Evaluating soil acidification risk and its effects on biodiversity–ecosystem multifunctionality relationships in the drylands of China

Background:Soil acidifcationn caused by anthropogenic activities may aft soil biochemical cydling,bidiversity,productivity,and multiple eosystem-related functions in drylands.However,to date,such information is lacking to support this hypothesis.Methods Based on a transect survey of 78 naturally assembled shrub communities,we caloulated acid deposition flux in Northwest China and evaluated its likely ecological ffets by testing three altemnative hypotheses,namely:.nidche complementarity,mass ratio,and vegetation quantity hypotheses Rao's quadratic entopy and community-weighted mean traits were employed to represent the complementary aspect of niche complementarity and mass ratio effects,respectively.Resulbs:We observed that in the past four decades,the concentrations of exchangeable base cations in soil in Northwest China have decreased significantly to the extent of having faced the risk of depletion,whereas changes in the calium carbonate content and pH of soil were not significant.Adid deposition primani ly increased the aboweground biomass and shrub density in shrublands but had no sigmificant effect on shrub richness and ecasystem multifunctionality(EMF),indicating that acid deposition had positive but weak ecological effects on dryland ecosystems.Community wd ghted mean of functional traits(representing the mass ratio hypothesis)correlated negatively with EMF,whereas both Rao's quadratic entropy(representing the niche complementarity hypothesis)and aboveground biomass(representing the vegetation quantity hypothesis)correlated positively but insignifcantly with EMF.These biodiversity-EMF relationships highlight the fragility and instability of drylands relative to forest ecasystems.Concuions:The findings from this study serve as important reference points to understand the ris of soil acidification in arid regions and its impacts on biodiversity-EMF relationships.

Analysis of Soil Acidification Trend on the South Bank of Hongze Lake during Recent 30 Years

Based on soil monitoring data in nine sites of Jinhu, Xuyi and Hongze counties on the south bank of Hongze Lake from 1982 to 2013, changes in soil p H, total nitrogen（TN） content, available phosphorus content, organic matter（OM）content and cation exchange capacity（CEC） were analyzed. The results show that due to excessive application of chemical fertilizer in soil on the south bank of Hongze Lake, soil p H reduced by about 2 on average, while TN content and available phosphorus content in soil increased by more than one time and 2-5 times respectively. Soil acidification caused by agricultural production was very serious. In addition, low soil p H resulted in serious loss of soil cation, so that soil CEC in2013 accounted for less than 50% of that in 1982 and affected mineral nutrient metabolism of crops. Therefore, application of calcium, potassium and trace-element fertilizer should be paid more attention to during agricultural production in future.

Effects of Soil Acidification on Yield of Late Rice and Differences in Acid Resistance among Varieties

Effect of soil acidification on yield of late rice was studied and acid resistance of late rice varieties were compared with 23 late rice varieties as materials in Changsha County, Hunan Province. The results indicated that the difference in yield among varieties was obvious, yield in common field was among 5 226.6-9 202.1kg/hm^2, and yield in acidified field was among 3 643.2-7 714. 8 kg/hm^2. Compared with common field, yield of Yueyou 6135, Huayou 18, Jinyou 284 and Ⅱyou 46 increased by 3.24%-26.33% in acidified field, while yield of other varieties decreased by 2.04%-56.79% in acidified field. According to acidification sensitivity, Wufengyou T025, Jinchuyou No.148, Yueyou No.6135, Shenyou No.9586, Xiangfengyou No.103,Zhongyou No.288, Nongxiang No.18, Shanyou No.432, Ⅱ you No.6, and Zhong 9A/R10402 were sensitive to soil acidification; Wuyou No.308, Zhunliangyou No.608,Fengyuanyou No.227, Fengyou No.1167, Fengyuanyou No.299, T you No.272, and Zhong 9A/R9963 were moderately sensitive to soil acidification; Yueyou No.9113,Jinyou No.284, Shenyou No.9588, Huayou No.18, Ⅱ you No.46 and Ⅱ you No.3027 were slightly sensitive to soil acidification

Influence of some agricultural practices on the soil acidification in acid precipitation areas

Both acid precipitation and unreasonable agricultural practices are notorious artificial factors resulting in soil acidification. To sort out reasonable agricultural practices favorable to abating soil acidification, the task of this study was directed to a long-term field trial in Chongqing, dudng which chemical fertilizer, organic fertilizer were applied to different crop rotations and the soil pH value was measured. The results indicated that all treatments decreased pH value in the 0 to 20 cm soil layer after ten years. Problems were more serious when chlorine-containing fertilizer, excessive chemical fertilizer and mixed fertilizer were applied. It is demonstrated that balance rates of N, P and K fertilizers, application of muck in field are advantageous to abating soil acidification. Oil plants affect soil acidification more than cereal in different crop rotation.

