Effects of Surface-Applied Limestone on the Efficiency of Urea-Containing Nitrogen Sources for No-Till Corn

Fertilizer N and lime amendments are commonly surface-applied to no-till (NT) production systems, but research on these practices under NT is limited. We examined the effect of surface-applied limestone on the efficiency of urea, urea-NH₄NO₃ (UAN), and NH₄NO₃ applied broadcast or injected for NT corn (Zea mays L.) production on loessal soils. No-till field studies were established on two loessal soils in western Tennessee: a Memphis silt loam (fine-silty, mixed, active, thermic Typic Hapludalt) that had been in NT for 7 yr and a Collins silt (coarse-silty, mixed, acid, thermic Aquic Udifluvent) that had been under conventional tillage. Corn, with a wheat (Triticum aestivum L.) cover, was established on the Memphis soil in 1990. In 1994, corn was established on the Collins soil. The experimental design was a randomized complete block with a split-plot arrangement of treatments. Agricultural limestone was surface-applied at rates of 0 and 1.12 Mg ha⁻¹, 1 to 3 wk before N treatment. The N treatments were UAN broadcast (UAN-B), UAN injected (UAN-I), urea broadcast or split-applied (Urea-B and Urea-S), and NH₄NO₃ broadcast (AN-B). Nitrogen treatments were applied at 168 kg ha⁻¹ within 5 d after planting. For the split urea treatment, 84 kg ha⁻¹ N was broadcast at planting and 84 kg ha⁻¹ N was surface-banded at the 8-leaf growth stage. Applications of AN-B, UAN-B, and Urea-B resulted in lower grain yields and leaf N concentrations than UAN-I. These reductions were attributed to N immobilization and NH₃ volatilization. Average yield reductions attributed to N immobilization were 8% on the Memphis soil and none on the Collins soil. Volatilization losses attributed to UAN-B were 8 and 12% for the Memphis and Collins soils, respectively. Yield reductions attributed to NH₃ volatilization from Urea-B were 22 and 19% for the Memphis and Collins soils. Splitting the urea application increased yields relative to the Urea-B treatment only on the Memphis soil. Surface application of limestone decreased Urea-B yields. Contribution of the Dep. of Plant and Soil Sci., Univ. of Tennesse.