Roots of Stylosanthes hamata create macropores in the compact layer of a sandy soil

A field experiment with five lime rates (0, 3.75, 7.50, 11.25, and 15.00 Mg ha^–1) was maintained on a red soil (Ultisol) for 15 years to determine changes of soil acidity and effect on crop yields. The soil acidity decreased while exchangeable Ca in plough layer (0–20 cm) increased with lime rate and time. The decreased subsoil (20–60 cm) acidity started to occur four years after liming, and the extent of decreased soil acidity increased with lime rate and time. The increased ranges of exchangeable Mg²⁺ in subsoil were greater than that of exchangeable Ca²⁺, suggesting that downward movement of Mg²⁺ into the subsoil was faster than that of Ca²⁺. Lime application significantly increased the yields of crops studied. During the period of experiment, the maximum yield increased 4.67 times for barley, 2.24 times for mungbean, 57.3% for wheat, 53.4% for sesame, 52.8% for broad bean, 44.1% for potato, 35.1% for rapeseed, 32.1% for cotton, 28.4% for corn, 18.5% for watermelon, 11.0% for cowpea and 8.8 % for soybean. Liming at the highest rate was in favor to the decline in subsoil acidity and yield increase, especially for the later period of the experiment. Residual effects of reducing soil acidity by liming for the treatments of 0.5 L, 1.0 L, 1.5 L, and 2.0 L could last for 5, 7, 12, and 14 years, respectively, and the effects of lime application on the yields could last for more than 15 years.