Soil quality of two Kansas soils as influenced by the Conservation ...

Soil quality of two Kansas soils asinfluenced by the Conservation ReserveProgramX. Huang, E.L. Skidmore, and G.L. TibkeABSTRACT: Achieving and maintaining a good soil quality is essential for sustaining agriculturalproduction in an economically viable and environmentally safe manner. The transition of landmanagement provides an opportunity to measure soil-quality indicators to quantify the effects ofthose management practices. This study compared soil chemical and physical properties after ioyears of grass on Conservation Reserve Program (CRP) land with those in continuously croppedland (CCL). The sample sites, located in central Kansas, have two mapping units, Harney silt loam(fine, montmorillonitic, mesic Typic Arigiustolls) and Naron fine sandy loam (fine-loamy, mixed,thermic Udic Argiustolls). Soil samples were collected at two depth increments, o to 5 cm and 5to io cm. Soil-quality indicators measured were soil acidity (pH), exchangeable cations,nutrients, total carbon, structure, and aggregation. Soil pH was significantly lower in CCL than inCRP. Soil total C and N in the surface layer (0 to 5 cm) was much greater than in the deeper layer(s to io cm) in the CRP site. The mass of total carbon of Naron soil was significantly higher foro to 5 cm and lower for 5 to io cm depth in CRP land than in CCL. However, the mass of totalcarbon of Harney soil was significantly higher in no-tilled CCL than in CRP. Bulk densitysignificantly increased in CCL. Based on dry and wet aggregate stability analysis, the resultsindicated that CRP land had a greater resistance to erosion by both water and wind than CCL. Theimprovements in soil quality resulting from CRP included reducing soil acidification, alleviatingcompaction, and reducing topsoil susceptibility to erosion. However, when CRP was taken out forcrop production with conventional tillage, total carbon in the surface layer (0 to 5cm) andaggregate stability gradually decreased. This suggested that appropriate land managementpractices are needed to extend residual benefit from CRP on soil quality.Keywords: Aggregate stability, CRP, soil quality, soil total carbon, wind erosionContinuous cultivation and addition ofammonical fertilizers are generallythought to decrease soil quality by alteringsoil acidity, depleting soil organicmatter, disrupting soil structure, andreducing biological activity (Staben et al.1997, Hill 1990, Lal et al. 1994). In addition,soil under continuous production is vulnerableto accelerated erosion. To reduce soilerosion and improve soil quality, the U.S.Congress enacted the Conservation ReserveProgram (CRP) in 1985. CRP put highlyerodible (erodibility index 2 8) and environmentallysensitive lands into grass or otherperennial planting. Nationally, 14.8 millionhectares were enrolled in CRP in the first 12signups, with nearly 60% of CRP acreagelocated in the Great Plains and 1.13 millionhectares in Kansas alone (Osborn 1993,Lindstrom et al. 1994).Many studies were reported that soilerosion has been greatly reduced with permanentvegetative cover in CRF'. Airbornedust in the southern High Plains ofTexas wassigdicantly reduced because of CRP (Ervinand Lee 1994). Through remote sensingimaging, Wu et al. (1997) found higher soilfertility and lower soil erodibility in CRPland, compared with continuous cropland inFinney County, Kansas. Davie and Lant(1994) studied two watersheds in southernIllinois and reported that CRP land showeddecreases in erosion of 24% in one watershedand 37% in another. Less erosion by runoff inthe first year of conversion &om CRP wasreported by Gilley et al. (1997).In addition to erosion reduction, CRPsoil-quality improvement was noted byincreasing soil organic matter and soil tilth(Staben et al. 1997). Soil structure improveswhen continuously cultivated land is put intograss (Lindstrom et al. 1994). Karlen et al.