Irrigation in the dry season is helpful to optimize yield of the field-grown Sacha Inchi (Plukenetia volubilis), a tropical woody vine and a promising new oilseed crop species belonging to the family Euphorbiaceae. Deficit irrigation (DI), the application of irrigated water below full crop water requirement for evapotranspiration, is a watersaving irrigation technique. However, the physiological and biochemical responses are difficult to quantify.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) conducted field experiments to investigate the effects of different levels of DI and fertilization on the physiological traits, plant growth, yield, and resource use efficiency (i.e., WUE and NUE) of P. volubilis plants in Xishuangbanna. They aimed to provide a better understanding of irrigation and fertilizer managements for the species at both the local and regional levels, and thus to increase seed and oil yields for commercial-scale oil production.
They used a field split-plot experiment to evaluate the physiological features, growth and seed and oil yield of Sacha Inchi plants responded to DI and fertilization.
They found that the growth and root to stem mass ratio had lower sensitivity responded to DI, probably owing to their extremely low root mass fraction and seasonal short-term effect of DI on leaf photosynthetic traits. Irrigation affected the seasonal variations in seed size, seed oil concentration and seed yield, depending on the harvest date; whereas, with constant mean seed size and mean seed oil concentration across irrigation and fertilization treatments, the total seed and seed oil yield over the growing seasons were largely determined by the seed numbers per unit area.
Carbon storage as the active process occurred at the expense of growth. Carbon and nitrogen shortages affected the final seed yield during the drought. No irrigation× fertilizer interaction on total seed or seed oil yield was found, indicating the magnitude of increase in total seed and seed oil yield by fertilization was similar among different irrigation regimes.
As a water-demanding crop species, Sacha Inchi plants under water-saving techniques with the similar values to full irrigation had the highest total seed yield and agronomic nutrient use efficiency, but at the expense of water use efficiency.
They further found that the maximum seed yield and water use efficiency, or maximum water use efficiency and nutrient use efficiency are not compatible.