RESEARCH REPORTS Soil Physical Properties and Potato Yield in No-till, Subsurface-till, and Conventional-till Systems Charlotte Mundy,1 Nancy G. Creamer,1 Carl R. Crozier,2 L. George Wilson,1 and Ronald D. Morse3 ADDITIONAL INDEX WORDS. bulk density, soil moisture, cone index, cover crop, Sorghum bicolor x S. sudanense, Solanum tuberosum SUMMARY. Conservation tillage using residue from a cover crop grown before potato (Solanum tuberosum L.) production has been infrequently and inconclusively studied. The objectives of this study were to 1) conduct a field study to evaluate soil physical properties, and potato growth and yield, in conventional-tillage (CT), no-tillage (NT), and subsurface-tillage (SST) systems and 2) conduct a greenhouse study to evaluate the ρ effect of soil bulk density ( b) on potato growth and yield. Potatoes (‘Atlantic’) were planted into residue of sorghum–sudangrass [Sorghum bicolor (L.) Moench x S. sudanense (Piper) Staph] at two sites in eastern North Carolina—Plymouth into Portsmouth fine sandy loam and Lewiston into Norfolk sandy loam. Potatoes in the NT and SST system emerged more slowly than potatoes This paper is a portion of the thesis submitted by C. Mundy in partial fulfillment of MS requirements at N.C. State Univ. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1Department of Horticultural Science, North Carolina State University, Box 7609, Raleigh, NC 27695. 2Department of Soil Science, North Carolina State University, Vernon James Research and Extension Cen- ter, 207 Research Station Road, Plymouth, NC 27962. 3Department of Horticulture, Virginia Polytechnic In- stitute and State University, Blacksburg, VA 24061. 240 ● April–June 1999 9(2) planted conventionally. There were no (Prestt and Carr, 1984). No-till (NT) tor is varied among the NT, SST, and differences in plant population or size soils tend to have higher bulk densities CT plots as is common among systems by 8 weeks after planting at Ply- (ρ ) than conventional-till (CT) soils experiments (Abdul-Baki et al., 1996; mouth, but plant population and size b ρ (Naderman, 1991). Increased b can Creamer et al., 1996). were less in NT and SST systems at decrease potato yield (Blake et al., Lewiston. Reducing tillage also Materials and methods affected soil compaction, increased 1960) and make harvest more difficult soil moisture early in the season at (Grant and Epstein, 1973). Field study ρ To plant potatoes in early spring, Experiments were conducted for both sites, and increased b at Lewiston. Yield of U.S. No. 1 traditional fall-sown cover crops, like one production cycle at two sites: the potatoes planted in NT and SST hairy vetch (Vicia villosa Roth.) or rye Tidewater Research Station near Ply- systems were comparable to potatoes (Secale cereale L.), would have to be mouth, N.C., and at the Peanut Belt planted in a CT system at Plymouth, killed before they produce their great- Research Station near Lewiston, N.C. but were less than potatoes planted in est amount of biomass. Cover crops, (Abdul-Baki et al., 1997; Franco et al., a CT system at Lewiston. There were like sorghum–sudangrass, planted the 1997). The soil in Plymouth was a no differences in yield between summer before potato production to potatoes planted with NT and SST. Portsmouth fine sandy loam (Typic ρ allow for maximum biomass produc- Umbraquults, ≈5% organic matter con- In the greenhouse study, b did not affect leaf area or tuber yield or tuber tion, and kept on the field through the tent); and at Lewiston a Norfolk sandy grade. Specific sites and soils may winter as mulch, may be an appropri- loam (Typic Paleudults, <1% organic allow for comparable potato produc- ate alternative. However, sorghum– matter content). Main plots were 21 m tion with no or SST, but further sudangrass used as a green manure (70 ft) long and consisted of four 97- research, conducted on different soil crop before potatoes reduced plant cm (38-inch) wide rows. types would promote further under- growth and yield compared to pota- CT SYSTEM. Plots were left fallow standing of the impacts of reducing toes following a fallow period or rape- after corn harvest in August 1996. Just tillage in potato production. seed (Brassica napus L.) (Boydston before planting potatoes, plots were and Hang, 1995); and sorghum– disked once before forming hills. Fer- sudangrass also increased the amount tilizer (NH4–NO3–P2O5–K2O) was n the Coastal Plain region of of wireworm (Melanotus communis broadcast by hand at 119 kg·ha–1 (106 eastern North Carolina, Gyllenhal) damage to potatoes, espe- lb/acre) N–P–K. ‘Atlantic’ seed pieces I≈9,000 ha (22,230 acres) of