Soil Acidification Stimulates the Emission of Ethylene from Temperate Forest Soils

Soil acidification via acid precipitation is recognized to have detrimental impacts on forest ecosystems, which is in part associated with the function of ethylene released from the soil. However, the impacts of acidification on the cycling of ethylene in forest soils have not been fully taken into consideration in global change studies. Forest topsoils （0-5 cm） under four temperate forest stands were sampled to study the effects of a pH change on the emissions of ethylene and carbon dioxide from the soils and concentrations of dissolved organic carbon （DOC） released into the soils. Increasing acidification or alkalinization of forest soils could increase concentrations of DOC released into the soils under anoxic and oxic conditions. The ethylene emission from these forest topsoils could significantly increase with a decreasing pH, when the soils were acidified experimentally to a pH〈4.0, and it increased with an increasing concentration of DOC released into the soils, which was different from the carbon dioxide emission from the soils. Hence, the short-term stimulating responses of ethylene emission to a decreasing pH in such forest soils resulted from the increase in the DOC concentration due to acidification rather than carbon mineralization. The results would promote one to study the effects of soil acidification on the cycling of ethylene under different forest stands, particularly under degraded forest stands with heavy acid depositions.

Hierarchical responses of soil organic and inorganic carbon dynamics to soil acidification in a dryland agroecosystem,China

Soil acidification is a major global issue of sustainable development for ecosystems. The increasing soil acidity induced by excessive nitrogen （N） fertilization in farmlands has profoundly impacted the soil carbon dynamics. However, the way in which changes in soil pH regulating the soil carbon dynamics in a deep soil profile is still not well elucidated. In this study, through a 12-year field N fertilization experiment with three N fertilizer treatments （0, 120, and 240 kg N/（hm-2·a）） in a dryland agroecosystem of China, we explored the soil pH changes over a soil profile up to a depth of 200 cm and determined the responses of soil organic carbon （SOC） and soil inorganic carbon （SIC） to the changed soil pH. Using a generalized additive model, we identified the soil depth intervals with the most powerful statistical relationships between changes in soil pH and soil carbon dynamics. Hierarchical responses of SOC and SIC dynamics to soil acidification were found. The results indicate that the changes in soil pH explained the SOC dynamics well by using a non-linear relationship at the soil depth of 0-80 cm （P=0.006）, whereas the changes in soil pH were significantly linearly correlated with SIC dynamics at the 100-180 cm soil depth （P=0.015）. After a long-term N fertilization in the experimental field, the soil pH value decreased in all three N fertilizer treatments. Furthermore, the declines in soil pH in the deep soil layer （100-200 cm） were significantly greater （P=0.035） than those in the upper soil layer （0-80 cm）. These results indicate that soil acidification in the upper soil layer can transfer excess protons to the deep soil layer, and subsequently, the structural heterogeneous responses of SOC and SIC to soil acidification were identified because of different buffer capacities for the SOC and SIC. To better estimate the effects of soil acidification on soil carbon dynamics, we suggest that future investigations for soil acidification should be extended to a deeper soil depth, e.g., 200 cm.

Cellular Cd^(2+)fluxes in roots confirm increased Cd availability to rice(Oryza sativa L.)induced by soil acidifications

Soil acidifications become one of the main causes restricting the sustainable development of agriculture and causing issues of agricultural product safety.In order to explore the effect of different acidification on soil cadmium(Cd)availability,soil pot culture and hydroponic(soil potting solution extraction)were applied,and non-invasive micro-test technique(NMT)was combined.Here three different soil acidification processes were simulated,including direct acidification by adding sulfuric acid(AP1),acid rain acidification(AP2)by adding artificial simulated acid rain and excessive fertilization acidification by adding(NH_(4))_(2)SO_(4)(AP3).The results showed that for direct acidification(AP1),DTPA-Cd concentration in field soils in Liaoning(S1)and Zhejiang(S2)increased by 0.167-0.217 mg/kg and 0.181-0.346 mg/kg,respectively,compared with control group.When soil pH decreased by 0.45 units in S1,the Cd content of rice stems,leaves and roots increased by 0.48 to 6.04 mg/kg and 2.58 to 12.84mg/kg,respectively,When the pH value of soil S1 and S2 decreased by 0.20 units,the average velocity of Cd^(2+)at 200μm increased by 10.03-33.11 pmol/cm~2/sec and 21.33-52.86pmol/cm^(2)/sec,respectively,and followed the order of AP3>AP2>AP1.In summary,different acidification measures would improve the effectiveness of Cd,under the same pH reduction condition,fertilization acidification increased Cd availability most significantly.

