Depletion of Soil Potassium under Exhaustive Cropping in Inceptisol and Alfisol

Pot-culture studies of intensive cropping without potassium (K) application, taking three successive crops of rice on Sonakhali (Inceptisol) and Ranibundh (Alfisol) soils, revealed that all the forms of soil K declined after the third crop compared to the corresponding initial soil status. A similar trend was also found for nonexchangeable K extracted sequentially and termed as Step K and CR-K (constant rate K). The CR-K contents showed little variations with cropping. Except for the potential buffering capacity of the soil for K at equilibrium (PBC^K ₀) values, all the quantity/intensity (Q/I) parameters, namely activity ratio of potassium (AR^K _e), labile K (–ΔK₀), specifically held K (K_X), and total labile pool of K (K_L) values, decreased in both the soils as they were subjected to repeated cropping. The PBC^K ₀ values changed to a smaller extent in both the soils. In both soils, the threshold levels for release of intermediate K in terms of activity ratio, exchangeable K, and K concentration in soil solution decreased after the third cropping as compared to the initial status. The dry-matter weight of rice, K concentration, and K uptake decreased with the cropping sequence. The difference in values of each parameter between initial status and the third crop was much wider in Inceptisol than in Alfisol.     

Plant Availability Index by Potassium Exchange Isotherms in Selected Rice Soils of Lesser Himalayas

Potassium (K) exchange isotherms (quantity–intensity technique, Q/I) and K values derived from the Q/I relationship provide information about soil K availability. This investigation was conducted to study Q/I parameters of K, available K extracted by 1 N ammonium acetate (NH₄AOc) (exchangeable K plus solution K), K saturation percentage (K index, %), and the properties of 10 different agricultural soils. In addition, the relationship of mustard plant yield response to the K requirement test based on K exchange isotherms was investigated. The Q/I parameters included readily exchangeable K (ΔK₀), specific K sites (K_X), linear potential buffering capacity (PBC^K), and energy of exchange of K (E_K). The results of x-ray diffraction analysis of the oriented clay fractions indicated that some mixed clay minerals, illite clay minerals, along with chlorite/hydroxy interlayered vermiculite and kaolinite were present in the soils. The soil solution K activity ratio at equilibrium (AR₀) ranged from 8.0 × 10^?4 to 3.1 × 10^?3 (mol L^?1)^0.5. The readily exchangeable K (ΔK₀) was between 0.105 to 0.325 cmol_ckg^?1 soil, which represented an average of 88% of the exchangeable K (K_ex). The soils showed high capacities to maintain the potential of K against depletion, as they represented high linear potential buffering capacities (PBC^K) [13.8 to 50.1 cmol_c kg^?1/(mol L^?1)^0.5. The E_K values for the soils ranged from ?3420 to ?4220 calories M^?1. The percentage of K saturation (K index) ranged from 0.7% to 2.2%. Analysis of variance of the dry matter (DM), K concentrations, and K uptake of mustard plants indicated that there were no significant differences among the adjusted levels of K as determined by the exchange-isotherm curve.     

Effect of 15-Year-Long Fertilization on Potassium Quantity/Intensity Relationships in Black Soil in Northeastern China

The effect of long-term fertilization and cropping on soil potassium (K)–supplying capacity has not been extensively studied. Five treatments [control, nitrogen (N), N–potassium (P), NPK, and NPK + manure (NPKM)] were used to evaluate the quantity and intensity relationship (Q/I) of K in black soil (Luvic Phaeozems soil) after a 15-year (1990–2005) long-term fertilization with a continuous corn cropping located in Changchun, Jilin Province, northeast China. Results showed that the long-term K fertilization of NPK or NPKM markedly increased the values of equilibrium active ratio (AR₀ ^K) and nonspecifically available K (?ΔK₀) but decreased the potential buffering capacity (PBC^K) value. Values of the AR₀ ^K and??ΔK₀ in the NPK and NPKM treatment were about four and two times greater than those in the control, N, and NP treatments, respectively. Compared with the non-K fertilization, PBC^K values were decreased by 40–49% under the K fertilization. The black soil suffered from K deficiency even with NPK fertilization as evidenced from the greater free energies of K⁺ exchanging for calcium (Ca²⁺) and magnesium (Mg²⁺) (?ΔG) (14.7–18.8 kJ mol^?1) than the threshold value of 14.6 kJ mol^?1, from the lower soil K⁺ saturation (1.34%–1.44%) than the critical value of 2.00%, and from the response of corn yield to K fertilization. Our results demonstrated that the increment of the current K application rate through fertilizer and/or manure is needed to improve corn yield in the long run in northeastern China.     