pota- cially when the cover crop was planted were planted 11 and 12 Mar. 1997, 10 toes are grown for use in the potato early in the summer (Jansson and cm (4 inch) deep and 25 cm (10 inch) chip industry. Conservation tillage Lecrone, 1991). in-row spacing in all CT plots. Seed could benefit agricultural production In addition to conserving topsoil pieces were planted by hand and in this region by controlling topsoil and retaining moisture in the soil, the rehilled mechanically at Plymouth; and loss from wind erosion and conserving presence of crop residue or mulch also planted and hilled mechanically with soil moisture as a reserve against com- changes the environment for insects an Oliver two-row pick planter at mon summer droughts. However, re- and changes soil temperature fluctua- Lewiston. duction in tillage does have the poten- tions. Zehnder et al. (1990) found the REDUCED TILLAGE SYSTEMS. Sor- tial to negatively affect tuber produc- number of Colorado potato beetles ghum–sudangrass seed was broadcast tion because of the potato plant’s sen- (CPB) (Leptinotarsa decemlineata on preformed beds at 39 kg·ha–1 (35 sitivity to soil physical conditions. Say), including overwintering adults, lb/acre) in late August 1996, after Localized high intensity rain- egg masses and larvae, was reduced in corn had been harvested and stubble storms are characteristic of the sum- mulched plots. Soils with crop residue, was disked under. At planting of the mer months in eastern North Caro- or a mulch on the soil surface remain cover crop, 135 kg·ha–1 (120 lb/acre) lina, and rainfall can be poorly distrib- cooler for a longer period in the grow- N and 78 kg·ha–1 (70 lb acre) N were uted throughout the cropping season ing season (Cox et al., 1990), which broadcast at Lewiston and Plymouth, (Reicosky et al., 1977). Morse (1993) can slow emergence (Grant and respectively. concluded that the major advantage of Epstein, 1973). However, crop resi- The 21.3-m (70-ft) plots with conservation tillage in the short term is dues or mulches are known to reduce cover crop residue were split into two improved soil moisture, due primarily soil temperature fluctuation compared 9-m (30-ft) lengths with a 3-m (10-ft) to residue remaining on the soil sur- to CT, bare soils (Teasdale and Mohler, border between the NT and SST sys- face. 1993), and maximum soil tempera- tems. A modified tiller–transplanter Erosion also presents problems, tures are lower in soils with a residue (B&B No-Till Transplanter, Laurel not just for potatoes, but for all agri- cover, compared to bare soils (Creamer Fork, Va.) was used to cut through the cultural production. Used with other et al., 1996). cover residue, open a furrow, place the conservation tools at specific sites, 50% The objectives of this study were fertilizer below the seed piece at the residue cover has been shown to re- to 1) evaluate soil physical characteris- rate of 120 kg·ha–1 (106 lb/acre) N– duce erosion by 83%, and 10% cover tics and potato growth and yield in P–K, and place the seed piece in the can reduce erosion by 30% (Langdale CT, NT, and subsurface-tillage (SST) row (Morse et al., 1993). ‘Atlantic’ and Moldenhauer, 1995). systems and 2) evaluate the effect of seed pieces were planted 11 and 12 The main purpose of tillage in bulk density on potato growth and Mar. 1997, 15 cm (6 inch) deep and at potato production is to control weeds, yield in the greenhouse. Because this a 25-cm (10-inch) in-row spacing in facilitate planting, and increase the experiment was designed to compare all reduced tillage plots. Rows were ease of later cultivation and harvest different systems, more than one fac- raked by hand to cover seed pieces. ● April–June 1999 9(2) 241 RESEARCH REPORTS Nt system. In the NT system, a The experimental design was a ran- with four replications, with one pot straight fertilizer knife was used to cre- domized, complete block (conventional per replication, was used. ate minimal disturbance of the soil dur- vs. cover-cropped) with a split-plot (NT Both soils were packed to two rb ing the planting operation. vs. SST), with four replications. All data values each by adding a known mass Sst system. In the SST system, a were subjected to analysis of variance. (M) of soil into a known volume (V) in winged fertilizer knife was used. The Means were separated with Fisher’s (pro- a pot. The rb values used for the green- LSD ρ wings on the knife disturbed the soil tected) least significant difference ( ) house study were based on field b below the surface to a depth and width tests (Wilkinson, 1990). values in CT and NT soils. Soil mois- of ≈20 cm (8 inch).