Potato response to environment, planting date and genotype was studied
for different agro-ecological zones in Lesotho. Field experiments were conducted at
four different sites with altitudes ranging from 1,655 to 2,250 m above sea level
during the 2010/2011 and 2011/2012 summer growing seasons. Treatments consisted
of three cultivars that varied in maturity type, two planting dates and four sites
differing in altitude and weather patterns. Various plant parts were measured periodically.
To understand and quantify the influence of abiotic factors that determine
and limit yields, the LINTUL crop growth model was employed which simulated
potential yields for the different agro-ecological zones using weather data collected
per site during the study period. Observed actual crop yields were compared with
model simulations to determine the yield gap. Model simulations helped to improve
our understanding of yield limitations to further expand potato production in subtropical
highlands, with emphasis on increasing production through increased yields
rather than increased area. Substantial variation in yield between planting date,
cultivar and site were observed. Average tuber dry matter (DM) yields for the highest
yielding season were above 7.5 t DM ha−1 or over 37.5 t ha−1 fresh tuber yield. The
lowest yield obtained was 2.39 t DM ha−1 or 12 t ha−1 fresh tuber yield for cultivar
Vanderplank in the 2011/2012 growing season at the site with the lowest altitude.
Modelled potential tuber yields were 9–14 t DM ha−1 or 45–70 t ha−1 fresh yield.
Drought stress frequently resulted in lower radiation use efficiencies and to a lesser
degree harvest indices, which reduced tuber yield. The site with the lowest altitude
and highest temperatures had the lowest yields, while the site with the highest altitude
had the highest yields. Later maturing cultivars yielded more than earlier maturing
ones at all sites. It is concluded that the risk of low yields in rain-fed subtropical highlands can be minimised by planting late cultivars at the highest areas possible as
early as the risks of late frosts permit.