Effects of soil acidity amelioration by surface liming on no-till corn, soybean, and wheat root growth and yield

No-till management has rapidly increased the cultivated area in Brazil. To control soil acidity in no-till systems, lime is broadcast on the surface without incorporation. The effectiveness of surface application of lime to soils under a no-till system, particularly with regard to subsoil acidity, is uncertain. Crop root growth and grain yield can be affected by chemical modifications in the soil profile due to surface lime application. A 3-year field trial examined the effect of newly and previously surface-applied lime in a long-term no-till system on the root growth and crop yield of corn (Zea mays L.), soybean (Glycine max L. Merrill), and wheat (Triticum aestivum L.) on a loamy, kaolinitic, thermic Typic Hapludox in Paraná State, Brazil. The experiment consisted of four lime treatments: (i) no lime (control); (ii) liming at 3 t ha-1 in 2000; (iii) liming at 6 t ha-1 in 1993; (iv) liming in 1993 and re-liming in 2000. Corn was grown in 2000-2001 and soybeans were grown in 2001-2002 and 2002-2003 without rainfall limitation. Wheat was grown in 2003 with a water deficit during the vegetative stage and soon after flowering.Liming in 2000 increased pH and the content of exchangeable Ca2+, and decreased the exchangeable Al3+ level mainly in the surface layer of the soil (0-5 cm). Compared with the no lime control, liming in 1993 ameliorated soil acidity and decreased aluminum toxicity to a 60 cm depth. Liming in 2000 on the previously limed plots compared with the liming in 1993 increased pH to a 10 cm depth about 1 year after application and to a 60 cm depth 3 years after application, indicating that the surface-applied lime in 2000 moved deeper when the topsoil was only slightly acidic. Root length density and grain yields of corn and soybean were not influenced by surface liming treatments. Liming in 2000 on the previously limed plots provided increases >=100% in length density of wheat roots at 0-10 and 10-20 cm depths, and increased the wheat grain yield by over 210%. A soil exchangeable Al3+ level of 3 mmol(+) dm-3 was considered critical for wheat root growth. Wheat grain yield was well correlated with root length per soil surface area. The results suggest that aluminum toxicity is low in no-till systems during cropping seasons that have adequate and well-distributed rainfall, but in unfavorable rainfall conditions, the toxicity of aluminum severely compromises root growth and yield.