Aboveground dry matter and leaf area per plant were measured when potato was at tuber initiation in June and tuber bulking in July (Table 3 and Table 4). In 2006 all the mulched treatments had more dry matter and leaf area than the non-mulched treatment, but mulching duration had no significant effect on these two agronomic parameters (F-test, P > 0.05). However, in 2007 the first sampling results demonstrated that treatments M90 and Mw had significantly more dry matter than M40 and M60, when the mulch for M40 and M60 had been removed for several days and M90 and Mw were still mulched. The second sampling results showed a similar pattern. This is reasonable because the higher soil temperature under mulch could increase above ground dry matter (Kar and Kumar, 2007). Leaf area had a similar trend to above ground dry matter. The difference between the two years’ results might be explained by two reasons: (1) the sample number in 2006 was not large enough for statistic analysis, which could lead to sampling error; (2) the mean maximum air temperature during June–August in 2006 was higher in 2007 and very close to 30 °C, which might be detrimental to aboveground dry matter and leaf area.