Tillage and Nitrogen Placement Effects on Nutrient Uptake by Potato

Deep tillage of compacted soils can improve potato (Solanum tuberosum L.) tuber yield and quality if no other production factors are limiting. We hypothesized that within-row subsoiling and N placement would affect tuber yields and availability of plant nutrients. Potato (cv. Russet Burbank) was grown after winter wheat (Triticum aestivum L.) in 1989 and after dry bean (Phaseolus vulgaris L.) in 1990 on a furrow irrigated Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid). Fall tillage treatments (disking, chiseling, and moldboard plowing) were split with zone subsoiling after planting. Nitrogen was broadcast before planting or banded beside the seed piece at planting across all tillage combinations. We estimated plant nutrient status and uptake each year with whole-plant and petiole samplings during tuber growth. Final tuber yield and quality were determined in early October. Fall tillage did not influence nutrient concentration and uptake, tuber yield, or quality. Zone subsoiling increased average plant dry weights 9%, total tuber yields 10% (4 Mg ha '), and quality, and increased P uptake an average of 11.6% (1.8 kg P ha ') without appreciably changing whole-plant or petiole P concentrations. Banding N increased average plant dry weight 6.4%, total tuber yield 9%, and N uptake 28% compared with broadcast N. Petiole NO 3-N, P, K, and Zn concentrations were higher where N was banded. There were no consistent zone subsoiling x N placement interactions. Higher nutrient applications may be required with zone subsoiling or to compensate for soil compaction problems. M ANY sons used for irrigated crop production contain indigenous or tillage-induced compacted layers. Potato is particularly sensitive to soil compaction (Bishop and Grimes, 1978; Dickson et al., 1992; Ross, 1986; von Loon and Bouma, 1978). McDole (1975) observed that a plow pan restricted potato root growth to the plow layer in silt loam and coarser textured soils. Compaction can also affect external tuber quality by physically constraining developing tubers. It is difficult to predict compaction's effect on plants because many soil properties and processes affect root growth, nutrient movement, and uptake. Even a slight uptake reduction may seriously affect plant growth and yield when nutrient availability is marginal. Reduced root growth from compaction may limit the plant's water and nutrient extraction zone to a smaller soil volume or to a soil volume with lower available nutrient concentrations. If water uptake is not seriously influenced, reduced root growth and exploration may reduce uptake of ions that move to the root by diffusion (e.g., P) more than those that move to the root by mass flow, e.g., NO 3-N (Parish, 1971). Potassium might be intermediate since it moves to the root by both diffusion and mass flow (Barber, 1995). Some compaction may actually increase nutrient uptake if it increases the movement of ions to the roots via diffusion. Roots may also partially compenUSDA-ARS. Northwest Irrigation and Soils Research Lab., 3793 N 3600 E, Kimberly, ID 83341. Received 19 June 1995. *Corresponding author (dtw@ kimberly .ars.pn.usbr.gov). sate for reduced root growth with increased uptake per unit length (Hoffmann and Jungk, 1995: Shierlaw and Alston, 1984). Subsoil compaction of a fine-loamy soil reduced P and K uptake by corn (Zea mays L.) 25% when rainfall was low but enhanced it when rainfall was average or above average (Dolan et al., 1992). Surface compaction affected P uptake less than subsoil compaction. In irrigated cotton (Gossypium hirsutum L.) grown on a low-K, claypan soil, K uptake was not increased by deep K placement compared with surface-broadcast K when both placement treatments were in-row subsoiled, even though tillage increased subsoil root densities (Mullins et al., 1994). Deeper tillage is not always necessary or desirable for best crop growth or yields if available soil nutrients and plant root distributions are similar, as in the surface soil layer under conservation tillage systems (Hargove, 1985). Zone subsoiling of furrow-irrigated potato hills before plant emergence increased infiltration and reduced soil erosion, while improving tuber yields and grade (Sojka et al., 1993a). Tuber yield and quality effects from zone subsoiling were also favorable under sprinkler irrigation (Halderson et al., 1993; Sojka et al., 19936). Many arid soils in the western USA have subsoils or tillage-induced pans that restrict root growth (Linford and McDole, 1977). These subsoils often have high lime concentrations and typically are low to very low in plant available P, K and Zn. Nitrogen fertilizer is normally required for high crop yields on these soils. The advantage of zone subsoiling in potato production is dependent on identifying its effect on nutrient availability and uptake. This information will facilitate the development and use of improved tillage and nutrient management strategies. Our objectives were to identify zone subsoiling and N placement effects on potato yield and selected plant nutrient uptake. METHODS AND MATERIALS Potato was grown after winter wheat in 1989 and after dry bean in 1990 on a Portneuf silt loam. Most experimental details were given by Sojka et al. (1993a). In summary, half of each fall tillage (FT) treatment (disking, chiseling, and moldboard plowing) was in-row zone subsoiled (ZS) after spring planting. Zone subsoiling was done with paratill shanks after hill ing as the last tillage operation before fall harvesting. The shanks were placed such that the soil disturbance was below the potato hill. The disturbed area was about 0.6 m wide at the soil surface and tappered down to the paratill shank point, 0.45 m below the soil surface. Each subplot was split and N fertilizer (urea ammonium nitrate, UAN-32, at 220 kg N ha-') was either broadcast and immediately tilled in (disking followed by roller harrowing) before planting or banded 0.12 m to the side of the seed piece at planting across all tillage combinations. Furrow irrigations were Abbreviations: FT, fall tillage; ZS, zone subsoiling: NPlac, nitrogen Published in Soil Sci. Soc. Am. J. 60:1448-1453 (1996). placement.