IMPACT OF CONTINUOUS SUGAR BEET CROPPING ON POTASSIUM QUANTITY-INTENSITY PARAMETERS IN CALCAREOUS SOILS

One hundred-eighteen surface soil samples (59 samples from cultivated areas and 59 samples from virgin soils) were studied to ascertain if potassium (K) quantity-intensity (Q/I) parameters of the soils are being changed by long-term sugar beet cropping. Long-term cultivation resulted in a significant decline in the equilibrium activity ratio (AR_e ^K) values from 0.012 to 0.0047 (moles/L)^1/2 (a drop of 61%) and from 0.013 to 0.008 (a drop of 38%) in Typic calcixerpts and Typic endoaquepts, respectively. Paired t-test revealed that continuous sugar beet cultivation led to significant changes in the easily exchangeable K (ΔK₀) values from ?0.69 to ?0.28 cmol_c/kg (a rise of 59%) the Typic calcixerepts soils. The highest values for PBC^K were associated with the soil types which had the greatest clay contents and smectite clay minerals. Results suggest that continuous sugar beet cropping caused a great decline in K supplying power of the soils.     

Quantity‐intensity parameters of potassium in relation to uptake by guinea‐corn in representative soils of the ecological zones of Nigeria

Abstract

Quantity‐intensity (Q‐I) relation studies were often used to supplement information obtained from conventional soil tests for the estimation of potassium (K) needs of crops. With a view to ascertaining the reliability of the Q‐I relation parameters for comprehensive characterization of K dynamics in typical Nigerian soils, K values derived from Q‐I isotherms were related to neutral normal ammonium acetate (1 N NH₄OAc, pH 7.0) (exchangeable) K, other soil K forms [non‐exchangeable (K_ne), exchange (K_e), mineral K (K _m ), and solution K (K_s)] and the K uptake by Guinea‐corn (Sorghum bicolor, var. LS 187) subjected to weekly cuts in Neubauer cultivation vessels. Most of the soil K (about 98%) was in the form of soil minerals while less than 1% was plant available whereas about 1% was trapped within the interlattice layers of the clay minerals (as fixed K or K_ne). Mineral K (K_m) content was closely related to total K (K_t), but not to the other forms, K_ne, K_e, and K_s. A close relationship was noted between the two components of labile K (K_e and K_s). Except for % K saturation, the relationships between the K measurements with plant response were poor. The results of these investigations clearly demonstrate that the Q‐I relation could not adequately characterize the K dynamics of these tropical soils.     

Potassium Quantity–Intensity Parameters and Their Correlation with Bean Plant Indices in Some Calcareous Soils

Plant availability of potassium (K) in soils is controlled by dynamic interactions among its different pools. Potassium quantity–intensity (Q/I) parameters were determined to relate them to bean plant indices in a pot experiment. The results showed that the activity ratio at equilibrium (AR^k) ranged from 0.015 to 0.358 (mmol L^?1)^0.50, the potential buffering capacity (PBC) ranged from 7.54 to 26.32 mmol kg^?1/(mmol L^?1)^0.50, the labile K (Δk°) ranged from 9.1 to 112.2 mg kg^?1, and the K adsorbed at specific sites (Kx) ranged from 6.51 to 69.69 mg kg^?1. The results of pot experiment showed that some K Q/I parameters were significantly correlated with some plant indices. Also, the correlation study showed that readily exchangeable K was significantly correlated with K Q/I parameters except K_x. The results of this research show that the K Q/I method can be used for estimating of soil K availability for bean.     

Exchange equilibria of potassium in soils. III. Effect of K-fertilization on K-Ca exchange

Exchange behaviour of potassium versus calcium in relation to K-fertilization of four soils from Bavaria, viz. Aquic Hapludalf (Kreutenbach), Aquic Chromudert (Groeben), Typic Hapludalf (Geldersheim) and Typic Humaquept (Anglberg), having a wide range after K fertilization in their cation exchange capacity and clay mineralogy was investigated. Experimental results were analysed using Q/I, thermodynamic and empirical approaches. Application of K decreased the potential buffering capacity (PBC_o^K) and increased AR_o^K in all the four soils; Q/I curves followed a second degree polynomial regression. The negative value of standard free energy of K-Ca exchange (ΔGo) decreased with the application of K in all soils. The values of Gapon (K_G) and Vanselow (K_V) selectivity quotients, particularly at low K-saturation, became small with the application of K. K_V was more strongly K-saturation dependent than K_G. The experimental results have been discussed in the light of quantity and type of glycerol-18 Å-minerals.     

