Soil Property Changes during Conversion from Perennial Vegetationto Annual Cropping

resources by placing highly erodible land into perennial vegetation for 10 yr. Similar programs have been used Management practices for conversion of land supporting perennial historically in the USA to control erosion (e.g., soil vegetation to crop production are needed. Effect of haying (hayed bank program) and influence grain supplies. Programs or not hayed), cropping (annual crop with no-tillage, minimum tillage, or conventional tillage, and no-tilled perennial crop), and N fertilizaencouraging producers to plant perennial vegetation on tion (0 or 67 kg ha 1) on soil properties were measured in 1995 and cropland to reduce grain surpluses are also used in Eu1997 at a Conservation Reserve Program (CRP) site in North Dakota rope (Olaf Christen, 2000, personal communication). having an Amor loam (Fine-loamy, mixed, superactive, frigid, Typic Establishment of perennial vegetation on previously Haplustoll) soil in a spring wheat (Triticum aestivum L.), winter cropped lands reduces the potential for wind and water wheat, pea (Pisum sativum L.) rotation. Soil physical properties were erosion and sequesters C in soil organic matter and not affected negatively by the management practices used. Haying vegetation. As CRP contracts expire, one option availand tillage practices influenced soil chemical properties. Organic C able to landowners is to return these lands to crop proand total N content declined (1.2 Mg ha 1 for C and 0.1 Mg ha 1 for duction. Over half of the land enrolled in CRP was N) from 1995 to 1997. In hayed plots, organic C and total N increased located in the Great Plains. Management practices that as tillage intensity decreased while in non-hayed plots no pattern was observed. Haying and tillage influenced soil biological properties. maintain gains made in soil and water conservation and Potentially mineralizable N at 0 to 0.05 m increased as tillage intensity C sequestration during CRP years are needed by landdecreased in 1997. In the 0.05to 0.15-m depth, potentially mineralizowners returning these lands to crop production (Lindsable N increased from 1995 (118 kg ha 1) to 1997 (146 kg ha 1). By trom et al., 1994). 1997, soil properties in hayed plots responded to cropping practices Conversion of CRP land to crop production will resimilarly to those in established cropping systems in this region. In quire practices that manage the extensive vegetation non-hayed plots, management induced patterns had not developed residue that accumulated during the contract years by 1997. Haying, conservation tillage, and annual cropping are viable prepare a seedbed that will allow crop establishment approaches for converting land to annual crop production. and production, and provide sufficient fertility to meet crop needs. Residue management can be accomplished through fire, tillage, or haying. Fire results in losses of T united states food security act of 1985 estabC and N and may leave the soil susceptible to wind and lished the Conservation Reserve Program (CRP) water erosion. Cultivation has been shown to increase as a management program for conserving soil and water greatly the susceptibility of many soils to wind and water erosion (Low, 1972). Haying removes much of the B.J. Wienhold, USDA-ARS, Soil and Water Conservation Research aboveground biomass while leaving plant crowns and Unit, Lincoln, NE 68583-0934; D.L. Tanaka, USDA-ARS, Northern other residue as protection against wind and water eroGreat Plains Research Lab., Mandan, ND 58554. Contribution of sion. Initially, as residues decompose, N mineralization USDA-ARS and Univ. of Nebraska-Lincoln. Journal Ser. no. 13088. or immobilization may occur, depending on the proporU.S. Department of Agriculture, Agriculture Research Service, Northern Plains Area, is an equal opportunity/affirmative action emtion of legumes present in the stand. Since N is the ployer and all agency services are available without discrimination. nutrient most commonly limiting crop production and Received 21 July 2000. *Corresponding author (BWIENHOLD1@ added in greatest amounts by producers in the northern unl.edu). Great Plains, the effect of residue management on N availability is a major concern. Published in Soil Sci. Soc. Am. J. 65:1795–1803 (2001). 