Calcium-based polymers for suppression of soil acidification by improving acid-buffering capacity and inhibiting nitrification

Soil acidification is a major threat to agricultural sustainability in tropical and subtropical regions.Biodegradable and environmentally friendly materials,such as calcium lignosulfonate(CaLS),calcium poly(aspartic acid)(PASP-Ca),and calcium polyγ-glutamic acid(γ-PGA-Ca),are known to effectively ameliorate soil acidity.However,their effectiveness in inhibiting soil acidification has not been studied.This study aimed to evaluate the effect of CaLS,PASP-Ca,andγ-PGA-Ca on the resistance of soil toward acidification as directly and indirectly(i.e.,via nitrification)caused by the application of HNO_(3)and urea,respectively.For comparison,Ca(OH)_(2)and lignin were used as the inorganic and organic controls,respectively.Among the materials,γ-PGA-Ca drove the substantial improvements in the pH buffering capacity(pHBC)of the soil and exhibited the greatest potential in inhibiting HNO_(3)-induced soil acidification via protonation of carboxyl,complexing with Al~(3+),and cation exchange processes.Under acidification induced by urea,CaLS was the optimal one in inhibiting acidification and increasing exchangeable acidity during incubation.Furthermore,the sharp reduction in the population sizes of ammonia-oxidizing bacteria(AOB)and ammonia-oxidizing archaea(AOA)confirmed the inhibition of nitrification via CaLS application.Therefore,compared to improving soil pHBC,CaLS may play a more important role in suppressing indirect acidification.Overall,γ-PGA-Ca was superior to PASP-Ca and CaLS in enhancing the soil pHBC and the its resistance to acidification induced by HNO_(3) addition,whereas CaLS was the best at suppressing urea-driven soil acidification by inhibiting nitrification.In conclusion,these results provide a reference for inhibiting soil re-acidification in intensive agricultural systems.

Mitigation strategies for soil acidification based on optimal nitrogen management

Soil acidification is a serious constraint to food production worldwide.This review explores its primary causes,with a focus on the role of nitrogen fertilizer,and suggests mitigation strategies based on optimal N management.Natural acidification is determined by the leaching of weak acid mainly caused by climate and soil conditions,whereas the use of ammonium-based fertilizers,nitrate leaching and removal of base cations(BCs)by crop harvesting mostly accounts for anthropogenic acidification.In addition,low soil acid buffering capacity,mainly determined by soil parent materials and soil organic matter content,also accelerates acidification.This study proposes targeted mitigation strategies for different stages of soil acidification,which include monitoring soil carbonate content and p H of soils with p H>6.5(e.g.,calcareous soil),use of alkaline amendments for strongly acidic soils(p H<5.5)with aluminum toxicity risk to p H between 5.5 and 6.5,and decreasing acidification rates and supplementing BCs to maintain this optimal p H range,especially for soils with low acid buffering capacity.Effective mitigation involves optimizing the rate and form of N fertilizers used,regulating N transformation processes,and establishing an integrated soil–crop management system that balances acid production and soil buffering capacity.

LARGE-SCALE FARMING BENEFITS SOIL ACIDIFICATION ALLEVIATION THROUGH IMPROVED FIELD MANAGEMENT IN BANANA PLANTATIONS

Large-scale farming by agricultural land transfers has been increasingly promoted in recent years,but the possible impacts on crop production,especially cash crops,and soil acidification remain unclear.This study obtained data for 110 banana plantations in Long’an County,China,and categorized them into small(<0.67 ha),medium(0.67−6.7 ha),and large(>6.7 ha)to determine banana cultivation,nutrient management,and soil acidification rates on farms of the three sizes.Banana yield per unit area significantly increased with increased farm size,and large farms had the highest average yield(48.9 t·ha^(−1))with the least variation.Despite a significant increase in organic fertilizer and base cation inputs,nitrogen(N)surplus did not differ significantly with increasing farm size.With large farms,actual soil acidification rate was significantly lower by 19.1 to 24.0 keq·ha^(−1)·yr^(−1);however,potential soil acidification rate increased with increased overuse of phosphorus.Overall,larger banana plantations used fewer mineral N fertilizers reducing the rate of soil acidification and increasing the H+buffering provided by organic fertilizers.It is concluded that larger farms deliver the dual benefits of higher,less variable banana yield and mitigation of soil acidification by substituting organic N for mineral N fertilizers,supporting sustainable soil management and food production.