(1999) reported that CRP sites had a higherpercentage of water-stable soil aggregatesthan cropland sites.Karlen et al. (1999) measured total organicC in paired CRP and cropland sites in Iowa,Minnesota, North Dakota, and Washington.In all states, microbial biomass carbon was17% to 64% higher at CRP sites than at croplandor fallow sites, while nitrate-N was 18%to 74% higher in cropland than CRP sites.This multistate project showed that severalsoil-quality indicators were improved by placinghighly erodible cropland into perennialgrass.Gebhart et al. (1994) analyzed soil organicmatter levels of soils sampled &om cropland,native pasture, and five-year-old CRP sites inTexas, Kansas, and Nebraska.They found thatsoil organic matter levels for cropland, nativepasture, and five-year old CRP sites were59.2,63.1, and 90.8 metric tons C ha-' in thesurface 300 cm, respectively. However, Stabenet al. (1997) found no sigrufcant aerencesin total organic carbon between CRP andwheat-fallow soils in eastern Washington on asilt loam. Based on C mineralization, they did,however, suggest that a higher-quality soilorganic matter was found on CRP land.Soil-quality benefits derived &om CRP mayrapidly decline once an area is tilled and thenleft fallow during the noncropped period(Gilley et al. 1997).Soil biological properties are sensitiveindicators that reflect land-practice change(Huggins et al. 1998, Karlen et al. 1999).Karlen and Parkin (1996) found microbialbiomass was sigrufcantly higher for CRPthan for cultivated areas and suggested soilquality was improved &om the biological344JOURNALOF SOIL AND WATER CONSERVATION N/D 2002Reprihted &om the Journal of Soil and Wafer ComervationVolume 57, Number 6Copyight 0 2002 Soil and Water Conservation Society

perspective. Staben et al. (1997) investigatedmicrobial aspects of soil quality betweenCRP and wheat-fallow soils on a silt loam ineastern Washington. They concluded thatactive bacterial biomass and potential enzymeactivities were higher in the CRP soil than inthe wheat-fallow soil.The need is urgent to understand longtermland-management effects on soil qualityat various scales-pedon and point, to fieldand plot, to farm and watershed, and toregional and national levels (Karlen et al.1998). Expiration of CRP contracts andsubsequent return of highly erodible lands tocontinuous cropping concerns policymakers,conservationists, and farmers (Ervin 1993,Osborn 1993, Lindstrom et al. 1994).Knowledge of changes in soil properties during10 years of CRP enrollment is importantfor evaluating the program effectiveness.Also, the return of CRP land to cultivationprovides a chance to evaluate changes inchemical and physical properties for soilquality.The objectives of this study were to comparesoil properties between 10 years of grassplantingConservation Reserve Program landand adjacent continuously cropped land, andto evaluate effects of the ConservationReserve Program on soil quality during its10-year enrollment and its transition backinto crop production.Methods and MaterialsField description. Two fields located in centralKansas were selected as study sites. Onewas near Larned of Pawnee County.The soil was deep, well-drained, Harney siltloam (fine, montmorillonitic, mesic TypicArigiustolls, 21% sand, 64% silt, and 15% clayat 0 to 10 cm depth).The sampling site forCRP was about 150 m fbm CCL at this1ocation.The CCL was in nonirrigated, notill,wheat-corn [Zea mays L.] rotation for fiveyears before the beginning of this study.Theother site was located near Zenith of StaffordCounty.The soil was Naron, fine, sandy loam(fine-loamy, mixed, thermic Udic Argiustolls,75% sand, 15% silt, and 10% clay at 0 to 10cm depth). In this field, CRP land was adjacentto CCL.The cropping system for thisfield was dryland continuous winter wheat[Triticum asetivium