1796 SOIL SCI. SOC. AM. J., VOL. 65, NOVEMBER–DECEMBER 2001 range from a maximum of 21 C during the summer to a miniSubstantial work has been done in the northern Great mum of 11 C during the winter. Plains to develop conservation tillage practices and anThe field was enrolled in CRP and seeded with alfalfa nual cropping rotations that replace the traditional con(Medicago sativa L.) and wheatgrass (Agropyron spp.) in 1989. ventionally tilled crop-fallow system. These more intenThe initial seeding did not establish well and the site was sive systems make more efficient use of available water reseeded in 1991. In the fall of 1994, a cropping practice by (Norwood, 1994; Peterson et al., 1996), reduce wind N-rate experiment was initiated with half of the plots being erosion, and are economically viable (Dhuyvetter et hayed and half of the plots not hayed prior to the initial al., 1996). More intensive cropping has been shown to tillage. Haying of the main plots was done on 11 Oct. 1994 increase microbial activity and biomass (Biederbeck et and removed 4500 kg ha 1 of biomass. The initial tillage and herbicide applications was done on 14 Oct. 1994. The experial., 1984; Campbell et al., 1989; Wienhold and Halvormental design was a randomized complete block with a splitson, 1999), increase N-mineralization rates (Biederbeck split plot treatment arrangement. The experiment was blocked et al., 1984; Campbell et al., 1989; Janzen, 1987; Wienhold across soils to control potential variation in results caused by and Halvorson, 1998), and maintain higher soil organic differences in slope and topographic position. Hayed and nonC levels (Biederbeck et al., 1984; Campbell et al., 1995; hayed treatments served as the whole plot treatments; cropBlack and Tanaka, 1997) when compared to crop-fallow ping treatment, annual crop with conventional tillage (CT), systems. Potential exists for the use of existing conservaannual crop with minimum tillage (MT), annual crop with notion tillage practices during conversion of land supporttillage (NT), and perennial vegetation with no-tillage, as the ing perennial vegetation to annual cropping. split plot treatment; and N rate, 0 and 67 kg N ha 1 as NH4NO3 Tillage, N fertilization, and conversion from perennial surface applied prior to spring tillage, as the split-split plot treatment. The plots in perennial vegetation with no-tillage vegetation to annual cropping will affect a number of served as reference plots. The experiment was replicated four physical, chemical, and biological soil properties. Tillage times. Whole plots were 27 by 30 m, split plots were 9 by increases soil-residue contact by incorporating surface 30 m, and split-split plots were 9 by 15 m. These plots were residue and creating a more oxidative environment of sufficient size to allow use of commercial field scale equip(Doran, 1980). Adding N increases the amount of inorment for all operations. Conventional tillage utilized an underganic N available to microorganisms decomposing high cutter (sweep plow), a chisel plow, and a double disk in the C:N residue. Replacement of perennial vegetation with fall and spring to control weeds and incorporate crop residue. annual crops alters the quality and quantity of residue Minimum tillage utilized one or two passes with an undercutter added to the soil. Quantifying the magnitude and direcin the spring and herbicides to control weeds. No-tillage relied tion of change in these soil properties may serve as a on herbicides for weed control. Surface residue cover at planting averaged 30% with CT, between 30 and 60% with MT, way of rapidly assessing the effect various management and 60% with NT. Spring wheat was planted 12 June 1995, practices have on the soil during CRP conversion. In winter wheat was planted 3 Oct. 1995, and pea was planted 1994, a study was initiated to compare changes in soil 9 May 1997. Seeding was done using a Haybuster no-tillage properties under various haying, tillage, and N fertilizadrill (Duratech Industries International, Jamestown, ND). tion practices with those under perennial vegetation at a CRP site in North Dakota. The objective of the study Soil Sampling and Laboratory Methods was to identify practices that can be used to convert sites under perennial vegetation to annual cropping In the spring of 1995 and 1997, soil samples were collected from the 0to 0.05and 0.05to 0.15-m depths of each plot. without degrading physical, chemical, or biological soil Within each block soil was collected from a similar slope properties. position area of each plot. These soil samples were collected prior to fertilizer application each year and represent condiMATERIALS AND METHODS tions 1 to 2 wk prior to seeding. Soils were passed through a 4-mm sieve to remove root material, soil mass was recorded, Study Site and moisture content was determined. Soils were stored at The research site was located in Morton