The objectives of this work were to (1) asses how Shoemaker-McLean-Pratt (SMP), Sikora, and Mehlich buffers, titratable acidity, and soil properties relate to soil pH change due to liming, (2) study the variation of soil pH and crop response to lime within fields, (2) identify optimum soil pH for corn and soybean, (3) evaluate the effect of subsoil pH on crop response to lime in Iowa, and (4) evaluate the rate of soil pH increase from application of different lime sources. Fourteen replicated strip trials with lime were established in Iowa from 2007 to 2009 using precision agriculture technologies and were evaluated two, three, or four years. Soil samples were collected before applying lime and also after each crop harvest. Also, four replicated field small plot trials with rates and sources of lime were established in 2009. Soil samples were collected at eight sampling dates during a period of 16 months following liming. Within-field initial soil pH variation varied widely across fields. Sikora and SMP were highly correlated, did not differ for most soil series. Soil pH was by far the best variable to predict pH change variation. Limestone application significantly increased soil pH in all sites, and maximum pH values were generally reached during the second year after liming. Crop grain yield was increased due to liming in 12 of 42 site-years. The yield response to lime did not differ between crops. Crop response decreased with increasing initial soil pH, but was highly affected by subsoil pH. Optimum pH range for corn and soybean was 6.0-6.5 for soil series with subsoil having pH<7.0 but was significantly lower (pH 5.0-5.5) for soils with subsoil having a higher pH. Results from the small plots showed that the soil pH increase over time for the three lime sources was curvilinear with decreasing increments to a plateau maximum that was reached about 100 days after liming. However, the early pH increases and maximum pH reached were greater for pure CaCO3 than for the calcitic and dolomitic limestones. Results showed that the time of limestone reaction in the soil was faster than usually assumed.