L.] with disk tillage.Initially, native grasses were seeded in CRPfields in 1987. No grazing or burningoccurred in CRP fields until the contractexpiration in spring 1998.The main grasses inCRP fields were little bluestem [Andropogenscoparius], Indiangrass [Sovgkastntm nutans], andSwitchgrass [Paniurn vivgatum].Field and laborutoy methods. At Naronsoil field, the soil samples were taken from the400 m long transect spanning 200 m in CRPand 200 m in CCL, respectively. Each treatmentaccounted for 20 sites in 10 m spacing.At Harney soil field, 19 samples were collectedalong two diagonal transects with 10 mspacing in the CRP field. Grid sampling wasapplied in the CCL field. In a 100x100 mfield, 35 samples were taken in 20 m spacing.Each sample site for both chemical andphysical properties was located using a GPSsystem to repeat sampling at the same locationover time.In the CRP sites, 10-year grasses wereburned in early April 1998. Soils were sampledin late May 1998. CCL samples at Naronsoil were taken July 2, 1998, a few days afterwheat harvest. CCL samples at Harney soilwere taken May 27,1998, where the field wasfallowed with no-tilled corn residue. TheCRP fields were moldboard plowed in fall1998 and cultivated for wheat in Harney sitein 1999 and for irrigated corn at Naron sitein 1999.The soil samples were again taken atthe same location in May 1999 to comparethe changes in the properties after return ofCRP land to production.For the soil chemical properties, soil coreswere collected to depth of 0 to 5 cm and 5 to10 cm using a 2 cm diameter hand probe.A total of 20 bore holes and 250 g soils werecollected in each sample site. The soil wascrushed and placed in a bag, air-dried andtaken to the Soil Testing Laboratory at KansasState University. In the laboratory, a portionof each soil sample was ground to passthrough a 2 mm sieve. Soil pH was measuredon a 1:l soil/distilled water paste. Phosphoruswas tested by the Bray 1 method. Potassium,Ca, Mg, and Na were extracted by 1MNH40Ac. Exchangeable Ca, Mg, K, and Nawere measured by atomic absorption. Cationexchange capacity (CEC) was determinedby saturating the soil sample with NH4'and then replacing NH4' by K' ions. Thereplacing NH4' concentration was measuredcolorimetrically. Total carbon and nitrogenconcentrations were determined by dry combustionusing a LECO CNS-2000 automaticanalyzer (LECO Corp., St. Joseph, MI).Soil samples were taken fbm the surface 5cm of soil using a flat shovel and used foraggregate analysis. Aggregate size distributionwas determined by rotary sieving (Lyles et al.1970). Dry aggregate stability of 6.5 to 19mm aggregates was measured as described bySkidmore and Powers (1982) with the crushingdevice built by Boyd et al. (1983).The dryaggregate stability was expressed as the naturallogarithm of the aggregate crushingenergy(J/kg). Wet aggregate stability of 1to 2 mm size hction was determined bydirectly immersing 1 to 2 mm fractions intodistilled water for 20 minutes. The rest ofthe procedures described by Kemper andRosenau (1986) were followed.A double cylinder, hammer-driven, soilcoresampler (76 x 76 mm) was used toobtain 3 incremental soil-core samples (0 to10 cm, 10 to 20cm, and 20 to 30 cm depth).The soil cores were trimmed flush with bothends of the retaining cylinder. The soilsamples were put into a plastic box with asponge bottom, kept undisturbed and takento the lab. These samples were first used todetermine low-tension water-release characteristicsand then to determine bulk density.Soil-moisture release curves were determinedusing hanging water column techniques(Klute 1986, Kutilek and Nielsen 1994).Thedevice used for low-tension water-releasemeasurement was composed of a glass funnelwith a porous plate and hanging water forpressure head.The water outflow was measuredunder different potential.The minimumpotential was -200 cm H2O.When the