County, North 5 C until biological attributes were assessed. After assessDakota, (46 46 N 100 50 W, elevation 549 m above sea ment of biological attributes the remaining soil was passed level) approximately 20 km southwest of the city of Mandan. through a 2-mm sieve, air-dried, ground, and used for chemiSoil at the site was an Amor loam (Fine-loamy, mixed, supercal analysis. active, frigid, Typic Haplustoll) with slopes of 9 to 15%. While Bulk density, water content, and water-filled pore space, soil properties and crop response are affected by topographic were the physical soil attributes measured. Bulk density was position and slope (Jenny, 1980) the objective of this study calculated by dividing the mass of soil, corrected for moisture was not to determine the effect of topography and slope on content, by the volume of soil collected (Blake and Hartge, soil properties and crop response. Hence, this study used 1986). Soil volume was determined by measuring the dimenblocking in the experimental design and soil sampling stratesions of the soil pit excavated in each plot. Water content was gies to control variation associated with topography and slope. determined gravimetrically (Lowery et al., 1996). Water-filled Blocks were located across the slope of the study site such that pore space was calculated by means of the measured bulk each block was homogenous in terms of slope and topographic density and water content values and assuming a particle denfeatures. Within each block soil was collected from a similar sity of 2.65 g cm 3 (Arshad et al., 1996). slope position area of each plot. This sampling strategy was Total organic C, total N, inorganic N, pH, and electrical used to minimize confounding of treatment effects with topographic effects on soil properties. Annual precipitation has been highly variable and averages 1 Mention of trade names or proprietary products does not indicate 410 mm with 60% typically received during the growing seaendorsement by USDA and does not imply its approval to the exclusion of other products that may be suitable. son. Average annual temperature is 4 C and daily averages WIENHOLD & TANAKA: CROPPING EFFECTS ON POST-CRP SOIL PROPERTIES 1797 conductivity (EC) were chosen as chemical attributes of soil solution to evaporate between additions) added to tin cups. The tin cups were carefully crushed to avoid loss of crystals quality. Total N and C were determined by dry combustion with a Carlo-Erba NA 1500 NCS (Carlo Erba Instruments, and C and N concentrations determined with a Carlo-Erba NA 1500 NCS analyzer (Carlo Erba Instruments, Milan, Italy). Milan, Italy) analyzer (Schepers et al., 1989). Total organic C concentration was determined by correcting total C concentraSoil attributes were compared among treatments by a repeated measures split-split plot model in PROC MIXED of tions for carbonate content when soil pH was greater than 7.2. Inorganic N was measured in 0.01 M CaCl2 (10 g of soil SAS (Littell et al., 1996). Differences were declared significant at 0.05 probability level. Results are reported as treatment in 100 mL of solution) extracts colorimetrically with a Lachat flow-through ion analyzer (Zellweger Analytics, Lachat Inmeans and differences among means were determined by pairwise comparisons made with the DIFF option of the struments Div., Milwaukee, WI). Nitrate-N was determined by the Cd reduction method and NH 4 -N was determined by LSMEANS statement. Pearson correlation coefficients were calculated to test the correlation among physical, chemical, the Indophenol blue method (Mulvaney, 1996). Distilled water was added (1:1 on a gravimetric basis) to 10 g of air-dried soil and biological attributes in this study. and pH determined with a glass electrode (McLean, 1982). The soil slurry was then filtered and EC determined with a RESULTS AND DISCUSSION conductivity meter (Rhoades, 1982). Biological soil quality attributes assessed included: N-minPhysical Attributes eralization; numbers of culturable fungi, bacteria, and actinoIn the 0to 0.05-m depth, bulk density exhibited a mycetes; and microbial biomass C and N. Nitrogen mineralization rate was determined by a laboratory incubation method pretillage haying cropping practice interaction. In similar to that described by Stanford and Smith (1972). Silica hayed treatments, bulk density was lower with CT than sand and 15 g of soil were added together in equal amounts with MT and NT while bulk density in hayed reference and thoroughly mixed. The mixture was transferred to a glass treatments was similar to that in the three annually leaching tube and glass wool was