Effects of various organic materials on soil aggregate stability and soil microbiological properties on the Loess Plateau of China

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1 Vol. 59, 213, No. 4: Plnt Soil Environ. Effets of vrious orgni mterils on soil ggregte stility n soil miroiologil properties on the Loess Plteu of Chin F. Wng 1, Y.A. Tong 1, J.S. Zhng 1, P.C. Go 1, J.N. Coffie 2 1 College of Resoures n Environment, Northwest A&F University, Yngling, P.R. Chin 2 Deprtment of Environmentl Siene n Tehnology, University of Mryln, Mryln, USA ABSTRACT A fiel experiment ws onute to exmine the influene of vrious orgni mterils on soil ggregte stility n soil miroiologil properties on the Loess Plteu of Chin. The stuy involve seven tretments: no fertilizer (CK); inorgni N, P, K fertilizer (NPK); low mount of mize stlks plus NPK (LSNPK); meium mount of mize stlks plus NPK (MSNPK); high mount of mize stlks plus NPK (HSNPK); mize stlk ompost plus NPK (CNPK); ttle mnure plus NPK (MNPK). The orgni fertilizer tretments improve soil ggregte stility n soil miroiologil properties ompre with CK n NPK tretments. Compre with the NPK tretment, soil trete with LSNPK h signifint inrese of 27.1% in 5 3 mm ry ggregtes. The > 5 mm wter stle ggregtes trete with CNPK inrese y 6.5% ompre to the NPK. Soil miroil iomss C n N n urese tivity were signifintly inrese in CNPK y 42., 54.6 n 19.8%, respetively. The stuy inite tht the vrition tren in the mount of soil ggregte (.5 5 mm) for orgni fertilizer tretments ws similr to the ontent of soil miroil ron n nitrogen n soil enzyme tivity. Consiering the gret vilility of orgni mteril, espeilly stlk ompost in this region, pplition of orgni mterils is reommene to improve soil struture n fertility. Keywors: vilility of orgni mteril; mize stlk ompost; soil struture n fertility; miroil iomss C; miroil iomss N The Loess Plteu is one of the most severely eroe res in Chin. Extensive soil erosion hs resulte in poor soil fertility. Sustining griulturl proution on the Loess Plteu is very importnt in orer to ensure suffiient foo supply for the growing popultion (Zhng et l. 29). It ws suggeste tht improving soil fertility oul inrese griulturl proution in this re s muh s threefol (Fn n Zhng 2). Although soil fertility hs improve in reent yers, soil orgni mtter ontent n rop yiel re still low. Applition of orgni mterils is effetive t improving soil fertility, soil physil n iologil properties (Tlgre et l. 212). Mintining high stility of soil ggregtes is neessry for mintining soil proutivity, eresing soil egrtion n thus minimizing environmentl pollution s well. Aoym et l. (1999) foun tht n inrese in soil orgni mtter with the ition of orgni fertilizer use Supporte y the Soil Qulity Fountion of Chin, Grnt No. 212BAD5B3, n y the Youth Siene Foun of Northwest A&F University, Projet No. Z

2 Plnt Soil Environ. Vol. 59, 213, No. 4: formtion of isperse-resistnt ggregtes. Soil miroil iomss n enzymti tivity re ll more sensitive to the hnges of soil qulity thn soil orgni mtter (Allison et l. 28). However, orgni fertilizers hve the potentil to inrese soil miroil iomss n enzyme tivities (Ehin Msto et l. 26). Numerous stuies investigte the effet of long term fertiliztion on soil ggregte stility or miroil iomss (Wng et l. 212). However, there is limite informtion ville for the short term effets of mixe inorgni n orgni fertilizers on soil physil properties omine with soil miroiologil properties. We ssume tht short term ition of ifferent fertilizers in rle soil woul not only ffet the soil