equilibriumwas reached at -200 cm pressurehead, wet samples were weighed, then ovendriedat 105°C for 24 hours, and dry soil wasweighted to determine the soil water content,porosity, and bulk density.Macroporosity was calculated by soil watercontent between saturation and potentialof -50 cm H20 head. Mesoporosity wascalculated by soil water content betweenpotential of -50 and -200 cm H2O head(Kutilek and Nielsen 1994, Poulsen et al.1999). Correspondingly, the pore radiusranges in macropore and mesopore calculatedby capillary equation are 2 30 pm, and 30 to7.5 pqrespectively.Soil saturated hydraulic conductivity (Ks)was estimated using the equation developedby Poulsen et al. (1999). The equation forpredicting Ks is based on the water-filledporosity at a soil-water potential of -100 cmHzO. Ln(Ks) = 2.8Ln(8100) + 4.3, where Ks isin cm d-', and 8100 is air-filled porosity atsoil-water potential of -100 cm H20 in cm3~m-~. A portion of soil from the bulk density1 NID 2002 VOLUME 57 NUMBER 6 I 345 I

Table 1. Comparison of soil acidity and exchangeable cations between CRP and CCL and between two depths on two Kansas soils.Soildepth (cm), treatment PH CEC K Ca Mg NaNaron fine sandy loamHarney silt loamcmol kgiComparison between treatments0-5 CRP 5.8f0.025 7.75f1.24CCL 5.1f0.06 6.49f0.85Diff. 0.7*** 1.27NS5-10 CRP 5.3f0.02 6.90k0.76CCL 4.9f0.04 6.62k0.78Diff. 0.4*** 0.27NSComparison between depths within treatmentCRP 0-5 5.8 7.755-10 5.3 6.90Diff. 0.47*" 0.85NSCCL 0-5 5.1 6.495-10 4.9 6.62Diff. O.1NS -0.13NSComparison between treatments0-5 CRP 6.0f0.06 13.8k0.19CCL 5.4f0.02 16.5f0.22Diff. 0.6*" -2.7";5-10 CRP 5.7f0.07 14.0f0.42CCL 5.4f0.02 16.6k0.25Diff. 0.3'** -2.6"'244f31285f42-41NS195f15221f34-26NS24419549NS28522164NS580f26494f1485.4"546f20297f11249***667f84558f52109NS524f54565f50-41NS667524143NS558565-7NS1214f1151728f31-514"'1159f731740f27-58 1* *154f1599fll55-127f121OOf1127NS15412727NS99100-lNS242f4275f4-33"'233k7288f6-55"'5.36f0.702.66f0.092.71***5.18f0.672.74k0.212.44"'5.365.180.18NS2.662.74-0.08N S13.6f2.786.89f0.356.71*16.1f2.7311.1f0.645*Comparison between depths within treatmentCRP 0-5 6.0 13.8 5801214 24213.6510 5.7 14.0 5461159 23316.1Diff. 0.3*' -0.2NS 34NS55NS 9NS -2.5NSCCL 0-5 5.4 16.5 4941728 2756.895-10 5.4 16.6 2971740 288 11.1Diff. 0.02NS -0.09 N S 197" -12NS -13NS -4.21:Mean value with standard error. Diff. = CRP - CCL, or Diff. = 0-5 - 5-10.., *', *** Significant at 0.05,0.01, and 0.001 probability level by2-tailed t-test, respectively. NS indicates no significant difference.-sample was use for particle-size distributionanalysis. Particle-size distribution was determinedby sieving the sand &action and pipettingthe clay fraction, according to themethod of Gee and Bauder (1986).Bulk-density data were used to convert soilP, total C and N concentration (mg kg-') to P,total C, and N mass (kg ha.'). We measuredbulk densities at every sample site &om 0 to10 cm depth; those values were used for conversionof mass at 0 to 5 cm and 5 to 10 cmdepths.Statistical analysis. The statistical indices(mean and standard error) for soil chemicaland physical properties were performed withthe statistic sofiware package for WindowsSYSTAT 9.0 (SPSS Inc., Chicago, IL 1999).Means for each soil property between CRPand CCL at two soils and two depths werecompared using the 2-tailed two-samplet-test with unequal variance assumed withthe SYSTAT.Results and DiscussionSoil pH. Soil pH was sigtllficantly lower(p

