cm) by about 20%. Thirty percent of the K removed by the crop originated from nonexchangeable soil K. With the highest K rate (450 kg ha−1 applied twice), 50% could be attributed to plant uptake, 15% to increased exchangeable K, and 35% to fixation in the nonexchangeable form. It is concluded that response to applied K on irrigated Brown and Dark Brown Chernozemic soils of southern Alberta is unlikely, even with intensive cropping, for some time in the future. A practical strategy for producers could be to apply moderate rates of K as a conservation measure when economic conditions are favorable and to rely on soil reserves in times of financial pressures. Key words: K-release, K-fixation, leaf analysis, fertilizer K requirements, soil water stress, K deficiency

IMPORTANCE OF EXCHANGEABLE AND NONEXCHANGEABLE SOIL NH4+ IN NITROGEN NUTRITION OF LOWLAND RICE

In lowland rice (Oryza sativa L.) soils, NH4+-N is considered the most important inorganic nitrogen form. Therefore, we examined the influence of NH4+ fertilizer application and N uptake of the crop on the level of exchangeable and nonexchangeable soil NH4+ Field experiments at three sites in major rice-growing areas in the Philippines showed that NH4+ fertilizer application was clearly reflected by an increase of exchangeable and nonexchangeable soil NH4+, while N uptake resulted in a decrease of both NH4+ fractions. We found major NH4+ contributions from nonexchangeable soil NH4+ only in Maligaya silty clay loam, which is rich in vermiculite. On all soils in the wet and dry seasons the exchangeable soil NH4+ was depleted during the first 8 wk of crop growth, indicating that this fraction is easily available to the crop. The net release of exchangeable and nonexchangeable NH4+ throughout the growth period ranged from 0 to 100% of the N uptake of rice and depended greatly on soil and weather conditions. In the wet season most of the N taken up by the crop could be accounted for by the net release of NH4+, whereas in the dry season most of the N taken up by the crop originated from soil organic N.

Effects of N and K Fertilizers on Cynodon IB.8 and on Soil K in Southern Nigeria

SUMMARYCynodon IB.8 was subjected to (i) various levels of N under cutting management, and (ii) various levels of K under grazing management. The results indicated significantly higher DM and CP production with 168 kg./ha. of N under cutting management, with resultant significant reduction in exchangeable and non-exchangeable soil K. Under grazing management, increased K application increased K content in the herbage, but showed a negative correlation with Ca uptake. Results indicated that the initial soil K status was adequate to supply the requirements of Cynodon, and that under grazing management the soil K status could be maintained at adequate levels to support lengthy cropping.

Changes in magnesium and calcium in soils of the Broadbalk wheat experiment at Rothamsted from 1865 to 1966

SUMMARYChalk in the 0–9 in topsoil of Broadbalk has declined from nearly 5% in 1865 to less than 1 % in some plots in 1966, and fastest in plots given ammonium sulphate. Losses were equivalent to 5–8 cwt limestone/acre annually. The paper relates these rates to estimated anion losses, especially bicarbonate, from the plots. Af-ammonium acetate dissolved Ca and Mg from chalk particles in the soils. After correcting for this, exchangeable magnesium had increased during the first 50 years but decreased since 1914 in the F.Y.M. plot. In plots given none or 10 lb/acre of magnesium in fertilizer annually, exchangeable magnesium had changed little since 1865. Thissuggests that equilibrium was soon established between additions and losses of Mg in all except the F.Y.M. plots. Estimates of annual additions and losses of Mg from each plot show that an equilibrium is feasible without large gains from non-exchangeable soil resources. A method of calculating losses of Mg in the drainage using activity ratios and annual calcium losses was developed.

The Release of Nonexchangeable Soil Potassium to Cation‐Exchange Resins as Influenced by Temperature, Moisture and Exchanging Ion

AbstractThe release of nonexchangeable potassium (K) from a Haldimand clay to H‐saturated Dowex 50‐W cation‐exchange resin was found to increase with increasing temperature although the increase in release was greater for a temperature increase from 50° to 80°C. than from 5° to 50°C. A decrease in moisture content decreased the rate of K‐release at the higher temperature range but had little effect at 5° and 25°C. The effect of moisture content apparently resulted from an influence on movement of K from the point of release to the resin particle rather than on the release of K from the soil particles.No release of nonexchangeable K to Na‐ or Ca‐saturated Dowex 50‐W resin occurred but the release increased linearly with the proportion of H‐saturated resin added in combination with Na‐ or Ca‐saturated resin. It appeared that the presence of the H+ ion was required for release. It could not be determined whether the mechanism of release involved an exchange of H+ or Al3+ for K in the mineral lattices or an acid decomposition of the K‐bearing minerals.