Acidification of Soils in Mount Lushan over the Last 35 Years

INTRODUCTION Soil acidification due to acid deposition has been one of the major environmental prob-lems concerned by soil scientists and ecologists for the recent 20 years(van Breemen,1990).Soil acidification with a marked pH decrease of forest soils within various time intervals hasbeen reported in Germany,Sweden,the Netherlands,Australia and the United

Enhanced carbon acquisition and use efficiency alleviate microbial carbon relative to nitrogen limitation under soil acidification

Background:Soil microbial communities cope with an imbalanced supply of resources by adjusting their element acquisition and utilization strategies.Although soil pH has long been considered an essential driver of microbial growth and community composition,little is known about how soil acidification affects microbial acquisition and utilization of carbon(C)and nitrogen(N).To close the knowledge gap,we simulated soil acidification and created a pH gradient by adding eight levels of elemental sulfur(S)to the soil in a meadow steppe.Results:We found that S-induced soil acidification strongly enhanced the ratio of fungi to bacteria(F:B)and microbial biomass C to N(MBC:MBN)and subsequently decreased the C:N imbalance between microbial biomass and their resources.The linear decrease in the C:N imbalance with decreasing soil pH implied a conversion from N limitation to C limitation.To cope with enhanced C versus N limitation,soil microbial communities regulated the relative production of enzymes by increasing the ratio ofβ-glucosidase(BG,C-acquiring enzyme)to leucine aminopeptidase(LAP,N-acquiring enzyme),even though both enzymatic activities decreased with S addition.Structural equation modeling(SEM)suggested that higher C limitation and C:N-acquiring enzyme stimulated microbial carbon-use efficiency(CUE),which counteracted the negative effect of metal stress(i.e.,aluminum and manganese)under soil acidification.Conclusions:Overall,these results highlight the importance of stoichiometric controls in microbial adaption to soil acidification,which may help predict soil microbial responses to future acid deposition.

Sensitivity to Acidification of Forest Soils in Two Watersheds with Contrasting Hydrological Regimes in the Oil Sands Region of Alberta

Input of large amounts of N and S compounds into forest ecosystems through atmospheric deposition is a significant risk for soil acidification in the oil sands region of Alberta.We evaluated the sensitivity of forest soils to acidification in two watersheds(Lake 287 and Lake 185)with contrasting hydrological regimes as a part of a larger project assessing the role of N and S cycling in soil acidification in forest ecosystems.Fifty six forest soil samples were collected from the two watersheds by horizon from 10 monitoring plots dominated by either jack pine(Pinus banksiana)or aspen(Populus tremuloides).Soils in the two watersheds were extremely to moderately acidic with pH(CaCl_2)ranging from 2.83 to 4.91.Soil acid-base chemistry variables such as pH,base saturation,Al saturation,and acid-buffering capacity measured using the acetic acid equilibrium procedure indicated that soils in Lake 287 were more acidified than those in Lake 185. Acid-buffering capacity decreased in the order of forest floor>subsurface mineral soil>surface mineral soil.The most dramatic differences in percent Ca and Al saturations between the two watersheds were found in the surface mineral soil horizon.Percent Ca and Al saturation in the surface mineral soil in Lake 287 were 15% and 70%,respectively;the percent Ca saturation value fell within a critical range proposed in the literature that indicates soil acidification.Our results suggest that the soils in the two watersheds have low acid buffering capacity and would be sensitive to increased acidic deposition in the region.