Assessment of Soil Potassium Sufficiency as Related to Quantity‐Intensity in Montmorillonitic Soils

Abstract

No studies have been conducted to evaluate the potassium (K) quantity‐intensity (Q/I) relationships that exist in eastern South Dakota soils and how that may affect K fertility interpretations. The objectives of this study were to i) evaluate the K status of smectite‐dominant soils through quantity‐intensity relationships and (ii) relate the findings to current research on soil K release and plant availability. Soil and plant tissue samples were collected from eight different corn production fields across east‐central South Dakota. Samples were collected from areas where corn plants did or did not exhibit K deficiency symptoms. Quantity‐intensity plots were developed and used to derive the typical Q/I parameters. Little difference existed in Q/I parameters and the form of Q/I plots among field sites. The AR_e ^K and ΔK⁰ values ranged from 0.0013 to 0.0113, and ?0.47 to 0.18 cmol_c kg^?1, respectively, and most sites were considered K insufficient. The predominant phyllosilicate present in the clay‐sized fraction was montmorillonite with an estimated 17% tetrahedral charge. These soils would not be expected to contribute much plant‐available, nonexchangeable K and would be in need of frequent K fertilization. Presumably, these and similar soils, upon K exhaustion, rely heavily on K released from K‐bearing silt‐sized particles and may be highly dependent on surface‐controlled dissolution processes for labile K replenishment. Additional research needs to be conducted concerning the release kinetics of K from K‐bearing minerals of these soils.     

Evaluation of quantity‐intensity relationships of potassium in deeply weathered soil profile developed over granite from peninsular Malaysia

Abstract

The potassium (K) supplying capacity of a deeply weathered profile developed over granite from Peninsular Malaysia was investigated by employing the quantity‐intensity (Q/I) approach. The values of potential buffering capacity (PBC^K), labile K (K_L), specific K (K_O), and specific K sites (K_X) were considerably higher in the saprolite zones as compared to the solum layers. This indicated that depletion of K on cropping would be faster in the solum materials than in the saprolites. Potassium equilibrium activity ratio was in the sequence: solum > middle saprolite > upper saprolite. Free energy values showed low, but sufficient, level of available K reserve in this profile. The relationships of Q/I parameters with physico‐chemical characteristics and clay mineralogy of the profile were discussed. The changes in the Q/I parameters as a function of depth were found to be associated with the contents of clay and organic matter in the solum, while in the saprolites, the clay mineralogy which composed mainly of K‐feldspar, mica, and mica‐smectite seemed to be the main factor.     

Potassium isotherm partitioning based on modified quantity‐intensity relation and potassium buffering characterization of soils of North India

Background : Potassium (K) availability in soil and plant uptake is restrained by the dynamic interactions among the different pools of K. Aims : To understand these interactions, a study was undertaken to assess the quantity–intensity (Q/I) and buffering characteristics of rainfed maize (Zea mays L.) growing soils. Ten contrasting soils were evaluated for K partitioning changes in exchangeable K (ΔEK) and non‐exchangeable K (ΔNEK) pools in the soil‐solution phase and buffering characteristics using a modified version of Q/I approach. Results : The partitioned Q/I isotherms showed strong adsorption with the increase in K concentration ratio (CR^K) and the changes due to ΔEK were higher than changes due to ΔNEK. Total buffering capacity (PBC^K) significantly correlated (r = 0.92, p <0.01) with clay content with a major share contributed by buffering capacity owing to non‐exchangeable K ( ${\mathrm{PBC}}_{\Delta \mathrm{NEK}}^K$) rather than exchangeable K ( ${\mathrm{PBC}}_{\Delta \mathrm{EK}}^K$). The fixation capacity (β) factor, the magnitude of added K converted into a non‐exchangeable pool, ranged from 41 to 63%, whereas release (α) factor, the magnitude of added K converted to the exchangeable pool, ranged from 19 to 36%. Both threshold solution K (CK_r) and threshold exchangeable K (EK_r) values were found to be high in Satran clay loam (S2) and lower in Doon silty clay loam (S3) soils. The equilibrium exchangeable K (EK_o) was found close to minimum exchangeable K (E_min) in Doon silty clay loam (S3) and Babaweyl sandy clay loam (S1) soils and overall E_min constituted about 8.94 to 0.57% of the EK_o. Conclusion : It may be concluded that K Q/I isotherm partitioning provides a valuable insight to assess the dynamic relations. The ratio of α/β (K recharge index) could be used to evaluate the K enrichment capacity of soil to K additions while EK_r and E_min can be potentially useful in the elucidation of exchangeable K as K fertility index especially in soils with poor K fertilizer management.     

