Abstract:
Understanding the photosynthetic behaviour, radiation use efficiency (RUE) and water use
efficiency (WUE) of potatoes in response to diurnal and seasonal fluctuations in weather,
is important for optimizing growth and production. The net ecosystem exchange (NEE) of
carbon dioxide (CO2), is a parameter used to measure the balance between gross CO2 assimilation (also referred to as gross primary production (GPP)) and ecosystem respiration (Reco).
The objectives of this study were (i) to quantify the NEE of potato grown in two contrasting
agro-ecologies and partition NEE into Reco and GPP; (ii) to describe seasonal patterns in daily
photosynthesis, RUE and WUE in potato; and (iii) to analyse the variability in photosynthesis
rate, RUE and WUE as affected by weather and crop growth stage. We measured CO2 and
water vapour fluxes using eddy covariance techniques in potato fields in two production
regions of South Africa. The winter crop had higher mean RUE and WUE values, whereas
the summer crop absorbed more CO2. RUE had a negative relationship with incident radiation. To optimize dry matter production, WUE and RUE, potato crops must be well established and develop a full canopy early during the season. Maintaining the crop for a longer
period in the field has yield benefits, although they appear to decline over time due to reduced
efficiencies as the crop matures. The RUE observed over the growing period in the present
study was high, relative to findings by other field studies, despite relatively warm growing conditions that were likely sub-optimal for potato.
