One-Time Tillage of No-Till: Effects on Nutrients, Mycorrhizae, and Phosphorus Uptake

Stratification of nutrient availability, especially of P, that develops with continuous no-till (NT) can affect runoff nutrient concentration and possibly nutrient uptake. The effects of composted manure application and one-time tillage of NT on the distribution of soil chemical properties, root colonization by arbuscular mycorrhizae (AM), and plant P uptake were determined. Research was conducted on Typic Argiudoll and Moffic Hapludaff soils under rainfed corn (Zea mays L.) or sorghum [Sorghum bicolor (L.) Moench.] rotated with soybean [Glycine max (L.) Men.] in eastern Nebraska. Tillage treatments included NT, disk, chisel, moldboard plow (MP), and mini-moldboard plow (MMP). Subplots had either 0 or 87.4 kg P ha -Iapplied in compost before tillage. Bray-P1 was five to 21 times as high for the 0to 5-cm as compared with the 10to 20-cm soil depth. Greater redistribution of nutrients and incorporation of compost P resulted from MP tillage than from other tillage treatments. One-time chisel or disk tillage did not effectively redistribute nutrients while MMP tillage had an intermediate effect. Compost application reduced AM colonization of roots at R6 for all crops. Tillage reduced AM colonization with reductions at R6 due to MP tillage of 58 to 87%. The tillage effect on colonization persisted through the second year with no indication of AM recovery. Root P concentration was increased by MP and was negatively correlated to colonization. Decreased colonization did not result in decreased plant P uptake. Infrequent MP tillage can reduce surface soil P and the potential for P loss in runoff, but may reduce AM colonization of the roots, possibly reducing P uptake with some low P soils. The results do not indicate any advantage to one-time tillage of NT if runoff P loss is not a concern. S OIL NUTRIENT STRAIll. ICATION with NT is common with relatively high nutrient concentrations in the 0to 5-cm soil depth (Morrison and Chichester, 1994; Pezzarossa et al., 1995). Nutrients derived from crop residues and applied fertilizer and manure, especially P and other relatively immobile nutrients, accumulate at or near the soil surface in long-term no-till systems because of limited soil mixing (Karathanasis and Wells, 1990). Stratification of P, K, and pH with no-till may not affect crop performance unless the surface soil is often dry during the growing season and there is low nutrient availability in subsurface soil (Mallarino et al., 1999). Bordoli and Mallarino (1998 and 2000) did not find increased soybean yield response to deep placement comJ.P. Garcia, C.S. Wortmann, M. Mamo, and R. Drijber, 279 Plant Science, Univ. of Nebraska, Lincoln, NE 68583-0915; and D. Tarkalson, 461 W. University Dr., West Central Research and Extension Center, Univ. of Nebraska, North Platte, NE 69101. Contribution of the Univ. of Nebraska-Lincoln Agricultural Research Division. This research was partly funded by the Hatch Act, the Charles B. and Katherine W. Baker Endowment, and the U.S. Agency for International Development under the terms of Grant No. LAG-G-00-96-900009-00. Received 15 Sept. 2006. *Corresponding author (cwortmann2@unledu). Published in Agron. J. 99:1093-1103 (2007). Tillage doi:10.2134/agronj2006.0261 © American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA pared with surface placement of P for stratified no-till soils. Schwab et al. (2006) did not find a tillage x P placement interaction for several crops, but sorghum grain yield was more with deep placement than with broadcast application for all tillage treatments. McGonigle et al. (1999) compared no-till, ridge-till, and conventional tillage and found that soybean P uptake was unchanged while maize P uptake was more with no-till. Phosphorus stratification may result in excessively high P concentration in runoff water as runoff P concentration is related to surface soil P concentration (Daverede et al., 2003). Stratification of soil pH and K may be of less environmental concern. Runoff P loss is often more sensitive to changes in rates of erosion and runoff than to soil P concentration (Wortmann and Walters, 2006). The potential for increased P runoff due to P stratification may be offset by reduced erosion with no-till because of good ground cover and improved soil aggregation in the 0to 5-cm depth (Doran, 1987; West and Post, 2002). One-time tillage of NT, conducted once in 10 or more years, to mix high-nutrient surface soil with deeper soil may be practiced to redistribute nutrients and reduce the potential for nutrient loss in runoff. Quincke et al. (2007a, 2007b) found that such tillage can be done without loss of soil organic C, soil aggregate stability, or grain yield during the 2 or 3 yr following the one-time tillage. Sharpley (2003) found that in P-stratified soils, the P sorption maxima were 2 to 4.5 times higher at the 5to 20-cm depth as compared with the surface 5 cm of soil. Guertal et al. (1991) also found less P sorption capacity for soil at the 0to 2-cm depth as compared with the 2to 20-cm depth for P-stratified, manure applied soils. Tillage may reduce the potential for P loss in runoff by redistributing nutrients in the soil as well as increasing the P sorption capacity of the surface soil. The effect of one-time MP on the distribution of P and K, but not of soil pH, was still significant 5 yr after tillage (Pierce et al., 1994). One-time tillage of NT may, however, reduce AM colonization of crop roots and the potential for P uptake. The extent of AM hyphal networks can be several meters per cubic centimeter of soil, providing the major nutrient-absorbing interface between plant and soil (Jakobsen et al., 1992). Damage to the hyphal network by tillage can reduce AM growth and root colonization due to death or reduced infectivity of the hyphal fragAbbreviations: AM, arbuscular mycorrhizae; ARDC, Agricultural Research and Development Center of the University of NebraskaLincoln; CH2O and CH30, chisel tillage at the 20and 30-cm depths; FAME, ester-linked fatty acid methyl ester; MMP, mini-moldboard plow; MP, moldboard plow; NT, continuous no-till; R6, stage of physiological maturity for corn and sorghum or full enlargement of soybean seed; RMF, Rogers Memorial Farm of the University of Nebraska-Lincoln; TP, total phosphorus; V6, six-leaf growth stage.