Yield response of polyethylene mulched tomato to potassium source and rate on sand

Tomato (Lycopersicon esculentum Mill. cv. Sunny) was grown with the full‐bed polyethylene mulch‐seepage (modified furrow) irrigation system for three seasons to evaluate the effects of potassium (K) sources and K rates on fruit yields and leaf K concentrations. Soil in the experimental area was an Eau Gallie fine sand (sandy, siliceous, hyperthermic Alfic Haplaquods) that varied from 12 mg kg^‐1 (very low) to 56 mg kg^‐1 (medium) K by Mehlich I extraction prior to planting. Potassium sources, potassium chloride (KC1), potassium nitrate (KNO₃), and potassium sulfate (K₂SO₄) were evaluated at 0, 90, 180, 270, and 360 kg kg^‐1 K rates. Nitrogen (N) was applied at 270 kg kg^‐1 and P at 43 kg kg^‐1 with all K rates. Yields of extra‐large and marketable total yields in one season were higher (P<0.05) with potassium nitrate (KNO₃) than with KC1. Maximum yields were produced from 270 to 360 kg K kg^‐1, regardless of pre‐plant soil K concentrations. In the shoots, K concentrations increased with increasing K rates. At 90 and 180 kg K kg^‐1 application rates, K concentrations in the shoots were <2% and the plants and fruits had K‐deficiency symptoms.     

Effects of calcium lignosulphonate on Mehlich‐III extractable calcium,magnesium, and potassium quantity‐intensity relationship in the soil with or without potassium dihydrogen phosphate

Abstract

Calcium lignosulphonate (CaLS), a waste product from the pulp and paper industry, is expected to affect reaction of K fertilizer in the soil, thus influences their availability to crops. A clay soil (Typic Humaquept) was incubated with various amounts of CaLS (0 to 150 g kg^‐1 soil) and potassium dihydrogen phosphate (0–25.64 mmol kg^‐1 soil) for 240 h under moist conditions at 5 and 15°C. Subsamples were extracted with deionized water and the Mehlich‐III (M3) solution for the analyses of pH, and P, Ca, K and Mg concentrations and K adsorption (K_ad). Higher temperature reduced M3 extractable K (K_M3). CaLS and K additions increased M3 extractable Mg (Mg_M3) with Ca contributed more than did K as indicated by the standardized estimates. Additions of CaLS increased K_M3. Potassium adsorption decreased with the increases in CaLS addition rates. Significant positive linear relationships were observed between K_ad and the concentration ratio of [K⁺]/[Ca²⁺]^½, suggesting that the potassium buffering capacity of the soil was reduced by the additions of CaLS, with the desugared CaLS being more effective than the non‐desugared CaLS. The increased slope values with the increases in CaLS additions of the linear relationships between K_M3 and [K]/[Ca²⁺]^½ indicated that CaLS improved the quantity and intensity relationships and increased the power of the soil supplying plants with K.     

Response of soil exchangeable and crop potassium concentrations to variable fertilizer and cropping regimes in long-term field experiments on different soil types

Annual potassium (K) balances have been calculated over a 40‐year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha^?1 year^?1 in rotation I, compared with 10–26 kg ha^?1 year^?1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (K_ex). Significant depletion of K_ex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ～2% (dry weight) was maintained during the 40‐year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K.     