Soil acidification of alfisols influenced by nitrate and ammonium nitrogen level in tea plantation

Nitrogen is an important fertilizer in tea production,but it is also an important factor in tea garden soil acidification.The relationship between absorption and transport of different forms of nitrogen in the tea plant and soil acidification is still unknown.In order to explore the different characteristics of absorption,utilization and distribution of nitrogen,stable isotope 15N tracer technique was used to measure the absorption,utilization and allocation of nitrate nitrogen(NO_(3-)15N)and ammonium nitrogen(NH4-15N)under the same nitrogen application amount of tea tree seedlings as experimental materials.The results showed that the tea seedlings had the same pattern of nitrogen application:tissue nitrogen content increased after fertilization,remarkable rising at 7 d and the absorption speed increased quickly after 28 d,finally reached its maximum at 56 d.The nitrogen use efficiency of two nitrogen sources in two kinds of soil varied not significantly.The maximum NUE of NO_(3-)^(15)N reached 12.66%,and at the same time NH_(4)-^(15)N utilization rose up to 11.54%.According to the absorption of soil nitrogen and nitrogen fertilizer in the two kinds of soil,it is concluded that the soil nitrogen cannot meet the growth needs of tea tree and extra nitrogen supply was required.The declined soil pH indicated that fertilizer should be used in moderation,which can not only satisfy the growth of tea tree but also to restrict soil acidification.

Significance of Ligand Exchange Relating to Sulfate in Retarding Acidification of Variable Charge Soils Caused by Acid Rain

For the purpose of evaluating the role of ligand exchange of sulfate ions in retarding the rate of acidification of variable charge soils, the changes in pH after the addition of different amounts of HNO_3 or H_2SO_4 to representative soils of China were measured. A difrerence between pH changes caused by the two kinds of acids was observed only for variable charge soils and kaolinite, but not for consted charge soils and bentonite. The larger the proportion of H_2SO_4 in the HNO_3-H_2SO_4 mixture, the lower the calculated H￣+ ion activities remained in the suspension. The difference in H￣+ ion activities between H_2SO_4 systems and HNO_3 systems was larger for soils with a low base-saturation (BS) percentage than those with a high BS percentage. The removal of free iron oxides from the soil led to a decrease in the difference, while the coating of Fe_2O_3 ona bentonite resulted in a remarkable appearance of the difference. The effect of ligand exchange on the acidity status of the soil varied with the soil type. SurfaCe soils with a hash organic matter content showed a less pronounced effect of ligand exchange than subsoils did. It was estimated that when acid rain chiefly containing H_2SO_4 was deposited on variable charge soils the acidilication rate might be slower by 20%-40% than that when the acid rain chiefly contained HNO_3 for soils with a high organic matter content, and that the rate might be half of that caused by HNO_3 for soils with a low organic matter content, especially for latosols.

Acidification and change of physicochemical properties of Mt．Heng soils in last 34 years

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Proton accumulation accelerated by heavy chemical nitrogen fertilization and its long-term impact on acidifying rate in a typical arable soil in the Huang-Huai-Hai Plain

Cropland productivity has been significantly impacted by soil acidification resulted from nitrogen （N） fertilization, especially as a result of excess ammoniacal N input. With decades＇ intensive agricultural cultivation and heavy chemical N input in the Huang-Huai-Hai Plain, the impact extent of induced proton input on soil pH in the long term was not yet clear. In this study, acidification rates of different soil layers in the soil profile （0-120 cm） were calculated by pH buffer capacity （pHBC） and net input of protons due to chemical N incorporation. Topsoil （0-20 cm） pH changes of a long-term fertilization field （from 1989） were determined to validate the predicted values. The results showed that the acid and alkali buffer capacities varied significantly in the soil profile, averaged 692 and 39.8 mmolc kg-1 pH-1, respectively. A significant （P〈0.05） correlation was found between pHRC and the content of calcium carbonate. Based on the commonly used application rate of urea （500 kg N ha-1 yr-1）, the induced proton input in this region was predicted to be 16.1 kmol ha-1 yr-1, and nitrification and plant uptake of nitrate were the most important mechanisms for proton producing and consuming, respectively. The acidification rate of topsoil （0-20 cm） was estimated to be 0.01 unit pH yr-1 at the assumed N fertilization level. From 1989 to 2009, topsoil pH （0-20 cm） of the long-term fertilization field decreased from 8.65 to 8.50 for the PK （phosphorus, 150 kg P205 ha-1 yr-1; potassium, 300 kg K20 ha-1 yr-1; without N fertilization）, and 8.30 for NPK （nitrogen, 300 kg N ha-1 yr-1; phosphorus, 150 kg P2Os ha-1 yr-1; potassium, 300 kg K20 ha -1 yr-1）, respectively. Therefore, the apparent soil acidification rate induced by N fertilization equaled to 0.01 unit pH yr-1, which can be a reference to the estimated result, considering the effect of atmospheric N deposition, crop biomass, field management and plant uptake of other nutrients and cations. As protons could be consumed by some field practices, such as stubble return and coupled water and nutrient management, soil pH would maintain relatively stable if proper management practices can be adopted in this region.