ggregte istriution ut lso soil miroil iomss. The ojetives of this stuy were to etermine how the short term fertiliztion ffete soil ggregte stility n miroiologil properties on the Loess Plteu of Chin. MATERIAL AND METHODS Experimentl site. A fiel experiment ws estlishe in Septemer 27 in Gnjin villge, Heyng County, Shnxi provine in the southest prt of the Loess Plteu, Chin (35 19'87''N, 11 5'22''E, 88 m.s.l.). The site hs men nnul temperture of 1. C n men nnul preipittion of 572 mm. The loess soil t the site is lssifie s Chromi Cmisols. The generl soil properties ( 2 m) of the site re s follows: ph 8.24, orgni mtter 12.5 g/kg, totl N.81 g/kg, ville P 9.57 mg/kg, ville K 18 mg/kg, n soil ulk ensity 1.3 g/m 3. Winter whet (Tritium estivum L.) ws grown throughout the experiment. Experimentl esign. The stuy onsiste of seven tretments: no fertilizer (CK); inorgni N, P, K fertilizer (NPK); low mount of mize stlks plus NPK (LSNPK); meium mount of mize stlks plus NPK (MSNPK); high mount of mize stlks plus NPK (HSNPK); mize stlk ompost plus NPK (CNPK); ttle mnure plus NPK (MNPK). Eh tretment ws replite three times. The etils of fertilizer rte for ropping system re given in Tle 1. The LSNPK, MSNPK n HSNPK plots reeive 375, 75 n 15 kg (ir-rie) mize stlks per h, respetively. The ompost omprise mixture of mize stlk, hiken mnure n fungiie. All fertilizers were pplie one, just efore whet sowing. Soil smpling n mesurements. Soil smples were ollete t the en of My 29. For soil ggregte hrteriztion n stility nlyses, three unisture smples from eh plot were tken from 2 m epth y hn spe, whih onsiste of lrger los tht were then gently frtionte into 1 2 m ggregtes long nturl rek points. All smples from eh plot were refully mixe y hn to form omposite smple. For miroiologil smples, seven soil ores (5 m imeter) were ollete from 2 m epth. Cores from the sme epth were ulke to form one smple per epth n per tretment. Distriution n stility of soil ggregtes were etermine y using seprte ry n wet sieving Tle 1. Detils of fertilizer rtes for the ropping system (kg/h) Tretment C N P K CK NPK LSNPK MSNPK HSNPK CNPK MNPK the mount of N/P/K ontine in the e rop strw or orgni mnure. CK no fertilizer; NPK inorgni N, P, K fertilizer; LSNPK low mount of mize stlks plus NPK; MSNPK meium mount of mize stlks plus NPK; HSNPK high mount of mize stlks plus NPK; CNPK mize stlk ompost plus NPK; MNPK ttle mnure plus NPK 163

3 Vol. 59, 213, No. 4: Plnt Soil Environ. methos (Dne n Topp 22). The hloroform fumigtion metho ws use for the etermintion of soil miroil ron n nitrogen (Brookes et l. 1985, Vne et l. 1987). Urese, phosphtse n invertse tivities were etermine y the metho esrie y Gun (1986). Sttistil nlysis. Men weight imeter (MWD): MWD = n i= 1 xw i i x i w i Where: x i (mm) verge imeter of the openings of two onseutive sieves, n w i weight frtion in eh lss. Geometri men imeter (GMD): n log GMD = exp w i i= 1 i x i n w i= 1 i Where: w i (g) weight of ggregtes in size lss with n verge imeter, n x i (mm) the sme s ove. Perentge of ggregte estrution (PAD): PAD = (M M w ) 1/M Where: M mss frtion of >.25 mm ggregtes (ry sieve) n M w mss frtion of >.25 mm ggregtes (wet sieve) (Kemper n Rosenu 1986). For etermintion of ggregte size istriutions (ASD), the weight rtio of ggregtes of eh sieve to the totl weight of ggregtes ws lulte. All t (mens ± stnr evition, n = 3) were nlyze y one-wy ANOVA, n ifferenes in mens were ompre y the lest signifint ifferene test t P <.5. All sttistil nlysis ws rrie out y SAS softwre (version 8., Cry, USA). RESULTS