Effect of potassium fertilizers on quantity‐intensity parameters in some argentine soils

Abstract

The parameters obtained from the quantity‐intensity (Q/I) isotherms have been used by several authors as criteria to estimate the immediate availability of labile potassium (K) in a soil. The aim of this work was to study how these parameters have been modified in four agricultural soils in Argentina by the addition of K (0 to 936 kg K₂O ha^‐1) in an incubation trial simulating K fertilizers application. In two of the soils, the increase in the labile forms of K was proportional to the amount of added K and the recovery percentages were high. In the other soils, a contrasting behavior was found. This difference might be due to different fixing capacity of the soils, which was related to the clay content and mineralogical composition of this fraction. The slopes of the Q/I curves for each soil indicate that the potential buffer capacity (PBC) was similar for the different treatments over the range of K added. The addition of K produced proportional increases in ARe and ?Ko values. This could be attributed to the presence of non saturated planar sites at the highest rates of K applied.     

Bio-extraction of Potassium from Glauconite Nano-particle in an Alfisols of Southern India

ABSTRACT

Glauconite is a potassium (K) bearing mineral, which generally contains 6–10% K₂O and mostly available in various natural deposits in India. Glauconite mineral was converted to nano-particle form by grinding in a high-energy ball mill. The release of K from glauconite nano-particle in soil was studied in a pot culture experiment. Five different treatments viz., 0 mg K₂O kg^?1, 100 mg K₂O kg^?1, 150 mg K₂O kg^?1, 200 mg K₂O kg^?1 used glauconite nano-particle (GNP) as a K source and 100 mg K₂O kg^?1 from muriate of potash (MOP), were applied in soil to grow maize (Zea mays L.) plant. The highest K⁺ concentration was observed in shoot at the application of 200 mg K₂O kg^?1 through GNP and recorded 2 times more K⁺ concentration in shoots as compared to 0 mg K₂O kg^?1 treatment whereas 1.1 times more than the MOP treated soil at 5^th harvesting stage. Selected plant physiological parameters namely electrical conductivity of plant cell, height, leaf area and nitrate reductase activity were also recorded maximum at 200 mg K₂O kg^?1 GNP treated soil. Overall, glauconite nano-particle could supply K throughout the growth period and enhanced biomass yield of maize plant without showing any K deficiency symptom.     

Kaliumernährung des Tabaks auf einem K-fixierenden nordwestiranischen Boden

Potassium nutrition of tobacco on a potassium fixing alluvial soil A field experiment was conducted to study the effects of K-fertilization on potassium uptake by tobacco and the K-dynamics in an alluvial soil rich in clay and carbonate content. It was observed that the amount of exchangeable potassium and the concentration of K in the soil solution increased on fertilization. There were only small changes in exchangeable potassium and significant reduction in the concentration of K in the soil solution during the growth period. Uptake of potassium by plants increased during first month due to its high concentration in soil solution. Decrease in the concentration of potassium after one month caused a rapid reduction in the uptake of potassium by plants (Figure 1). K Fertilization decreases the K-Ca and K-Mg potentials especially during the first month (Table 2) which increase again during the experimental period (because of the slow release of K from the solid phase and its rapid uptake by plants). Where as the concentration of potassium in the soil solution is closely related with K-Ca and K-Mg potentials on the one hand and with K-uptake by plants on the other, no relationship was observed between exchangeable potassium content and K-uptake (Figure 2). The potassium exchange curves of soils from K₀ and K₅ treatments show that the extent of K-adsorption is greater in K₀ soil. A major part of K adsorbed during the shaking experiment can be easily removed by CaCl₂ solution in K₅soil, where as in K₀ soil a part of adsorbed potassium exists in nonexchangeable form. Illite is the dominant clay mineral in this soil which show wedge type structures (expansible at edges).     

Potassium Dynamics in Inceptisols as Influenced by Graded Levels of Potash for Banana: I. Potassium Fractions

Knowledge of forms of potassium (K) in soil is of great importance for formulating sound fertilizer recommendation to banana. Field experiments were conducted to study the effect of graded levels of potash application on forms of potassium at juvenile, grand growth, shooting, and harvest stages of banana on Vertic Haplustept soil. The negative balance of soil-available K was observed in the treatments of 0, 100, and 200 g K₂O plant^?1. However, at 300-g K₂O plant^?1 level, the balance was a mere –11 kg ha^?1, and positive balance was observed in the treatments of 400 and 500 g K₂O plant^?1. Significant positive correlation among different forms of K indicated the interdependency and dynamic equilibrium between K forms. Application of K₂O above the level of 300 g plant^?1 for banana resulted in the build-up of potassium fractions in soil.     