Table 2. Comparison of masses and distribution with depth of soil nutrients between CRP and CCL on two Kansas soils.Soil P Total C Total Ndepth (cm), treatment May 1998 May 1999 May 1998 May 1999Namn fine sandy loamkg ha"Comparison between treatments0-5 CRP 27.6f2.55 6519f1068 49805562 599f67 571f49CCL 53.6f4.1 5124f581 5010f521 562557 5945241Diff. -26"' 1395* -30NS 37' -23NS5-10 CRP 24.1f2.1 3341f297 4446f4459 420523 461f36CCL 52.6f4.6 5100f534 4459f434 554554 478f42Diff. -28.5***-1759"-13NS-134* -17NSComparison between depths within treatmentCRP 0-5 27.6510 24.1Diff.3.5NSCCL 0-5 53.65-10 52.6Diff.1NS651933413178**5124510024NS49804446534NS50104459551NSkg ha-i599 571420 461179' 11ONS562 594554 4788NS116NSHamey silt loamComparison between treatments0-5 CRP 30.151.28915f1859041536339f18872f44CCL 33.8f1.0 11961f252 11997f264 1258f29 1140f25Diff. -3.7* -3046"' -2956"' -419*** -268***5-10 CRP 27.2f1.6 7111f122 7974f124 712f15 738514CCL 15.3f0.8 8078k156 91285~312 877f20 871f30Diff. 11.9'** -967"' -1154*** -165"* -133*Comparison between depths within treatmentCRP 0-5 30.1 89159041 839 8725-10 27.2 71117974 712 738Diff. 2.9NS 1804"'1067* 127*** 135**CCL 0-5 33.8 1196111997 1258 11405-10 15.3 80789128 877 871Diff. 18.5"' 3883"' 2869*** 381*'* 269"'5 Mean value with standard error. Diff. = CRP - CCL, or Diff. = 0-5 - 5-10. *, **, *** Significant at 0.05,0.01, and 0.001 probability level by2-tailed t-test, respectively. NS indicates no significant difference.was greater than 6.0.CEC. No sigruficant Werence in CECbetween CRP and CCL was observed inNaron soil (Table 1). For Harney soil, CECwas sigmiicantly lower in CRP than in CCLat both depths (p

Table 3. Comparison of means for bulk density, soil porosity, and hydraulic conductivity between CRP and CCL in Naron soil.SoilHydraulicdepth (cm), treatment Bulk density Total porosity Macroporosity Mesoporosity conductivityNaron fine sandy loam0-1010-202030CRPCCLDiff.CRPCCLDiff.CRPCCLDiff.Mg ma m3 ma cm d l1.46f0.0251.42f0.020.04NS1.60f0.021.66f0.02-0.06'1.60f0.021.61f0.02-0.OlNS0.45f0.010.46f0.01-0.OlNS0.40f0.010.37f0.010.03*'0.40f0.010.39f0.01O.01NS0.20f0.010.20f0.02ONS0.14f0.010.13f0.01O.01NS0.12f0.020.14f0.01-0.02NS0.09~0.01O.llfO.O1-0.02'0.06f0.010.07f0.01-0.OlNS0.05f0.010.07f0.01-0.02'537f61688585-151*197f38187f3110NS164f66211f36-47NSHarney silt loam0-10 CRPCCL1.24f0.0101.36f0.040.53f0.010.49f0.020.15f0.010.10~0.100.07f0.010.06+0.01193f35102f21 .Diff. -0.12***0.04***0.05***0.flNS91+10-20 CRPCCL1.31f0.021.41f0.020.51f0.010.47f0.010.10~0.010.09f0.010.06f0.010.06f0.0076f1093f31Diff.-0.1***0.04"'-0.OlNSONS-17NS20-30 CRP 1.34f0.02 0.50f0.010.12f0.01 0.05f0.0096f14CCL 1.38f0.01 0.48f0.000.11fO.01 0.03f0.0073f19Diff. -0.04' 0.02* O.01NS 0.02* 23NS5 Mean value with standard error. Diff. = CRP - CCL. t, *, **, *** Significant at 0.1, 0.05,0.01, and 0.001 probability level 2-tailed t-test,respectively. NS indicates no significant difference.Naron fine sandy loam, would have reducedability to & P; as a result, P availabilityincreased.Total C mass of the Naron soil at 0 to 5 cmdepth was sigdicantly higher (p

Table 4. Comparison of soil dry and wet aggregate stability between CRP and CCL on two Kansas soils.Soil Treatment Dry aggregate stability Wet aggregate stabilityNaron fine sandy loamHamey silt loamMay 1998 May 1999 May 1998 May 1999CRP 2.67f0.155 3.29f0.14 72f13 57211CCL 2.41f0.12 2.96f0.16 51f7 51f6Diff. 0.26t 0.33t 21'** 6NSCRP 3.28f0.07 3.08f0.10 55+3 40f2CCL 3.03f0.05 3.34f0.07 50f2 41f1Diff. 0.25* -0.26' 5t -lNS5 Mean value with standard error. Diff. = CRP - CCL. +, *, and *** Significant at 0.1,0.05, and 0.001 probability level by 2-tailed t-test,respectively. NS indicates no significant difference.the CRP site in the Harney soil. Mixing ofsurface and subsurface soil by plowing causedthe rapid decline in surface soil C and N forcoarse-textured soil, but only slight changefor fine-textured soil. Naron soil is moreresilient in regenerating carbon with grasseswhile cultivation is discontinued.Soif structure. Compacted soils inhibitplant root growth and slow water infiltration.Placing land under CRP could benefit soilsby reversing some compaction. At the sitewith Naron soils, bulk density at a depth of 10to 20 cm sigruficantly (p

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