AND DISCUSSION Distriution of ggregte size lsses. The mount of ggregtes (> 1 mm) t orgni fertiliztion tretments were lower thn t NPK tretment, n the LSNPK tretment h the lowest mount (19.4%) of ggregtes of this size (Tle 2). There ws greter proportion of ggregtes of 5 3 mm (with n inresing tren from 2.5% to 27.1%) t the orgni fertilizer tretments (LSNPK, MSNPK, CNPK, MNPK) ompre with the NPK tretment. The proportion of ggregtes 1.5 mm t orgni fertiliztion tretments, exept CNPK, were signifintly higher thn t NPK. The perentge of <.25 mm ggregtes in ll tretments ws pproximtely 35%, n the HSNPK n CNPK tretments were lower thn NPK tretment (Tle 2). These results re similr to other stuies whih inite tht long-term pplition of hemil fertilizer espeilly omine with orgni fertilizer oul inrese the mount of lrger ggregte Tle 2. Effet of ifferent fertilizer tretments on ggregte size istriutions (ry sieve, %) Tretment CK NPK LSNPK MSNPK HSNPK CNPK MNPK Size lss (mm) > < ± 7.4 ± 2.61 ± 5.4 ±.48 ± 2.22 ± 1.8 ± 4.5 ± 36.6 ± ± 6.78 ± 2.21 ± 5.54 ±.53 ± 2.54 ± 1.1 ± 4.36 ± 35.4 ± ± 7.98 ± 3.44 ± 7.4 ±.64 ± 3.67 ± 12.5 ± 4.8 ± 39.7 ± ± 6.1 ± 2.6 ± 5.68 ±.78 ± 3.3 ± 11.8 ± 4.59 ± 35.6 ± ± 7.27 ± 2.41 ± 5.41 ±.74 ± 2.75 ± 1.3 ± 4.38 ± 33.8 ± ± 7.97 ± 2.81 ± 5.95 ±.64 ± 2.67 ± 1.24 ± 4.32 ± 32.8 ± ± 5.53 ± 2.55 ± 5.94 ±.67 ± 3.17 ± ± 5.6 ± 38.4 ± Vlues re mens ± SD (n = 3). Vlues with ifferent letters within olumn re sttistilly signifintly ifferent t P <.5. CK no fertilizer; NPK inorgni N, P, K fertilizer; LSNPK low mount of mize stlks plus NPK; MSNPK meium mount of mize stlks plus NPK; HSNPK high mount of mize stlks plus NPK; CNPK mize stlk ompost plus NPK; MNPK ttle mnure plus NPK 164

4 Plnt Soil Environ. Vol. 59, 213, No. 4: Tle 3. Effet of ifferent fertilizer tretments on ggregte size istriutions (wet sieve, %) n PAD (%) Tretment Size lss (mm) > <.25 CK 3.66 ± ± ± ± ± ± NPK 3.18 ± ± ± ± ± ± LSNPK 1.33 ± ± ± ± ± ± MSNPK 3.53 ± ± ± ± ± ± HSNPK 5.68 ± ± ± ± ± ± CNPK 6.49 ± ± ± ± ± ± MNPK 3.85 ± ± ± ± ± ± Vlues re mens ± SD (n = 3). Vlues with ifferent letters within olumn re sttistilly signifintly ifferent t P <.5. CK no fertilizer; NPK inorgni N, P, K fertilizer; LSNPK low mount of mize stlks plus NPK; MSNPK meium mount of mize stlks plus NPK; HSNPK high mount of mize stlks plus NPK; CNPK mize stlk ompost plus NPK; MNPK ttle mnure plus NPK; PAD perentge of ggregtes estrution PAD n erese the mount of isperse sustne (<.25 mm) n lrge pes (> 1 mm). Liu (27) foun tht long-term fertiliztion espeilly omine with orgni fertilizer plye n importnt role in inresing the mount of ggregtes (2 5, 1 2,.5 1,.25.5 mm) on surfe soil. This inrese my e ttriute to the inrese miroil iomss n tivity results in extr ellulr polyshries whih t s the goo ementing gent of soil ggregtes. Aggregte wter stility n soil ggregtion re known to ply mjor role in improving soil fertility n grin proution. The pplition of mnure inreses the perentge of lrge size wter stle ggregtes (> 5 mm) (Aoym et l. 1999). Similr results were foun in this stuy. Wter-stle ggregtes (> 5 mm) in CNPK tretment ws signifintly higher thn NPK n lso h the highest mount (6.49%) in ll tretments (Tle 3). The mount of ggregtes 5 2 mm inrese wekly with orgni menments n the CNPK tretment inrese y 78.