The national average potato yield of Sri Lanka is lower than its global average with the absence of an optimum temperature regime for tuber bulking being a major contributory factor. Increasing air temperatures due to the enhanced greenhouse effect have the potential to further reduce potato yields in Sri Lanka. Therefore, the primary objective of this study was to determine the response of phenology, growth and yield of potato to increasing temperature in the upcountry of Sri Lanka, which is the principal potato-growing region of the country. Furthermore, effectiveness of an integrated pest management (IPM) package and a modified soil management regime aimed at soil moisture conservation and reducing excessive use of synthetic pesticides and fertilizers were also tested. A field experiment was conducted during Maha 2012/2013 at Sita-Eliya (SE) and Rahangala (RG) of Sri Lanka, which represented a temperature increase of 5.2 °C from 15.1 °C to 20.3 °C. Potato (Solanum tuberosum L.) variety Arnova was grown with four treatments: T1 – Recommended crop management; T2 – Mulching with recommended crop protection (non- IPM) and fertilization (100 % inorganic fertilizer); T3 – Mulching with IPM and recommended fertilization and T4 – Mulching with IPM plus 25% of N provided as organic amendments. Crops matured a month earlier at the higher temperature site RG, i.e. in 81 days as compared to 111 days at SE. However, the thermal duration from planting to maturity was approximately similar at both sites (i.e. 1689 °Cd and 1662 °Cd at SE and RG, respectively). Crop growth rates were higher at RG, thus compensating for the lower crop duration so that total dry weights at harvest and tuber yields of T1 did not differ significantly between the two sites. At both sites, the tuber yield of T2 did not differ significantly from T1. The growth and yield response to mulching was greater at RG due to the lower rainfall and low soil fertility as compared to SE. The IPM treatments (i.e. T3 and T4) resulted in an effective control of the incidence and severity of late blight at SE but not at RG, where the prevailing temperature regime was optimum for spore formation of the late blight pathogen. Consequently, while the tuber yields did not show significant inter-treatment variation at SE, at RG the IPM treatments (i.e. T3 and T4) showed significantly lower yields than the non-IPM (T1 and T2) treatments. Analysis of the inter-relationships between tuber yield, yield components and growth data showed that potato yields of the present study were primarily source-limited.
Tropical Agricultural Research Vol. 25 (4): 555 – 569 (2014)