placed on the soil surface cropped treatments (Table 1). In non-hayed treatments, to prevent dispersion of the sample during leaching. The subbulk density was similar among the annual cropping strate was slightly compacted and leached with 100 mL of 0.01 treatments but was lower in NT than in reference treatM CaCl2 under a suction of 0.7 MPa to remove mineral N. ments. Bulk density in the 0.05to 0.15-m depth reLeachate was brought to 100 mL with 0.01 M CaCl2. The leachsponded to pretillage haying and cropping practices siming tube was covered with Parafilm (American National Can, ilarly to that in the 0to 0.05-m depth but higher within Greenwich, CT). A hole was made in the Parafilm to ensure aeration. Leaching tubes were weighed and stored upright treatment variation resulted in no significant differences in an incubator at 35 C. Tubes were reweighed weekly and using analysis of variance (Table 1). Pretillage haying weight adjusted with distilled water. Every 2 wk tubes were and tillage did not result in compaction problems at this leached with 100 mL of 0.01 M CaCl2 and returned to the site as observed bulk densities were below 1.65 g cm 3 incubator. Tubes were incubated for a total of 8 wk. Leachates which would restrict root penetration (Arshad et al., were stored at 5 C until they could be analyzed for inorganic 1996). Observed bulk densities were much lower than N content ( 60 d). Inorganic N content of leachate was deterthose commonly reported for cropped soil and are the mined by quickly thawing the samples and determining result of the large root biomass that accumulated during NH 4 -N and NO 2 2 -N plus NO 3 -N content by automated colorthe years the site supported perennial vegetation. imetric analysis with a Lachat flow-through ion analyzer (ZellWater content exhibited a year pretillage haying weger Analytics, Lachat Instruments Div., Milwaukee, WI). Fungi, bacteria, and actinomycete numbers were detertreatment cropping practice interaction in both mined by plating a serial dilution of a soil-water suspension depths. In 1995, water content in the 0to 0.05-m depth on selective media. Bacteria were grown out on tryptic soy was similar across cropping treatments that had been agar, actinomycetes were grown out on starch-casein agar, hayed prior to tillage and was higher in the NT treatment and fungi were grown on Martin’s Rose Bengal agar (Wollum, than in the other cropping treatments that had not been 1982). Plates were incubated at 27 C for 10 d and visible colhayed prior to tillage (Table 2). In 1997, water content onies counted. Microbial biomass N and C were determined using the Table 1. Soil bulk density in the 0to 0.05-m depth averaged chloroform fumigation extraction method as modified by Bruacross years and N fertilizer treatments as a function of cropulsema and Duxbury (1996). Duplicate soil samples equivalent ping practice and pre-tillage haying. to 25 g oven-dried soil were placed in 50-mL beakers and Cropping practice† sufficient distilled water added to bring the soil to approximately 60 m m 3 water-filled pore space. One soil sample, Haying treatment CT MT NT Reference designated as the control, was placed in a desiccator lined Mg m 3 with moist paper towels. The second soil sample, designated 0 to 0.05 m as the fumigated sample, was placed in a second desiccator Hayed 0.64a¶ 0.92b 1.00b 0.82ab also lined with moist paper towels. Both desiccators were Non-hayed 0.79ab 0.80ab 0.66a 0.93b placed in an incubator at 25 C for 10 d. Fumigation was accom0.05 to 0.15 m plished by placing a beaker containing 50 mL of purified Hayed 1.08§ 1.21 1.33 1.12 CHCl3 (Jenkinson and Powlson, 1976) in the appropriate desNon-hayed 1.18 1.38 1.09 1.17 iccator and evacuating the desiccator until the CHCl3 boiled. The desiccator was returned to the incubator for 24 h. Both † CT annual cropping with conventional tillage, MT annual cropping with minimum tillage, NT annual cropping with no-tillage, reference mainfumigated and nonfumigated soils were extracted with 50 mL tained in perennial vegetation. of 0.05 M K2SO4. Extracts were filtered into plastic bottles § Means are not significantly different at P 0.05. and stored at 5 C until analyzed for C and N. Extracts were ¶ Haying by cropping practice interaction (P 0.006). Means within a row followed by a different letter are significantly different at P 0.05. thawed and 0.5 mL (as five 0.1-mL increments allowing the 1798 SOIL SCI. SOC. AM. J., VOL. 65, NOVEMBER–DECEMBER 2001 Table 2. Soil moisture attributes averaged across N fertilizer treatments as a function of year, pre-tillage haying, and cropping practice.