% ompre to NPK tretment. The perentge of the ggregtes with other sizes (2 1, 1.5,.5.25 mm) were higher in the MNPK, HNPK, CNPK tretments y %, % n % thn the NPK respetively, whih is in greement with the results of Huo et l. (28). Lignin n ellulose n e erive from stlk s ville C n n promote soil ggregtion egree n stility. Our results showe tht the perentge of ggregtes estrution (PAD) rnge from % (Tle 3). This hppene euse there ws n inrese in soil orgni mtter with ition of stlks n Tle 4. Men weight imeter (MWD; mm) n geometri men imeter (GMD; mm) of ry n wet sieve uner ifferent fertilizer tretments Type Dimeter Tretment CK NPK LSNPK MSNPK HSNPK CNPK MNPK Dry sieve Wet sieve MWD 6.51 ± ± ± ± ± ± ±.35 GMD 4.23 ± ± ± ± ± ± ±.36 MWD 1.46 ± ± ± ± ± ± ±.11 GMD.86 ± ±.8.7 ±.2.76 ± ±.2.91 ± ±.5 Vlues re mens ± SD (n = 3). Vlues with ifferent letters within olumn re sttistilly signifintly ifferent t P <.5. CK no fertilizer; NPK inorgni N, P, K fertilizer; LSNPK low mount of mize stlks plus NPK; MSNPK meium mount of mize stlks plus NPK; HSNPK high mount of mize stlks plus NPK; CNPK mize stlk ompost plus NPK; MNPK ttle mnure plus NPK 165

5 Vol. 59, 213, No. 4: Plnt Soil Environ. () 5 () 6 Soil miroil iomss ron (mg C /kg ry soil) e Soil miroil iomss nitrogen (mg N /kg ry soil) f e Figure 1. Miroil iomss C (MBC) () n miroil iomss N (MBN) () t 2 m epth. Different letters etween tretments show signifint ifferenes t P <.5. CK no fertilizer; NPK inorgni N, P, K fertilizer; LSNPK low mount of mize stlks plus NPK; MSNPK meium mount of mize stlks plus NPK; HSNPK high mount of mize stlks plus NPK; CNPK mize stlk ompost plus NPK; MNPK ttle mnure plus NPK onsequently the formtion of orgni ementing mteril, so ggregte stility inrese (Tisll n Oes 1982). Men weight imeter n men weight imeter of soil ggregtes. Men weight imeter (MWD), men weight imeter (GMD) of soil ggregtes n the mount of >.25 mm ggregtes n strongly reflet the istriution n stility of ggregtes. Overll, MWD n GMD of ry ggregtes generlly erese in the orer CNPK > HSNPK > NPK > CK > MSNPK > MNPK > LSNPK (Tle 4). MWD n GMD of wter-stle ggregtes were higher thn NPK y % n 24.7% in ll of the orgni fertiliztion tretments. Usully, there ws signifint positive orreltion etween MWD n the mount of >.25 mm ggregtes (Guer et l. 25). This grees with our results. Most of the orgni fertiliztion tretments h lrge MWD n high mount of >.25 mm ggregtes. Soil miroil iomss. Soil miroil iomss n inite soil iologil proesses, inluing orgni mtter egrtion, minerliztion n nutrient reyling. Our results showe tht miroil iomss C (MBC) rnge from to 453. mg/kg n miroil iomss N (MBN) () MBC/MBN () MBC/SOC (%) Figure 2. Miroil iomss C (MBC)/miroil iomss N (MBN) () n MBC/soil orgni ron (SOC) () t 2 m epth. Different letters etween tretments show signifint ifferenes t P <.5. CK no fertilizer; NPK inorgni N, P, K fertilizer; LSNPK low mount of mize stlks plus NPK; MSNPK meium mount of mize stlks plus NPK; HSNPK high mount of mize stlks plus NPK; CNPK mize stlk ompost plus NPK; MNPK ttle mnure plus NPK 166

6 Plnt Soil Environ. Vol. 59, 213, No. 4: Tle 5. Soil urese, lkline phosphtse n invertse tivities in 2 m epth (μg/g/h) Tretment Urese Phosphtse Invertse CK 71.3 ± 4.32 e 7.1 ± ± 6.76 NPK 9.4 ± ± ± 2.55 LSNPK 97.9 ± ± ± 4.42 MSNPK 11.7 ± ± ± HSNPK 11.8 ± ± ± CNPK ± ± ± MNPK 19.2 ± ± ± e Vlues re mens ± SD (n = 3). Dt re mens ± SD (n = 3) n vlues followe y ifferent letters etween tretments show signifint ifferenes t P <.5. CK no fertilizer; NPK inorgni N, P, K fertilizer; LSNPK low mount of mize stlks plus NPK; MSNPK meium mount of mize stlks plus NPK; HSNPK high mount of mize stlks plus NPK; CNPK mize stlk ompost plus NPK; MNPK ttle mnure plus NPK rnge from 16.6 to 47.7 mg/kg in the 2 m epth (Figure 1). After 2 yers of menments, MBC n MBN generlly erese in the