Soil pH change after surface application of lime related to the levels of soil disturbance caused by no-tillage seeding machinery

Abstract On acid soils, no-tillage farmers are often advised to apply lime to the soil surface without incorporation by tillage. As such, it can take a number of years before the subsoil acidity is decreased. However, no-tillage seeders vary in the level of soil disturbance caused during seed placement. The consequence of such variations in soil disturbance for the effectiveness of lime in no-tillage cropping has not been explored. Our objectives were (i) to determine if the liming effect could be accelerated by increasing the rate of lime and level of soil disturbance during no-tillage seeding, and (ii) evaluate the effect of no-tillage seeding method, rate of lime and soil pH on yield of wheat, barley, canola and lupins. Three trials, each with a factorial design consisting of four seeding methods and four lime rates, were established in 1999 and continued until 2005. The soil had a texture contrast with about 15–20 cm of sand over yellow sandy clay loam and the initial pH (CaCl2) at both 0–10 and 10–20 cm was between 4.5 and 4.7. The four seeding treatments were: low disturbance zero-till disc openers (ZT), higher disturbance no-tillage tines with narrow knife-points (NT), higher disturbance full cut seeding with sweeps (FC) for the first three years followed by ZT from then on, and FC for the first year followed by NT thereafter. The four lime rates were 0, 1, 2 and 4 t ha−1. The liming effect was more rapid with the higher disturbance seeding of NT, FCZT and FCNT, compared with ZT; the seeding effect on soil pH diminished with time and was not detected in the subsoil after four years. Higher rates of lime increased this effect and there was no interaction between seeding method and lime rate. This indicated that soil pH under the different seeding methods responded in a similar manner to increased lime. Nonetheless, significant positive linear regressions were found between yield and soil pH for wheat and barley and a negative relationship for lupins. Canola showed no response to soil pH, possibly because establishment was affected by seeding method, and soil pH was not low enough to elicit a response. The ZT seeding method gave lower yields than the other methods for canola and lupins in some years, but had no effect on wheat and barley yields. Higher disturbance at the time of no-till seeding can, therefore, accelerate the liming effect, making earlier economic gains possible.