Changes in pore structure in a no-till chronosequence of silt loam soils, southern Ontario

Many research studies have dealt with the influences of minimum or no-till soil management practices on the major physical, chemical, biological and m orphological properties in the soil profile. However little work has been d one on the assessment of the rates of changes in pore properties as managem ent practices are converted from conventional to no-till (NT) methods. Shor t-term changes in soil micromorphology attributed to conversion to no-till from conventionally tilled management are evaluated in this paper. As the n umber of years in no-till increased there was a decrease in the number pore s of 30- to 100-mu m diameter in the no-till soils. However, pores from 100 - to 500-mu m diameter increased in number only after 4 yr of NT. The pores of this size are important for water storage, transmission and root develo pment. The decline in the number of these pores after no-till initiation fo llowed by the increase after 4 yr may explain why crop yields tend to be lo wer only after the first few years after implementing no-till. The 100- to 500-mu m diameter pores may be crucial for the proper development of roots in wheat and corn. The no-till soils had greater numbers of horizontally or iented elongated macropores in the top 5 to 15 cm of the soil profile due t o the lack of tillage and annual freeze-thaw processes. These pores may inh ibit proper drainage and root penetration. Rounded macropores increased wit h the number of years the soil was in no-till as these pores were maintaine d each year due to the lack of tillage and greater faunal activity in the n o-till soils.