orer CNPK > MNPK > (LSNPK, MSNPK, HSNPK) > NPK > CK. MBC n MBN in fertilize tretments were signifintly higher thn CK. The CNPK n MNPK tretments inrese the MBC signifintly. This ws similr to other stuies whih showe tht pplition of orgni mterils inrese MBC in fluvo-qui soil (Ni et l. 23). This inrese my e ttriute to inrese inputs to the soil from ove- n elow-groun resiues. These mterils re the min C n N soure for soil miroorgnisms n oul improve the utility of nitrogen n help to protet the environment (Zhou et l. 27). MBC/MBN n show the informtion of miroil popultion. Generlly, C/N of teri is 5:1, tinomyes 6:1 n fungus 1:1. MBC/MBN of CK ws the lowest for the few miroorgnisms there (Figure 2). Exept for MBC/MBN in the NPK n HSNPK tretments eing higher, it ws out 1:1 in the other tretments n h no signifint ifferene. MBC/SOC (soil orgni ron) is etter to show the soil ron pity n tivity ompre to MBC n SOC lone (Li et l. 28). MBC/SOC rnge from 2.2% to 6.18% in ll tretments n in fertilize tretments ws signifintly higher thn CK (Figure 2). These results were likely ue to the ition of mnure n fungiie. The ompost oul hve more orgni mtter from stlks ron eomposing ompre to mnure. Soil enzymti tivity. Soil enzymti tivity n inite soil iologil tivity. Soil urese reltes to soil ility of N supply losely, whih stns for egree of N supply. Our results showe tht the urese tivity ws 21.1% in the NPK tretment, whih ws higher thn CK n the urese tivity in orgni fertiliztion tretments were ll higher thn the NPK (Tle 5). Of ll the orgni fertiliztion tretments, the CNPK h the gretest inrese of 19.7% for urese tivity. Soil phosphtse tivity is the initor of soil phosphorus sttus. Overll, soil phosphtse tivity showe n inresing tren. Compre with the NPK tretment, MNPK inrese signifintly, in prtiulr, the CNPK, inrese y 7.93% (Tle 5). The ition of orgni mterils signifintly inrese soil phosphtse tivity n pity (Tylor et l. 22). The invertse tivity reflets the umultion n eomposition of soil orgni ron. In ition to the MNPK, ll fertiliztion tretments were higher thn CK to vrying egrees. The invertse tivity in the HSNPK tretment ws signifintly higher thn the other tretments n ifferenes mong the other orgni tretments were generlly smll (Tle 5). Long-term pplition of orgni fertilizer n improve invertse tivity mrkely, whih n then stimulte the turnover of soil orgni ron (Alih et l. 2). Our results showe tht the pplition of stlks oul improve the tivity of invertse, n invertse stimulte the eomposition gin, so synergi reltionship ws rete. In onlusion, fining resonle methos to improve soil fertility to promote sustinle griulturl proution on the Loess Plteu of Chin is very neessry. Applition of orgni mterils 167

7 Vol. 59, 213, No. 4: Plnt Soil Environ. is promising soil mngement prtie whih n improve soil struture n inrese soil miroil tivity, espeilly in the CNPK tretment. However, whether this is the optimum fertiliztion metho for the region, nees to e stuie with long term omprehensive evlution. REFERENCES Alih R., Cnet R., Pomnes F., Ingelmo F. (2): Miroil iomss ontent n enzymti tivities fter the pplition of orgni menments to hortiulturl soil. Bioresoure Tehnology, 75: Allison S.D., Czimzik C.I., Treseer K.K. (28): Miroil tivity n soil respirtion uner nitrogen ition in Alskn orel forest. Glol Chnge Biology, 14: Aoym M., Angers D.A., N Dyegmiye A., Bissonnette N. (1999): Protete orgni mtter in wter-stle ggregtes s ffete y minerl fertilizer n mnure pplitions. Cnin Journl of Soil Siene, 79: Brookes P.C., Lnmn A., Pruen G., Jenkinson