Management practices to control premature senescence in Bt cotton

Commercial cultivation of Bt cotton produced higher boll load which led to stiff inter-original competition for photosynthates, resulting in early cessation of growth (premature senescence) due to more availability of sink and less sources. To overcome this problem, field experiment was conducted during 2011 and 2012 using five treatments of plant growth manipulation viz. no fruiting branch removal (F₁), removal of first fruiting branch (F₂), removal of first and second fruiting branch (F₃), removal of all squares from first fruiting branch (F₄), removal of all squares from first and second fruiting branches (F₅), and three potassium (K) application rates viz. 50 kg ha^?1 (K₁), 100 kg ha^?1 (K₂), and 150 kg ha^?1 (K₃). More nodes above white flower were recorded in F₅, followed by F₃, while minimum were recorded in F₁. Among potassium levels, maximum nodes above white flower were recorded in K₃ followed by K₂ and K₁ during both years of study. Plant height recorded at physiological cutout stage or at maturity stage showed that plants gained more height with removal of all squares from first tosecond fruiting branches with higher potassium dose. Leaf K increased with increasing applied potassium and also with square/branch removal. So early removal of squares/fruiting branches along with higher potassium dose helped in delaying canopy senescence in Bt cotton.     

Oxalic Acid Effect on Potassium Release from Typical Rice Soils of Kashmir

Batch experiments were employed to examine the influence of oxalic acid on release kinetics of potassium (K) from soils along with adsorption and desorption of soil K⁺. The soils used were three rice soils from high-, mid-, and low-altitude zones. The results showed that soil K extracted using 0.2 mol L^–1 oxalic acid was similar to that of 1 mol L^–1 boiling nitric acid (HNO₃). The relation between K release (y) and concentrations of oxalic acid (c) could be best described as y = a + b log c, whereas the best-fit kinetic equation of K release was y = a + b √t. The K release for soils was in the order Bonbagh > Ganasthan > Kreeri. An oxalic acid solution with low pH was able to release more K. Oxalic acid decreased soil K⁺ adsorption and increased desorption, the effect of which tended to be greater at lower pH.     

Changes in Nitrogen,Phosphorus, and Potassium in a Long‐Term Continuous Maize–Wheat Cropping System in India

In a long‐term maize–wheat rotation at the Punjab Agricultural University, Ludhiana, India (subtropical climate), the effects of nitrogen (N), phosphorus (P), and potassium (K) addition on soil fertility and forms of inorganic P and K in the plow layer of an alkaline sandy loam soil were measured after 11 and 22 years of cropping. The treatments comprised four rates of N (0, 60, 120, and 180 kg N ha^?1) as urea, three rates of P (0, 17.5, and 35 kg P ha^?1) as single superphosphate, and two rates of K (0 and 33 kg K ha^?1) as muriate of potash. The treatments selected for the present study were N₀P₀K₀, N₁₂₀P₀K₀, N₁₂₀P_17.5K₀, N₁₂₀P₃₅K₀, N₁₂₀P_17.5K₃₃, and N₁₂₀P₃₅K₃₃. A significant year × treatment interaction in decreasing available N [alkaline potassium permanganate (KMnO₄)–oxidizable N) status of soils was found in all the treatments. Available P (Olsen P) in the control plot decreased over time whereas in plots with added P, available P increased significantly after years 11 and 22, with the greatest increase in the N₁₂₀P_17.5K_o treatment. Compared to the initial values, continuous P fertilization resulted in greater total P and chloride P concentrations after 11 and 22 years. Although sodium hydroxide (NaOH) P and sulfuric acid (H₂SO₄) P increased in P‐treated plots from the start of the trial to year 11, they decreased from year 11 to year 22. Among these inorganic P forms, chloride P was significantly positively correlated with P uptake (r = 0.811*). When only N and P were applied, available K [ammonium acetate (NH₄OAc)–extractable K] significantly decreased over time. In plots without K addition, water‐soluble and exchangeable K decreased from their initial status. Compared to year 11, water‐soluble K increased, whereas exchangeable K decreased after year 22 in plots receiving no K fertilizer. Compared with NPK treatments, a significant decrease of total K in NP treatment plots suggests the release and uptake of nonexchangeable K. Water‐soluble K and exchangeable K were not correlated with K uptake. These results suggest that long‐term application of P fertilizers resulted in the accumulation of P in the soil, which could have resulted in saturation of P binding sites. Of the soil inorganic P fractions, only chloride P appears to be a good indicator of plant‐available P. The gradual loss in native soil K and release of nonexchangeable K indicates the need for adding K fertilizer to maintain soil fertility.