Division S-6—notes Alleviate Soil Compaction

other crops, non-tillage methods to alleviate compaction CROP COVER ROOT CHANNELS MAY problems have not been extensively researched. DeepALLEVIATE SOIL COMPACTION rooted cover crops are one possible solution to compaction problems, especially in no-till farming systems (UnEFFECTS ON SOYBEAN CROP ger and Kaspar, 1994). The deep growing tap roots of the perennial alfalfa (Medicago sativa L.), can increase Stacey M. Williams* and Ray R. Weil infiltration rate on compacted no-till soils (Meek et al., Abstract 1990), and recolonization of root channels left by alfalfa have been shown to benefit corn (Zea Mays L.) root Deep-rooted cover crops may help alleviate effects of soil compacsystems that follow (Rasse and Smucker, 1998). Stirtion, especially in no-till systems. We evaluate compaction-alleviating zaker and White (1995) showed a doubling of yield ability of three Brassica cover crops and cereal rye (Secale cereale for lettuce (Letuca sativa L.) grown on compacted soil L.). Using a minirhizotron camera, we observed soybean [Glycine Max (L.) Merr.] roots growing through compacted plowpan soil using following a cover crop of subterranean clover (Trifolium channels made by decomposing cover crop roots. Soybean yield resubterraneum L.). They speculated that the yield insponse to the preceding cover crops was most pronounced at the site crease was due to biopores made by the cover crop with most severe drought and soil compaction. At this location, with roots. It has been proposed that biopores produced by or without deep tillage, soybean yields were significantly greater folcover crop roots might be used by the roots of later lowing a “forage radish rye” combination cover crop. Rye left a crops as low resistance pathways, a process dubbed “biothick mulch, resulting in conservation of soil water early in the season. drilling” (Cresswell and Kirkegaard, 1995). Root channels left by forage radish (Raphanus sativus L. ‘Diachon’) The objectives of this study were: (i) to observe soymay have provided soybean roots with low resistance paths to subsoil bean roots penetrating compacted soil layers during the water. Due to lower than normal winter precipitation, this study was summer via root channels made a preceding Brassica a conservative test of the cover crops’ ability to alleviate the effects cover crop; and (ii) to compare the effects of various of soil compaction. cover crops and deep tillage on the yield of soybeans on soils of differing compaction severity. We report direct observations of the proposed “biodrilling” proS compaction continues to be a major problem for cess and a preliminary evaluation in no-till fields of the farmers in intensely cropped areas of the eastern compaction-alleviating ability of three Brassica cover USA. The urgency of timely field operations, often accrops: canola, oilseed radish, and forage radish. companied by unpredictable precipitation, often results in heavy equipment traffic on wet soils (Bowman et al., Materials and Methods 2000). Due to the yield-reducing secondary effects of soil compaction, growers often purchase expensive tillSites and Soil Conditions age equipment to deep till their compacted soils. Deep Experiments were conducted at the University of Maryland tillage is expensive and energy intensive, and benefits Wye Research and Education Center (WREC) on a Mattapex are short-lived (Horn et al., 2000). Resorting to tillage silt loam (fine-silty, mixed, active, mesic Aquic Hapludults) in a no-till cropping system can also set back the develand at the USDA Beltsville Agricultural Research Center opment of improved soil quality and increase the suscep(BARC) on an Elkton silt loam (fine-silty, mixed, active, mesic tibility to erosion. Typic Endoaquults). Undisturbed soil cores were collected in 10-cm increments Buttery et al. (1998) reported that limited root peneto a depth of 40 cm to determine soil bulk density and soil tration on compacted soils aggravated the effects of water content at the time of penetration resistance measuredrought in reducing soybean yields. Soil strength inment (Table 1). Particle-size analysis was performed on the creases with compaction (Eavis, 1972), especially during same samples, using a modified hydrometer method (Day, the summer when compacted layers in the soil become 1965). To characterize soil compaction levels and distribution, dry and hard, therefore, roots are less able to penetrate a recording cone penetrometer with a 25 by 15 mm tip and deeply enough to access the water and nutrients stored 10-mm diameter shaft (Spectrum Technologies, Plainfield, IL) in the subsoil. was used to measure soil penetration resistance. MeasureWhile much is known about the negative effects of ments were taken on a 6 by 6 m grid on 28 Feb. 2001 at WREC and 9 Mar. 2001 at BARC (Barone and Faugno, 1996). At each soil compaction on the growth and yields of soybean and grid point, mean penetration resistance (kPa) was recorded in 5-cm increments to a depth of 45 cm by pushing the penetromS.M. Williams and R.R. Weil, Dep. of Natural Resource Sciences and eter tip into the soil at a constant rate. Landscape Architecture, Univ. of Maryland, College Park, MD 20742; S. Williams, current address: Dep. of Horticulture, Cornell Univ., Ithaca, Crop Treatments and Management NY 14853. Received 24 Sept. 2003. *Corresponding author (stacewms@ Four winter cover crops were used in the study (canola, hotmail.com). oilseed radish, forage radish, and cereal rye). The radishes Published in Soil Sci. Soc. Am. J. 68:1403–1409 (2004).  Soil Science Society of America Abbreviations: BARC, Beltsville Agriculture and Research Center; WREC, Wye Research and Education Center. 677 S. Segoe Rd., Madison, WI 53711 USA