D.S. (1985): Chloroform fumigtion n the relese of soil nitrogen: A rpi iret extrtion metho to mesure miroil iomss nitrogen in soil. Soil Biology n Biohemistry, 17: Dne J.H., Topp G.C. (22): Methos of Soil Anlysis. Prt 4, Physil Methos. Soil Siene Soiety of Ameri, Mison. Ehin Msto R., Chhonkr P.K., Singh D., Ptr A.K. (26): Chnges in soil iologil n iohemil hrteristis in long-term fiel tril on su-tropil ineptisol. Soil Biology n Biohemistry, 38: Fn X.L., Zhng F.S. (2): Soil wter, fertility n sustinle griulturl proution in ri n semiri regions on the Loess Plteu. Journl of Plnt Nutrition n Soil Siene, 163: Gun S.Y. (1986): Soil Enzyme n its Reserh Methos. Chin Agriulturl Press, Beijing, (In Chinese) Guer A.K., Phepsky Y.A., Levkovsky E.V. (25): Frtl mss-size sling of wetting soil ggregtes. Eologil Moelling, 182: Huo L., Wu T.Y., Lin H.M., Co S.Y., Tng W.X. (28): Effets of long-term fertiliztion on wter-stle ggregtes in li kstnozem of Loess Plteu. Chinese Journl of Applie Eology, 19: (In Chinese) Kemper W.D., Rosenu R.C. (1986): Aggregte Stility n Size Distriution. In: Klute A. (e.): Methos of Soil Anlysis. Prt 1. Physil n Minerlogil Methos. Amerin Soiety of Agronomy-Soil Siene Soiety of Ameri, Mison. Li J., Zho B.Q., Li X.Y., Hwt B.S. (28): Effets of long-term omine pplition of orgni n minerl fertilizers on soil miroiologil properties n soil fertility. Sienti Agriultur Sini, 41: Liu E.K. (27): Miroiologil fetures of soil uner ifferent fertiliztion systems n their relte soil fertility. PhD Thesis. Chinese Aemy of Agriulturl Sienes, Beijing. Ni J.Z., Xu J.M., Xie Z.M. (23): Dynmi of tive orgni mtter frtions in Fluvio-qui soil fter pplition of orgni fertilizers. Journl of Agro-environmentl Siene, 22: (In Chinese) Tlgre L., Luringson E., Roostlu H., Astover A., Mkke A. (212): Green mnure s nutrient soure for sueeing rops. Plnt, Soil n Environment, 58: Tylor J.P., Wilson B., Mills M.S., Burns R.G. (22): Comprison of miroil numers n enzymti tivities in surfe soils n susoils using vrious tehniques. Soil Biology n Biohemistry, 34: Tisll J.M., Oes J.M. (1982): Orgni mtter n wter-stle ggregtes in soils. Journl of Soil Siene, 33: Vne E.D., Brookes P.C., Jenkinson D.S. (1987): An extrtion metho for mesuring soil miroil iomss C. Soil Biology n Biohemistry, 19: Wng J.J., Li X.Y., Zhu A.N., Zhng X.K., Zhng H.W., Ling W.J. (212): Effets of tillge n resiue mngement on soil miroil ommunities in North Chin. Plnt, Soil n Environment, 58: Zhng S.L., Lövhl L., Grip H., Tong Y.A., Yng X.Y., Wng Q.J. (29): Effets of mulhing n th ropping on soil temperture, soil moisture n whet yiel on the Loess Plteu of Chin. Soil n Tillge Reserh, 12: Zhou W.J., Zeng X.B., Zhng Y.Z., Zhou Q., Guo H.Y., Yn X., Chen J.G. (27): Effet of fertiliztion on miroil iomss C n N in py soils erive from ifferent prent mterils. Chinese Journl of Applie Eology, 18: (In Chinese) Reeive on Otoer 21, 212 Aepte on Jnury 18, 213 Corresponing uthor: Prof. Yn An Tong, Northwest A&F University, College of Resoures n Environment, Yngling, 7121 Shnxi, P.R. Chin phone: , fx: , e-mil: tongynn@nwsuf.eu.n 168

SoilUse and Management. Abstract. Keywords: Long-term experiment, P fertilizer, aggregates, soil nutrients, soil enzymes.

SoilUse and Management. Abstract. Keywords: Long-term experiment, P fertilizer, aggregates, soil nutrients, soil enzymes. SoilUse nd Mngement Soil Use nd Mngement, Mrh 217, 33, 25 33 doi: 1.1111/sum.12322 Chnges in soil ggregte-ssoited enzyme tivities nd nutrients under long-term hemil fertilizer pplitions in phosphorus-limited