Effect of six years of nitrogen additions on soil chemistry in a subtropical Pleioblastus amarus forest, Southwest China

Soil chemistry influences plant health and carbon storage in forest ecosystems. Increasing nitrogen(N) deposition has potential effect on soil chemistry. We studied N deposition effects on soil chemistry in subtropical Pleioblastus amarus bamboo forest ecosystems. An experiment with four N treatment levels(0, 50, 150,and300 kg N ha-1a-1,applied monthly, expressed as CK,LN,MN, HN,respectively) in three replicates. After6 years of N additions, soil base cations, acid-forming cations, exchangeable acidity(EA), organic carbon fractions and nitrogen components were measured in all four seasons. The mean soil pH values in CK,LN,MN and HN were 4.71, 4.62, 4.71, and 4.40, respectively, with a significant difference between CK and HN. Nitrogen additions significantly increased soil exchangeable Al3+,EA, and Al/Ca,and exchangeable Al3+ in HN increased by 70%compared to CK. Soil base cations(Ca2+, Mg2+, K+, and Na+) did not respond to N additions. Nitrogen treatments significantly increased soil NO3--N but had little effect on soil total nitrogen, particulate organic nitrogen, or NH4~+-N. Nitrogen additions did not affect soil total organic carbon, extractable dissolved organic carbon,incorporated organic carbon, or particulate organic carbon.This study suggests that increasing N deposition could increase soil NO3--N, reduce soil pH, and increase mobilization of Al3+. These changes induced by N deposition can impede root grow and function, further may influence soil carbon storage and nutrient cycles in the future.

Changes in soil properties under Eucalyptus relative to Pinus massoniana and natural broadleaved forests in South China

The ecological effects of eucalypt plantations（EPs） have garnered increasing attention.To understand their effect on soil quality at a landscape scale,and to determine whether soil quality parameters differ due to different stand types,we evaluated soil characteristics in twenty-one groups of EPs,Pinus massoniana Lamb.plantations（PMPs） and natural broadleaved forests（NBFs）across Guangdong Province,China.Both the physical characteristics of soil hydrology and the properties of soil nutrients in A and B horizons were determined.Results showed that,compared to NBFs,EPs and PMPs produced a shallower litter layer,reduced canopy density,higher soil bulk density,significantly lower total porosity,non-capillary porosity,total water volume,and hygroscopic water in the A horizon（P〈0.05）.Moreover,total N,available K,and soil organic carbon（SOC） in EPs and PMPs were significantly lower than in NBFs.EPs and PMPs did not differ significantly in N,P or K content,but PMPs had significantly lower SOC and boron in the A horizon than EPs.Low p H and poor capacity to buffer acidification generally occurred in all cover types.Both EPs and PMPs showed a decline in soil properties relative to NBFs,but EPs and PMPs exhibited no significant difference.These results indicate that actions are needed to ameliorate the potential negative effects on soil quality in forestry plantations.

Liming reduces soil phosphorus availability but promotes yield and P uptake in a double rice cropping system

Liming is often applied to alleviate soil acidification and increase crop yield on acidic soils,but its effect on soil phosphorus(P)availability is unclear,particularly in rice paddies.The objective of this study was to examine the effect of liming on rice production,yield and P uptake in a three-year field experiment in a double rice cropping system in subtropical China.We also conducted an incubation experiment to investigate the direct effect of liming on soil available P and phosphatase activities on paddy soils in the absence of plants.In the incubation experiment,liming reduced soil P availability(measured as Olsenextractable P)by 14–17%and inhibited the activity of soil acid phosphatase.Nonetheless,lime application increased grain yield,biomass,and P uptake in the field.Liming increased grain yield and P uptake more strongly for late rice(26 and 21%,respectively)than for early rice(15 and 8%,respectively).Liming reduced the concentration of soil available P in the field as well,reflecting the increase in rice P uptake and the direct negative effect of liming on soil P availability.Taken together,these results suggest that by stimulating rice growth,liming can overcome direct negative effects on soil P availability and increase plant P uptake in this acidic paddy soil where P is not the limiting factor.